Gravity waves (and a land breeze boundary) in the Gulf of Mexico

November 22nd, 2016 |

GOES-13 Visible (0.63 µm) images, with hourly surface/buoy/ship reports [click to play animation]

GOES-13 Visible (0.63 µm) images, with hourly surface/buoy/ship reports [click to play animation]

GOES-13 Visible (0.63 µm) images (above) revealed a series of gravity waves propagating southeastward across the Gulf of Mexico on 22 November 2016. These waves appeared to be moving through or along the tops of the marine boundary layer stratocumulus cloud field; since the hourly winds from surface/buoy/ship reports were  generally from the southeast/east/northeast, these gravity waves were not likely surface-based.

Also of note was an apparent land breeze boundary that moved west-northwestward away from the Yucatan Peninsula of Mexico during the day.

Suomi NPP VIIRS Visible (0.64 µm) image, with NUCAPS sounding locations and surface analysis [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) image, with NUCAPS sounding locations and surface analysis [click to enlarge]

Gravity waves like those observed here are usually ducted within a strong air temperature inversion — so Suomi NPP NUCAPS (NOAA-Unique CrIS/ATMS Processing System) soundings around 1828 UTC (above) were examined for evidence of such an inversion. Training material for NUCAPS Soundings in AWIPS is available here.

One of the NUCAPS vertical profiles of temperature and moisture is shown below, for a point over the southern Gulf of Mexico (designated by the cyan rectangle, approximately 50 miles northwest of the coast of the Yucatan Peninsula) — several of the waves had passed through this location prior to the image time. A well-defined temperature inversion did indeed exist aloft, within the 1-2 km layer above the surface (and just above the top of the moist marine boundary layer, where the stratocumulus cloud field existed). It therefore appears likely that this series of southeastward-moving gravity waves was mildly perturbing the tops of the stratocumulus clouds.

NUCAPS sounding profile for a point over the Gulf of Mexico, north of the Yucatan Peninsula [click to enlarge]

NUCAPS sounding profile for a point over the Gulf of Mexico, north of the Yucatan Peninsula [click to enlarge]

Since there were no nearby surface frontal boundaries or areas of organized deep convection inland over the southern US during the preceding 24 hours, it is unclear as to what may have been the catalyst for these gravity waves.

Severe Weather in the Pacific Northwest

October 15th, 2016 |

Window Channel Infrared imagery from COMS-1 (10.8 µm) and GOES-15 (10.7 µm), every 6 hours from 1200 UTC on 7 October through 1800 UTC on 15 October [click to animate]

Infrared Window Channel imagery from COMS-1 (10.8 µm) and GOES-15 (10.7 µm), every 6 hours from 1200 UTC on 7 October through 1800 UTC on 15 October [click to animate]

Strong moisture-laden storms caused abundant precipitation and severe weather over the Pacific Northwest from 13-15 October 2016. The animation above shows two storms making landfall in the Pacific Northwest, one on 13-14 October and a second, on 15 October, which was a storm that originated from the remnants of Typhoon Songda. On 11-12 October, Super Typhoon Songda was recurving, subsequently racing towards the west coast of the United States, and making landfall as a strengthening extratropical cyclone on 15 October. The animation above uses two different satellites (COMS-1 and GOES-15), and includes a seam between the two views because the spectral characteristics of the two infrared window bands are not identical.

Daily precipitation from the Advanced Hydrologic Prediction Center from 13-15 October is shown here, with a weekly total shown below. A large area of precipitation exceeding 6 inches is apparent in the higher terrain.

ahps_7dprecip_15oct_1200

7-day Precipitation Totals ending 1200 UTC on 15 October 2016 (Click to enlarge)

The precipitation amounts were aided by the very moist airmass that accompanied the storms. Total Precipitable Water, shown below, from this site that manipulates data from here, shows the moisture. A larger-scale view that traces the moisture back to the time when Songda first reached typhoon intensity over the West Pacific is available here.

Total Precipitable Water, 12-15 October 2016 [Click to animate]

The strong storm before the one spawned by the remnants of Songda produced an EF2-rated tornado in Manzanita Oregon (YouTube Compilation; SPC Storm Reports; Blog post with damage picture) on 14 October 2016. GOES-15 Visible Imagery, below, shows a storm with overshooting tops moving over northwestern Oregon at the time of the tornado. (GOES-15 was performing a full-disk scan from 15:00-15:26 UTC, so 15-imagery was not available as the tornado moved ashore; the Advanced Baseline Imager on GOES-R will produce CONUS Imagery every 5 minutes in addition to Full-Disk Imagery every 15 minutes). The overshoots are especially apparent in the 1500 and 1530 UTC Images. GOES-13 provided a visible image at about the time of the tornado touchdown, but at a very oblique angle. The cirrus shield of the thunderstorm anvil is apparent, however.

GOES-15 Visible (0.62 µm) imagery, 1445, 1500 and 1530 UTC on 14 October. The Red Square indicates the tornado location [Click to animate]

GOES-15 Infrared Window (10.7 µm) imagery around the time of the severe weather in Oregon, below — which includes locations of SPC storm reports of tornadoes (red) and damaging winds (cyan) — also showed evidence of cold overshooting tops (the coldest clouds tops were around -50º C, yellow enhancement). An infrared image animation showing only the clouds is available here. NOAA-18 flew over the Oregon coast at 1427 UTC, and the AVHRR 12 µm Infrared image showed the parent thunderstorm offshore, upstream of Manzanita (larger-scale view).

GOES-15 Infrared Window (10.7 µm) imagery, 1400-1800 UTC on 14 October [Click to animate]

The Portland, Oregon NWS office issued 10 tornado warnings on 14 October — a record number for a single day.

 

GOES Sounder data can be used to created Derived Product Imagery (DPI) estimates of instability parameters (for example), and many are shown at this site. The GOES-13 Sounder has been offline for about a year after having suffered an anomaly back in November 2015, when the filter wheel became frozen, but the GOES-15 Sounder (and the GOES-14 Sounder) continue to operate. The animation below of GOES-15 Sounder Lifted Index shows values as low as -4ºC upstream of the Oregon Coast for many hours before the tornado; as such, it was a valuable situational awareness tool.

goes_sounder_dpi_14oct2016_1100_1700step

GOES-15 Sounder DPI Estimates of Lifted Index, 1100-1700 UTC on 14 October 2016 (Click to enlarge)

NOAA/CIMSS ProbSevere is a probabilistic estimate that a given thunderstorm will produce severe weather in the next 60 minutes. The animation below shows ProbSevere polygons overlain over radar from 1501 UTC (when the first ProbSevere polygon appeared around the radar cell that ultimately was tornadic) through 1521 UTC. Values from the ProbSevere output are below:

 

TIME PS CAPE SHR MESH GRW GLA FLSHRATE COMMENTS
1501 11% 1048 39.3 0.00 str str 0 fl/min Satellite from 1245/1241
1503 32% 1056 39.7 0.37 str str 0 fl/min Satellite from 1245/1241
1505 32% 1031 39.4 0.37 str str 0 fl/min Satellite from 1245/1241
1507 29% 1013 38.7 0.37 str str 3 fl/min Satellite from 1245/1241
1509 47% 974 37.9 0.62 str str 3 fl/min Satellite from 1245/1241
1511 47% 962 37.6 0.62 str str 3 fl/min Satellite from 1245/1241
1513 32% 745 33.1 0.52 str str 10 fl/min Satellite from 1245/1241
1515 34% 897 35.9 0.52 str str 1 fl/min Satellite from 1245/1241
1517 10% 887 35.7 0.52 N/A N/A 2 fl/min
1519 8% 762 33.6 0.54 N/A N/A 4 fl/min
1521 7% 737 33.1 0.49 N/A N/A 2 fl/min
realearthprobsevere_14october2016_1501_1521anim

NOAA/CIMSS ProbSevere output in RealEarth, 1501-1521 UTC on 14 October 2016 (Click to animate)

The Sounder also has a 9.6 µm “ozone absorption band”, and another example of GOES Sounder DPI is Total Column Ozone, shown below. Immediately evident is the sharp gradient in ozone (yellow to green color enhancement) located just north of the polar jet axis that was rounding the base of a large upper-level low (500 hPa analyses). The GOES-R ABI instrument also has a 9.6 µm band that is sensitive to ozone; however, there are no current plans to produce operationally a similar Total Column Ozone product.

 

GOES-15 Sounder Total Column Ozone DPI [click to animate]

GOES-15 Sounder Total Column Ozone DPI [click to animate]

Suomi NPP Day/Night Band Visible (0.70 µm) Image, 1057 UTC on 14 October 2016, Green Arrow points to Manzanita OR [click to enlarge]

Suomi NPP Day/Night Band Visible (0.70 µm) Image, 1057 UTC on 14 October 2016, Green Arrow points to Manzanita OR [click to enlarge]

Suomi NPP overflew the Pacific Northwest about 4 hours before the severe weather was observed at Manzanita. The Day/Night Visible Image above, courtesy of Jorel Torres at CIRA (Jorel also supplied the NUCAPS Sounding Imagery below), shows a well-developed storm offshore with thunderstorms off the West Coast of the United States (Click here for an image without the Green Arrow). Multiple overshooting tops can be discerned in the imagery.

NUCAPS Soundings are produced from the Cross-Track Infrared Sounder (CrIS, with 1300+ channels of information) and the Advanced Technology Microwave Sounder (ATMS, with 22 channels) that are present on Suomi NPP (in addition to the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument that provides the Day/Night band imagery). The image below shows the location of NUCAPS Soundings — the color coding of the points is such that Green points have passed Quality Control, whereas yellow points denote sounding for which the Infrared Sounding retrieval has failed to converge and Red points denote soundings for which both Infrared and Microwave sounding retrievals have failed to converge).

Suomi NPP Day/Night Band Visible Image, 1057 UTC on 14 October 2016, with NUCAPS Sounding Locations indicated.  The Green Circle shows the location of the Sounding below [click to enlarge]

Suomi NPP Day/Night Band Visible Image, 1057 UTC on 14 October 2016, with NUCAPS Sounding Locations indicated. The Green Circle shows the location of the Sounding below; Refer to the text for the Dot Color meaning [click to enlarge]

NUCAPS Soundings can give valuable information at times other than those associated with radiosonde launches (0000 and 1200 UTC, typically), and over a broad region. The point highlighted above, between the occluded storm and the coast, shows very steep mid-level lapse rates that suggest convective development is likely.

NUCAPS Sounding, location as shown by the Green Circle in the figure above. [click to enlarge]

NUCAPS Sounding, location as shown by the Green Circle in the figure above [click to enlarge]

The imagery below shows soundings a bit farther south, near convection that looks supercellular. The NUCAPS Soundings there suggest very steep mid-level lapse rates.

slide11

Historic Winter Storm Along the US East Coast

January 22nd, 2016 |

MIMIC Total Precipitable Water, 1500 UTC 19 January -- 1400 UTC 22 January [click to enlarge]

MIMIC Total Precipitable Water, 1500 UTC 19 January — 1400 UTC 22 January [click to enlarge]

A storm forecast to produce near-record snowfalls over the Nation’s Capitol has started to move up the east coast of the United States on 22 January 2016. Snow that will fall requires two things: abundant moisture, and cold temperatures. The MIMIC Total Precipitable Water Product, shown above for the 72 hours ending at 1400 UTC on 22 January (Source) shows the circulation of the developing storm drawing moist air northward from both the Gulf of Mexico and the western Atlantic Ocean. Similarly, the toggle below shows the NESDIS Operational Blended Total Precipitable Water Product (Source, a product that ‘blends’ Total Precipitable Water observations from GPS and GOES-Sounder*). Significant moistening is apparent over the southeastern part of the United States.

*As the GOES-13 Sounder continues to be off-line due to an anomaly (Link), the principle driver of this product over the eastern US is now GPS data.

NESDIS Blended Total Precipitable Water, 1400 UTC on 21 and 22 January 2016 [Click to enlarge]

NESDIS Blended Total Precipitable Water, 1400 UTC on 21 and 22 January 2016 [click to enlarge]

Cold air is also present. The MODIS Land Surface Temperature product from 0731 UTC on 22 January shows temperatures (in cloud-free regions) colder than -5º C southward into Virginia. Dewpoints in this region are colder than -10º C. High Pressure over the East Coast is promoting cold air damming along the Appalachians as well.

MODIS-based Land Surface Temperature, 0722 UTC and the 0900 UTC WPC Surface Analysis, 22 January 2016 [Click to enlarge]

MODIS-based Land Surface Temperature, 0722 UTC and the 0900 UTC WPC Surface Analysis, 22 January 2016 [click to enlarge]

Suomi-NPP carries on board two instruments that provide vertical profiles of moisture and temperature in the atmosphere, the CrIS and the ATMS. NUCAPS Soundings combine information from those two soundings. NUCAPS Soundings sites from the early morning Suomi NPP Pass on 22 January are shown superimposed on the MODIS Land Surface Image below; five sounding sites (highlighted in red) were selected: northwest of Boston, over western Connecticut, New York City, Washington DC and central Virginia. These soundings all have common attributes: They are dry (although the vertical profiles from DC and Virginia show the most moisture: ~0.3″ of total precipitable water), they are too warm near the surface (detection of low-level inversions from satellite data is difficult) and they show lapse rates at mid-levels that suggest vigorous ascent may be possible. The 0600, 1200 and 1800 UTC Soundings from KIAD (below) also show dry air (at least initially: total precipitable water doubled from 0.24″ at 1200 UTC to 0.49″ at 1800 UTC) and steep mid-level lapse rates.

MODIS-based Land Surface Temperature, 0722 UTC and 0700 UTC NUCAPS Sounding Sites (in green) and the 0900 UTC WPC Surface Analysis, 22 January 2016 [Click to enlarge]

MODIS-based Land Surface Temperature, 0722 UTC and 0700 UTC NUCAPS Sounding Sites (in green) and the 0900 UTC WPC Surface Analysis, 22 January 2016 [click to enlarge]

Rawinsonde from KIAD (Dulles International Airport) at 0600, 1200 and 1800 UTC on 22 January 2016 [Click to enlarge]

Rawinsonde from KIAD (Dulles International Airport) at 0600, 1200 and 1800 UTC on 22 January 2016 [click to enlarge]

The Aqua Satellite, bearing the MODIS instrument, overflew the eastern United States shortly before 1900 UTC on 22 January 2016. MODIS samples the atmosphere at 36 different wavelengths, and selected images are shown below.

The toggle between the Visible (0.65 µm) and the ‘Snow Ice’ Channel in MODIS (1.63 µm), below, highlights regions of ice clouds. Ice particles absorb radiation with wavelength of 1.63 µm but water droplets scatter such radiation. Thus, regions in visible imagery that are white that include mostly ice crystals (or snow on the ground), for example the cirrus shield on the East Coast, will appear dark in the 1.63 µm imagery but bright in visible because clouds are highly reflective to visible light. Water-based clouds (over Mississippi, for example, or southeastern West Virginia; in fact, low clouds are apparent just to the west of the cirrus shield associated with the developing baroclinic leaf, from West Virginia southward to Savannah Georgia!) will appear bright in both channels.

MODIS Visible (0.65 µm) and near Infrared (1.63 µm) Imagery at 1836 UTC [Click to enlarge]

MODIS Visible (0.65 µm) and near Infrared (1.63 µm) Imagery at 1836 UTC [click to enlarge]

MODIS also includes a channel (1.38 µm) in a region in the electromagnetic spectrum where strong water vapor absorption occurs; this channel is ideal for high cloud detection. (GOES-R will also detect radiation at this wavelength) The toggle below shows the Visible (0.65 µm), Cirrus channel (1.38 µm) and Infrared window channel (11.02 µm) from MODIS. The storm at mid-day on 22 January was producing an extensive cirrus shield that had the classic baroclinic leaf structure (a structure that was also evident in the infrared window channel).

MODIS Visible (0.65 µm), Cirrus Channel (1.38 µm) and Window Channel Infrared (11.02 µm) Imagery at 1836 UTC [Click to enlarge]

MODIS Visible (0.65 µm), Cirrus Channel (1.38 µm) and Window Channel Infrared (11.02 µm) Imagery at 1836 UTC [click to enlarge]

Careful inspection of the visible and near-infrared channels from MODIS reveals transverse banding (features commonly associated with turbulence) along the western edge of the Cirrus Shield along the East Coast. The toggle below of the MODIS Water Vapor imagery (6.8 µm) shows distinct transverse banding. Pilot reports of turbulence with this system are widespread.

MODIS Infrared Water Vapor (6.8 µm) Imagery at 1836 UTC along with Pilot Reports of Turbulence (PIREPS) [Click to enlarge]

MODIS Infrared Water Vapor (6.8 µm) Imagery at 1836 UTC along with Pilot Reports of Turbulence (PIREPS) [click to enlarge]

To better monitor the long-duration storm, the GOES-13 (GOES-East) satellite was placed into Rapid Scan Operations (RSO) mode for a 2-day period beginning at 1215 UTC on 22 January. During RSO, images are available as frequently as every 5-7 minutes, an improvement over the routine 15-minute image interval (note: the ABI instrument on GOES-R will be able to provide images as often as every minute, or even every 30 seconds). Animations of RSO Visible (0.63 µm), Water Vapor (6.5 µm), and Infrared window (10.7 µm) imagery during the daylight portion of Day 1 of the storm are shown below.

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 Water Vapor (6.5 µm) images [click to play animation]

GOES-13 Water Vapor (6.5 µm) images [click to play animation]

GOES-13 Infrared window (10.7 µm) images [click to play animation]

GOES-13 Infrared window (10.7 µm) images [click to play animation]

Though they lack the temporal resolution provided by geostationary satellites such as GOES, polar-orbiting satellites such as the NOAA series (with their AVHRR instrument), Terra and Aqua (with their MODIS instrument), and Suomi NPP (with the VIIRS instrument) offer imagery with significantly improved spatial resolution. Shown below is a series of AVHRR, MODIS, and VIIRS Infrared window channel images (10.8 µm, 11.0 µm, and 11.45 µm, respectively) on 22 January, with the data projected into a 1-km AWIPS-I grid. Areas with cloud-top IR brightness temperatures in the -50º to -60º C range (orange to red color enhancement) can be seen as the storm moved across the eastern US.

AVHRR (10.8 µm), MODIS (11.0 µm), and VIIRS (11.45 µm) Infrared window channel images [click to enlarge]

AVHRR (10.8 µm), MODIS (11.0 µm), and VIIRS (11.45 µm) Infrared window channel images [click to enlarge]

Excellent detail can also be seen in a series of 1-km resolution MODIS Water Vapor (6.7 µm) images spanning the 21-22 January period, shown below.

MODIS Water Vapor (6.7 µm) images [click to enlarge]

MODIS Water Vapor (6.7 µm) images [click to enlarge]

One interesting aspect to note was that the cold front associated with the intensifying storm had moved southward across the Gulf of Mexico (surface analyses), crossed the mountainous terrain of Mexico, and emerged as an area of strong gap winds over the Pacific Ocean south of Mexico (in the Gulf of Tehuantepec). The leading edge of the gap wind flow, known as a Tehuano wind (or a “Tehuantepecer”), was marked by a thin arc cloud fanning out away from the southerrn coast of Mexico, with hazy plumes of blowing dust seen streaming southward off the coast as the strong northerly winds persisted during the day.

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 Visible (0.63 µm) images [click to play animation]

The hazy signature of blowing dust resulting from the strong gap wind flow was even more recognizable on Suomi NPP VIIRS true-color RGB imagery, below.

Suomi NPP VIIRS true-color RGB image [click to enlarge]

Suomi NPP VIIRS true-color RGB image [click to enlarge]

GOES-13 satellite-derived atmospheric motion vector (AMV) winds, below, were showing cloud targets moving at speeds around 30-35 knots. Unfortunately, there was no good Metop ASCAT wind coverage of the Tehuano winds (as was the case for past events such as these documented here and here).

GOES and ASCAT satellite winds [click to play animation]

GOES and ASCAT satellite winds [click to play animation]

===== 23 January  Update =====

As the surface low deepened to a minimum central pressure of 983 hPa and moved northeastward just off the US East Coast (surface analyses), GOES-13 Visible (0.63 µm) images, below, showed  the moisture — with some embedded convective elements, judging from the texture and shadowing of the cloud tops — moving inland from the Atlantic Ocean north of the storm. Thundersnow was in fact reported at a number of locations. A similar animation of GOES-13 Visible images covering the daylight portions of the 22-23 January period is available here, with the entire 48-hour Infrared window channel (10.7 µm)  animation here.

GOES-13 Visible (0.63 µm) images with surface weather symbols [click to play animation]

GOES-13 Visible (0.63 µm) images with surface weather symbols [click to play animation]

Consecutive Suomi NPP VIIRS true-color RGB images at 1652 and 1828 UTC, below, provided a more detailed view of the convective elements that were moving inland north of the storm center.

Suomi NPP VIIRS true-color RGB images at 1652 and 1828 UTC [click to enlarge]

Suomi NPP VIIRS true-color RGB images at 1652 and 1828 UTC [click to enlarge]

===== 24 January Update =====

MIMIC Total Precipitable Water product [click to enlarge]

MIMIC Total Precipitable Water product [click to enlarge]

Shown above is a 72-hour animation of the MIMIC TPW product (from 00 UTC on 21 January to 00 UTC on 24 January), which — as mentioned at the beginning of this blog post — revealed the large amount of moisture-rich air that was drawn northward and subsequently wrapped into the storm. South of Mexico, a narrow tongue of dry air (a signature of the aforementioned Tehuano wind event) was also clearly seen, moving southwestward over the Pacific Ocean.

GOES-13 Water Vapor (6.5 µm) images, with surface weather symbols [click to play MP4 animation]

GOES-13 Water Vapor (6.5 µm) images, with surface weather symbols [click to play MP4 animation]

The entire 48-hour period of Rapid Scan Operations GOES-13 Water Vapor (6.5 µm) imagery with plots of surface weather symbols (above; also available as a large 66 Mbyte animated GIF) depicted the evolution of the storm as it moved across the Eastern US from 1215 UTC on 22 January to 1215 UTC on 24 January. The storm produced widespread heavy snowfall, areas of freezing rain and sleet, hurricane-force winds (peak gusts), and coastal flooding (WPC storm summary | NWS impacts statement | Capital Weather Gang blog) — it was ranked a Category 4 on the NESIS scale, and the 4th most intense since 1950 (NCEI overview). Features seen on the water vapor imagery included the development of a well-defined dry slot, cold conveyor belt, and elongated comma head / deformation zone that helped to produce the prolonged period of heavy snow. Interesting gravity waves were also seen within the offshore dry slot on 23 January, which appeared to be propagating westward back toward the coast. Larger-scale GOES-13 animations covering the entire 48-hour RSO period are also available [Water Vapor (6.5 µm): MP4 | animated GIF ; Infrared window channel (10.7 µm): MP4 | animated GIF].

The illumination of a Full Moon helped to provide a vivid “visible image at night” using the Suomi NPP VIIRS 0.7 µm Day/Night Band (below), highlighting the clouds associated with the departing storm along and just off the US East Coast, as well as the vast areas inland that were snow-covered. In the toggle between the corresponding Infrared window (11.45 µm) image, cloud streets due to cold air streaming southward and southeastward across the Gulf of Mexico toward Cuba were also seen.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared window channel (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared window channel (11.45 µm) images [click to enlarge]

With the arrival of daylight on the morning of 24 January, the expansive area of snow cover was very apparent on GOES-13 Visible (0.63 µm) images, shown below. Snow depth values (inches) are plotted in cyan — 12 UTC depths for the earlier images, and 18 UTC depths for the later images.  The 18 UTC snow depth values were a bit less at many locations (due to compaction and/or melting), and parts of the extreme southern and southeastern edges of the snow cover were seen to melt away during the late morning hours.

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 Visible (0.63 µm) images [click to play animation]

False-color Red/Green/Blue (RGB) images made using Terra MODIS Visible (0.65 µm) and Snow/Ice (1.61 µm) images, below, showed how such RGB images can be useful for the discrimination of snow/ice (shades of red) vs. supercooled clouds (shades of white). Bare ground appears as shades of cyan.

Terra MODIS Visible (0.65 µm) and False-color RGB images [click to enlarge]

Terra MODIS Visible (0.65 µm) and False-color RGB images [click to enlarge]

The full-resolution Terra MODIS true-color RGB images viewed using the SSEC RealEarth web map server, below, showed even better detail, including the very sharp northern edge of the snow cover from New York and Connecticut to Massachusetts.

Terra MODIS true-color RGB iimage [click to enlarge]

Terra MODIS true-color RGB iimage [click to enlarge]

Terra MODIS true-color RGB image [click to enlarge]

Terra MODIS true-color RGB image [click to enlarge]

The wider swath of the VIIRS instrument on the Suomi NPP satellite provided a good true-color vs false-color image comparison, shown below. In this particular RGB image, show/ice (and glaciated ice crystal clouds) appear as shades of cyan, while supercooled water droplet clouds appear as shades of white.

Suomi NPP VIIRS true-color and false-color images [click to enlarge]

Suomi NPP VIIRS true-color and false-color images [click to enlarge]

Even greater detail could be seen in a 30-meter resolution Landsat-8 false-color RGB image, centered over the Washington DC area (below). Snow and ice also appear as shades of cyan in this image — ice can be seen in parts of the Potomac and Anacostia Rivers. The partially-plowed runway network of Reagan National Airport appears at the bottom center of the image.

Landsat-8 false-color image of the Washington DC area [click to enlarge]

Landsat-8 false-color image of the Washington DC area [click to enlarge]

A close-up Landsat-8 view of the Baltimore, Maryland area (below) also showed some ice forming in a few of the rivers.

Landsat-8 false-color image [click to enlarge]

Landsat-8 false-color image [click to enlarge]

Table of Maximum Wind Gusts [click to enlarge]

Table of Maximum Wind Gusts [click to enlarge]

Widespread strong gusts occurred with this storm, as shown in the Table above (from the National Weather Service). The hourly animation, below, of GOES-13 Water Vapor (6.5 µm) with Wind Gusts superimposed, shows that the strongest gusts occurred as the storm’s dry slot, depicted as darker shades in the water vapor imagery and a region which is often associated with strong subsidence, was nearby.

Hourly GOES-13 Infrared Water Vapor (6.5 µm) and surface reports of Wind Gusts (knots) [click to play animation]

Hourly GOES-13 Infrared Water Vapor (6.5 µm) and surface reports of Wind Gusts (knots) [click to play animation]

Suomi NPP VIIRS Visible and Near-Infrared imagery, below, shows the extent of the snowcover on 25 January. The benefit of multi-spectral imagery (as is available today from Suomi NPP, and will also be available from GOES-R) appears by comparing the 0.64 µm, 0.86 µm and 1.61 µm channels. For example, regions of snow vs. no snow are less distinct in the 0.86 µm (over northwest Connecticut, for example), but land/water differences are accentuated. Comparing the visible and the 1.61 µm brings out snow/ice features. The band of snow over southern New England is dark in the 1.61 µm because snow/ice absorbs radiation at that wavelength. Snow is highly reflective in the visible, however, and it appears bright white on that image. This comparison of visible and 1.61 µm can also be used to highlight ice clouds (as noted higher up in this blog post).

Suomi NPP VIIRS Visible (0.64 µm) and Near-Infrared (0.86 µm and 1.61 µm) imagery, 1753 UTC on 25 January 2016 [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Near-Infrared (0.86 µm and 1.61 µm) imagery, 1753 UTC on 25 January 2016 [click to enlarge]

RGB Imagery allows a one-image perspective (vs. an image toggle) to highlight features. The RGB image from Suomi NPP VIIRS imagery (0.64 µm and 1.61 µm) below shows snow cover (shades of red) over the Northeast. In the mid-Atlantic states, thin patchy clouds are present. The brightness of these clouds in the 1.61 µm channel suggests they are composed of supercooled water droplets.

Suomi NPP VIIRS RGB Imagery showing snow/ice features (red), water droplet cloud features (white) and bare ground (cyan), 1753 UTC on 25 January 2016 [click to enlarge]

Suomi NPP VIIRS RGB Imagery showing snow/ice features (red), water droplet cloud features (white) and bare ground (cyan), 1753 UTC on 25 January 2016 [click to enlarge]


===== Added 28 January =====
Rich Grumm, the SOO from the WFO in State College, discussed this storm as part of VISIT’s Satellite Chat series.

GOES-14 SRSO-R Imagery over North Carolina

May 21st, 2015 |



 

GOES-14 0.62 µm visible imagery, above, (here as an mp4, and here as a very large (220+ megabytes) animated gif) shows the development of convection over eastern North Carolina in a region of slight risk according to SPC (below).

Day 1 Outlook for Convection from SPC, issued at 1300 UTC 21 May 2015 [click to enlarge]

Day 1 Outlook for Convection from SPC, issued at 1300 UTC 21 May 2015 [click to enlarge]

==================================================================================

Mesoscale Discussion #713 from SPC, below, referenced the Super-Rapid scan imagery:

MESOSCALE DISCUSSION 0713
NWS STORM PREDICTION CENTER NORMAN OK
1111 AM CDT THU MAY 21 2015

AREAS AFFECTED…E-CNTRL AND ERN NC / SC GRAND STRAND

CONCERNING…SEVERE POTENTIAL…WATCH POSSIBLE

VALID 211611Z – 211745Z

PROBABILITY OF WATCH ISSUANCE…60 PERCENT

SUMMARY…SCATTERED STORMS ARE FORECAST TO DEVELOP OVER THE NEXT FEW
HOURS. AN ISOLATED SEVERE THREAT WILL LIKELY DEVELOP AND A WATCH
WILL STRONGLY BE CONSIDERED.

DISCUSSION…SUBJECTIVE SURFACE MESOANALYSIS PLACES A LOW 30 MI W
SOP WITH A WEST-EAST ORIENTED WARM FRONT AND A TRAILING COLD FRONT
ACROSS THE SC PIEDMONT. A PREFRONTAL CONFLUENCE/SURFACE TROUGH
EXTENDS FROM THE LOW SEWD THROUGH THE GRAND STRAND VICINITY.
OBSERVATIONS TO THE E OF THE SURFACE TROUGH AND LOCATED WITHIN THE
WARM SECTOR SHOW TEMPS WARMING TO NEAR 80 DEG F WITH BOUNDARY LAYER
DEWPOINTS IN THE MID-UPPER 60S INLAND AND AROUND 70 NEAR THE COAST.
SUPER RAPIDSCAN VISIBLE IMAGERY SHOWS A BUILDING TCU FIELD
IMMEDIATELY E OF THE LOW AND ALONG THE PREFRONTAL TROUGH/CONFLUENCE
.

WATER VAPOR IMAGERY LATE THIS MORNING IMPLIES A WEAK LEAD
DISTURBANCE MOVING ACROSS W-CNTRL NC AHEAD OF THE MID MS VALLEY
SHORTWAVE TROUGH FORECAST TO APPROACH THE CNTRL APPALACHIANS LATER
TODAY. IT SEEMS THE WEAK UPPER FORCING FOR ASCENT PROVIDED BY THE
LEAD IMPULSE COUPLED WITH ADDITIONAL DIABATIC HEATING WILL ERODE THE
CAP OVER THE NEXT 1-2 HOURS AND SCATTERED STORM COVERAGE IS PROBABLE
BY THE 18-19Z TIMEFRAME.

VEERING AND A GRADUAL STRENGTHENING OF WINDS WITH HEIGHT WILL
SUPPORT STORM ORGANIZATION ONCE A FEW VIGOROUS UPDRAFTS BECOME
ESTABLISHED. FORECAST SOUNDINGS DEPICT MODERATE BUOYANCY AS OF 16Z
ACROSS THE WARM SECTOR AND THIS SHOULD FAVOR STORM INTENSIFICATION
OVER THE NEXT SEVERAL HOURS ONCE INITIATION COMMENCES. ISOLD LARGE
HAIL AND DMGG WINDS WILL BE THE PRIMARY THREATS. DESPITE TEMPERED
LOW-LEVEL SHEAR…A TORNADO MAY ALSO BE POSSIBLE ESPECIALLY IF A
SUPERCELL CAN DEVELOP AND FAVORABLY TRACK ALONG THE WARM FRONT.

..SMITH/THOMPSON.. 05/21/2015

ATTN…WFO…AKQ…MHX…RAH…ILM…CAE…

LAT…LON 35267979 36097844 36297643 35847549 34977597 33737851
33897960 34497991 35267979

==================================================================================

The GOES-13 Sounder captured some of the destabilization that occurred ahead of the developing line of convection. Values less than -5 are widespread over southeastern North Carolina at 1600 UTC, after which time cirrus blowoff obscured the satellite view.

GOES-13 Sounder DPI values of Lifted Index, 1600 UTC 21 May 2015 [click to enlarge]

GOES-13 Sounder DPI values of Lifted Index, 1600 UTC 21 May 2015 [click to enlarge]

Suomi NPP’s orbits on 21 May allowed successive views of the developing convection, once at 1725 UTC and once near 1905 UTC. The convection developed near the edge of the swath in both images, however, so NUCAPS soundings did not view the environment closest to the storms. Infrared imagery, below, shows the quick evolution of convection.

Suomi NPP VIIRS 11.45 µm infrared imagery and NUCAPS Sounding Points (in green), ~1730 and ~1900 UTC 21 May 2015 [click to enlarge]

Suomi NPP VIIRS 11.45 µm infrared imagery and NUCAPS Sounding Points (in green), ~1730 and ~1900 UTC 21 May 2015 [click to enlarge]

VIIRS visible (0.64 µm) and near-infrared (1.61 µm) imagery, below, shows that the developing storms glaciated quickly; the 1.61 µm imagery over the convection shows the darker grey values characteristic of regions where ice crystals are strongly absorbing radiation. Water-based clouds — over Kentucky, for example — appear as bright white in both channels.

Suomi NPP VIIRS 0.64 µm visible imagery and 1.61 µm near-infrared imagery 1903 UTC 21 May 2015 [click to enlarge]

Suomi NPP VIIRS 0.64 µm visible imagery and 1.61 µm near-infrared imagery 1903 UTC 21 May 2015 [click to enlarge]