Bonnie

May 29th, 2016

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

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

Tropical Depression 2 was upgraded to Tropical Storm Bonnie at 2100 UTC on Saturday 28 May, the second named storm of the 2016 Atlantic Season (Hurricane Alex, which formed in January, was the first named storm). The water vapor animation above shows that Bonnie’s initial spin may be traced to a front associated with an occluded system which crawled through the eastern United States, exiting on about 23 May 2016. It’s not uncommon for vorticity associated with extratropical cyclone fronts to sow the seed of a tropical cyclone, especially early (or late) in the season. In this case, the cold front failed to pass Bermuda, and by 27 May, persistent thunderstorms about halfway between Bermuda and the Bahamas suggested tropical cyclogenesis was underway (GOES-13 visible image animations: 26 May | 27 May).

MIMIC Total Precipitable Water derived from Microwave imagery, 1800 UTC 28 May - 1700 UTC 30 May [click to enlarge]

MIMIC Total Precipitable Water derived from Microwave imagery, 1800 UTC 28 May – 1700 UTC 30 May [click to enlarge]

Total Precipitable Water fields from the microwave MIMIC product, above, show the system was embedded deep within tropical moisture (24-26 May animation). Tropical moisture associated with the storm moved up the east coast of the United States into the mid-Atlantic States with local flooding reported. This longer animation (from 21 through 28 May) shows that persistent westward motion of moisture occurred over the tropical Atlantic well in advance of Bonnie’s formation.

Rapidscat Scatterometer Winds, 1012 UTC on 27 May [click to enlarge]

Rapidscat Scatterometer Winds, 1012 UTC on 27 May [click to enlarge]

The tropical wave that produced Bonnie showed a closed circulation as early as 1012 UTC on 27 May according to Rapidscat scatterometer winds, above, and MODIS Sea Surface Temperatures, below, showed very warm water (with SST values of 80º F) over the Gulf Stream.

MODIS-based Sea Surface Temperatures, 1848 UTC on 27 May [click to enlarge]

MODIS-based Sea Surface Temperatures, 1848 UTC on 27 May [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.70 µm Visible) and Infrared (11.45 µm) Imagery at 0621 UTC on 27 May 2016 [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.70 µm Visible) and Infrared (11.45 µm) Imagery at 0621 UTC on 27 May 2016 [click to enlarge]

Suomi NPP overflew this tropical system at various times during its lifecycle. Shortly after midnight on 27 May 2016, above, strong convection was centered just north of the apparent surface circulation (as inferred by the curved bands of low-level clouds, clouds made visible by moonlight in the night-time VIIRS Day/Night Band visible imagery). Twenty-four hours later, at 0742 UTC on 28 May, below, in a more zoomed-in view, the (then) Tropical Depression Number 2 is supporting strong convection that is obscuring the low-level circulation center.

Suomi NPP VIIRS Day/Night Band (0.70 µm Visible) and Infrared (11.45 µm) Imagery at 0742 UTC on 28 May 2016 [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.70 µm Visible) and Infrared (11.45 µm) Imagery at 0742 UTC on 28 May 2016 [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.70 µm Visible) and Infrared (11.45 µm) Imagery at 0723 UTC on 29 May 2016 [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.70 µm Visible) and Infrared (11.45 µm) Imagery at 0723 UTC on 29 May 2016 [click to enlarge]

Finally, at 0723 UTC on 29 May, (above) after strong wind shear has displaced all convection well north of the center, the low-level circulation of Tropical Storm Bonnie is southeast of the South Carolina Coast. Strong convection is over North Carolina. This shear was noted in the 0300 UTC and 0900 UTC (29 May) Discussions from the National Hurricane Center. The effect of shear is apparent in the two GOES-13 Infrared Images below, from 2045 UTC on 28 May when convection was close to the center, and from 1045 UTC on 29 May, shortly before landfall, when convection was stripped from the center and displaced well to the north.

GOES-13 Infrared (10.7 µm) Imagery at 2045 UTC on 28 May and at 1045 UTC 29 May 2016; the Yellow Arrow points to the low-level circulation center [click to enlarge]

GOES-13 Infrared (10.7 µm) Imagery at 2045 UTC on 28 May and at 1045 UTC 29 May 2016; the Yellow Arrow points to the low-level circulation center [click to enlarge]

Closer views of the sheared system on 28 May can be seen on 1906 UTC VIIRS and 1937 UTC AVHRR Visible and Infrared images, as well as a GOES-13 Visible animation.

===== 01 June Update =====

GOES-13 Visible (0.63 µm) images [click to play MP4 animation]

GOES-13 Visible (0.63 µm) images [click to play MP4 animation]

The remnant circulation of Bonnie moved very slowly northeastward during the 30 May – 01 June period, as seen in GOES-13 Visible (0.63 µm) images covering each of those 3 days (above; also available as a large 95 Mbyte animated GIF). The periodic formation of deep convective clusters continued to produce heavy rainfall over parts of far eastern North and South Carolina.

On the morning of 01 June, an overpass of the Metop-B ASCAT instrument sampled the flow around the low-level circulation center (LLCC) off the coast of North Carolina; several hours later, Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images provided a high-resolution view of the system at 1755 UTC (below). Cloud-top IR brightness temperatures were as cold as -78º C within the small convective cluster located just north of the LLCC.

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Rapidly intensifying mid-latitude cyclone off the US East Coast

March 5th, 2016

GOES-13 Water Vapor (6.5 µm) images [click to play MP4 animation]

GOES-13 Water Vapor (6.5 µm) images [click to play MP4 animation]

An area of low pressure rapidly intensified off the US East Coast during the 04 March05 March 2016 period (surface analyses). GOES-13 (GOES-East) Water Vapor (6.5 µm) images (above; also available as a large 57 Mbyte animated gif) showed classic signatures of the various stages of strong mid-latitude cyclone development — most notably the formation of a well-defined comma head and dry slot. Even though the storm was well offshore, impacts near and along the coast included snowfall amounts as high as 6.7 inches at Princess Anne, Maryland, 5.0 inches at Montross, Virginia, and 2.6 inches at Topsfield, Massachusetts; winds gusted to 55 mph at Jennettes Pier, North Carolina and 53 mph at Nantucket, Massachusetts. In Newfoundland, Gander received 17.3 inches of snow, and winds gusted to 77 mph at Cape Pine.

Aqua MODIS Water Vapor (6.7 µm), Infrared (11.0 µm), and Visible (0.65 µm) images [click to enlarge]

Aqua MODIS Water Vapor (6.7 µm), Infrared (11.0 µm), and Visible (0.65 um) images [click to enlarge]

Aqua MODIS Water Vapor (6.7 µm), Infrared Window (11.0 µm), and Visible (0.65 µm) images at 1737 UTC (above) and Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 1722 UTC (below) showed the storm around the time the Ocean Prediction Center indicated that it began producing hurricane force winds (18 UTC analysis).

Suomi NPP VIIRS Visible (0.64 µm) and Infrared (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared (11.45 µm) images [click to enlarge]

A sequence of POES AVHRR Infrared (12.0 µm) images at 1852, 2205, and 0100 UTC along with Metop ASCAT surface scatterometer winds (below) showed the storm as it continued to intensify. Even though AWIPS labeled the ASCAT winds with a time stamp of 0228 UTC, cursor sampling found winds as strong as 57 knots south of the storm center and 59 knots north of the storm center at 0155-0156 UTC.

POES AVHRR Infrared (12.0 µm) images at 1852, 2205, and 0100 UTC, with Metop ASCAT winds at 0155 UTC [click to enlarge]

POES AVHRR Infrared (12.0 µm) images at 1852, 2205, and 0100 UTC, with Metop ASCAT winds at 0155 UTC [click to enlarge]

The Ocean Prediction Center posted an animation of Geocolor images of the storm on Twitter:


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.

Hurricane Alex

January 13th, 2016

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

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

Subtropical Storm Alex (NHC advisory archive) formed in the far eastern Atlantic Ocean on 13 January 2016. Animations of GOES-13 (GOES-East) 0.63 µm Visible (above) and 10.7 µm Infrared images (below) showed the initial evolution and northeastward motion of the storm. Alex is only the 4th known January tropical or subtropical storm to have formed in the Atlantic since the historical record began in 1851.

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

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

===== 14 January Update =====

A comparison of Suomi NPP VIIRS Infrared (11.45 µm) and Day/Night Band (0.7 µm) images at 0320 UTC (below) showed the well-defined eye of Alex. With the Moon in the Waxing Crescent phase (at 30% of Full) there was enough illumination to demonstrate the “visible image at night” capability of the Day/Night Band. A magnified version of the Infrared image showing the eye can be seen here.

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

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

As of 15 UTC on 14 January, Alex had made the transition from subtropical storm to Category 1 hurricane (eastern Atlantic Ocean surface analyses). GOES-13 Infrared (10.7 µm) images (below) showed the well-defined eye that had formed. Alex became the first known hurricane to form in the Atlantic Ocean since 1938, and only the second hurricane on record to from north of 30ºN latitude and east of 30ºW longitude.

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

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

A DMSP-16 SSMIS Microwave (85 GHz) image (below) revealed the eye structure at 1653 UTC.

DMSP-16 SSMIS 85Ghz microwave brightness temperature image [click to enlarge]

DMSP-16 SSMIS 85Ghz microwave brightness temperature image [click to enlarge]

===== 15 January Update =====

While still classified as a hurricane, Alex was undergoing a weakening trend as it approached the Azores Islands during the early morning hours on 15 January. GOES-13 Infrared (10.7 µm) images (below) showed a strong convective band that produced a brief period of heavy rain at Ponta Delgata and Lajes Acores several hours prior to the passage of the eye of Alex (which occurred in the 11-14 UTC time frame — and Alex was downgraded at that point to a Tropical Storm). At Ponta Delgata a peak wind gust of 50 knots was recorded at 1130 UTC.

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

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

ISS-Rapidscat surface scatterometer winds (below) showed the center of circulation of Alex just south of the Azores Islands at 1118 UTC.

Rapidscat surface scatterometer winds [click to enlarge]

Rapidscat surface scatterometer winds [click to enlarge]

===== 16 January Update =====

Using a long animation of GOES-13 Water Vapor (6.5 µm) images covering the 06-16 January period (below; also available as a large 165-Mbyte animated gif), the origination of Hurricane Alex could be traced back to a strong baroclinic mid-latitude cyclone that rapidly intensified off the southeast coast of the US on 07 January.

GOES-13 Water Vapor (6.5 µm) images [click to play MP4 animation]

GOES-13 Water Vapor (6.5 µm) images [click to play MP4 animation]

The origin and motion of Alex could also be identified using the satellite-derived atmospheric motion vector 850 hPa Relative Vorticity product (below). A region of lower-tropospheric vorticity over Cuba on 06 January began moving northeastward across the Bahamas, then eastward across the Atlantic Ocean on 07 January.

850 hPa Relative Vorticity product [click to play animation]

850 hPa Relative Vorticity product [click to play animation]

For another perspective on the history of the development of Alex, see this article from The Weather Channel.