Severe thunderstorms in the Midwest

April 9th, 2015
GOES-13 0.63 µm visible images, with Cloud-Top Cooling Rate, Overshooting Tops Detection, and SPC storm reports (click to play animation)

GOES-13 0.63 µm visible images, with Cloud-Top Cooling Rate, Overshooting Tops Detection, and SPC storm reports (click to play animation)

A deepening area of low pressure (21 UTC surface analysis) was moving northeastward across the Midwest region of the US on 09 April 2015; GOES-13 0.63 µm visible images combined with the Cloud-Top Cooling Rate and Overshooting Tops Detection products (above; click image to play animation) showed a line of severe thunderstorms which quickly developed along the associated cold frontal boundary as it moved eastward across Iowa and Missouri during the afternoon hours. Cloud-Top Cooling Rates with some of the storms in Missouri were in excess of 50º C per 15 minutes (violet color enhancement) during their early stage of development (18:25 UTC image).

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 18:51 UTC or 1:51 PM local time (below) showed that the line of thunderstorms was beginning to produce a number of cloud-to-ground lightning strikes.

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image with cloud-to-ground lightning strikes

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image with cloud-to-ground lightning strikes

Focusing our attention on eastern Iowa and northern Illinois — where there were widespread reports of large hail, damaging winds, and tornadoes (SPC storm reports) — the organization of large, discrete supercell thunderstorms can be seen on GOES-13 0.63 µm visible channel images (below; click image to play animation), which exhibited numerous overshooting tops.

GOES-13 0.63 µm visible channel images, with SPC storm reports (click to play animation)

GOES-13 0.63 µm visible channel images, with SPC storm reports (click to play animation)

The corresponding GOES-13 10.7 µm IR channel images (below; click image to play animation) showed that the coldest cloud-top IR brightness temperatures were -67º C (darker black enhancement).

GOES-13 10.7 µm IR images, with Overshooting Top Detection and SPC storm reports (click to play animation)

GOES-13 10.7 µm IR images, with Overshooting Top Detection and SPC storm reports (click to play animation)

The NOAA/CIMSS ProbSevere product (below; click image to play animation) gauges the likelihood of a storm first producing severe weather (of any kind) within the next 60 minutes. It combines information about the environment (Most Unstable CAPE, Environmental Shear) from the Rapid Refresh Model, information about the growing cloud (Vertical Growth Rate as a percentage of the troposphere per minute and Glaciation Rate, also as a percentage per minute), and Maximum Expected Hail Size (MESH) from the MRMS. In this event, the ProbSevere product performed well for the storm that spawned the EF-4 tornado, although due to the cloudiness of the satellite scene the ProbSevere model was unable to diagnose vertical growth rate and glaciation rate (which diminished the potential lead-time). Below is a chronological timeline of events for that storm:

2308 UTC: first ProbSevere > 50%
2310 UTC: first ProbSevere > 70%
2311 UTC: NWS Severe T-Storm Warning
2312 UTC: ProbSevere = 88%
2323 UTC: 1.00″ hail 2 SE Dixson (15 min lead-time for ProbSevere@50, 13 min for ProbSevere@70, 12 min for NWS Svr Warning)
2335 UTC: NWS Tornado Warning (ProbSevere = 94%)
2340 UTC: Tornado report 2 NE Franklin Grove

Radar reflectivity with NOAA/CIMSS ProbSevere model contours and NWS warning polygons (click to play animation)

Radar reflectivity with NOAA/CIMSS ProbSevere model contours and NWS warning polygons (click to play animation)

In spite of widespread cloudiness, the GOES-13 Sounder single-field-of-view Lifted Index (LI), Convective Available Potential Energy (CAPE), and Total Precipitable Water (TPW) derived product images (below) were able to portray that the air mass in the warm sector of the low ahead of the strong cold front was was both unstable — LI values of -4 to -8º C (yellow to red color enhancement) and CAPE values of 3000-4000 J/kg (yellow to red color enhancement) — and rich in moisture, with TPW values of 30-40 mm or 1.2 to 1.6 inches (yellow to red color enhancement).

GOES-13 Sounder Lifted Index derived product images (click to play animation)

GOES-13 Sounder Lifted Index derived product images (click to play animation)

GOES-13 Sounder Lifted CAPE derived product images (click to play animation)

GOES-13 Sounder CAPE derived product images (click to play animation)

GOES-13 Sounder Total Precipatable Water (TPW) derived product images (click to play animation)

GOES-13 Sounder Total Precipatable Water (TPW) derived product images (click to play animation)

On the following day (10 April), it was cloud-free as the Landsat-8 satellite passed over northern Illinois at 16:41 UTC or 11:41 AM local time — and the 30.2 mile long southwest-to-northeast oriented tornado damage path that produced EF-4 damage and was responsible for 2 fatalities and 22 injuries (NWS Chicago event summary) was evident on 15-meter resolution Band 8 0.59 µm panchromatic visible images viewed using the SSEC RealEarth web map server (below). An aerial survey of part of the tornado damage path can be seen here.

Landsat-8 0.59 µm panchromatic visible image of southwestern portion of tornado damage track (click to enlarge)

Landsat-8 0.59 µm panchromatic visible image of southwestern portion of tornado damage track (click to enlarge)

Landsat-8 0.59 µm panchromatic visible image of northeastern portion of tornado damage path (click to enlarge)

Landsat-8 0.59 µm panchromatic visible image of northeastern portion of tornado damage path (click to enlarge)

A Landsat-8 false-color image (using Bands 6/5/4 as Red/Green/Blue) is shown below. The 2 tornado-related fatalities occurred in Fairdale.

Landsat-8 false-color image (using Bands 6/5/4 as R/G/B)

Landsat-8 false-color image (using Bands 6/5/4 as R/G/B)

On a side note, in the cold (northwestern) sector of the low it was cold enough for the precipitation type to be snow — and up to 4 inches of snow fell in western Iowa. GOES-13 0.63 µm visible channel images (below; click image to play animation) showed the swath of snow cover as it rapidly melted during the daytime hours on 10 April.

GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

In fact, the swath of snow cover across eastern Nebraska and western/northern Iowa was also evident on a Suomi NPP VIIRS Day/Night Band (DNB) image at 08:49 UTC or 3:39 AM local time (below), highlighting the “visible image at night” capability of the DNB (given ample illumination from the Moon).

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Antecedent Conditions for a Nor’easter

January 26th, 2015
GOES-13 Sounder Skin Temperature derived product image

GOES-13 Sounder Skin Temperature derived product image

Forecasts have been consistent in the past days for a storm of historic proportions over parts of southern New England. What conditions that are present now argue for the development of a strong winter storm? The image above is the GOES Sounder Land Surface Temperature (or “Skin Temperature”) product; cold air is present over southeastern Canada, with surface temperatures near -30 C, associated with a surface high pressure system. The high pressure will act to reinforce the cold air at the surface, preventing or delaying any changeover to liquid or mixed precipitation (a MODIS Land Surface Temperature product at 1500 UTC on 26 January similarly shows cold air banked over southern Canada).

GOES_SkinT_1400_26January2015

GOES Sounder estimate of Skin Temperature, 1400 UTC 26 January 2015 (Click to enlarge)

Winds over southern New England early on the 26th continued out of the north and northwest, maintaining cold air at the surface. The ASCAT (from METOP-A) imagery above shows brisk northwesterly winds south of southern New England just before 0100 UTC, with southwesterlies east of Georgia and South Carolina just before 0300 UTC. Those southwesterlies are helping moisten the atmosphere, and heavy snows require abundant moisture. MIMIC Total Precipitation (below; click image to play animation) testifies to the moistening that is occurring off the southeast coast as this system develops; the storm appeared to tap moisture from both the Gulf of Mexico and a pre-existing atmospheric river over the Atlantic Ocean.

[Added: The 1540 UTC ASCAT winds show the surface circulation east of Hatteras and the mouth of the Chesapeake Bay! Winds south of New England have shifted to northeasterly. The location of the circulation well off the coast suggests cold air can be maintained over land.]

MIMIC total Precipitable Water (click to play animation)

MIMIC total Precipitable Water (click to play animation)

Given that moisture and cold air are present, what features argue for the development of a strong storm? The GOES-13 water vapor images (below; click image to play animation; also available as an MP4 movie file) with cloud-to-ground lightning strikes superimposed show the potent system developing off the US East Coast and blossoming over the Gulf Stream as a secondary warm conveyor belt forms (a water vapor image with lightning animation from 25-26 January is available here). Strong sinking motion behind the system is indicated by the development of warm water vapor channel brightness temperatures (yellow color enhancement), and strong rising motion ahead of the system helps to generate widespread, strong convection. Convection also occurred over the Deep South late on 25 January in response to solar heating. The system depicted in the Water Vapor imagery is obviously quite vigorous.

GOES-13 6.5 µm water vapor channel images (click to play animation)

GOES-13 6.5 µm water vapor channel images (click to play animation)]

Suomi NPP VIIRS 11.45 µm IR channel and 0.64 µm visible channel images (below) showed that there was a great deal of convective banding within the secondary warm conveyor belt.

Suomi NPP VIIRS 11.45 µm IR channel and 0.64 µm channel images, with lightning, surface fronts and METAR reports

Suomi NPP VIIRS 11.45 µm IR channel and 0.64 µm channel images, with lightning, surface fronts and METAR reports

Total Column Ozone is frequently used as a proxy of tropopause folding; tropopause folds accompany very strong storm development and the vertical circulation associated with the potential vorticity anomaly (maximum) associated with the folding draws stratospheric ozone down into the troposphere. GOES Sounder Total Column Ozone derived product images (below; click to play animation; also available as an MP4 movie file) show that the dynamic tropopause — taken to be the pressure of the PV1.5 surface, red contours — descends below the 400-450 hPa level along the southern gradient of the higher ozone values (green to red color enhancement) as the potential vorticity anomaly pivots eastward along the Gulf Coast states and then northeastward toward the intensifying storm. The presence of clouds prevented ozone retrievals over many areas, but some ozone values over 400 Dobson Units (red color enhancement) could be seen, which is characteristic of stratospheric air.

GOES Sounder Total Column Ozone derived product images (click to play animation)

GOES Sounder Total Column Ozone derived product images (click to play animation)

As the storm approached New England, a MODIS 11.0 µmIR channel image (below) revealed the presence of widespread embedded convective elements within the broad cloud shied, with some cloud-top IR brightness temperatures as cold as -65ºC (darker red color enhancement). These pockets of convection could enhance snowfall rates once they moved inland.

MODIS 11.0 µm IR channel image, with lighting strikes, METAR surface reports, and fixed buoy reports

MODIS 11.0 µm IR channel image, with lighting strikes, METAR surface reports, and fixed buoy reports

An overlay of the RTMA surface winds (below) helped to locate the position of the surface low east of the Delmarva Peninsula. That position agrees well with ASCAT winds from 0158 UTC on 27 January.

MODIS 11.0 µm IR channel image, with RTMA surface winds

MODIS 11.0 µm IR channel image, with RTMA surface winds

A comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm IR channel images at 06:39 UTC or 1:39 AM Eastern time is shown below. With illumination from the Moon in the Waxing Gibbous phase (at about 60% of Full), the DNB provided a “visible image at night” which showed the expansive offshore “comma cloud” of the storm, along with the locations of bright cloud illumination from dense lightning activity (note the bright lightning signature east of Cape Cod, which corresponded well with a cluster of positive cloud-to-ground lightning strokes). Numerous pockets of convective development were seen well off the coast of North and South Carolina, due to strong cold air advection over the warm waters of the Gulf Stream.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images (with cloud-to-ground lightning strikes)

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images (with cloud-to-ground lightning strikes)

Significant rainfall event in California

December 2nd, 2014
MIMIC Total Precipitable Water product, with surface analysis overlays

MIMIC Total Precipitable Water product, with surface analysis overlays

As of 25 November 2014, much of the state of California was experiencing extreme to exceptional drought conditions.  However, the development of a large occluded mid-latitude cyclone over the far eastern Pacific Ocean during the 01 December – 02 December time period began to draw high values (up to 60 mm or 2.4 inches, darker red color enhancement) of total precipitable water (TPW) northward from the Inter-Tropical Convergence Zone (ITCZ), as seen on AWIPS images of the MIMIC TPW product (above). While the rainfall was beneficial in terms of drought mitigation, amounts of up to 12 inches did cause flooding and mudslide problems in some locations.

An animation of hourly MIMIC TPW images from 30 November – 02 December (below; click image to play animation) showed the northward surge of moisture toward the California coast, and also hinted at a complex inner structure associated with the occluded low.

MIMIC Total Precipitable Water product (click image to play animation)

MIMIC Total Precipitable Water product (click image to play animation

Comparison of MODIS 6.7 um and GOES-15 6.5 µm water vapor channel images

Comparison of MODIS 6.7 um and GOES-15 6.5 µm water vapor channel images

On 02 December, comparisons of AWIPS II images of 1-km resolution MODIS 6.7 µm and 4-km resolution GOES-15 6.5 µm water vapor channel data around 11 UTC (above) and around 22 UTC (below) demonstrated the importance of improved spatial resolution for more clearly identifying some of the smaller-scale structure features within the core of the occluded low.

Comparison of MODIS 6.7 µm and GOES-15 6.5 µm water vapor channel images

Comparison of MODIS 6.7 µm and GOES-15 6.5 µm water vapor channel images

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 22:18 UTC (below) shows a few areas of embedded convection, some of which had produced cloud-to-ground lightning strikes in the hour preceding the images.

Suomi NPP VIIS 0.64 µm visible channel and 11.45 µm IR channel images, with cloud-to-ground lightning strikes

Suomi NPP VIIS 0.64 µm visible channel and 11.45 µm IR channel images, with cloud-to-ground lightning strikes

Major lake effect snow event downwind of Lake Erie and Lake Ontario

November 18th, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

Cold arctic air (surface air temperatures in the upper teens to lower 20s F) flowing across the still-warm waters of Lake Erie and Lake Ontario (sea surface temperature values as warm as the middle to upper 40s F) were 2 ingredients that helped create a major lake effect snowfall event on 18 November 2014 (VIIRS visible image with surface analysis). Storm total snowfall amounts were as high as 65 inches in Erie County, New York (NWS Buffalo Public Information Statement). GOES-13 0.63 µm visible channel images (above; click image to play animation) showed the large and well defined single-band lake effect cloud features that developed over each of the lakes. The band over Lake Erie was nearly stationary for several hours, producing snowfall rates as high as 4 inches per hour at some locations in the Southtowns of Buffalo. The stationary behavior (and very sharp northern edge, due to a “locked thermal convergence zone“) of the Lake Erie snow band was quite evident on composite radar reflectivity (below; click image to play animation; images courtesy of the College of DuPage). The formation and growth of this band benefited from a long fetch of southwesterly winds oriented along the axis of Lake Erie.  Isolated negative cloud-to-ground lightning strikes were observed at 16:45 and 22:15 UTC, implying the presence of embedded pockets of thundersnow.

Composite radar reflectivity (click to play animation)

Composite radar reflectivity (click to play animation)

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 18:17 UTC or 1:17 pm local time is shown below. The coldest cloud-top IR brightness temperature was -37º C (green color enhancement), which corresponded to a pressure of 437 hPa (or an altitude around 6 km) on the 12 UTC Buffalo NY rawinsonde report.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Comparisons of Terra and Aqua MODIS true-color Red/Green/Blue (RGB) images covering the Lake Erie/Lake Ontario region along with a high-resolution view centered on Buffalo NY are shown below.

Terra and Aqua MODIS true-color RGB images

Terra and Aqua MODIS true-color RGB images

Terra and Aqua MODIS true-color RGB images

Terra and Aqua MODIS true-color RGB images

A 15-meter resolution Landsat-8 0.59 µm panochromatic visible channel image from the SSEC RealEarth web map server (below) showed great detail to the Lake Ontario snow band as it was moving inland over the Watertown NY area at 15:45 UTC.

Landsat-8 0.59 µm panochromatic visible image

Landsat-8 0.59 µm panochromatic visible image

Looking back to the preceding nighttime hours, a toggle between Suomi NPP VIIRS 0.7 µm Day/Night Band, 3.74 µm shortwave IR, 11.45 µm IR, and 11.45-3.74 µm IR brightness temperature difference “Fog/stratus product” images at 06:54 UTC or 1:54 am local time (below) showed that the lake effect bands were already well-developed, with minimum 11.45 µm IR brightness temperatures of -30º C and colder (yellow color enhancement). Even with minimal lunar illumination — the Moon was in the Waning Crescent phase, at only 7% of full — the lake effect cloud bands features could still be seen on the Day/Night Band image.

Suomi NPP VIIRS 0.7 µm Day/Night Band, 3.74 µm shortwave IR, 11.45 µm IR, and

Suomi NPP VIIRS 0.7 µm Day/Night Band, 3.74 µm shortwave IR, 11.45 µm IR, and “Fog/stratus product” images

For a more in-depth discussion of this lake effect snow event, watch the VISIT Satellite Chat session.