Severe convection in South Dakota

July 9th, 2009 |
GOES-12 10.7 µm IR images + hail and wind reports

GOES-12 10.7 µm IR images + hail and wind reports

Severe convection developing over eastern South Dakota during the pre-dawn hours on 09 July 2009 exhibited an unusually large and well-defined “enhanced-v” storm top signature on AWIPS images of the GOES-12 10.7 µm IR channel (above) as it produced large hail (up to 2.50 inches in diameter) and damaging winds (gusting as high as 90 mph) across parts of South Dakota and extreme northeastern Nebraska.

An overlay of negative and positive cloud-to-ground lighting strikes (below) showed that this storm was producing a large amount of lightning in the vicinity of the overshooting top (near the vertex of the enhanced-v signature), but there was also a number of strikes located a fair distance to the northeast, far away from the coldest cloud tops.

GOES-12 10.7 µm IR images + cloud-to-ground lightning strikes

GOES-12 10.7 µm IR images + cloud-to-ground lightning strikes

A comparison of the 4-km resolution GOES-12 10.7 µm IR data with 1-km resolution NOAA-15 AVHRR 10.8 µm IR data (below) demonstrated the advantage of improved spatial resolution in detecting the cloud top temperature structure of the enhanced-v signature. The coldest/warmest cloud top temperatures on the NOAA-15 IR image were -80º C / -59º C (deltaT = 21º C), compared to -68º C / -56º C (deltaT = 12º C) on the GOES-12 IR image.

4-km GOES-12 10.7 µm IR + 1-km NOAA-15 10.8 µm IR images

4-km GOES-12 10.7 µm IR + 1-km NOAA-15 10.8 µm IR images

A NOAA-15 AVHRR Red/Green/Blue (RGB) false-color composite image (below) displayed a stunning view of the storm just after sunrise (at 11:33 UTC), about 20 minutes after it produced a wind gust to 90 mph, hail up to 1.00 inch in diameter, and brief heavy rain near Scotland in southeastern South Dakota.

Note that the overshooting top was casting a shadow onto the anvil of the storm below — and this very tall thunderstorm complex was casting an impressive shadow to the west and southwest across South Dakota and Nebraska. Also note the presence of a boundary layer gravity wave train oriented southwest-to-northeast across Nebraska, which was positioned in advance of a cold frontal boundary.

NOAA-15 AVHRR Red/Green/Blue (RGB) false color composite image

NOAA-15 AVHRR Red/Green/Blue (RGB) false color composite image

Additional radar and satellite images of this storm can be found on the AccuWeather WeatherMatrix Blog.

Convective storm tops and different sizes of cloud ice crystals

July 6th, 2009 |
MODIS visible, 11.0 µm IR window, and 3.7 µm shortwave IR images

MODIS visible, 11.0 µm IR window, and 3.7 µm shortwave IR images

AWIPS images of the 1-km resolution MODIS visible, 11.0 µm IR window, and 3.7 µm shortwave IR channel data (above) showed some interesting differences in the appearance of convective storm tops over the northern and central Rocky Mountain region on 06 July 2009. Note that some portions of the storm tops appear significantly warmer (darker gray colors) on the 3.7 µm image — this is due to solar reflection off of smaller ice particles within the upper anvil layer. Such differences in cloud top particle size are not apparent on the visible or the standard IR window images (nor do they necessarily correspond to differences seen in the IR brightness temperature patterns on the storm tops). Storms forming with stronger updrafts may produce a higher concentration of smaller ice crystals within the anvil region of the storm top, due to less time for the ice particles to grow in size during their rapid ascent.

Wildfires in Alaska

July 3rd, 2009 |
GOES-11 visible images

GOES-11 visible images

The 2009 wildfire season roared to life in Alaska on 02 July – 03 July 2009, with a number of very large and very intense fires breaking out across interior portions of the state. A ridge of high pressure was in place over the region, allowing Fairbanks to experience a high temperature above 80º F (27º C) on both days. GOES-11 visible images (above) showed some impressive smoke plumes developing on 02 July, especially from the fire located to the east-southeast of Fort Yukon (station identifier PFYU) — note the pulses of “pyrocumulus” that emanated from this >19,000 acre “Little Black One” fire complex:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
1033 AM AKDT FRI JUL 3 2009

…WILDFIRES BRING SMOKE TO INTERIOR…

THE MAJORITY OF THE SMOKE IS COMING FROM A WILDFIRE KNOW AS LITTLE BLACK ONE. THIS FIRE IS LOCATED NORTHEAST OF CIRCLE IN THE YUKON FLATS. AS OF 230 PM YESTERDAY THIS FIRE WAS OVER 19000 ACRES. CURRENT SATELLITE IMAGERY SHOWS THIS FIRE TO BE CONTINUING TO INCREASE IN AREA.

OTHER SMALLER FIRES ARE ALSO BURNING ACROSS THE AREA. WINDS ARE CURRENTLY BLOWING THE SMOKE FROM NORTHEAST TO SOUTHWEST ON THE FIRES.

The large and dense smoke plume originating east of Fort Yukon continued to drift southwestward overnight, and had moved over the Anchorage area (station identifier PANC) by the morning hours on 03 July.

Also, in spite of the very large satellite viewing angle, another feature that could be followed on the GOES-11 visible imagery was the southwestward movement of fog and stratus from the Arctic Ocean into interior portions of the North Slope region of Alaska after about 06:00 UTC on 03 July. The visibility dropped to less than 1/2 mile at Kuparuk (station identifier PAKU) at 06:00 UTC, with an air temperature at that time of 34º F (+1º C).

GOES-11 visible image

GOES-11 visible image

It is interesting to note the presence of a thin volcanic plume (likely from an earlier eruption of the Sarychev Peak volcano in the Kuril Islands) farther to the east, located over the Alaska/Yukon border region (above) — this very high altitude volcanic plume feature is illuminated early in the day (when the sun angle was low, and forward scattering was the highest), but then “disappears” on the visible imagery as the sun angle increases and forward scattering diminishes. In contrast, the low-altitude smoke features become brighter as the sun angle increases during the day, allowing more solar reflection to better illuminate the top of the thick smoke (below).

GOES-11 visible images

GOES-11 visible images

GOES-11 3.9 µm shortwave IR images (below) revealed a number of very hot fire pixels (black to red color enhancement) — the hottest pixels in the “Little Black One” fire exhibited an IR brightness temperature of 341.0 K (the saturation temperature of the GOES-11 shortwave IR detectors) at 06:30 UTC. The fire located to the west-northwest of Nenana (station identifier PANN) exhibited IR pixels as hot as 340.0 K at 02:30 UTC. The large area of saturated (red) pixels across the Arctic Slope region at 09:00 UTC was due to sun glint (which also caused the very bright pixels to appear at 09:00 UTC on the visible imagery).

GOES-11 3.9 µm shortwave IR images

GOES-11 3.9 µm shortwave IR images

A comparison of the 1-km resolution NOAA-16 AVHRR 3.7 µm and the 4-km resolution GOES-11 3.9 m shortwave IR images (below) demonstrates the importance of better spatial resolution for detecting hot fire pixels. The hottest IR pixels in both the NOAA-16 and the GOES-11 images were 330.0º K (darker red color) — but note that the large fire located southeast of Fort Yukon (PFYU) was only as hot as 307.0º K (darker black color) on the GOES-11 shortwave IR image.

GOES-11 3.9 µm + NOAA-16 3.7 µm shortwave IR images

GOES-11 3.9 µm + NOAA-16 3.7 µm shortwave IR images

The GOES-11 Wildfire Automated Biomass Burning Algorithm (ABBA) product (below) analyzed the first fire pixels east of the Fort Yukon region around 19:30 UTC on 02 July, several hours before the large smoke plume began to form.

GOES-11 Wildfire ABBA product

GOES-11 Wildfire ABBA product


Wildfire ABBA legend

Outflow boundary in the Bay of Campeche

July 2nd, 2009 |
GOES-12 visible images

GOES-12 visible images

GOES-12 visible images (above) revealed the northward propagation of an large convective outflow boundary across the Bay of Campeche (in the far southwestern Gulf of Mexico) on 02 July 2009. A larger-scale GOES-12 visible image (below) showed that at one point this outflow occupied an area approximately the size of the state of Wisconsin!

GOES-12 visible image

GOES-12 visible image

An overpass of the QuikSCAT satellite provided SeaWinds near-surface wind data (below) which showed that there was southeasterly flow across much of the Bay of Campeche region, but the wind speeds increased from about 10-15 knots ahead of the outflow boundary to 15-25 knots behind the outflow boundary (the winds at Buoy 42055 gusted to 21 knots around 12 UTC). The QuikSCAT wind vectors showing speeds of 34-50 knots (yellow to red colors) were not valid, due to rain flags greater than 90%. The air temperature and dew point values barely budged with the passage of this outflow boundary, due in part to the very warm (84º F or 29º C) water temperature.

GOES-12 visible + GOES-12 IR + QuikSCAT winds

GOES-12 visible + GOES-12 IR + QuikSCAT winds

AWIPS images of the Blended Total Precipitable Water (TWP) product (below) suggest that the TPW dropped from about 57 mm (2.24 inches, red color enhancement) to around 46 mm (1.81 inches, yellow color enhancement) in the wake of this outflow boundary.

Blended Total Precipitable Water product

Blended Total Precipitable Water product