03 August 2008 marked the 22nd  consecutive day of daily high temperatures of 90º F or higher at Denver, Colorado (the old record was 18 consecutive days, set back in 1874 and 1901). AWIPS images of the MODIS Land Surface Temperature (LST) product (above) revealed daytime LST values as high as 140º F in southeastern Colorado and 134º F in southwestern Nebraska — while the surface “skin temperatures” were quite warm, the actual air temperatures (measured within shaded instrument shelters located about 5  feet above the surface) were only the in upper 90s to low 100s F.

It is interesting to note that the LST values were significantly lower across much of southcentral and southeastern Nebraska (in the upper 80s to low 90s F, green to yellow colors), even though the air temperatures were similar to those seen in eastern Colorado at that time (in the upper 90s to low 100s F).  These lower LST values were due to a much higher density of vegetation in eastern Nebraska, as shown by a comparison with the MODIS Normalized Difference Vegetation Index (NDVI) product (below) — NDVI values were greater than 0.7 in Nebraska, compared to 0.1 to 0.3 across much of eastern Colorado. In addition, very dry conditions had prevailed across eastern Colorado — Denver had only received 3.28 inches of precipitation so far in the year (the normal is 10.25 inches for the 01 January  – 31 July period) — in contrast with Hastings in eastern Nebraska, which had received 6.77 inches of precipitation so far in the year (the normal precipitation is 3.81 inches for the 01 January – 31 July period). The combination of drier soils and sparse vegetation  helped contribute to such high MODIS LST values.

MODIS true color imagery from the SSEC MODIS Today site (below) confirmed the presence of a much higher density of vegetation (denoted by darker green colors) across eastern Nebraska, compared to that found across eastern Colorado.

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AWIPS images of GOES-12 10.7 µm IR channel (Animated GIF)

AWIPS images of the GOES-12 10.7 µm IR channel (above) showed a cluster of strong thunderstorms moving eastward across parts of Nebraska and South Dakota on 03 August 2008 — at one point these storms exhibited an “enhanced-v” signature on the IR imagery around 02:32 UTC over north-central Nebraska. As the cluster of storms began to dissipate and collapse, a convective heat burst was observed at Sioux Falls in southeastern South Dakota around 09:15-09:45 UTC (04:15-04:45 am local time). The surface temperature abruptly rose from 74º F to 101º F, with wind gusts of 50-60 mph.

GOES-12 and GOES-13 10.7 µm IR images (Animated GIF)

A comparison of GOES-12 and GOES-13 10.7 µm IR channel images (above) showed a closer view of the dissipating convection (GOES-13 had just been taken out of on-orbit storage for a period of operational testing). Note the rapidly warming cloud top temperatures as the convection approached Sioux Falls — the coldest cloud top IR brightness temperatures warmed from -68/-69º C at 05:02 UTC to -42/-43º C at 09:45 UTC (below).

GOES-12 and GOES-13 IR brightness temperature plot

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Parts of interior Alaska experienced heavy rainfall and significant river flooding during the last week of July 2008; AWIPS  composite images of the GOES-11 and GOES-12 water vapor channels (above) showed a rather unusual moisture plume — one having a long northwesterly fetch — stretching from the Russian arctic coast across the Chukchi Sea and into the interior of Alaska on 30-31 July. Rainfall amounts during the 28-31 July period were in the 2-6 inch range; in the Fairbanks area, 2.17 inches fell at North Pole (their second-highest daily rainfall amount on record), and this rainfall helped Eielson Air Force Base reach 7.30 inches for the month of July (their wettest July on record).

A comparison of the 06:00 UTC GOES water vapor image and the 05:20 UTC POES AMSU Total Precipitable Water (TPW) image (below) revealed  that TPW values were as high as 38 mm or 1.49 inches (green colors) within the moisture plume over the Chukchi Sea.

The heavy rainfall caused flooding along parts of the Chena River and the Tanana River in the Fairbanks area — the flood crest of the Tanana being the highest since August 1967 — and many residential areas had to be evacuated. The photo composite shown below (taken just after attending the Alaska Environmental Satellite Workshop) is of the Chena River at the “Ice Bridge” at  Pike’s Landing in Fairbanks on the afternoon of 31 July, when portions of the river were near flood stage (for additional photos and video, see the Fairbanks Daily News-Miner and the Alaska Superstation websites). In addition, the Alaska Railroad was forced to suspend passenger service north of Denali National Park because of rising waters in the Nenana area, with train passengers  being bused between the park and Fairbanks.

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There are a number of satellite signatures that denote areas of potential turbulence, and AWIPS images of the GOES-12 10.7 µm IR channel on 27 July 2008 (above) displayed two of the more common indicators: rapidly developing convection, and transverse banding. A decaying mesoscale convective system was moving southeastward across Minnesota and Iowa, with pulses of new convection developing rapidly over northern Iowa — one pilot reported a severe updraft that caused a rapid increase in altitude of 2000 feet as the aircraft was flying over the Minnesota/Iowa border region.

Along the periphery of the northeastern quadrant of the decaying MCS, a well-defined area of “transverse banding” formed (the narrow cloud band features were generally perpendicular to the mean wind direction aloft) –  there were a few reports of turbulence that appeared to be associated with this transverse banding feature: over Lake Michigan around 17:30 UTC,  over northeastern Wisconsin around 19:20 UTC, and over western Lower Michigan around 20:09 UTC.

The transverse banding features that were seen on the 4-km resolution GOES IR imagery were even more obvious on an AWIPS image of the 1-km resolution MODIS 11.0 µm IR channel (above), and also on a comparison of 250-m resolution MODIS true color images from the SSEC MODIS Today site (below).

Since we’re on the topic of potential aviation hazards, also note the hazy features that were evident on the MODIS true color images (just to the east of the transverse banding) — these hazy features were due to the presence of thick smoke from wildfires that had been burning over parts of northern Saskatchewan, Canada for several days (see the US Air Quality “Smog Blog” for details).  GOES-12 visible imagery indicated that this smoke began moving southeastward across Manitoba and into the north-central US on 25 July (QuickTime animation). The smoke was likely confined to layers aloft, but aircraft flying through those smoke layers would encounter significantly reduced visibilities at those altitudes. An AWIPS image of the 1-km resolution MODIS 3.7 µm IR channel (below) showed a large number of fire “hot spot” signatures across far northern Saskatchewan at 04:05 UTC (10:05 PM the previous evening, local time).

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