CIMSS Satellite Blog

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.

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).

The GOES-12 satellite was placed into Rapid Scan Operations (RSO) mode to monitor Tropical Storm Dolly on 21 July 2008 — the RSO visible images at 5-10 minute intervals (above) showed that deep convection was increasing around the core of the tropical cyclone. Dolly was moving northwestward across the Gulf of Mexico –  AWIPS images of the MODIS Sea Surface Temperature (SST) product (below) showed rather warm SST values (mid 80s to near 90 F, red colors) across much of the western Gulf of Mexico on the previous day, which argued in favor of a trend of intensification to hurricane strength. For additional satellite imagery and the latest information on  Dolly, see the CIMSS Tropical Cyclones site.

** 23 July UPDATE: Dolly reached hurricane intensity late in the day on 22 July (CIMSS Advanced Dvorak Technique intensity plot). GOES-12 RSO visible images (below) show the ragged eye of Hurricane Dolly approaching  South Padre Island along the southern coast of Texas. A peak wind gust of 76 mph was reported at Port Mansfield and Rincon in Texas, with a ship captain off South Padre Island estimating a wind gust of 100 mph — wave heights over 24 feet were recorded by an offshore buoy. In addition to the strong winds, there were also several tornadoes and waterspouts, along with rainfall in excess of 12 inches.

AWIPS  images of the 4-km resolution GOES-12 10.7 µm IR channel (below) revealed that cloud top brightness temperature values around the eye and in the outer band regions were in the -70º to -80º C range (black to white colors).

AWIPS images of the 1-km resolution MODIS 11.0 µm IR channel (below) indicated that cloud top brightness temperatures were as cold as -84º C (purple colors) on 22 July as the storm reached hurricane intensity.