Unusually large and persistent dry region aloft over the central Pacific Ocean

January 31st, 2012
GOES-15 full disk 6.5 µm water vapor channel images (click image to play animation)

GOES-15 full disk 6.5 µm water vapor channel images (click image to play animation)

An animation of McIDAS images of GOES-15 (GOES-West) 6.5 µm water vapor channel data from 27 January to 31 January 2012 (above; click image to play animation) revealed the presence of an unusually large and persistent warm/dry region over the central Pacific Ocean (centered southwest of Hawaii). Water vapor brightness temperatures as warm as +3.5 C (darker orange color enhancement) were seen — such warm values are rarely seen on water vapor imagery.

AWIPS images of the MIMIC Total Precipitable Water (TPW) product (below; click image to play animation) showed a number of areas exhibiting TPW values as low as 15 mm (0.6 inch) within the large dry feature seen on GOES-15 water vapor images. At 00 UTC on 30 January, the Hilo, Hawaii rawinsonde data indicated a TPW value of 0.93 inch, with very dry air above the 800 hPa pressure level. The strong subsidence aloft was acting to prevent significant rainfall over the Hawaiian Islands, prompting a Red Flag Warning to be issued for elevated fire danger during the 29-30 January period. It was also very warm in Hawaii — the highest temperature recorded in the 50 United States was 84 F at Kahului on 28 January, and 85 F at Kalaeloa on 30 January.

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

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

A comparison of an AWIPS water vapor image composite with the corresponding MIMIC TPW product (below) offers a good example of the fact that not all features of high TPW are evident on water vapor imagery. In particular, note the plume of higher TPW being drawn northeastward along a frontal boundary west and northwest of Hawaii — this plume crossed through the western portion of the dry feature on water vapor imagery.

Water vapor image + MIMIC TPW product + surface analysis

Water vapor image + MIMIC TPW product + surface analysis

“Hot spot” from the fire that caused the deadly I-75 crashes in Florida?

January 29th, 2012
POES AVHRR 3.74 µm shortwave IR image

POES AVHRR 3.74 µm shortwave IR image

 

Thick smoke from a 62-acre brush fire that was burning in the Paynes Prairie Preserve State Park just southwest of Gainesville, Florida (station identifier KGNV) was blamed for causing a deadly multiple-vehicle crash along Interstate 75 at around 07:45 UTC (3:45 am local time) on 29 January 2012. Detection of the fire “hot spot” on shortwave IR satellite imagery was difficult due to the relatively small size of the fire, and the fact that some thin cirrus clouds were drifting over the region. However, evidence of what could be the fire hot spot was seen on a 06:58 UTC  AWIPS image of 1-km resolution POES AVHRR 3.74 µm data (above), with an IR brightness temperature (BT) of +9 C at the darker black pixel that is circled.

The fire “hot spot” was a bit easier to see on a 06:53 UTC  McIDAS image of 375-meter resolution Suomi NPP VIIRS 3.74 µm data (below). The darker black pixel that is circled exhibited an IR brightness temperature of +24.7 C.

Suomi NPP VIIRS 3.74 µm shortwave IR image

Suomi NPP VIIRS 3.74 µm shortwave IR image

Record cold continues across interior Alaska

January 29th, 2012
POES AVHRR 12.0 µm and MODIS 11.0 µm IR images (with METAR surface reports)

POES AVHRR 12.0 µm and MODIS 11.0 µm IR images (with METAR surface reports)

Record cold continued across the interior of Alaska, with Fairbanks reaching a minimum temperature of -50º F on 28 January 2012 and -51º F on 29 January 2012. These were the first -50º F temperatures at Fairbanks since 2006 (NWS Fairbanks public information statements). The coldest temperature reported was -65º F at Galena and by a coopertive observer at Fort Yukon (Fairbanks region temperature and precipitation data).

A sequence of AWIPS images of 1-km resolution POES AVHRR 12.0 µm IR and MODIS 11.0 µm IR data (above) revealed the expansion of surface IR brightness temperatures of -50º C or colder (violet to white color enhancement) during the early morning hours on 28 and 29 January. The coldest surface air temperatures at the times of the IR images included -50º F at Fairbanks (station identifier PAFA) and -60º F at Fort Yukon (station identifier PFYU) and Tanana (station identifier PATA). The signature of cold air drainage into lower elevation terrain (such as the relatively narrow river valleys along the south side of the Brooks Range, and also the broad Yukon Flats) could be seen on the 1-km resolution IR images.

Suomi NPP VIIRS 11.450 µm (Band I5) IR image

Suomi NPP VIIRS 11.450 µm (Band I5) IR image

The pattern of cold air drainage into lower elevations could be seen in even greater detail using McIDAS images of 375-meter resolution Suomi NPP VIIRS 10.450 µm IR data at 12:06 UTC on 28 January, over northwestern Alaska and the Yukon Territory of Canada (above), and also just to the southwest over the eastern interior of Alaska (below). These 2 VIIRS images use a different color enhancement, where the coldest surface IR brightness temperatures are darker blue.

Unfortunately, there was no surface air temperature report for Arctic Village (station identifier PARC) at this time, but the coldest surface IR brightness temperatures within some of the deeper valleys near that site was -58.4º C (-73.1º F).

To the south, a broad area of very cold (dark blue) surface IR brightness temperatures was seen across the Yukon Flats, with a minimum value of -58.3º C (-72.9º F). The hourly surface air temperature at the Fort Yukon (PFYU) reporting station close to the time of the satellite image was -56º F, while the surface IR brightness temperature at that location was -54º F. Although there is not always a direct 1:1 correspondence between satellite-sensed IR surface temperature values and the actual air temperature measured within an instrument shelter at a height of 5 feet above ground level, the IR satellite imagery can be used to located areas that might have the coldest surface air temperatures.

Suomi NPP VIIRS 11.450 µm (Band I5) IR image

Suomi NPP VIIRS 11.450 µm (Band I5) IR image

Rain-cooled ground across much of Texas and Oklahoma

January 27th, 2012
1-day observed precipitation for 25 and 26 January 2012

1-day observed precipitation for 25 and 26 January 2012

Maps of the 1-day total precipitation for 25 January and 26 January 2012 (above) showed that much of Texas and Oklahoma received several inches of rainfall during that 48 hour period.

AWIPS images of the MODIS 0.65 µm visible channel and the corresponding  MODIS Land Surface Temperature (LST) product (below) revealed a large swath of rain-cooled ground across much of that region. LST values where heavy rain fell were in the 60s F (yellow to light orange color enhancement), in contrast to LST values in the 70s and 80s F (darker orange to red color enhancement) to the north and the to the south of the rain-cooled areas.

MODIS 0.65 µm visible chanel image + MODIS Land Surface Temperature product

MODIS 0.65 µm visible chanel image + MODIS Land Surface Temperature product