Winter weather « CIMSS Satellite Blog

Unusally cold across the North Slope region of Alaska

January 24th, 2012

POES AVHRR 12.0 µm IR images + surface reports

Unusually cold conditions were seen across the North Slope region of Alaska during the 22 January – 24 January 2012 period. A sequence of AWIPS images of 1-km resolution POES AVHRR 12.0 µm IR channel data (above) showed the expansion of a large area of surface IR brightness temperatures of -50 C and colder (violet to white color enhancement) across the interior portions of the North Slope. Nuiqsut (station identifier PAQT) was as cold as -62 F (-52 C) on 24 January, and Barrow (station identifier PABR) reached a low temperature of -45 F (-43 C) on 23 January (the record low temperature for the date was -47 F, and the normal low for the date is -20 F).

Another feature of interest over the Arctic Ocean was the appearance of a number of what resembled “warm cracks” in the sea ice, where IR brightness temperatures were -30 C or warmer (yellow color enhancement) — significant amounts of thermal energy from the warmer waters below were able to “bleed up” through weaknesses and thinner areas of the sea ice, showing up as warm anomalies on the IR imagery.

A Public Information Statement was issued by the National Weather Service forecast office at Fairbanks:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
700 PM AKST TUE JAN 24 2012

…SEVERE COLD CONTINUES OVER THE NORTH SLOPE OF ALASKA…

A VERY COLD AIR MASS CONTINUES OVER THE NORTH SLOPE…COMBINED
WITH WINDS IN SOME AREAS. HERE ARE SOME LOW TEMPERATURES RECORDED SO FAR TODAY ACROSS THE NORTH SLOPE OF ALASKA.

NUIQSUT……………..62 BELOW
UMIAT……………….59 BELOW
INIGOK………………54 BELOW
ALPINE………………53 BELOW
ATQASUK……………..48 BELOW
DEADHORSE……………47 BELOW
WAINRIGHT……………44 BELOW
KAKTOVIK…………….40 BELOW
BARROW………………39 BELOW

TEMPERATURES OVER THE NORTH SLOPE WILL REMAIN IN THE 40S AND 50S BELOW WITH POCKETS NEAR 60 BELOW FOR THE NEXT FEW DAYS…AND POTENTIALLY INTO THE WEEKEND.

$$

JM

Posted in Arctic, AVHRR, POES, Winter weather | No Comments »

Cold air and snowfall invade the Pacific Northwest

January 15th, 2012

POES AVHRR 0.86 µm visible channel + POES AVHRR 12.0 µm IR channel images

A surge of cold air brought the first measurable snowfall to parts of the Pacific Northwest states on 14 January – 15 January 2012. The Seatle-Tacoma aiport received 2.4 inches of snow on 15 January. A comparison of 1-km resolution POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel data (above) displayed a classic example of “open cell convection” — this type of open-cell mesoscale convective cloud pattern is a signature of strong instability (via boundary layer cold air advection over relatively warmer waters) in an environment of cyclonic flow.

A sequence of 1-km resolution POES AVHRR 12.0 µm IR channel images (below) showed the inland progression of the open cell convection, eventually producing snowfall at Seattle, Washington (station identifier KSEA) and Portland, Oregon (station identifier KPDX).

POES AVHRR 12.0 µm IR channel images

Posted in AVHRR, General interpretation, POES, Winter weather | No Comments »

Snow cover across west Texas and southeast New Mexico

January 10th, 2012

GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible images (click image to play animation)

Snowfall amounts as high as 10-15 inches fell across parts of west Texas and southeast New Mexico on 09 January 2012 as a strong upper level disturbance moved across that region (NWS Lubbock TX storm summary). On the following morning, a comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel images (above; click image to play animation) showed the areal coverage of the snow cover that remained on the ground. Note how the patch of snow began to melt from the outer edges inward as the full day of sunshine warmed the ground surface. Also note the curious “donut hole” of bare ground on the northern end of the main snow cover — this feature rapidly disappeared, as the snow depth associated with this feature was not very high.

A comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) showed greater detail in the snow cover (snow on the ground appears as darker shades of cyan on the false color image) at 18:02 UTC.

MODIS true color and false color Red/Green/Blue (RGB) images

A comparison of AWIPS images of MODIS 0.65 µm visible channel data and the corresponding false color RGB image (below) offered another tool that can be used to discriminate between snow cover (which in this example appears as darker shades of red on the false color image) and supercooled water droplet clouds (which appeared as varying shades of white).

MODIS 0.65 µm visible image + MODIS false color RGB image

A comparison of the MODIS 0.65 µm visible image with the corresponding MODIS Land Surface Temperature (LST) product (below) revealed how the deep snow cover was helping to keep surface air temperatures significantly colder than adjacent regions with bare ground. MODIS LST values were in the low to middle 30s F across the deeper snow cover, in the upper 40s to low 50s F in the “donut hole” region where the snow had just melted, and in the 60s F to the north over bare ground. Also note how the urban areas of Midland and Odessa stand out in the LST image, with LST values in the low to middle 40s F.

MODIS 0.65 µm visible image + MODIS Land Surface Temperature product

The mechanism for the creation of the “donut hole” snow cover feature is unclear at this point. A comparison the MODIS Land Surface Temperature product with the regional topography (below) seems to suggest that this feature was not topographically-driven.

MODIS Land Surface Temperature product + Topography

The MODIS true color image viewed using Google Earth (below) showed that the community of Brownfield (which did received about an inch of snowfall the previous day) was aptly named, being located within the brown-colored snow-free region at 18:02 UTC.