EUMETSAT Meteosat-9 0.635 µm visible channel images (click image to play animation)

McIDAS images of EUMETSAT Metosat-9 0.635 µm visible channel images (above; click image to play animation) showed a very large outbreak of airborne Saharan dust streaming off the continent of Africa and moving west-southwestward out over the adjacent waters of the eastern Atlantic Ocean on 07 February 2012. In addition, a pair of long von Karman vortex streets can be seen moving southwestward from the Cape Verde islands.

While the viewing angle was more extreme, the Saharan dust could also be seen on GOES-13 0.63 µm visible channel images (below).

GOES-13 0.63 µm visible channel images + surface reports

The emergence of this Saharan dust over water can be seen to occur around 00:00 UTC on 06 February on the Meteosat-9 Saharan Air Layer tracking product (below).

EUMETSAT Meteosat-9 Saharan Air Layer tracking product

GOES-13 fog/stratus product (click image to play animation)

AWIPS images of the 4-km resolution GOES-13 10.7 µm – 3.9 µm “fog/stratus product” (above; click image to play animation) showed a large area of fog and/or stratus (yellow to orange color enhancement) that was increasing in areal coverage during the pre-dawn hours on 06 February 2012. Although the fog/stratus product is useful for locating the presence and temporal trends of such features, it does not offer any reliable indication of whether it is fog on the ground or stratus cloud aloft.

One product that attempts to give the forecaster some quantitative information is the GOES Low CLoud Base (LCB) prodcut (below; click image to play animation), which attempts to blend surface observations with satellite data to indicate whether the cloud base is above or below the threshold of 1000 feet.

GOES-13 Low Cloud Base product (click image o play animation)

With 1-km resolution data, the MODIS instrument aboard the polar-orbiting Terra and Aqua satellites offers a similar “fog/stratus product” (below) that provides better clarity, especially regarding the exact location of the edges of the fog and/or stratus.

MODIS fog/stratus product images

In this particular case, a number of locations beneath the western and southern edge of the fog/stratus feature were expereincing freezing fog (below) and visibilities of 1/4 mile or less, which was creating hazardous road conditions and prompting the issuance of Freezing Fog Advisories.

MODIS fog/stratus product with METAR surface reports

As part of CIMSS participation in GOES-R Proving Ground activities, products are being developed which can provide more quantitative information about such parameters as Fog Depth and the Probability of Marginal Visual Flight Rules (MVFR) or Instrument Flight Rules (IFR) conditions (below). In this case, across the southwestern part of Iowa (where widespread freezing fog was being reported), the fog depth was as high as 1400-1500 feet, with probabilities of MVFR and IFR conditions as high as 75-90% and 60-75%, respectively.

MODIS Fog Depth, MVFR Probability, and IFR Probability products

Shortly after sunrise, it is interesting to note that a comparison of 1-km resolution POES AVHRR 0.63 µm visible channel, 3.74 µm “shortwave IR” channel, and 10.8 µm channel “IR window” channel images (below) revealed that part of the swath of fresh snow cover (as deep as 4-6 inches) across western Iowa could be seen through the translucent western edge of the fog/stratus deck that was beginning to burn off during the morning hours. The fog/stratus deck appears warmer (darker gray enhancement) om the 3.74 µm image, due to the sensitivity of that channel to the reflection of solar radiation off the tops of supercooled water droplet clouds.

Farther to the south, note the presence of narrow fingers of valley fog in the Ozark Mountains and surrounding regions in Oklahoma, Arkansas, and Missouri.

POES AVHRR 0.63 µm visible, 3.74 µm "shortwave IR", and 10.8 µm "IR window" images

GOES-13 6.5 µm water vapor channel images (click image to play animation)

AWIPS images of 4-km resolution GOES-13 6.5 µm water vapor channel data (above; click image to play animation) showed the middle-tropospheric circulation and cloud features associated with the large storm system which brought heavy snow, heavy rainfall, and severe thunderstorms to much of the central US on 03 February – 04 February 2012. Snowfall amounts included 51.1 inches at Pinecliffe, Colorado, 26.0 inches at Laramie, Wyoming, 17.0 inches at Tyron, Nebraska, and 11.5 inches at Cumberland, Iowa.

Denver received 15.9 inches of snow during 02/03/04 February, setting a new 3-day record accumulation for the month of February. Boulder also set a new single-storm snowfall record, with 22.7 inches of snowfall (NWS Denver/Boulder CO storm summary).

POES AVHRR 0.63 µm visible channel + 3.74 µm shortwave IR channel images

As the storm departed, a comparison of AWIPS images of 1-km resolution POES AVHRR 0.63 µm visible channel and 3.74 µm shortwave IR data (above) at 15:06 UTC (8:06 am local time) on 04 February showed that some low clouds persisted across much of northeastern Colorado, backed up against the highest terrain of the Continental Divide in some places. The low clouds showed up as darker gray features on the shortwave IR image, due to the sensitivity of reflection of solar radiation off of cloud top supercooled water droplets at the 3.74 µm wavelength.

At 17:47 UTC (10:47 am local time), a comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel data with the corresponding MODIS false-color Red/Green/Blue (RGB) image (created using MODIS channel 01/07/07 as the red/green/blue components of the image) indicated that most of the low clouds (which appeared as varying shades of white on the false-color image) had dissipated, revealing a good deal of the snow cover (which appeared as darker shades of red on the false-color image). A few streaks of high-level cirrus clouds could also be seen over the snow cover. Bare ground appeared cyan on the false-color image.

MODIS 0.65 µm visible channel + False-color Red/Green/Blue (RGB) images

About 2 hours later, a more detailed example of using false color images to discriminate between snow cover and supercooled water droplet clouds can be seen with a 375-meter resolution Suomi NPP VIIRS Red/Green/Blue (RGB) image (below), created using Band I1 (0.64 micrometer visible) as the red component and Band I3 (1.61 micrometer near-IR) as the green and blue components of the image.

Suomi NPP VIIRS false color RGB image

Farther to the east and south, heavy rainfall amounts included 9.30 inches at Romayer, Texas, 5.69 inches at Alexandria, Louisiana, and 4.34 inches at Medicine Lodge, Kansas. Wichita, Kansas received 2.86 inches of rain — the wettest February day on record at that location. Severe thunderstorms produced one tornado and hail up to 2.0 inches in diameter in Texas (SPC storm reports). A McIDAS image of 375-meter resolution Suomi NPP VIIRS 11.45 µm IR channel data (below) showed very intricate detail to the cloud top IR brightess temperature structure associated with strong thunderstorms producing heavy rainfall and flash flooding across the Interstate 35 corridor in the Austin/San Antonio, Texas region during the pre-dawn hours on 04 February. VIIRS IR brightness temperatures were as cold as -81º C with the far southwestern storm — and rare “warm trench” signatures (a ring of warmer cloud top temperatures surrounding a well-defined cold overshootng top) were seen associated with the 2 storms located near Austin-Bergstrom International airport (KAUS) and Houston County Airport (KDKR).

Suomi NPP VIIRS 11.45 µm IR image + Station locations and Interstate highways

===== 05 February Update =====

A large portion of the resulting swath of snow on the ground across parts of Wyoming, Colorado, Nebraska, and Kansas could be seen on a 250-meter resolution MODIS true color RGB image from the SSEC MODIS Today site (below, viewed using Google Earth) at 20:17 UTC on 05 February 2012.

MODIS true color image (viewed using Google Earth)

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)

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

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

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

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

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

Aqua MODIS: 11.0 µm IR images (grayscale, and color-enhanced) + "Fog/stratus product"

A comparison of AWIPS images of 1-km resolution Aqua MODIS 11.0 µm “IR Window” channel data (both grayscale, and color-enhanced) and the corresponding MODIS “Fog/stratus product” (above) showed some areas of fog and/or stratus cloud over the eastern half of Hudson Bay, Canada on 26 January 2012. On the fog/stratus product, low clouds and/or fog appear as the yellow-to-red enhanced features, while cirrus cloud features appear darker black.

The primary feature of interest here is the very thin – almost “translucent” – patch of fog/stratus located in the upper center portion of the image, to the west of Akulivik (station identifier CYKO) and Povungnituq (station identifier CYPX). The exact edges of this feature were difficult to identify in either the grayscale or the color-enhanced IR images — but the conventional “Fog/stratus product” (simply the difference in IR brightness temperature between the 11.0 µm and 3.7 µm channel data) allowed unambiguous identification of the edges.

About 45 minutes earlier, a similar comparison using McIDAS images of of 375-meter resolution Suomi NPP VIIRS 11.450 µm IR data (both grayscale, and color-enhanced) and the corresponding VIIRS “Fog/stratus product” (below) showed much more detail associated with this particular thin fog/stratus feature. The higher spatial resolution allowed many more of the  ice leads to be seen — even some of the larger ones that were located below the thin fog/stratus feature.

Suomi NPP VIIRS: 11.450 µm IR (grayscale, and color-enhanced) + "Fog/stratus product"

Suomi NPP VIIRS visible and IR images of the eye of Tropical Cyclone Funso

On 24 January 2012 NASA renamed the recently-launched NPP satellite (formerly known as the NPOES Preparatory Project)  the Suomi National Polar-orbiting Partnership (or Suomi NPP) in honor of Dr. Verner Suomi, recognized as “the father of satellite meteorology” (see: NASA News | University of Wisconsin News). A comparison of Suomi NPP 375-meter resolution VIIRS 0.640 µm visible channel and 11.450 µm IR channel images (above) showed the eye of Category 4 Tropical Cyclone Funso, which was located in the Mozambique Channel between Africa and Madagascar at 11:02 UTC on 24 January (track of Tropical Cyclone Funso).

On 25 January 2012, another Suomi NPP 375-meter resolution VIIRS 11.450 µm IR image (below) displayed very cold cloud top IR brightness temperatures (as low as -77º C) associated with a large thunderstom complex over Texas — this storm produced hail up to 1.25 inches in diameter (SPC storm reports) and heavy rainfall of up to 9.29 inches at Uhland (NWS Austin/San Antonio Texas Public Information Statement).

Suomi NPP VIIRS 11.450 µm IR image

The corresponding 4-km resolution GOES-13 (GOES-East) 10.7 µm IR image (below) showed much less structure to the cloud top temperature field, with the coldest IR brightness temperature being -70º C.

GOES-13 10.7 µm IR image

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