High winds and wildfire activity over the Mid-Atlantic region

February 19th, 2011
GOES-13 6.5 µm water vapor channel imagery (click image to play animation)

GOES-13 6.5 µm water vapor channel imagery (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) revealed an extensive “mountain wave signature” across much of the Mid-Atlantic region of the US on 19 February 2011. Strong winds (gusting to 71 mph in Virginia and 63 mph in Maryland and Pennsylvania) in the wake of a cold frontal passage were interacting with the terrain of the Appalachian Mountains to create the widespread mountain waves — and some of the mountain waves were responsible for pilot reports of moderate to severe turbulence.

1-km resolution MODIS 6.7 µm water vapor images (below) offered a more detailed view of the mountain wave structure.

MODIS 6.7 µm water vapor images

MODIS 6.7 µm water vapor images

On occasion, these mountain waves appear in “clear air’ with no clouds present — this can be seen from Virginia to the Delmarva Peninsula in a comparison of a MODIS 0.65 µm visible image with the corresponding MODIS 6.5 µm water vapor image (below). Aircraft sometimes encounter “clear air turbulence” under such circumstances.

MODIS 0.65 µm visible image + MODIS 6.5 µm water vapor image

MODIS 0.65 µm visible image + MODIS 6.5 µm water vapor image

It is interesting to note that the MODIS 2.1 µm near-IR “snow/ice channel” image (below) displayed  a signature of what appeared to be the effect of atmospheric gravity waves over the adjacent offshore waters. A similar signature was discussed on the MODIS Image of the Day site off the coast of New Zealand on 21 December 2010.

MODIS near-IR 2.1 µm "snow/ice channel" image

MODIS near-IR 2.1 µm "snow/ice channel" image

The combination of strong winds and dry vegetation (MODIS Normalized Difference Vegetation Index) created an environment favorable for wildfire activity — and on this day there were more than 100 wildfires reported across the state of Virginia alone. The “hot spots” signatures (black to yellow to red color enhancement) from many of the larger fires could be seen on 4-km resolution GOES-13 3.9 µm imagery, with many more of the smaller fires exhibiting such signatures on the corresponding 1-km resolution POES AVHRR 3.7 µm shortwave IR image (below).

GOES-13 3.9 µm shortwave IR image + POES AVHRR 3.7 µm shortwave IR image

GOES-13 3.9 µm shortwave IR image + POES AVHRR 3.7 µm shortwave IR image

A MODIS “true color” Red/Green/Blue (RGB) image (below; displayed using Google Earth) showed a few of the longer smoke plumes that were emanating from the largest fires located from western Virginia to the Washington, DC area.

MODIS true color RGB image (displayed using Google Earth)

MODIS true color RGB image (displayed using Google Earth)

Gulf of Mexico “Loop Current” affecting cumulus cloud development

February 13th, 2011
GOES-13 0.63 µm visible channel imagery (click image to play animation)

GOES-13 0.63 µm visible channel imagery (click image to play animation)

McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed the development of a batch of cumulus clouds over the central Gulf of Mexico during the day on 13 February 2011. Other features of interest on the visible imagery include the rapidly-melting snow cover over the portions of the southern Plains, and a few small smoke plumes drifting northeastward due to fires burning in some of the Gulf Coast states.

A comparison of AWIPS images of the 1-km resolution MODIS 0.65 µm visible channel and the corresponding MODIS Sea Surface Temperature (SST) product (below) indicated that this area of cumulus development was occurring over the warmer waters of the Gulf of Mexico “Loop Current”, where SST values were as warm as 78º F (darker orange color enhancement). As a seasonally cool northeasterly flow of air moved across the warmer Loop Current, enough instability was generated to lead to the formation of shallow cumulus clouds.

MODIS 0.65 µm visible image + MODIS Sea Surface Temperature product

MODIS 0.65 µm visible image + MODIS Sea Surface Temperature product

About 3 hours later, a similar comparison of a 1-km resolution POES AVHRR 0.63 µm visible image with the corresponding POES AVHRR Sea Surface Temperature product (below) showed a few more cumulus lines forming over the northern portion of the Loop Current, with the cumulus cloud field becoming more dense in the southern portion.

POES AVHRR 0.63 µm visible image + POES AVHRR Sea Surface Temperature product

POES AVHRR 0.63 µm visible image + POES AVHRR Sea Surface Temperature product

Yet another Northeast US winter storm

January 26th, 2011
MODIS 6.7 µm water vapor image

MODIS 6.7 µm water vapor image

The third major storm  of the 2010/2011 winter season  (storm #1 | storm #2) impacted much of the Mid-Atlantic and Northeast states on 26 January 2011 27 January 2011. An AWIPS image  of MODIS 6.7 µm water vapor channel data at 18:28 UTC  (above) revealed a large and complex dry slot, with convective elements developing ahead of the leading edge of the dry slot across Virginia. In addition, to the east of the dry slot over the western Atlantic Ocean a well-defined packet of high altitude “transverse bands” was seen (close-up view) which was forming in the right entrance region of an upper level jet streak.

On a POES AVHRR false-color Red/Green/Blue (RGB) image at that same time (below), high cloud features appeared brighter white, with low clouds taking on a slight yellow tint.

POES AVHRR Red/Green/Blue (RGB) false color image

POES AVHRR Red/Green/Blue (RGB) false color image

An animation of GOES-13 10.7 µm IR images (below; click image to play animation) showed the development of the transverse banding cloud structures — the bands were oriented perpendicular to the southwesterly high-altitude wind flow over that region. This transverse banding pattern is a cloud signature that is often associated with areas of turbulence — and in this case there were two pilot reports of moderate turbulence at altitudes of 34,000 feet and 36,000 feet.

GOES-13 10.7 µm IR images (click image to play animation)

GOES-13 10.7 µm IR images (click image to play animation)

A comparison of a GOES-13 10.7 µm IR image with the corresponding MODIS 11.0 µm IR image (below) demonstrated the advantage of higher spatial resolution, with the fine transverse band structure more apparent on the 1-km resolution MODIS image. The coldest IR brightness temperatures within the bands on the MODIS image were -58º C (red color enhancement).

MODIS 11.0 µm IR + GOES-13 10.7 µm IR images

MODIS 11.0 µm IR + GOES-13 10.7 µm IR images

A number of cloud-to-ground lightning strikes were associated with the convective elements that had formed over Virginia (below), ahead of the leading edge of the dry slot that was seen on water vapor imagery. Thundersnow was reported across a wide portion of the Mid-Atlantic and Northeast states, with snowfall rates as high as 1-4 inches per hour at some locations.

MODIS 11.0 µm IR image + lightning strikes + METAR surface reports

MODIS 11.0 µm IR image + lightning strikes + METAR surface reports

=========== 27 JANUARY UPDATE ===========

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

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

This storm was not particularly intense in terms of a low central pressure or strong winds, but it was able to tap a significant plume of deep moisture (in excess of 30-40 mm or 1.2-1.6 inches) from the Gulf of Mexico and the Caribbean, as can be seen on AWIPS images of the MIMIC Total Precipitable Water (TPW) product (above; click image to play animation) and the Blended Total Precipitable Water product (below; click image to play animation). This contributed to the high snowfall totals at many locations (Weather Underground blog| WeatherMatrix blog).

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

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

Parts of this plume of moisture represented TPW values in excess of 200% of normal (below; click image to play animation).

Percent of Normal TPW product (click image to play animation)

Percent of Normal TPW product (click image to play animation)

The “warming effects” of the Arctic Ocean

January 25th, 2011
POES AVHRR 12.0 µm IR images

POES AVHRR 12.0 µm IR images

The North Slope region of far northern Alaska had been abnormally cold for a number of days in late January 2011: for example, Barrow had minimum temperatures of -43ºF / -42ºC and -45ºF / -43ºC on 23 January and 24 January, respectively (the normal low temperature on those days is -20ºF/-29ºC). While the sun actually rose at Barrow on 23 January for the first time in 2011 (from 1:05 pm to 2:14 pm local time), it had little effect on warming the temperatures there (which were around -40ºF/-40ºC at the time).

However, a sequence of AWIPS images of POES AVHRR 12.0 µm IR data (above) revealed something that did appear to have a pronounced effect on the warming of surface air temperatures at Barrow: a shift of winds from southerly (offshore, from the cold interior) on 24 January 2011 to northeasterly (onshore, from off the Arctic Ocean) on 25 January 2011.  Around the same time as the northeasterly wind shift, a number of long, narrow features — resembling large “cracks” in the sea ice — began to exhibit significantly warmer IR brightness temperatures (-20º to -30ºC, yellow to orange color enhancement) just offshore of Barrow. Apparently a great deal of heat was able to “bleed upward” through these thinner areas of sea ice, which was then transported toward the coast of Alaska by northeasterly winds.

Although the temperature at Barrow (station identifier PABR) rose to -24ºF / -31ºC by 15:09 UTC on 25 January, farther to the southeast the temperature at Nuiqsut (station identifier PAQT) remained at a very cold -51ºF / -46ºC. Note that North is to the upper right, due to the AWIPS “North America” projection of these particular images.

The much larger yellow to orange colored features seen across the interior of Alaska and also over parts of the Arctic Ocean were clouds. The purple colored areas farther inland were regions that exhibited surface IR brightness temperatures of -47ºC or colder.