NE Heat Wave Coming to an End
Posted by JAC on 7/8/2010, 1:01 pm
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
317 AM EDT THU JUL 08 2010

VALID 12Z THU JUL 08 2010 - 12Z SAT JUL 10 2010

UPPER PATTERN ACROSS THE CONUS WILL SEE A SLOW RETURN TO MORE
ZONAL FLOW ACROSS THE NORTHERN TIER STATES...WHILE A FLAT RIDGE
EXPANDS ACROSS THE SOUTHERN STATES. THE STRONG RIDGE SUPPORTING
THE HEAT-WAVE IN THE EASTERN U.S. WILL WEAKEN RAPIDLY THIS PERIOD
WITH A RETURN TO MORE NORMAL JULY TEMPERATURES BY FRIDAY.

A COLD FRONT FROM THE UPPER GREAT LAKES INTO THE SOUTHERN PLAINS
ON THURSDAY...WILL PUSH SOUTHEASTWARD AND BE ALONG THE
NORTHEASTERN U.S. COAST BY SATURDAY MORNING...THEN EXTEND WESTWARD
ACROSS THE NORTHERN GULF STATES INTO THE SOUTHERN PLAINS. SHOWERS
AND THUNDERSTORMS WILL ACCOMPANY THE FRONT AS IT PUSHES THROUGH
THE REGION...WITH THE POTENTIAL FOR SPOTTY HEAVY RAINFALL.






A stagnant area of high pressure situated over the Northeast and Mid-Atlantic states contributed to a prolonged heatwave over that part of the US, with widespread temperatures over 100 F (38 C) for several days - including 106 F (41 C) at Williamsburg, Virginia and Frederick, Maryland on 06 July 2010. McIDAS images of GOES-13 0.63 m visible channel data (above) showed a large area of very hazy sky conditions covering much of the Northeast and Mid-Atlantic regions on that particular day - and corresponding MODIS Aerosol Optical Depth values were also quite high within the hazy areas seen on visible imagery, with surface Air Quality Index values deteriorating into the "Moderate" to "Unhealthy for Sensitive Groups" categories.

An AWIPS image of the MODIS Land Surface Temperature (LST) product (below) revealed that while many air temperatures (measured in an instrument shelter about 5 feet above the surface) were only as warm as about 100 F at 18:05 UTC (2:05 pm local time), the "skin temperature" of the ground surface was much warmer - with many areas exhibiting LST values in the 120-130 F range (darker orange to red color enhancement). The warmest LST value seen at that time was 136 F in southeastern Pennsylvania. As an aside, MODIS Sea Surface Temperature values were as warm as 87 F in the southern portion of Chesapeake Bay.






Other notable features seen on the GOES-13 visible imagery above included (1) the development of a line of severe thunderstorms along a frontal boundary from Nebraska and South Dakota, which produced a number of tornadoes and large hail up to 2.75 inches in diameter, (2) a extensive area of cloudiness over the Yucatan Peninsula of Mexico, which was being monitored for the potential to develop into a tropical disturbance, and (3) the dissipation of fog and stratus along the California coast during the late morning and afternoon hours (with convection developing further inland over the Sierra Nevada mountain range).

In terms of the coastal fog and stratus in southern California, GOES-15 0.63 m visible channel images (below) showed how slow these features were to burn off in some areas. In fact, a number of locations in the San Diego, California area experienced record low maximum temperatures for the date - including a daily high temperature of only 65 F at San Diego International Airport (labeled SAN on the images), which was 10 degrees below the normal high temperature (75 F) for San Diego on 06 July. It is also interesting to note that heating of the higher terrain of some of the offshore islands appeared to help initiate the earlier clearing of the marine layer stratus cloud deck.








A 250-meter resolution MODIS true color Red/Green/Blue (RGB) image (created using Bands 1/4/3) from the SSEC MODIS Today site (below) shows even greater detail in the structure of the coastal fog/stratus features at 21:23 UTC (2:23 pm local time).




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NE Heat Wave Coming to an End - JAC, 7/8/2010, 1:01 pm
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