March Comes in Like a Lion
March 1st Wind Chills Followed by March 2nd Frost
Morning low temperatures across Deep South Texas and the Lower Rio Grande Valley, March 2, 2009
ASOS: Automated Surface Observing Systems, National Weather Service. AWOS: Automated Weather Observing Systems, Federal Aviation Administration. Coop: National Weather Service Cooperative Observing Program. Mesowest: Real time Observation Monitor and Analysis Network, generally used for Fire Weather conditions.

Summary
A small but intensifying late winter storm, rotating southeast from the central Great Plains at the end of February to Alabama and Georgia on March 1st, combined with a ridge of high pressure aloft across the Rocky Mountain states, strengthened a surface high pressure ridge extending from southern Canada through the western Great Plains. Northerly flow between the systems drew Canadian air deep into the southern U.S., leading to a blustery start to March across much of Texas, followed by a clear, cold night into the early morning of March 2nd.

While an initial surge of northerly flow behind the February 28th cold front brought sharp change to the record setting heat across the western portion of the Rio Grande Valley on Friday, February 27th, the real chill followed with a secondary surge before daybreak on March 1st. By daybreak on the 1st, the combination of temperatures in the upper 30s to mid 40s with north winds gusting to 25 mph made it feel more like 30 to 35 degrees, areawide. The Lion had arrived.

Afternoon sunshine on the 1st tempered the chill, but high temperatures were generally in the 60s across the entire area, well below early March averages and closer to a sunny day in early January. Diminishing winds and clear skies set the stage for rapid evening temperature falls; winds were generally calm in all areas by midnight, allowing uninterrupted cooling. As the map above shows, nearly everyone, save for the immediate coast, fell below 40°F early on the 2nd. Patchy frost was common across much of the Lower Rio Grande Valley, and near surface observations suggest thicker frost in rural pockets, with more coverage from Kenedy through Brooks County. In clear, calm situations, the coldest temperatures are often found close to the surface; generally, at or below 10 feet. This may have been the case here, as as lowest temperatures tended to be recorded at around 2 meters, or near 6 feet above the ground.

Some climatological records were threatened, but a sampling of calendar day records show that the coldest temperatures recorded on March 2nd were a few degrees lower, in the upper 20s to lower 30s.

What’s to Come
The Lion’s "roar" will be a memory by midweek, as temperatures recover back into the 80s inland, 70 to 75 at the beaches, along with the springtime gusty southeast winds.

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