climate, weather

A Significant Dixie chill (H. Michael Mogil, CCM, CBM, NWA-DS*)

 

Across the South, this Sunday morning, Jan. 8, 2017, folks were pulling out their winter clothing. Temperatures that plunged to below freezing levels across Texas and much of the Gulf Coast east to the western Florida Panhandle on Saturday morning did so again this morning. However, today, the sub-freezing chill also made it nearly as far south across Florida as a Tampa-Orlando line. Even in parts of far south Florida temperatures in the upper 30’s and lower 40’s led to highly unusual wind chill readings that dipped to near 32 degrees. It’s easy to see the expanse of the cold weather by viewing this National Weather Service (NWS) “watch-warning” map (Fig. 1). Wind chill advisories and freeze and hard freeze warnings covered the entire Gulf Coast from the Rio Grande Valley in south Texas to Naples and nearby locales in southwest Florida. In south Florida, palm trees were shivering (swaying) in the cold winds!

                             T

There are several culprits at work, here. First, a significant upper level trough (Fig. 2) has allowed northwesterly winds to drive a surface level high-pressure system southward. This high-pressure system, an unusually strong one, had a central pressure of 1043 millibars (30.80 inches of mercury) near Dallas, TX early this morning (Fig. 3). The record high-pressure reading at Dallas (records dating back to 1898) was 31.06 inches during an extreme arctic outbreak on Dec. 24, 1982. The record high pressure in Dallas during January was 31.05 inches in 1962.

As northerly winds blew south from the Plains into Texas yesterday morning, and over the entire Gulf Coast today, the trajectory involved passage over an extensive snow cover. Hence, air that would have normally passed over warmer ground did not. This allowed cold air to penetrate much further southward than expected. Early on Jan. 7, snow was observed on the ground in every one of the 48 contiguous states except Florida (Fig. 4).

In short, this has been a highly unusual, but not unprecedented, arctic outbreak.

The good news is that the high is moving to the east and warmer air is slated to return to many south and southeastern locales fairly quickly.

© 2017 H. Michael Mogil

Originally posted 1/8/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.