The bad news is the threat for severe weather isn’t zero. And, like Monday, finding severe weather on the radar, in order to alert you, may also prove a difficult task for the local NWS offices.
The timeline
This is where one of the changes occured. There are going to be two time periods to focus on the threat for storms. A 2p – 5p window and then a 7p – 3a window.
The 2p to 5p window is going to only be for a few areas (listed below) and the 7p – 3a is going to be for the whole area.
From the SPC
No changes to the previous outlook area. A midlevel shortwave trough over the southern Plains this morning will accelerate east-northeastward and lose amplitude through the period, as a primary northern stream trough amplifies over the upper
Midwest/Great Lakes, and a subtropical ridge persists over FL. The ejecting trough will glance the northwest edge of the surface warm sector today, with weak cyclogenesis expected along a baroclinic zone from the ArkLaMiss this afternoon to the TN Valley this evening and the Appalachians overnight.
SPC Severe Risk areas // Courtesy: spc.noaa.gov
Low-level moisture will spread inland rather quickly today in advance of the developing surface cyclone, with boundary-layer
dewpoints in the 60s expected as far north and southern middle TN by this evening. However, regional 12z soundings revealed poor lapse rates below relatively warm temperatures near 600 mb (associated with the subtropical ridge). Surface heating will also be limited by clouds (aside from possibly southeast LA into southwest MS).
SPC Tornado Risk areas // Courtesy: spc.noaa.gov
hus, narrow CAPE profiles (MLCAPE 250-500 J/kg) are expected in an environment with otherwise increasing low-level and deep-layer vertical shear beginning this afternoon across MS and spreading into the TN Valley this evening. The poor lapse rates/weak buoyancy suggest it will be difficult to form and sustain warm-sector supercells this afternoon, and the majority of the deeper convection should be confined to the track of the surface low and trailing cold front from mid afternoon into early tonight. Since convection will tend toward a linear mode along the front, the main threat should be damaging winds and perhaps a couple of tornadoes with embedded circulations. Lingering frontal convection will likely weaken overnight toward the southern Appalachians.
Round 1: 2p – 5p
Okay, I lied. I drew a circle.
Area with a brief window of opportunity for a severe storm this afternoon
It looks like there might be a short window of opportunity for a few rotating storms this afternoon between 2p and 5p in the circled area. This is currently underneath the 2% / 5% tornado risk area from the SPC. And this is out ahead of the “Main Event” of storms that will be rolling in later tonight and into the overnight hours.
The main concern with these rotating storms this afternoon will be heavy rain, frequent lightning, gusty wind (up to 60mph), small hail (up to the size of nickels) and the potential for a brief and weak tornado (EF-0 or EF-1).
Round 2: 7p – 3a
Overnight tonight, when the main line rolls through the area between 7p and 3a, storms will be possible for the entire area. The threat for severe weather at this point will move to heavy rain and wind gusts up to 65mph. The tornado threat should be pretty minimal and the hail threat should remain pretty low as well.
Storms will move through from NW to SE and everyone will see a short burst of heavy rain with some wind gusts of at least 30mph. That will last about 10 to 15 minutes for everyone.
For the areas that get stuck underneath the stronger storms, the rain and wind will last a bit longer.
Some science
Despite the cloud cover, a warm front has lifted back to the north through South Mississippi. This has ushered in temperatures that will climb back into the mid to upper 70s this afternoon. That will allow moisture pumped in from the Gulf to really get juicy. Dewpoint values may get up into the low 70s in the area I circled above highlighting a threat from 2p to 5p.
Because that juicy air will be sitting underneath an atmosphere capable of rotating updrafts, it will be a matter of if a storm can develop in that area.
If so, and that is still an if at this point, the 0-1km shear and 0-1km SRH are sufficient enough (35kts shear, 200m2/s-2 helicity) to promote the development of a low-level rotating updraft. CAPE values will be in the 700-1300 J/kg range, which is more than enough ‘umph’ in the atmosphere to keep a storm up and moving.
The question is, will we get one “up” or not.
The CIPS Analogs seems to think so. It pegs the area with a 30-percent chance for a severe storms to develop.
CIPS Analogs severe weather threat areas // Courtesy: Saint Louis University
With a bullseye of 45-percent north of I-20.
But keep in mind, the CIPS doesn’t take into account a specific time period. It is saying ‘by the time the entire line rolls through, here are the chances for severe weather.’
What about where I live, Nick? Will it be bad for my town?
The the Round 2 threat, everyone in the area is looking at storms. Who will see the strongest storms? We can’t know that. No one can know specifically where a tornado will happen this far in advance. Nor can anyone predict if one town will get a regular storm while the other town gets a severe storm. But, if you live in a town that is anywhere within th shaded areas ont eh SPC maps above or inside the circled area on the map I made, you have a chance for storms and “bad” weather.
If you don’t know where you are located on a map, use the map below – supplied by google – to search for your town:
Author of the article:
Nick Lilja
Nick is former television meteorologist with stints in Amarillo and Hattiesburg. During his time in Hattiesburg, he was also an adjunct professor at the University of Southern Mississippi. He is a graduate of both Oregon State and Syracuse University that now calls Houston home. Now that he is retired from TV, he maintains this blog in his spare time.
