Short Term Update

SHORT TERM [Monday Through Wednesday Night]...
The fast zonal flow in the mid-upper troposphere will quickly
amplify Monday and Tuesday as a progressive major trough develops
over the western CONUS. An initial short wave (currently over NM)
will drag a cold front close to our forecast area on Monday, but
this front will stall to our north. Nonetheless, there should be
enough deep layer moisture and Q-G forcing for at least a chance
of rain, mainly around Dothan and Albany where the PoP will be
around 40%. Rain chances will decrease a bit Monday night and
early Tuesday as the aforementioned front moves farther north,
ahead of the main trough (a strong one at that) in the southern
Plains. While rain will be likely around Dothan and Albany Tuesday
(closer to the best deep layer moisture and Q-G forcing associated
with the warm front), the highest PoP will be overnight on
Christmas as a strong cold front moves through the region.
Temperatures will return to above-average levels Monday and
Tuesday, most notably during the overnight hours. (Cloud cover and
onshore winds traveling over the now-chilly shelf waters along the
northwest Gulf Coast) will prevent highs from getting above the
mid 70s. High temperatures behind the front on Wednesday will
range from the upper 50s (north) to lower 60s (south).

Not much has changed regarding the large scale setup for severe
storms. Although SBCAPE values will be unusually high for this
time of year (500-1000 J/kg in the FL Panhandle) Christmas
afternoon, and the vertical wind shear will be increasing, it is
unclear how much large scale forcing there would be with the warm
front well to our north and the cold front well to our west.
Typically such broad, warm air advection regimes mean shallow
weak, moist convection, often in showery convergence bands. Thus
it`s questionable how much severe weather we would get Christmas
Day. Christmas Night is a different story. There should be plenty
of deep layer moisture, Q-G forcing, surface convergence, and
vertical wind shear to support storm organization. We should get a
better idea of the convective mode Monday when we begin getting
Convection Allowing Model runs that go out that far in time, but
right now we think a fairly strong QLCS is likely to precede the
cold front Christmas evening through early Wednesday. This means
the primary threat would be damaging wind gusts, though isolated
tornadoes would be possible as well (especially in discrete cells
ahead of the main squall line, and in any bookend vortices that
develop in the favored portions of expected LEWP signatures).

With such favorable wind and moisture profiles, healthy
700-500 mb lapse rates, and large scale forcing, why only a
"Slight Risk"? There are a couple of potentially limiting factors.
The 12 UTC GFS and ECMWF both forecast the strongest SBCAPE to be
quickly shunted southward into the Gulf of Mexico overnight on
Tuesday, which could keep the primary threat confined to the
region west of the Apalachicola River. Another limiting factor
could be the recently chilled shelf waters along the northwest FL
coast. Strong, cold, offshore surface winds on Friday and Saturday
caused upwelling along the coast, sending SSTs into the upper 50s
to lower 60s. This could cause a shallow, stable marine layer to
develop near the coast, which could keep storms slightly elevated
(reducing the threat of damaging winds). These types of subtleties
are difficult to forecast this far out. For now the main point to
take away from this is that conditions point to at least a "Slight
Risk" of severe storms Christmas afternoon through early
Wednesday, and that it`s a good idea to monitor later forecasts
for updates.


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