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FXUS62 KFFC 031012
AFDFFC
Area Forecast Discussion
National Weather Service Peachtree City GA
512 AM EST Fri Mar 3 2023
...Morning Area Forecast Discussion...
.SHORT TERM...
(Today through Saturday)
Issued at 408 AM EST Fri Mar 3 2023
Overview:
Over the last 24 hours, trends have shown an increase in severe
potential for both an environmental wind threat and the threat for
severe thunderstorms this afternoon. Due to these increasing trends,
a High Warning is now in place for portions of the far northwest and
far north central Georgia to accompany the pre-existing Wind
Advisory for the remainder of the forecast area; both hazard products
are in place from 7am through 11pm, however High Wind criteria in
the Warning area is expected in the 12-5pm time frame. Additionally,
The Enhanced Risk (3 out of 5 risk level) within the Day 1
Convective Outlook has been expanded to include portions of NW
Georgia due primarily to a damaging thunderstorm wind threat, with
tornadoes, which have conditional potential to be strong and long-
track, being the secondary storm hazard for this afternoon.
Analysis:
A sharp but deep shortwave trough will be lifting from the ArkLaTex
region this morning to the Great Lakes by this evening. An extremely
quick progression with divergent flow downstream of the shortwave
and a 110+ mph jet streak at 500 hPa aiding the progression of the
system. An accompanied surface low pressure is located in South
Central Arkansas at the time of this writing with a marginally
severe squall line through central Louisiana and a warm front
through the Mid-Mississippi River Valley where prolonged rainfall
has developed a cold pool-propagated sub-severe squall line with
training cells all along the central Mississippi River. This surface
low pressure is forecast to continue pushing into the Midwest by
late this afternoon, with the HREF now resolving a non-occluded low
pressure system in S Indiana around 20 UTC this afternoon with a
central pressure of 980hPa. This is significant in two ways, first
this low is deeper than previously forecasted and begins to occlude
and weaken much later than originally forecasted as well; both of
these factors increase the severe thunderstorm threat for our area
this afternoon. A cold front is forecast to push into far NW Georgia
at the time as well with a wave of showers and thunderstorms. Storm
mode is yet to be determined with CAMs resolving anywhere from a
QLCS to semi-discrete cells along the front, with pre-frontal
showers and storms also a possibility throughout the afternoon.
The prefrontal environment will be ripe with parameters for strong
environmental winds and ingredients capable of producing severe
thunderstorms. Winds aloft indicate that at the 1 km/850 hPa level,
a low-level jet with 70+ kt wind speeds will be present, with a
pressure gradient of approximately 14 hPa from the NW corner of the
forecast area to the SE corner; both of these factors are also
enhancements compared to analysis conducted yesterday morning. For
these reasons, the High Wind Warning was introduced with afternoon,
prefrontal wind gusts increasing by about 5 mph from previously
forecast with forecast wind gusts up to 40-50 mph possible ahead of
the cold front in far north and northwest GA due to the closer
proximity to the well-formed parent low, the strong pressure
gradient, and potential momentum transfer of winds aloft due to
boundary layer mixing and downdrafts in prefrontal showers.
As for the severe thunderstorm threat, several small changes in
parameters and ingredients have elevated the severe potential this
afternoon. As discussed earlier, the parent low is now forecast to
be stronger, more mature, and is slowing down which places the
timing of storms during peak heating hours. The stronger low will
also advect higher dewpoints (mid 60s) and PWATs (1.5+ inches) into
the forecast area ahead of the storms. Increased moisture will also
help boost surface-based instability to around 1000 J/kg ahead of
the storms, with models resolving stronger storm updrafts as a
result. Shear, both in terms of speed and direction, is really
impressive, with 0-1 km shear and SRH expected to be around 50+ kts
and 300-500 m2/s2, respectfully, across North Georgia this
afternoon, which will elevate the potential for rotating supercells
this afternoon.
With all that in mind, the severe outlook for in North Georgia
remains conditional with several inhibiting factors, though several
of these factors has slightly diminished over the last 24 hours.
First, models are still struggling to resolve deep, convective
storms along the frontal zone. While PWATs have increased slightly,
dry air remains aloft at 500 hPa and above. This dry air will make
it difficult for deep updrafts to sustain themselves and will make
it harder for storms to realize their rotational potential. However,
drier air aloft is a double-edged sword as it will also promote
evaporational cooling within the storms which could form stronger
downdrafts more capable of transferring the extremely strong, upper-
level winds to the ground. Additionally, CAPE profiles remain long
and skinny with suboptimal lapse rates in the mid-levels, and this
could result in less aggressive updrafts that take longer to harness
the environmental shear. This delay may allow storms to be sheared
off more quickly, before deep rotation can form within the storms.
This is one reason why Updraft Helicities remain limited in our
convective storm-resolving models, but if storms can hang on long
enough to form a strong rotating updraft, in may persist for a
prolonged period of time and being produce tornadoes which have the
potential of being strong. Additionally, models are still resolving
some prefrontal showers, but look less likely to develop upstream of
the airflow into the line of potentually severe thunderstorms.
Careful attention will be needed for these threats throughout the
day, and we encourage all to have plans ready if they find themselves
in Convective Watches and Warnings throughout the day. While there
is some Forecasted Convective Amplification Deficiency potential in our area (more likely for the tornado
threat than the severe wind threat), potential also remains for
dangerous situations if storms become tornadic. Please stay weather
aware throughout the afternoon. After the cold front passes,
temperatures will drop down overnight into the 40s and mid 50s, with
temperatures rebounding into the mid 60s and mid 70s on Saturday
under clear skies and light NW winds.
Thiem
