Severe Thunderstorm Warning 437, NWS Tallahassee, FL

Area Forecast Discussion
National Weather Service Tallahassee FL
829 PM EDT Fri Jul 21 2023

...New UPDATE...

.UPDATE...
Issued at 825 PM EDT Fri Jul 21 2023

The surface analysis reveals typical weak surface flow over the area
for this time of year with the sea breeze boundary pushing slowly
northward into portions of far southern Georgia and southeast
Alabama. At the same time, isolated to scattered strong to severe
convection continues across portions of central Alabama extending
eastward into northern and central Georgia. The 00z KTAE sounding
reveals a strongly unstable airmass with SBCAPE around 2800 j/kg and
DCAPE quite high around 1170 j/kg. However, a cap is in place from
about 830-800 mb, which suppressed convection across our area
today.

For later this evening, the hi-res guidance does still show the
potential for some of that activity to our north to move
southeastward and clip the northern section of our forecast area
before eventually weakening. Forecast soundings across our northern
counties show less of a cap while maintaining high instability and
about 20 knots of deep layer shear, which is actually decent for
summer standards. Thus, we would still not rule out a few strong to
severe storms across our northern counties this evening with gusty
winds.

&&

.NEAR TERM...
(Through Saturday)
Issued at 316 PM EDT Fri Jul 21 2023

Upper ridge will break down tonight into Saturday as a series of
short waves helps to deep a trough over the eastern U.S. The first
shortwave will support increased chances for thunderstorms this
evening into the overnight hours, especially across the northern and
eastern portions of the forecast area. With modest deep layer shear
(25-30kt) and mid-level lapse rates (6.5-7/km), a few strong to
severe storms cannot be ruled out with this activity.

For Saturday, another shortwave will move into the base of the
developing trough, supporting additional showers and thunderstorms
across the entire forecast area. With plenty of instability and
still around 25kt of keep layer shear, a few strong to severe storms
will still be possible. Thus, SPC continues to highlight the region
with a marginal risk for severe storms.

Heat-wise, temperatures should be a bit cooler than today, both due
to the lower 500mb heights as the ridge breaks down, and the
increased convective coverage by mid to late afternoon.

&&

.SHORT TERM...
(Saturday night through Sunday night)
Issued at 316 PM EDT Fri Jul 21 2023

Upper troughing continues establishing itself across the Eastern US
late this weekend as its base cascades down further into the region.
This pattern will keep cyclonic flow aloft in place while prompting
a corresponding frontal boundary to sag/linger towards the coast.
The environment should remain seasonably unstable and very moist
with above-normal lift to support additional rounds of scattered to
widespread showers and thunderstorms capable of strong to damaging
wind gusts, small hail, and heavy rainfall. Axis of highest
precipitation is expected to be along the front. Its slow-moving,
zonally oriented nature could spell flooding trouble via training
convection that is likely to be ongoing into Saturday evening. By
Sunday, elevated rain chances shift across/south of the I-10
corridor as relatively drier air attempts to filter in from the
north Sunday night into Monday morning.

The SPC has a Marginal Risk (level 1 of 5) for severe weather over
the Deep South for Day 2 - valid 12Z Saturday to 12Z Sunday. Modeled
soundings showing plentiful instability, rich moisture, steep
low/mid-level lapse rates, and unseasonably strong deep-layer shear
with afternoon Inverted-V profiles justify this outlook. A Marginal
Risk (level 1 of 4) for Excessive Rainfall also remains in place
and spills over into Monday. One silver lining to the short-term
period is a reprieve from dangerous heat thanks to considerable
cloud cover from increased convective coverage. Forecast highs are
in the upper 80s with heat indices around the low 100s while
overnight lows drop into the 70s.

&&

.LONG TERM...
(Monday through Thursday)
Issued at 316 PM EDT Fri Jul 21 2023

At the beginning of the period, high temperatures will remain in
the upper 80s to low 90s on Monday with prevailing westerly winds
from 5-10 kts throughout Monday and Tuesday. Scattered
thunderstorms are also likely as moisture lingers along a nearby
front while upper troughing is slow to lift. Heavy rainfall
appears to still be a concern, so cannot rule out some flooding
problems. Best rain chances are along and south of I-10 into the
Gulf on Monday with diminishing chances throughout Tuesday as
relatively drier air continues advecting from the north.
Otherwise, partly cloudy conditions are expected. Upper ridging
then begins to build back in, which should revert us to more of a
typical summertime pattern.

Low temperatures will be in the mid to low 70s throughout the
period, preceded by very warm to hot daytime temperatures for the
following days. High temperatures for next week likely reach the
mid to upper 90s with widespread peak heat indices returning to
the low 100s near the end of the long term. Winds will be variable
throughout the rest of the period thanks mainly to prevailing
surface high pressure. Scattered thunderstorms are possible from
Wednesday, onward mainly along the seabreeze, with convection
shifting over the Gulf during the overnight/early-morning hours.
A mix of late-July sun and clouds are forecast inland away
from thunderstorms.

&&

.AVIATION...
(00Z TAFS)
Issued at 742 PM EDT Fri Jul 21 2023

A few showers may be possible this evening at DHN and ABY as
storms to the northwest across SE Alabama continue moving
southeast. Storm intensity is expected to decrease into the
overnight hours, turning into mostly shower activity as
instability decreases post-sunset. Mostly VFR conditions are
expected tomorrow as convection fires off along a stationary
boundary to the north late in the TAF period with widespread
thunderstorms possible, impacting all terminals. However,
confidence is currently low on timing and coverage.

&&

.MARINE...
Issued at 316 PM EDT Fri Jul 21 2023

Generally favorable boating conditions prevail outside of
thunderstorms, for which chances return to the forecast this
weekend into next week. The main concern with maritime convection
would be strong to gusty, erratic winds, frequent lightning, and
the potential for waterspouts. A west to southwest wind around 15
knots or less persist with wave heights around 2 feet the next few
days.

&&

.FIRE WEATHER...
Issued at 316 PM EDT Fri Jul 21 2023

Wetter and slightly less hot conditions are on tap for the weekend
as the coverage of showers and thunderstorms increases for Saturday
and Sunday. Therefore, fire weather concerns are relatively low
outside of the potential for lightning and winds from
thunderstorms.

&&

.HYDROLOGY...
Issued at 316 PM EDT Fri Jul 21 2023

Multiple rounds of showers and thunderstorms are expected this
weekend into early next week. The presence of a sagging frontal
boundary within a moist/unstable airmass supports a marginal threat
for isolated instances of flash flooding from training convection
through at least Monday. Saturday and Sunday are shaping up to be
the wettest days of the period. Seven-day forecast amounts are
widespread 1-2" (isolated higher). However, local CAMs paint high
probabilities for 3" this weekend nearly areawide and lower-end
potential for 6" over the same time span. The latter is currently
the reasonable "worst case" that is focused over parts of SE AL,
FL Panhandle, and lower I-75 corridor. Meanwhile, all area rivers
remain in good shape, but could see some rises depending on the
precipitation pans out.

&&

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not requested. However, spotters are always
encouraged to safely report significant weather conditions when they
occur by calling the office or tweeting us @NWSTallahassee.

&&

.PRELIMINARY POINT TEMPS/POPS...
Tallahassee   77  95  75  88 /  20  70  50  70
Panama City   80  91  77  86 /  20  60  60  80
Dothan        76  92  73  88 /  30  70  70  50
Albany        76  92  73  88 /  50  70  60  50
Valdosta      76  95  74  88 /  30  70  50  60
Cross City    78  94  78  87 /  20  60  30  80
Apalachicola  80  91  79  86 /  20  60  40  80

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AL...None.
GM...None.
&&

UPDATE...DVD
NEAR TERM...Camp
SHORT TERM...IG3
LONG TERM....SHB
AVIATION...Oliver
MARINE...SHB
FIRE WEATHER...Camp
HYDROLOGY...IG3

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