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000
FXUS62 KCAE 091022
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
622 AM EDT Tue Apr 9 2024

.SYNOPSIS...
Mainly dry weather with near or slightly above normal
temperatures are expected through early Wednesday as a surface
high shifts off to our east. There is a slight chance of showers
in our northern counties on Tuesday, but the next chance for
impactful rain waits until Wednesday night into Thursday as a
strong trough approaches. Strong thunderstorms are possible with
this activity. Strong wind gusts are likely on Thursday and
Friday as a strong low pressure system pushes to our north. Drier,
warmer weather fills in behind the front for the upcoming
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Upper ridge axis will be shifting off the coast today resulting
in south-westerly flow aloft and moisture transport.
The surface ridge remains offshore. With persistent south flow,
low level moisture will be increasing as well. Precipitable
water increase to around 1.3-1.4 inches by this evening. There
is a short wave trough, currently across Alabama/southwest Ga
that will be moving through the area this morning. DPVA noted
ahead of the trough to provide some lift. Isentropic lift/warm
advection today with a focus across the western Midlands and
Piedmont. Deeper moisture across the Upstate. Radar at 07z
showing some light rain showers over west-central Ga ahead of
short wave. The HREF and latest HRRR suggest showers will move
northeast and focus in the Upstate region through most of the
day. Kept chance pops mainly in the western and northern portion
of the CWA with lower pops southeast. Any qpf should be quite
light with the NBM showing only around 0.01 inch. Extensive mid
and high level clouds should keep temps down a bit, cooler than
yesterday with high temps mainly in the low to mid 70s. Upper
70s extreme southeast Midlands. Considerable clouds tonight with
low pops as moisture flux shifts to the north and northwest of
the area. Guidance consistent with low temps near 60.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Active forecast period on tap, as a strong surface low quickly
organizes over the MS Valley and moves into the OH Valley, bringing
impacts to the FA by Thursday. High confidence that Wednesday will
remain quiet, though, as shortwave ridging precedes the big system
and helps to keep us dry. Expect high clouds most of the day, but we
should still warm into the upper 70s and low 80s across the FA. High
pressure is forecast to slowly shift eastward into the Atlantic,
helping to slowly strengthen the pressure gradient on Wednesday
night. Southeasterly flow is expected to develop as strong surface
pressure falls envelop the Carolinas as the surface low organizes
and deepens. This will lead to an isallobaric component of the low-
level wind vector, helping to back flow as the low moves northward.

This brings us to late Wednesday night and Thursday, and the
potential for severe weather with this system on Thursday. From a
synoptic scale setup, the signal has been there for several days
now. The mid/upper level shortwave is forecast to take on a negative
tilt as it pushes into the OH Valley on Wednesday night and
Thursday, placing the southeastern US within a broad area of
increasingly strong upper level diffluence. Vorticity & warm air
advection will also be very strong, fueling the intense synoptic
scale ascent across the area. The upper level diffluence is expected
to yield a mass response in the lower levels of the troposphere,
with an 850 hPa jet streak of 50+ knots overspreading the area from
the west on Thursday. As such, given southwesterly flow in the
mid/upper levels atop southeasterly flow near the surface,
kinematics are expected to be intense across the area on Thursday.
Pretty much everything you`d expect - 300 m2/s2+ of 0-3km SRH, 50-70
knots of 0-6km shear, etc. So from a dynamic & kinematic
perspective, model guidance continues to hold steadfast that this is
an impressive system.

However, thermodynamically, things are a bit dicey. I would note
that this barely satisfies the definition of a high shear/low cape
(HSLC) set up as the low cape part of it is nearly zero cape. There
has been increased model support in a large, intense MCS developing
across the southern MS Valley, pushing eastward into south-central
AL by Wednesday evening. South of this, more convection is forecast
to develop and grow upscale, pushing eastward through the night.
Little instability is forecast to precede this in addition to the
rain likely approaching the FA by Thursday mid-morning at the very
latest. Combine that with copious cloud cover & limited diurnal
heating and meager mid-level lapse rates, and the scenario where we
see severe convection becomes limited and unlikely. Guidance does
show some destabilization ahead of the surface front by the
afternoon hours, but we`ll be directly under the axis of the 500 hPa
jet streak, with an intense dry slot noted in model RH forecasts and
forecast soundings. Despite having strong synoptic forcing, it is
unlikely we will be able to see enough instability develop to
sustain updrafts in such a detrimental environment to them. SPC
maintains a Slight Risk for severe storms, and I agree with this
solely on the basis that the kinematics that will be in place.
However, this event possesses the common "high ceiling, low floor"
setup that composes the majority of HSLC events. If there is enough
surface instability ahead of the morning convection, then we may see
isolated instances of damaging winds and tornadoes. But it seems
increasingly unlikely that we will have that instability.

The other issue to be concerned about on Thursday is high non-
convective wind gusts. Surface pressure falls ahead of the front and
rises behind it are forecast to be intense, so intense wind fields
are expected near the surface. Even with the marginal heating &
mixing that the GFS shows developing Thursday results in the
potential for 40+ mph wind gusts throughout the day. So a Lake Wind
Advisory looks like a no brainer again, with the possibility that a
Wind Advisory may be needed considering the NBM is showing fairly
high probabilities of 40mph winds or greater. Further supporting
this that the ECMWF EFI has been trending up the last several runs
with the wind potential, indicative of an anomalous event
potentially occurring. Highs on Thursday should be in the 70s, with
upper 70s possible given that we clear out by the afternoon hours.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Confidence is fairly high in this period. Cold front will come
through Thursday night, ushering in surface high pressure very
quickly behind it by Friday night. This likely means we`ll have
another windy day on Friday, with models showing deep mixing & 850
hPa flow still in the 35-40 knot range. It is likely that we`ll be
able to mix all of that down with forecast soundings showing strong
subsidence in the low-levels. So expect another day of 30-40 mph
gusts on Friday. Expect highs in the 70s under sunny skies.
Temperatures are then expected to moderate as an interesting upper
level pattern takes shape through the weekend and into next week.
General troughiness is likely to be set up Sat-Mon, with shortwave
ridging setting in by Tuesday. LREF members are in great agreement
on this pattern, with 850 hPa temps warming into the 12-14C range by
Mon/Tues as well. This should result in temps in the mid 80s & lows
in the low 60s by the end of the forecast period.

&&

.AVIATION /10Z TUESDAY THROUGH SATURDAY/...
VFR conditions to continue through the TAF period.

High pressure remains off the SC coast. Moisture will increase
across the area today as the south-southwest flow increases.
An upper level disturbance will move through the area this
morning and possibly trigger a few showers. Restrictions not
expected at this time and any rainfall should be very light.
Ceilings will primarily be mid level early this morning with
broken strato-cumulus 4000-5000ft mid to late morning into the
afternoon at times. Deeper moisture should remain north and
west of the area. South-southwest 5 to 10 knots becoming
southeast after 00z.

EXTENDED AVIATION OUTLOOK...Potential and confidence for
restrictions increases Wednesday through Thursday as a cold
front approaches and moves through the region. Increasing winds
Wednesday night with very strong and gusty winds expected
Thursday through Friday.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...None.
GA...None.

&&

$$