429
FXUS62 KCAE 081930
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
230 PM EST Wed Jan 8 2025

.SYNOPSIS...
A cold and dry air mass remains in place through the mid to
late week period. The next storm system moves in from the
southwest on Friday and could produce a period of wintry
precipitation in the northern portion of the area. The potential
exists for an impactful winter event across the norther
Midlands and CSRA. Dry weather returns behind the storm with
continued below normal temperatures.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Message(s):

- Cold and dry with temperatures generally 10 to 15 degrees below
average.

Upper trough digging into the Mid Mississippi Valley this
afternoon will move southeast overnight. Models indicate a short
wave trough moving through this evening with a dry surface cold
front. Expect a few mid level clouds ahead of the upper trough
then clear after Midnight. Cold advection early this evening
behind the front will be weakening. Boundary layer winds
increase a bit this evening with a few gusts to near 20 mph
possible especially in the CSRA as the front moves. Light
northwest winds after Midnight as the pressure ridge to the
northwest builds into the area. The air mass is cold and dry
with precipitable water about 30 percent of normal for this time
of year. So expect low temps to fall again into the low 20s as
winds subside toward daybreak. Wind chill temps in the teens,
remaining just above cold weather advisory criterion.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
Key Message(s):

- Cold and dry on Thursday with high pressure in control.

Another quiet period of weather is expected on Thursday. Our weather-
maker for Friday and Friday night will continue to organize to our
west, with strong upper-level convergence and surface high pressure
overspreading the area through the day. So mostly sunny skies and
dry conditions are expected during the day, with temperatures again
below normal across the area. Look for highs generally in the low-
mid 40s across the forecast area. Overnight, axis of the shortwave
ridging will begin to pass over and east of the area as the trough
begins to eject from the southern Rockies and moves eastward. The
surface high pressure should continue to slowly weaken and move
eastward, with a surface ridge axis across the area overnight
Thursday night. Dewpoints are forecast to be very low (in the
mid teens), with bufkit time/height plots showing weak winds in
the lower atmosphere. This combination should yield cold temps
on Thursday night and Friday morning, as radiational cooling
will be near ideal for much of the night. So look for lows in
the lower 20s for most of the forecast area, with some mid 20s
possible in the south or in our typically warm locations.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Key Message(s):

- High confidence in storm system impacting the area, with
  potentially impactful winter weather
- Significant uncertainty in the forecast remains, specifically
  with respect to the low-level temperatures
- Dry weather returns this weekend, with cool weather over the
  area for the remainder of the period

...Potentially Impactful Winter Weather Event expected Friday
afternoon and Friday night in the northern Midlands...

Guidance continues to be in good agreement on a quick hitting, but
potentially impactful, winter weather event on Friday and Friday
night. However, even at this shorter timeframe, significant
uncertainty regarding the temperature profile casts quite a bit of
overall uncertainty on the way things may pan out with this event.

============================================
SYNOPTIC OVERVIEW
============================================

Deep, longwave, positively tilted trough axis across the central US
is forecast to begin pushing slowly eastward after 06z Friday.
Strong, upper level jet streak is expected to develop and yield
widespread upward motion across the deep south on Thursday night and
Friday morning, with widespread precipitation developing ahead of
the trough axis across the southeast. Meanwhile, the aforementioned
surface high pressure will continue to slowly translate eastward
across the Mid-Atlantic and gradually weaken as it does so. A cold
airmass is forecast to be in place, and it is anticipated it may be
colder than guidance is suggesting right now. Clouds are
expected to quickly increase between 09z and 15z from west to
east across the forecast area as ascent and mid/upper level
moisture increases in advance of the approaching trough axis.
Deep isentropic lift is expected to overspread the area
initially in the morning hours, with a band of precipitation
potentially putting down a wintry mix of snow/sleet/rain is
possible with this initial batch. Accumulations of anything are
expected to be limited given very dry low-level air across the
forecast area. Isentropic lift is likely to quickly exit the
area with this initial batch, by Friday evening. Moisture
transport is forecast to be quite impressive as the surface low
approaches, with NAEFS forecasting 90th-95th percentile values
overspreading the area between 2p Friday and 2a Saturday. This
is in response to the upper level jet overspreading the area,
and drawing a strong 850 hPa jet in response. Warm advection
should dominate precipitation forcing as a result. Widespread,
light to moderate precipitation is expected to overspread the
area after 4p Friday. The depth and strength of the remnant cold
layer across the forecast area on Friday afternoon and evening
remains to be seen and is the single biggest synoptic/mesoscale
question mark with this evening. As the evening does along, the
better moisture and forcing should push eastward, exiting the
area no later than 7a on Saturday.

============================================
SENSIBLE WEATHER DISCUSSION
============================================

Sensible weather is going to be driven by the how cold we get on
Friday morning and how cold we are able to stay throughout the
event. This is an unusual type of winter event for us, as the
surface low does not normally track this close to the forecast area.
The low is forecast to track from near New Orleans through the
Savannah area before departing stage right. This typically would
result in surface temperatures a bit too warm for any frozen or
freezing precipitation. However, our antecedent airmass is
quite cold and is expected to remain that way as the surface
high shifts from the Mid-Mississippi valley and into the Mid-
Atlantic and then offshore. Much of the global guidance is too
warm with temperatures on Friday morning (as discussed above),
and just how cold we are able to get will likely modulate the
overall threat for wintry precipitation on Friday and Friday
night.

Overall, the initial band of precip shouldn`t do much other than
produce some light snow or sleet, but it will help our temperatures
to fall via cooling by evaporation. This could lock in colder
than expected temperatures ahead of the primary batch of
rainfall, which would really complicate things. By Friday
evening, robust warm advection should keep the precip type
issues contained to either sleet or freezing rain, and there is
an increasing trend towards a bit more of a sleet sounding
profile across the northern forecast area. Temperatures in this
layer may be underdone, especially given how robust the warm
advection is expected to be. So the fear is that we end up with
an extended period of time of freezing rain across the northern
half of the forecast area. GEFS/GEPS guidance continues to be
bullish with respect to freezing rain totals, with nearly all
members showing impactful ice accumulations on Friday night.
This is much more aggressive than the NBM, and given the
expectation that temps on Friday could be cooler than much of
the global guidance is forecasting, we are opting towards a
slightly colder solution than the NBM is showing.

It must be stressed that confidence is quite low in this right now.
Model mean soundings are quite favorable for a freezing rain event
right now, but the surface layer is a key question mark that we have
yet to answer. Looking at soundings throughout the event, the
surface layer is way too close to freezing on either side to say
where an exact line will setup. If we end up warmer on Friday, then
that will modulate much of the area away from an impactful ice
event. It just isn`t very certain right now, casting a lot of doubt
on the forecast overall. However, if there is an area of increasing
concern, it looks to be from Newberry to Fairfield to Lancaster
counties, where cold air may be locked in enough through the event
to given them a longer timeframe of frozen precipitation. The trend
towards a slightly cooler column up there adds some additional doubt
on overall totals though as some sleet may mix in with the freezing
rain during the event, cutting down on the ice threat overall. We
should continue to grow increasingly confident over the next 24-36
hours as we gather more guidance and more observations.

Beyond this event, we look colder than normal & dry through early
next week as high pressure and large scale troughing sets up across
the eastern Conus.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
VFR conditions through the TAF period.

A dry cold front will move southeast through the area this
evening. Satellite showing a few mid and high level clouds ahead
of the front. West winds 5 to 10 knots becoming northwest
behind the front with a few gusts to near 20 knots around 00z as
the front moves through. The winds will diminish by around 06z
with clear skies.

EXTENDED AVIATION OUTLOOK...Ceiling and visibility restrictions
possible late Friday into early Saturday morning as a low
pressure over the Deep South moves northeast across the area.
Wintry precipitation is possible late Friday/Friday night.

&&

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

&&

$$