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104
FXUS62 KCAE 202335
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
735 PM EDT Tue Apr 20 2021

.SYNOPSIS...
Winds ramp up ahead of and behind a dry cold front Wednesday
bringing an elevated fire danger risk with already dry fuels and
low relative humidity. So a Fire Weather Watch is in effect for
Wednesday afternoon and evening. As cool high pressure settles
in, there is a slight frost risk both Thursday and Friday
mornings. The first rain chance in quite sometime starts
Saturday afternoon as a strong low pressure system tracks over
the area. Clear and seasonable weather fills in behind late
Sunday through Tuesday.

&&

.NEAR TERM /UNTIL 7 AM WEDNESDAY MORNING/...
Short wave trough moving east of the area. Light showers from
earlier have dissipated so dropped pops.

Skies clearing behind the shortwave but radiational cooling
does not look as favorable tonight as boundary layer winds will
remain up due to a 20-25 knot low level jet. Expect overnight
lows in the lower to mid 50s.

&&

.SHORT TERM /7 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
A diving shortwave and strong low pressure system over the northeast
US will swing a dry cold front through the CWA Wednesday afternoon.
The synoptic setup and lack of moisture will keep the front dry, but
the main story will be the strong pressure gradient that develops
in front of and behind the cold front. A deep high pressure
building over the central US and the strengthening low pressure over
the northeast US will quickly ramp winds up. With top of mixed
layer winds around 30 knots, the MOS, hi-res, and blend guidance
all put sustained west-northwest winds at 15-20 mph with gusts to
near 30 mph. Given the setup, stayed on the high end of guidance.
High temps will reach the low 80`s ahead of the front combined
with some warm downsloping behind it. More on Wednesday in the
Fire Weather section.

As high pressure builds into the area overnight Thursday, the strong
cold advection regime will drop temperatures into the mid-upper 30`s
Thursday morning. MOS and blend guidance have trended slightly
colder for morning lows as winds have trended weaker. However since
winds are expected to remain up as least somewhat, the frost risk is
somewhat lessened but this will be monitored closely. Thanks to the
strong cold advection, highs Thursday stay in the upper 60`s and low
70`s.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
The high pressure will move directly over the CWA heading into
Friday morning. With winds consequently falling off and clear skies,
a strong radiational cooling night brings a frost risk Friday
morning. Ensemble, MOS, and blend guidance has bounced around a bit
with the placement of high and therefore wind speeds, but temps are
expected to fall into the upper 30`s or low 40`s. The NBM
distribution suggests only has a few members below 40 for the
Columbia metro but our northern counties have the majority of
members under 40. So the northern CWA looks especially prone to
the frost risk. Otherwise clear and calm with Friday with temps
in the low 70`s.

The main weather story of the weekend will be a potentially
significant rain event as a developing low pressure and warm front
cross the area late Saturday into Sunday. GEFS and NBM
distributions suggest a widespread 1-3 inch type rainfall event as
strong warm advection and isentropic lift develops along the
warm front on Saturday, and then as the low moves over/near the
CWA. NAEFS shows low level moisture transport in the highest
half-percentile climatologically as a 50+ knot 850 mb develops
directly over the CWA. GEFS members range from 0.2 to 3.5
inches, with consistent clustering around 0.5 and 1.5 inches.
But given the trend, confidence is somewhat higher in the upper
end rainfall solutions. The blend additionally supports this
with a 50+% probability of the 1 inch or more across the CWA
over the last few cycles. From a synoptic perspective, this
appears to be much more favorable for strong moisture flow into
the Carolinas compared to the last few systems.

High pressure builds in behind the low pressure system for Sunday
and Monday with high confidence in seasonal and dry conditions.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
VFR. Mid and high level cloudiness clearing out early this
evening behind an upper shortwave. Boundary layer winds will
begin to pick up out of the S to SW tonight ahead of an
approaching front. Model data in BUFKIT indicating a low level
flow of 20-25 kt developing late tonight and would help preclude
fog. Some stratus possible, but low level air still quite dry.
Most guidance not indicating much in the way of stratus, and only
low probabilities in the SREF. So, for now, will not include
any CIG restrictions at this time. Expect W winds to increase
Wednesday as a dry cold front moves through, with breezy
conditions expected.

EXTENDED AVIATION OUTLOOK...Rain with CIG/VSBY restrictions possible
late Friday night and Saturday.

&&

.FIRE WEATHER...
A Fire Weather Watch is in effect Wednesday afternoon through
Wednesday evening. West winds at 15-20 mph with gusts to 30 mph
expected and with dew points falling into the 20`s and the
downslope component to the winds, relative humidity values are
expected to bottom out in the mid 20%`s Wednesday
afternoon/evening. Cool and dry conditions expected Thursday
with the relative humidity dropping to near 20% in the afternoon
and winds staying up, albeit nothing like Wednesday. So the
fire weather risk continues into Thursday and even into Friday
as dry high pressure settles over the area.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...Fire Weather Watch from Wednesday afternoon through Wednesday
     evening for GAZ040-063>065-077.
SC...Fire Weather Watch from Wednesday afternoon through Wednesday
     evening for SCZ016-018-020>022-025>031-035-037-038-041-
     115-116-135>137.

&&

$$