Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
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FXUS62 KRAH 042341
Area Forecast Discussion
National Weather Service Raleigh NC
641 PM EST Sun Dec 4 2016
Cold air damming surface high pressure will extend into the area
from the north tonight as weak low pressure develops along the Gulf
Coast. This weak low pressure will track NE along a coastal front
tonight and offshore Monday. High pressure will build in briefly
from the north Monday afternoon, then a second stronger low pressure
system will cross the Gulf States and Carolinas Monday night through
.NEAR TERM /THROUGH TONIGHT/...
As of 335 PM Sunday...
Cold air damming over interior areas of NC leading to chilly rain.
Rain to add up to 0.2 to 0.5 of an inch tonight before ending.
Surface high pressure (of sufficient strength - greater than 1025
MB) and preferred location (extending from NY state south into the
Carolina`s) to deliver a CAD event for our region, has evolved. The
center of the high pressure was slowly shifting east and was located
from eastern MD to western NC/SC. The CAA/DAA had essentially ended
as the rain continued to saturate the near surface layer. The
evaporative cooling process had already dropped temperatures into
the upper 30s to 40 west. As of mid afternoon, there was still
plenty of evaporative cooling to go as rain was slower to saturate
the surface layer in the NE. Rain thus far has been 0.1 to 0.2 in
the west, but only barely measurable in the NE. Rain will continue
to overspread the region with high confidence through the afternoon,
with temps steady in the west, and falling east.
For tonight, the impressive plume of deep moisture and a general
lift associated with the mid/upper jet and aided by the approaching
wave will keep rain widespread through around midnight. Model
consensus indicates a gradual shift of the rain out of the west
between midnight and 300 am, then in the east between 300 am and 600
am. Only the SE will have lingering light rain chances around
daybreak, with low clouds and some lingering fog and mist elsewhere.
As for QPF, expect a general 0.10 to 0.25 in the NW ranging to 0.25
to 0.50 in the SE for storm totals (through tonight) - the next
system will affect us with significant rain later Monday into
Tuesday. See discussion below.
The cold air damming will be locked in place tonight and the
residual affects will linger through Monday morning. Lows tonight
will hold where the evening temperatures land, mostly 38-43 NW to
Monday, areas of fog and low clouds will start Monday morning,
before most guidance suggests scouring out of low clouds from the
NNW Monday afternoon. This occurs only because of some weak
downslope flow from the NNW develops from VA mountains into our
Piedmont damming region (in the rear of the departing initial wave).
Highs Monday will be dependent on the timing of the scouring out of
the low clouds and the extent that the mid/upper level clouds linger
as well. We will go a bit below statical guidance in the north-
central and NE zone where the low clouds should linger longer with
the residual CAD affects. Highs generally in the 50s, some lower 60s
possible in the south. No POP during the day as central NC will be
in between systems.
.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 325 PM Sunday...
CAD again expected Monday night and Tuesday with a chilly rain.
QPF of 1 to 1.5 inches expected Monday night and Tuesday.
Miller B type storm (parent low tracks west of our area - weakens -
the secondary low becomes primary near the Carolina coast Tuesday,
tracks away Tuesday night).
Weak high pressure (less than 1025 mb) is forecast to move from the
TN valley Monday to the mid-Atlantic Monday night setting the stage
for the next significant system to approach our region from the
western Gulf Coast Monday night. Yet another CAD event is expected
even though the high pressure this time is weaker than the one
today. It is still expected to be just strong enough (near 1025 mb)
and in good position (PA to VA) Monday night to allow the
deliverance of CAA/DAA into the Piedmont Damming Region, just before
and early in the development of rain again Monday night. Dew points
in the 30s will feed into the northern Piedmont providing a good
start for evaporative cooling again once the rain arrives in
earnest. Timing for now appears to be near or after midnight in the
SW, spreading NE overnight to cover the area by 12z/Tuesday. Lows
Monday night will likely be at 12z/TUE - and readings will likely
fall further during the morning with the CAD. Lows 42-50 N to S with
falling temps into the upper 30s and 40s all areas during the day
Rain is expected much of the day Tuesday. Highs only in the 40s with
50s in the SE. The chance of the coastal front penetrating well
inland into our region is very low given the expected Damming and
Miller B type storm (and secondary development very near the coast
Tuesday). This would keep the warm sector well to our SE.
The storm system will lift NE and away Tuesday night with low
overcast conditions expected and rapidly ending rain from south to
north early in the evening. Temps should hold nearly steady in the
40s and lower 50s N to SE.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 335 PM Sunday...
Look for dry weather to return for Wednesday in the wake of
Tuesday`s system and as high pressure builds to our north. The
airmass will moderate as well as SW flow aloft resumes. Meanwhile,
a deep longwave trough will take shape of the middle of the country,
and will move east through the latter half of the week, pushing a
potent cold front across our area on Thursday. GFS and ECWMF agree
that any rain assoc with the front will be fairly light, generally
less than 1/2 inch, and gone before the colder air arrives. Highs on
Wednesday and Thursday expected to reach the mid-upr 50s in the
prefrontal airmass. Lows Wednesday night in the mid 40s.
The big weather story for the long term will be the cool-down that
comes in the wake of the aforementioned front. Cold high pressure
will build in for Friday through Saturday, resulting in dry weather,
however the accompanying airmass will support highs only in the
upper 30s across the Triad and lower 40s elsewhere, both Friday and
Saturday. Lows Thursday night from the mid 20s nw to lower 30s se.
The coldest night of the weekend now appears to be Friday
night/Saturday morning, with lows expected to bottom out from around
20 NW to mid 20s across the coastal plain.
Otherwise, will be closely watching the pattern evolution late next
weekend into the early part of the following week, as a couple weak
short waves embedded in broad cyclonic flow are progged in the
models to move across the eastern US during that time.
.AVIATION /00Z MONDAY THROUGH THURSDAY/...
-- Changed Discussion --As of 640 PM SUNDAY...
24-Hour TAF period: High confidence that light rain will persist
through daybreak and aviation conditions will continue the downward
trend to IFR, and possibly LIFR in the pre-dawn hours. Light rain
will end from west to east, when it does so. Some improvement in
CIGS and VISBYS will occur between 12Z-15Z Monday with a slow
progression to MVFR then VFR, mainly by 18Z. However, skies will
remain overcast around 25 KFT through 00Z Tuesday. -KC
Looking ahead: VFR conditions will last until around 06z Tue. Then
another storm system will cause IFR conditions to return after 06z
early Tue morning, lasting through much of Tue with steady
widespread rain returning. Rain will end late Tue, although IFR
clouds will hold into Tue night. Improvement to VFR is expected Wed
and Thu. -Badgett
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