NWS Area Forecast Discussion

000
FXUS62 KRAH 241909
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
210 PM EST Fri Nov 24 2017

.SYNOPSIS...
High pressure will remain over the Carolinas through tonight then
weaken Saturday. A dry cold front will approach from the northwest
Saturday afternoon and cross our region Saturday night. Cool high
pressure will build into the Carolinas Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 140 PM Friday...

An area of high pressure at the surface will gradually weaken
tonight as an area of low pressure develops offshore and moves newd
away from the coast. The cool dry air mass deposited by the high
will allow temperatures to coll quickly after sunset. Most locations
will be in the 30s to near 40 degrees by late evening. Under mostly
clear skies and a near calm wind, overnight temperatures will bottom
out between 30 and 35 degrees.

&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 140 PM Friday...

Saturday, an upper level disturbance accompanied by a dry sfc cold
front will drift across our region late Saturday and Saturday night.
Proceeding the s/w will be a deck of mid-high level clouds that will
thicken during the afternoon. While skies will be mostly cloudy-
overcast, little if any rain will occur as the overall lift appears
too weak to generate precip.  Southwest low level flow will advect a
warmer air mass into central NC. This should lead to afternoon
temperatures 3-5 degrees above normal for late November, in spite of
the thickening cloud cover. High temperatures should range between
63-68 degrees.

The sfc cold front will cross our region late Saturday evening into
the overnight hours. NW flow behind the front will advect a drier,
cooler air mass. Expect clouds to thin/dissipate from the northwest
overnight. Min temps will be a touch warmer than previous nights
thanks to warm air ahead of the front. Min temps 35-40 degrees.

&&

.LONG TERM /Sunday through Friday/...
As of 210 PM Friday...

Still appears to be a mostly dry week, and fairly mild. The forecast
vertical wind and thermal profile suggests that we may see some
orographically enhanced cirrus across the northern Piedmont early
Sun, but otherwise expect generally clear skies as a cold front
pushes well to our SE. Cooler air will funnel in behind the front,
dropping thicknesses down to 5-10 m below normal for Sun, yielding
near to slightly below normal highs in the mid 50s to lower 60s.
Moderation begins Mon as surface high pressure builds in from the
west before settling over the Mid-Atlantic region by Tue. A mid
level shortwave trough dropping through the Gulf States and
Southeast Mon into Tue will have little impact given the dry and
stable column in place. But the GFS does show this feature enhancing
baroclinicity along the SE coast and potentially drawing some
stratocu into the SE CWA late Tue through Tue night, as the surface
high weakens further and pushes offshore. The low level wind field
should remain weak, though, with a dry trajectory aloft, so it
should stay dry, albeit with a few more clouds. Another fast-moving
shortwave trough tracks through the Mid Miss Valley and Ohio Valley
through the Mid-Atlantic coast from late Wed through Thu, and this
will pull a diffuse warm front northeastward through the area,
reinforcing the warming trend. With thicknesses rising to slightly
above normal Tue and 20-25 m above normal for Wed/Thu, high temps
should trend to at least a couple of categories above normal, into
the 60s to around 70, under fair to partly cloudy skies.

The GFS/ECMWF solutions diverge considerably by Fri. While the ECMWF
has backed off its deep low over the Carolinas, the latest run still
depicts a progressive full latitude trough from E Canada down
through GA/FL early Fri, with ridging over Mexico/NM/TX. The GFS
lags the southern portion of this trough over the Southwest with a
broad/flat and progressive northern portion crossing SE Canada/St.
Lawrence Valley/Northeast states. The inconsistent ECMWF is still
rather wet on Fri (despite limited 850 mb moisture return) while the
GFS has a more westerly preceding flow and as a result is mostly
dry. Have opted to stay with the drier and more consistent GFS at
this time range, but overall confidence is not high. Highs Fri 60-
67. -GIH

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
As of 1220 PM Friday...

There is a high probability that VFR parameters will persist across
central NC through Sunday. An upper level disturbance and
accompanying sfc cold front will cross our region Saturday night.
While clouds will thicken and lower late Saturday through Saturday
night, ceilings are expected to remain in the VFR category, likely
no lower than 5000 ft. Sfc winds Saturday ahead of the front will be
swly, mainly less than 10kts. Sfc winds behind the front Sunday will
be nwly and less than 10 kts.

The next threat for sub VFR ceilings appears to be late Tuesday
through early Wednesday, mainly in vicinity of KRWI, KFAY, and
potentially KRDU, as a deck of stratocu may spread into the region
from the coast.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...Hartfield
AVIATION...WSS

NWS RAH Office Area Forecast Discussion