Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 170605
Area Forecast Discussion
National Weather Service Raleigh NC
105 AM EST Mon Jan 16 2017
High pressure along the Mid-Atlantic coast will gradually shift
offshore tonight and Tuesday, in advance of a cold front approaching
the mountains from the west. The cold front will progress east of
the mountains Tuesday night, track southeast through North Carolina
Wednesday morning, then southward offshore the Carolina coast
Wednesday afternoon as an associated upper level disturbance tracks
offshore the Mid-Atlantic coast.
.NEAR TERM /THROUGH TONIGHT/...
As of 10 PM Monday...
Cold air damming wedge will remain in place across Central NC
overnight. Surprising, earlier in the afternoon the sub-VFR ceilings
scattered out in a narrow corridor across the NW Piedmont. However,
nocturnal cooling of the lingering shallow moist layer in place over
central NC should result in lowering ceilings and potentially areas
of dense fog overnight. Additionally, weak shortwave disturbances
traversing the flat low-amplitude ridge in place across the region
could support an isolated shower overnight.
Temperatures the remainder of the night will be nearly steady with
lows ranging from lower to mid 40s northeast to lower 50s south.
.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 105 PM Monday...
The lingering CAD wedge is expected to undergo top-down erosion
during the day Tuesday as southwesterly low-level flow strengthens
in advance of a shortwave approaching the Mid-Atlantic from the
W/NW. Initially overcast skies should become broken by early
afternoon, perhaps scattering out entirely from the Triangle
southward and eastward. Broken to overcast cloud cover is most
likely to persist the longest across the N/NW Piedmont where
occasional sprinkles cannot be ruled out. Challenging temperature
forecast. Expect highs in the upper 50s (N/NW) to mid 60s (S/SE)
Tuesday afternoon. Expect rather mild lows Tuesday night as the MSLP
gradient tightens in advance of the approaching cold front and a
southwest breeze persists much of the night. Expect lows in the mid
to upper 50s, possibly a few degrees cooler in the Northern
Piedmont/NE Coastal Plain where precipitation assoc/w the front is
most likely to occur prior to sunrise Wed. It should be noted that a
large amount of uncertainty persists with regard to the precise
coverage/timing of precip assoc/w the upcoming cold frontal passage
early Wed. -Vincent
.LONG TERM /Wednesday through Monday/...
As of 230 PM Monday...
Fast progressive flow through the extended period will produce
several frontal passages Wednesday through early next week. The
sensible airmass change behind each system will be minor as arctic
air will remain blocked across the northern tier of the CONUS and we
will remain unseasonably mild through the period.
A rather vigorous short wave skating across the Ohio valley will
nudge a backdoor front south into the area by sunrise on Wednesday,
with fairly widespread rain in the morning tapering off during the
early afternoon. Despite the modest cold air advection, we will
benefit from a warm overnight min in the mid 50s bolstered by
increasing sun as the day progresses to allow highs to reach the mid
60s over most of the area, with some readings near 70 along the
southern tier. Lows Wednesday night will be cooler under mostly
clear skies...40 north to 45 south.
Dry weather will linger through Thursday night as upper ridging and
surface high pressure migrate overhead. The modestly cooler airmass
will be in place and highs on Thursday will stall within a degree or
two either side of 60. Will see some light rain begin to spread into
the west by late Thursday night as overrunning ensues in south to
southwest flow as the stacked ridging moves offshore. Mins will
remain mild in the southerly flow under increasing cloudiness...
again mostly in the 40 to 45 range.
A quick and perhaps vigorous round of showers is on tap on Friday as
a low over the plains rotates northward and deep southwest flow
lifts the stalled surface front north concurrent with reasonably
supportive mid and upper dynamics. Will increase PoPs to likely
across the entire area as uncertainty is on the rise with time in
this fast flow regime. Highs Friday should uptick a degree or two in
the warm air regime with mainly upper 50s north to lower 60s south.
We then see a repeat of a short-lived dry spell with low amplitude
mid level ridging Friday night and Saturday. Lows Friday night will
be in the mid 40s with highs Saturday mostly in the lower 60s.
Somewhat similarly, a stronger short wave moving across the mid west
will reassert southerly flow Sunday, pushing another mild but
potentially much wetter front across the area through Monday night.
This upper low will be deepening as it moves into the Tennessee
Valley, and as such, will produce more favorable conditions for
convection as H85 winds are progged to 50kt and supported aloft by a
favorably aligned upper jet. Will have 50-60 PoPs both Sunday into
early Monday as we let the details resolve themselves. Mild temps
linger both days...mid 50s northwest to lower 60s southeast.
.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --AS OF 100 AM Tuesday...
24 Hour TAF period: A mix of aviation conditions at this hour as
ceilings have dropped below VFR levels in most locations. There is
model disagreement this morning whether or not dense fog will occur.
At this point have not included it in the TAFs as the HRRR had
already depicted fog in the area which has not yet occurred. Low
ceilings should then be the main threat to aviation conditions with
everything down to LIFR possible. After sunrise, ceilings are
eventually expected to break out although it may take until the
afternoon to do so. Some gusty winds are possible up to 20 kts or so
Long term: A frontal system will move through the area on Wednesday.
High pressure returns on Thursday for a brief stay before the next
system moves in Thursday night through Friday night. High pressure
then returns once again for the weekend.
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