Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 270829

Area Forecast Discussion
National Weather Service Raleigh NC
425 AM EDT Tue Jun 27 2017

A moisture-starved cold front will cross NC today. Canadian high
pressure will follow and crest over the southern middle Atlantic
states Wed and Wed night.


As of 400 AM EDT Tuesday...

Mid and high cloudiness will become thicker and more widespread
today as an upper short wave and associated surface cold front move
east across the area. Moisture depth is shallow but a narrow zone
where low level convergence and mid level support coincide will
produce a few showers in the west this morning, with low chance PoPs
shifting east by around mid day. Diurnal cycle will have time to
build weak instability in the east(~500 joules MLCAPE), so an
isolated storm is possible. MOS and thicknesses support slightly
warmer temps than previous runs and will make a very minor tweak
upward in response as the thickening cloud coverage and virga will
be pulling in the other direction. Highs will range from ~80
northwest to as high as 87 in the southeast.


As of 400 AM EDT Tuesday...

The system will be east of the area by early tonight with decreasing
cloudiness leading to mostly clear skies after midnight as high
pressure builds in from the northwest. Mins will tumble in the
drying airmass with the clearing above, and most areas should be in
the upper 50s by sunrise Wednesday. Skies will remain clear through
Wednesday night as the high moves across the area, with highs
Wednesday edging up a bit under strong sun to reach the low and mid
80s, with mins Wednesday night in the lower 60s.


As of 350 AM Tuesday...

Initially zonal flow aloft, around the nrn periphery of a
developing/strengthening sub-tropical ridge centered over the wrn N.
Atlantic, will yield to (generally weakly) perturbed swly flow aloft
as a trough aloft now over wrn Canada amplifies across the central
U.S. The most notable (synoptic-scale and predictable) of these
disturbances in swly flow aloft will be a s/w trough now crossing
TX, which the models indicate will meander briefly over the nwrn GOM
before lifting newd across the Sern U.S. and Carolinas Thu-Fri.

At the surface, high pressure will drift across and remain over the
central N. Atlantic through early next week. Return flow around the
high will yield gradually increasing temperatures and humidity
levels, marked most abruptly by the passage of a warm front on Fri,
followed by a peak in the humidity this weekend and the heat Mon and
Tue. Despite mid level warmth associated with the sub-tropical
ridge, and resultant weak mid level lapse rates, the aforementioned
warming and moistening low levels should prove sufficient for at
least scattered diurnal convection throughout central NC during the
upcoming holiday weekend, after which time, a sharpening Appalachian-
lee trough and mixing out of surface dewpoints to the west will
probably shift the focus for convection over the ern half or third
of the forecast area.


.AVIATION /06Z Tuesday through Saturday/...
As of 155 AM Tuesday...

The approach of a mid-upper level disturbance and associated surface
cold front will result in patchy mid-high level cloudiness today.
Moisture will be in short supply, and while we may see a few
showers, coverage is expected to be too low to include in the TAFS.
Winds will shift to northerly at 6-8 knots this morning as the
surface front moves southeast across central NC, reaching the
coastal plain around mid day.

High pressure will settle in behind the exiting disturbance tonight
and linger through Thursday. As this high exits offshore Friday, the
return southerly flow will advect a moist unstable air mass into our
region, setting the stage for scattered afternoon-evening
convection, and early morning low clouds and fog. Thus, the
potential for periods of MVFR/IFR parameters will increase,
beginning Friday morning and continuing into the weekend.





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