Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Raleigh NC
833 PM EST Sat Nov 28 2015

Synopsis...high pressure over the southeast states will weaken in
advance of a strong cold front that will surge south through central
NC Sunday night. High pressure will follow and ridge south into the
Carolinas and Georgia and result in cold air isentropic
upglide occurs atop the surface high...through early week.


Near term /through Sunday/...
as of 830 PM Saturday...

Through tonight: ridging aloft over the southeast u... along with
surface high pressure centered just to the south and west of central
NC... will continue to weaken overnight as a strong cold front
draped from the northern middle Atlantic south and westward into the
western Gulf of Mexico slowly approaches the area. The cold front is
expected to remain well to the north and west of the area tonight.
However... middle to high level clouds will continue to increase...
which should keep low temperatures tonight a category or two warmer...
especially across the northwest Piedmont (where cloud cover is
expected to be the thickest). We still may see some breaks in the
cloud cover from time to time... but less than last night.... so
patchy fog may still be a threat... primary across the
east/southeast where cloud cover should be the least/thinnest.
Expect overnight lows to range from around 50/lower 50s across the
urban areas across the Piedmont to the upper 40s elsewhere. -77

Sunday: the cold front will accelerate south through Virginia once the
brunt of the parent Continental polar surface high driving it builds
east of the Appalachians...and geostrophic adjustment consequently
drives it south in cad fashion. Since the frontal passage will
likely not occur until after dark in central NC...or perhaps be in
the counties adjacent to the Virginia border by that time...another mild
day is anticipated...despite cloudy or mostly so conditions and a
continued lowering of ceilings. A few sprinkles or very light rain
will be possible as the middle level moist axis edges into the western
Piedmont during the afternoon...but the more appreciable probability
of rain will not ramp up until isentropic lift begins in
earnest Sunday night. -26


Short term /Sunday night and Monday night/...
as of 305 PM Saturday...

The cold front draped across the Midwest and middle-Atlantic on Sunday
will finally push south through central NC as a 1032mb high builds
over New England and down the eastern Seaboard. Modest pressure
rises may lead to some briefly gusty winds (15-20mph) after midnight
as colder air surges in. Differential thermal advection appears to
maximize between 06z and 12z as the cold advection undercuts
increasingly moist (though not terribly strong) warm advection above
850mb...with some weak support from concurrent and subtle
disturbances aloft. Categorical probability of precipitation should be warranted for
at least the northwest Piedmont...ranging to likely and chance
further southeast. Quantitative precipitation forecast amounts are heaviest in the northwest Piedmont as
well where isentropic accent is strongest and deepest. The cold
advection and wetbulbing will drive temperatures into the middle 40s by Monday
morning...with little movement during the day as classic cold air
damming sets in and at least periods of light rain and drizzle
continue well into Monday night. Thus...highs Monday will be in the
middle 40s northwest to lower 50s southeast....falling back into the
40s overnight.


Long term /Tuesday through Saturday/...
as of 305 PM Saturday...

Cold air damming will linger into Tuesday with no strong erosion
mechanism prior to the cold that will eventually sweep through the
area on Wednesday. However...Tuesday may not end up being as rainy
as once projected with models showing some decent drying in the middle- slowly increasing insolation and southerly flow should
allow temperatures to warm into the lower 50s northwest to middle 60s southeast by the end
of the day. The cold front just to our west should become
reinvigorated and active as shortwave swings into the base of the
upper low over the Great Lakes and provides the needed forcing to
kick it east. As of right now... the GFS and European model (ecmwf) keep the
heaviest precipitation more in the mountains and foothills...but this will
likely depend on the location of the front by Tuesday night and
early Wednesday.

The cold front will then sweep across the area on
Wednesday...settling offshore on Thursday. Meanwhile... a southern
stream shortwave will cross the southern US and lead to the
development of a low along the front off the southeast/florid coast
on Friday. Models continue to trend offshore with this low and show
less and less impact over NC. Have reduce probability of precipitation over the eastern County Warning Area
to slight chance...but there is enough uncertainty in the split
flow over the Continental U.S. To not completely right off precipitation.
Otherwise...temperatures will be slightly below normal.


Aviation /00z Sunday through Thursday/...
as of 715 PM Saturday...

High pressure across the area will provide VFR conditions through
most of the 24 hour period. Sub-VFR fog is again possible at krwi...
and increasing high level clouds should preclude development further

Outlook: a cold front will surge south Sunday night and result in a
blustery northeast wind...with a several hour period immediately
Post-frontal passage when gusts in the the middle-upper teens kts are much cooler air rushes in through Monday morning.
Ceilings will also steadily lower into IFR-LIFR range...with a
concurrent eastward-development of rain later Sunday night-early
Monday. Subsequent cold air damming will result in a continuation of sub-
VFR conditions and periods of rain until a cold front crosses
our region early Wednesday...though Fay and rwi may briefly scatter to VFR
late Tuesday or Tuesday night.


Rah watches/warnings/advisories...



near term...77/26
short term...22
long term...22

National Weather Service Glossary of Abbreviations