Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Raleigh NC
217 PM EDT Sat Apr 19 2014
Synopsis...low pressure will slowly move east off the the southeast
US coast through the weekend.
Near term /through Sunday night/...
as of 150 PM Saturday...
The slow moving middle/upper low was located over southeast Georgia
this afternoon. The latest WV satellite data indicated the middle level
dry punch that had worked into the southeast part of NC earlier was filling
in with additional moisture and cooling cloud tops due to the
circulation around the middle/upper low. Deep layered east-northeast flow was
continuing to transport moisture off the Atlantic across all of NC.
This moisture was being lifted up and over the coastal boundary
creating large areas of rain over NC. The latest radar trends
indicate the best rainfall had shifted to the western Piedmont...
foothills and Blue Ridge aided by the surface to 850 mb easterly low
level upslope flow into the Blue Ridge. Even thought the rainfall
rates have been less than 0.10 per hour with this large rain area...
it has been nearly continuous. The latest models suggest that this
rain area focused over west-central NC this afternoon may slow
develop eastward in time as the large circulation around the
middle/upper low gradually but slowly shifts eastward overnight. While
not a flooding threat... periods of light rain with spotty moderate
rain can be expected overnight. The far northern Piedmont extending
from Winston-Salem to Roxboro should have the lowest pop and quantitative precipitation forecast as
drier air is advected in from the NE (va). Dew points are expected
to fall through the night into the 30s across the northern tier of
NC. This region should only see a few hundredths of rainfall
tonight. Elsewhere... another 0.25 to locally 0.50 may still fall
due to the slow movement of the system. Eventually... the
strengthening surface high pressure to our north will win out later
Sunday... as the middle/upper low finally shifts into the Atlantic.
Sensible weather tonight... occasional light rain except a chance of
light rain far north. Breezy and cool. Lows in the middle to upper 40s.
Some spotty light rain may still linger through late morning
especially south and east of The Triad. Any quantitative precipitation forecast will be light... but
with the clouds and stiff NE breeze... it will continue to be
chilly. Skies becoming partly sunny northwest... and variably cloudy
elsewhere Sunday. Highs generally in the lower to middle 60s.
Sunday afternoon and Sunday night... a model consensus is for
gradual clearing from the north-northwest as the strengthening
surface high builds in from New England. However... if the cyclonic
flow lingers along the I-95 corridor... as some models hint... the
cloudiness may be slower to clear. Most areas should become mostly
clear west of I-95 Sunday night. Lows in the 40s.
Short term /Monday through Tuesday night/...
as of 200 PM Saturday...
Monday and Monday night: high confidence that Monday and Monday
night will be dry as the coastal low moves away from the Carolinas.
Surface high pressure will continue to ridge in from the northeast
while ridge also builds in aloft. Expect highs around 70 degrees
and overnight lows around 50 degrees.
Tuesday through Tuesday night: an upper level trough will approach
the area early Tuesday. The surface trough amplifies the surface low
over the Great Lakes moves east-northeast and deepens on Tuesday. Rain chances
will increase Tuesday afternoon as the cold front approaches.
Although southwest flow is expected to advect in some warm moist air
ahead of the front...the duration is relatively short...limiting the
available moisture and potential rainfall totals. As of the last
couple of model runs...the GFS appears wetter than the European model (ecmwf) with
this system...not helping to improve confidence. The warm southwest
flow will help high temperatures reach the middle to upper 70s across
the area. Given the projected marginal shear and instability Tuesday
aft/eve...an isolated strong/severe storm cannot be ruled out...but
the best upper level support is well to the north...which should
help limit the threat. Regardless...expect the cold front to move
through central NC Tuesday eve/night...with dry air advecting into
the middle level behind it helping cut off any remaining precipitation.
Though it will be dependent on timing of the front...for now expect
lows around 50 degrees northwest to middle 50s southeast Tuesday night.
Long term /Wednesday through Saturday/...
as of 215 PM Saturday...
High pressure builds in behind the front and remain in place through
Thursday night...yielding dry weather and temperatures within a few
degrees of normal...highs in the low to middle 70s and lows increasing
from middle 40s Wednesday night to low 50s Thursday night. Another low
pressure system traversing eastward across the northern U.S. At the
end of the week will gradually push the high offshore and yield the
return of southwest flow and increasing rainfall chances for Friday
and Saturday. Again with this system the models differ...with the
GFS being the wetter of the two...thus will continue to indicate a
slight chance for rain...although confidence in the timing and
amounts is not particularly high at this time. Expect highs in the
middle 70s to around 80 degrees and lows in the middle to upper 50s Friday
night...decreasing into the low to middle 50s for Saturday night.
Aviation /18z Saturday through Wednesday/...
as of 210 PM Saturday...
Periods of light rain with IFR to MVFR ceilings will likely persist
through 06z/20... except for the kgso/kint terminals where VFR ceilings
should prevail. Gusty NE winds at 15-25kt can be expected with the
strongest winds at kfay through 12z/20.
A return to VFR conditions are expected Sunday and Sunday night...
which should last through Monday night and Tuesday.