Turner Downs Forecast Discussion

FXUS62 KRAH 271917

Area Forecast Discussion
National Weather Service Raleigh NC
317 PM EDT Mon Mar 27 2023

An area of low pressure will track from the lwr OH Valley to off the
Northeast coast with a trailing cold front moving southeast across
the Carolinas through tonight. A mid and upper-level disturbance
will cross the region late Tuesday and Tuesday night.


As of 805 AM Monday...

Mesoscale subsidence behind an MCV and earlier severe complex of
thunderstorms that moved off the srn NC coast this morning has
caused rain to abruptly end from west to east across cntl NC during
the past few hours.

A trailing, convectively-modulated effective surface front stretched
from that now-offshore complex wwd across cntl SC and GA, then wswwd
across srn MS and LA. The bulk of the severe potential today will
reside along and south of that boundary, and consequently south of
cntl NC. However, a synoptic warm front was evident from the srn
Pamlico Sound nwwd to near RWI, then wwd across the nrn NC Piedmont.
That boundary will retreat nwd into srn VA through this afternoon,
ahead of low pressure that will migrate from ern KY this morning to
the DelMarva coast by this evening. A trailing surface cold front,
led by a closely-preceding pre-frontal trough, will settle southeast
across cntl NC this afternoon through mid-evening.

In the growing warm sector to the south of the aforementioned
synoptic warm front, diurnal heating into the 70s to around 80 of a
seasonably moist airmass characterized by surface dewpoints in the
upr 50s to lwr 60s, and beneath a steadily-reloading EML plume from
nrn Mexico and TX will, support the development of weak surface-
based instability across cntl NC this afternoon. While the
redevelopment of an isolated shower/storm cannot be ruled out
anywhere in cntl NC with diurnal heating today, widely scattered
ones are more likely to concentrate along the pre-frontal trough
and/or surface cold front. While coverage will likely be limited
owing to considerable dry air aloft accompanying the EML plume, the
strong, unidirectional mid-upper-level flow of recent days will
remain overhead and provide ample effective shear for a conditional
risk of splitting cells capable of producing hail. It will otherwise
be a breezy afternoon in the warm sector, with cold, dry advection
that will result in noticeably cooler/drier temperatures in the mid
40s-mid 50s by Tue morning.


As of 315 PM Monday...

Behind the cold fropa, cold/dry advection is expected to briefly
continue through the early morning hours as the front continues to
sag south over the Southeast before stalling in a west/east
orientation extending from the SC coast to just north of the central
Gulf coast states. A 120-150kt upper level jet streak over the OH
Valley extending into the lower MS Valley will sag slightly
southeast and strengthen as a shortwave over the Mid MS Valley
shifts ESE into the lower OH Valley by 00z. This will position the
southern Mid-Atlantic within the optimal location underneath the
right-entrance-region of the upper jet, strengthening mid-level
flow, and glancing DPVA to lead to excellent upper level support for
upward motion. As this upper forcing approaches the Mid-Atlantic and
the Southeast, a weak wave of low pressure is expected to develop
over the Gulf Coast along the remnant baroclinic boundary from the
fropa mentioned above. This area of low pressure should track
northeast into the Carolinas by 00z, coincident with the best upper
forcing. As the low approaches, 700mb WAA maximizes along with low-
level FGEN support at 925-850mb within the deformation zone to
blossom precipitation directly over central NC Tuesday evening.
Significant drying at 500mb will likely be punching into central NC
ahead of the shortwave, but deep saturation below this layer co-
located with ample multi-layer ascent should sustain precipitation
over central NC for roughly a 6-8 hour period until the shortwave
pushes through the area late Tuesday night and promotes deep layer
subsidence in its wake. A broad area of 1027mb high pressure will
shift into the OH Valley by early Wednesday morning promoting a
secondary, reinforcing fropa leading to 6-8mb surface pressure rises
into Wednesday morning. CAA should lead to a well mixed boundary
layer overnight and may promote wind gusts up to 25 mph over the
Sandhills and southern Coastal Plain between 2AM and 8AM.

Precipitation totals range from a tenth of an inch across the
southern tier to up to a third of an inch across the northern
Piedmont into the central/northern Coastal Plain were the best
overlap of deep layer forcing exists. A pencil thin layer of
orographic cirrus near the Triad extending up into VA should be
present early Tuesday morning with very thin cirrus elsewhere. Upper
level cloudiness within the moist upper level flow should thicken
and lower through the day, tempering temperatures a bit during the
afternoon with forecast highs peaking in the low/mid 60s (N) to low
70s (S). Lows will largely be driven by CAA behind the reinforcing
fropa and expected to bottom out in the 40s with upper 30s possible
in the coldest spots.


As of 230 PM Monday...

Wed-Fri AM: Upper ridging will slowly build east from the Rockies on
Wednesday to across the Carolinas by Friday. While the upper ridge
builds in, surface high pressure will build east from the Mid-
Mississippi River Valley Wednesday to across the Carolinas Wednesday
night and offshore Thursday. Another surface high will build from
the northern Plains Wednesday to the Ohio Valley Thursday and off
the Mid-Atlantic Coast by early Friday. These features will maintain
dry weather across central NC through early Friday. Highs will
increase from 5 degrees below normal on Wednesday to around 10
degrees by normal on Friday as subsidence increases across the
region. Slightly below normal lows Wednesday will increase to just
above normal by Friday morning.

Fri PM-Sat PM: As the surface ridge moves offshore, a prefrontal
trough may approach the region Friday afternoon, increasing chances
for showers from NW to SE throughout the day and night. By Saturday,
a cold front will approach from the west, and an upper trough will
swing east from the TN Valley to NC by Saturday night. These
features will provide a better chance of precipitation compared to
Friday. Additionally, strong low-level and deep-level shear, along
with weak instability, could generate thunderstorms across the
region, with the best chances closer to the Coastal Plain where
surface dewpoints in the low 60s remain. Winds will increase through
the period, and especially Saturday as a lower-level jet moves into
the area and pressure gradients increase. SW wind gusts could be as
strong as 30-40 mph on Saturday, then begin to diminish Saturday
night behind the front. Widespread mid-70s to low 80s are expected
for highs, with lows around 60, which is around 20 degrees above

Sun-Mon: Surface high pressure then builds east from the Midwest
Saturday to the Mid-Atlantic Sunday and off the coast around Monday.
At the same time, weak upper ridging returns as it builds in from
the west and will help keep conditions dry to start the next week.
Cold air advection behind Saturday`s front will help lower highs to
the 60s and 70s Sunday, then increasing subsidence and warm air
advection Monday increase highs to the 70s area-wide.


As of 200 PM Monday...

24-hour TAF period: Scattered MVFR ceilings are still being observed
across portions of the northern Piedmont and Coastal Plain,
including at RDU. These should continue to scatter out to VFR over
the next couple of hours, with VFR conditions expected for the
remainder of the period. A cold front and prefrontal trough are
resulting in a line of isolated showers and storms beginning to
develop just west of the Triad, and these will continue to push east
across INT/GSO over the next few hours, before potentially reaching
RDU and RWI late this afternoon and early evening. While widespread
severe weather is not expected, some hail and gusty winds will be
possible where any storms do occur, along with brief heavy rain and
reduced visibilities. Outside of these storms, W/SW surface winds
could gust to 15-25 kts for the rest of the afternoon, before winds
lessen and turn NW then N this evening and overnight behind the cold

Outlook: The approach and passage of a mid/upper-level disturbance
will result in a chance of rain and sub-VFR restrictions Tue night.
After a period of dry weather from Wednesday through Friday, a cold
front will bring another chance of showers/storms and sub-VFR
restrictions on Saturday.




SHORT TERM...Swiggett

NWS RAH Office Area Forecast Discussion