Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 202345

Area Forecast Discussion
National Weather Service Raleigh NC
745 PM EDT Wed Mar 20 2019

A low pressure along the coast will track northward across eastern
NC later tonight, then rapidly strengthen as it moves up the eastern
seaboard Thursday. A cold front will push through the region Friday,
bringing a dry but chilly weekend.


As of 745 PM Wednesday...

Only minor tweaks to the afternoon package needed. Will be
evaluating the need for extending POPs a bit further west with the
late evening update if current radar/CAM model trends hold true.

Previous valid discussion...

A wet night in store for much of the central NC, especially along
and east of highway 1, as an area of low pressure off the northeast
SC coast lifts nwd into the Coastal Plain of central NC. The
approach of a decent s/w from the west will cause the sfc low to
strengthen with time. This, in turn, will strengthen/deepen the
onshore flow and low level moisture advection and convergence,
leading to an expanding area of light-moderate rain late this
evening into the overnight. Additional lift will be supplied by a
125+kt upper jet crossing the Deep South into the SE U.S., placing
central NC in the left exit region of the jet. Based on the expected
track of the low, expect a sharp precip gradient somewhere over the
western Piedmont. Potential for this gradient to fall over the Triad
with locations in and around GSO measuring a tenth or two while
locations near Winston-Salem or close to Yadkin River measure a
trace to a couple hundredths. Anticipate the heavier totals to occur
in close proximity of the sfc low, generally near or in between
highway 1 and I-95, with the heavier totals approaching an inch by
early Thu.

Temperatures overnight will vary from the upper 30s to around 40 in
the west where rain will be more spotty and light, to the low-mid
40s east.


As of 330 PM Wednesday...

The sfc wave will lift nwd, exiting our NE counties by mid-late
morning, as a s/w digs into our region from the NW. Expect a
temporary lull in the rain across the region through most of the
morning, then anticipate scattered showers developing over the
western Piedmont in the afternoon, advancing eastward with time over
the rest of the central NC during the late afternoon-early evening.
Model sounding projections suggest decent mid level lapse rates
thanks to the cool pocket of air associated with the s/w. Not
certain if any thunder will occur (cannot rule out an sporadic
rumble), but considering the abnormally low freezing level (~5500 ft
agl), any showers with sufficient depth/sustained updraft may be
accompanied by small hail.

The s/w will swing through the area Thursday evening, then lift away
from our region overnight. Subsidence behind the s/w and
developing/deepening NW flow will aid to scour out the moisture
leading to dissipating cloud cover overnight Thu into early Friday.

Tricky temperature forecast Thu as extensive cloud cover and
scattered showers may inhibit temperature recovery. Shaded highs
toward the cooler NAM MOS guidance. If partial clearing permits some
sun to peek through for a couple of hours, high temperatures could
be 2-3 degrees warmer. This potential appears best over the southern
Piedmont into the Sandhills. Overnight temperatures Thursday night
will range from the mid-upper 30s west to near 40-lower 40s far east.


As of 210 PM Wednesday...

The main issue/hazard this weekend will be the chilly temperatures
and potential for frost and/or freezing conditions Saturday and
Sunday mornings. Since the Frost/Freeze program has begun in the
southeastern NC region, it may be necessary for Freeze Warnings or
Frost Advisories by Friday night into the weekend.

Early spring can bring hard freezes that damage early blooming crops
and ornamentals. Typically, the main threshold for severe damage is
28 degrees for 2-3 hours. It appears that portions of north-central
NC will have that chance, especially on Saturday night and early
Sunday morning. This is when the center of a cold high pressure is
forecast to be overhead of central NC.

The good news (if there is any associated with the cold) is that the
average last freeze of the season typically comes in the first two
weeks of April for much of our region. The exception is over
portions of the Sandhills and SE Coastal Plain. Here it is earlier
and typically late March. In other words, the SE zones have started
their growing season, and the rest of our region has not. Therefore,
the cold this weekend should not greatly impact our region, except
in the Sandhills and SE Coastal Plain. However, impacts of a
freeze for this region can be significant due to the blooming fruit
trees and berry crops.

Collaboration with the surrounding NWS forecast offices has lead to
a turn on date for the Frost/Freeze program (issuance of products
for Frost/Freeze conditions) as of today in these areas). Elsewhere,
we will wait until April 1st to begin the issuance of Advisories and
Warnings for Frost/Freeze conditions.

Friday and Friday night should be breezy and cool as a cold front
will move through the region. The main CAA should arrive late in the
day. Highs should be able to reach into the mid 60s to lower 70s
(SE). Breezy WNW winds at 10-20 mph and low relatively
humidities can be expected. It may be just a bit too mixed or
continued breezy well into Friday night. This may allow lows to
remain just above freezing in the Sandhills and Coastal Plain, where
lows in the 35-40 range are most likely. Elsewhere, lows in the 30-
35 range with clear skies and diminishing wind expected.

Saturday through Sunday... the high pressure will build from the
Midwest to over NC Saturday into Sunday morning. Highs Saturday
should hold in the 50s, except near 60 SE. Lows Saturday night 27-32
in the Piedmont, with lower to mid 30s SE. Highs Sunday should begin
to moderate into the lower to mid 60s as the return SW flow arrives
as the high departs.

Monday through Wednesday, low confidence as model spread continues.
We will carry a good chance of showers late Monday into Tuesday.
However the storm track and timing are still in debate, along with
the strength. For now, a low pressure track from the TN valley east
across SC or far southern NC is favored, with cold high pressure to
the north acting as a block from a more northward track. Most likely
the temperatures will remain fairly cool, except possibly in the SE
zones (if the warm sector can advance into that region). QPF could
be significant again (1+ inch), but too early to pin this down.
Much more on this potential system in the coming days.


As of 745 PM Wednesday...

Deteriorating aviation conditions will continue into the overnight
hours as an area of low pressure strengthens and pushes north along
the Interstate 95 corridor of NC/VA. As a result, sub-VFR
conditions will likely be achieved (or continue) at all terminals
through at least 12z, with some periods of IFR/LIFR CIGs/VSBYs
likely at the eastern terminals as the heaviest rain pushes in.
Winds should remain generally at or below 10kts tonight, gradually
veering from northerly to northwesterly to eventually westerly as
the area of low pressure pushes north into VA mid day Thursday. Some
gradual improvement will be likely as a brief period of subsidence
pushes in behind the departing low, with CIGs finally rising back to
near VFR parameters at KFAY/KINT/KGSO by 16z (noon) and a few hours
after at both KRDU and eventually KRWI. A second round of scattered
showers will be possible across the Piedmont Thursday afternoon as a
shortwave dives south out of the corn belts states, and into the
Sandhills early Thursday evening.

A passage of a cold front Thursday night will aid to scour our the
low level moisture leading to clearing skies. While aviation
ceilings will be lifting/dissipating by early Friday, breezy west-
northwest winds in the wake of the departing front will occur. Wind
gusts 25-30kts may occur at several sites Friday, especially across
the north half. Otherwise, VFR parameters expected Friday through
early Monday. An approaching area of low pressure will bring a
threat for sub VFR ceilings and visibilities to central NC Monday
night and Tuesday.




LONG TERM...Badgett
AVIATION...JJM/WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.