Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 270304
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1103 PM EDT Tue Mar 26 2024

.SYNOPSIS...
High pressure will extend southward across the region through this
evening. As a front approaches from the west and southwest, an area
of low pressure will lift northeast through the Southeast states and
eastern Carolinas Wednesday through Thursday. The cold front will
move eastward through central North Carolina Thursday night. Dry and
warming weather is expected Friday and Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 715 PM Tuesday...

Early evening update included adding thunder to portions of the
region as there is limited instability which is resulting in a few
rumbles of thunder of the line of precipitation moving across the
region. As this line of precip moves across the region over the next
few hours, instability is expected to be near zero, thus chances for
thunder of the next few hours diminish slowly. Rain will be mostly
light as is moves across the region, but there are a few moderate to
heavy showers developing along the line. A short lull from rain is
expected after this first round moves out, before another round of
more active weather is expected later tonight and continue through
the overnight hours.

As of 330 PM Tuesday...Water vapor imagery depicts a subtropical
ridge axis along the East Coast, sandwiched between a closed
mid/upper low meandering near Bermuda and broad troughing over the
central US. Within this broad troughing, one shortwave and occluded
surface low are currently centered over the upper peninsula of MI,
which will continue to push NE into southern Ontario through
tonight. This system is dragging a cold front to its south that will
slowly push east through the TN Valley and reach the Appalachians
tomorrow morning.

A period of rain will be possible over the western Piedmont from
late this afternoon into early evening, particularly over the Triad.
But kept POPs at only slight to low chance as model soundings show
the low levels staying fairly dry and high-res guidance depicts the
rain fizzling out as it heads NE. GLM satellite data and surface obs
even show isolated thunder over western NC, but not expecting it to
get this far east. Otherwise it will be dry across the rest of
central NC through this evening as the best forcing and moisture
stay to our west, and surface ridging noses down the Mid-Atlantic
coast from a high over the Canadian Maritimes. However, clouds will
continue to thicken and lower, becoming overcast in the west and
mostly cloudy in the east. A surface low or inverted trough has
developed over the northern Gulf of Mexico today and will slowly
lift NE, pushing a warm front that begins to push into southern NC
overnight.

The main NE-SW oriented axis of widespread showers will begin to
enter the Triad after about midnight, slowly spreading east into the
rest of the Piedmont overnight, where POPs are likely to
categorical. As the warm front lifts north, there could be enough
instability for an isolated storm especially south, but confidence
is not high enough to include in the forecast at this time. Low
temperatures tonight will be mild, ranging from mid-40s far NE to
mid-50s far SW.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 245 PM Tuesday...

Confidence remains high in a somewhat prolonged and briefly moderate
to heavy rainfall event, as a polar low over N MN and a large upper
level longwave trough over central NOAM (with embedded shortwaves)
early Wed lumbers eastward into and through E NOAM by Thu night. One
noteworthy player, a shearing vorticity lobe now diving through the
Desert Southwest in the southern portion of the longwave trough,
swings over the Gulf Coast through Wed evening and through the
Carolinas late Wed night through Thu, taking on a neutral to slight
negative tilt in the process. Our PWs will steadily ramp up, peaking
at 150-200% of normal over our area (approaching daily record maxes)
and over coastal NC Wed afternoon through early Thu before the
anomalously high values push further E. The highest rain amounts
will fall through the heart of central NC Wed and over the Coastal
Plain Wed night, coincident with peaks in upper divergence
generating bursts of greater large-scale ascent.

At the surface, low pressure over the Gulf will lift NNE through
GA/SC through Wed, with a cold front extending southward from it and
a warm front edging into our SE sections, while a weak inverted
trough extends NNW through W NC, keeping our NW sections in the
cooler/more stable air attached to a weak cool mesohigh centered
near and off the Mid Atlantic coast. By Wed night into Thu, the
approaching mid level shear axis deepens the surface frontal low (or
lows, most likely) to our S/SE as the frontal zone it sits along is
kicked eastward, resulting in a trend toward cool and more stable
low levels areawide Thu as high pressure begins to ease into the
area from the lower Miss Valley. An increasing MSLP gradient between
this high and the slowly exiting front should lead to brisk gusty
winds late Wed night through Thu. Most models are in fairly good
agreement on this pattern, although vary a bit with front and low
tracks, contributing to greater uncertainty with temps Wed, esp
through the Hwy 1 corridor which could end up on the cooler or
milder side of the low/front.

Forecast confidence is trending a bit higher with storm total
amounts through the heart of the precip area, topping out around 3-
3.25" surrounded by a 1-2" buffer, although important model
variations in placement persist. Last night`s traditional and AI
models as well as ensemble systems have trended further E with the
band of heaviest rain as compared to yesterday, although they most
recently have nudged back slightly west. Overall, we think that the
heaviest totals will be from Hwy 1 E, and possibly aligned along the
I-95 corridor where the greater moisture transport and longer
residence time of high PW will coincide with the peak upper
divergence and mid level DPVA. Confidence with overall timing is
fairly high, although models vary quite a bit with timing the
departure of the precip Thu into Thu evening. Think that the
NBM/LREF mean timing remains a bit too slow with the surge in NW and
N flow behind the front, so have sped up the precip exit a bit Thu.
Given that this precip will be spread out over 30+ hours in most
spots, the excessive rainfall outlook is maintained over our E half
this afternoon at a marginal risk. Our Coastal Plain areas should be
able to mostly handle these amounts, particularly given the existing
drought conditions there and long duration, so no plans for a flash
flood watch at this time. I could certainly see the potential need
for a few flood advisories esp in poor drainage areas, with an
uptick in river levels across the board, but there is high
uncertainty of any situation more dire than that occurring, and the
latest river forecasts keep our points just below flood stage at the
worst.

The overall rainfall timing is to bring likely to categorical pops
eastward through the CWA Wed, then move these higher pops to just
the E half Wed night into Thu morning before sweeping pops E and out
Thu afternoon. Some embedded thunder is likely within this system,
including a few short bows, focused on Wed into Wed night in the S
and E. Lapse rates stay rather muted overall until Thu, when upper
level clearing moves in from the W, and despite mid level SW flow
increasing to 40-50 kt Wed, the early rain arrival will limit
instability Wed, esp across our N and W. Certainly, though, an
isolated strong wind-maker is possible over our SE.

Expect highs 56-72 Wed, including mostly 50s across the far N and NW
Piedmont that will be NW of the low track, holding in the cooler and
more stable air with high rain chances through the day. Lows 44-53
Wed night, highs 53-64 Thu, and lows 36-42 Thu night with clearing
skies. Given the complexity of the expected surface pattern,
confidence in the details of these temps is not high. -GIH

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 250 PM Tuesday...

Dry and windy conditions Friday.
Warming temperatures through the weekend.
Rain chances increase early next week, although uncertainty exists.

Friday: Surface high pressure centered over the Tennessee Valley
will slowly shift over the Southeast and off the Florida/Georgia
coast by early Sat morning. A tight pressure gradient will exist
over central NC between this feature and the deepening low pressure
as it migrates into the Canadian maritimes. Surface winds will
increase Fri afternoon through the early evening as the boundary
layer mixes up into 25-35 kts of 925-850mb WNW flow. Momentum
transfer from point soundings range from the low 20 kts (SW) to
upper 20 kts (NE) with the top of the mixed layer suggesting up to
low 30 kts may perhaps be possible, but will likely depend on
coverage/thickness of afternoon stratocu that may prevent deeper
mixing and lower gusts. A dry downsloping component through the
mixed layer will also favor warming and drying downsloping winds and
have trended the forecast towards a drier (mid/upper 30s dewpoints)
and warmer (upper 60s to low 70s for highs) scenario through central
NC. This will result in RH falling into the 30s to mid/upper 20s
during the afternoon and may result in increased fire concerns if
soil moisture is able to recover from rainfall from Wed through
Thurs.

Sat through Tues: The remainder of the forecast is mostly dry
through Sun night. Zonal flow aloft and deepening return warm low-
level flow will continue to moderate temperatures into the 70s to
low 80s by Sun with weak disturbances bringing wisps of upper level
cloudiness. By Mon, surface high pressure ridging down from eastern
Canada into the Mid-Atlantic will push a cold front into the Mid-
Atlantic and would provide the focus for some light rain as
strengthening WAA at 850mb rides over top of the cooler air along
and behind the cold front (best chances across the NC/VA border).
The better shot at precipitation comes potentially Tues into early
Wed when there will be better H5 height falls from a northern-stream
trough as it dives out of central Canada and pivots across the Great
Lakes and northern Mid-Atlantic where PWATs ahead of the trough are
around 1.5 inches. Highs will be tricky early next week and will
entirely depend on the cold frontal placement and associated rain
chances behind it; highs will likely be in the mid 60s behind the
front to low/mid 80s to its south.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 800 PM Tuesday...

High confidence in all terminals dropping to IFR conditions on
Wednesday with LIFR ceilings also possible. A line of showers with
isolated thunderstorms is moving through the area at the beginning
of the period, but should not impact any terminals after 00Z. While
some scattered showers are possible during the evening at INT/GSO,
steady rain should not begin at those sites until after midnight,
also accompanied by ceiling restrictions. Meanwhile, lower ceilings
will develop along the coast and move inland this evening, meaning
that RDU/FAY/RWI will have MVFR restrictions develop before the
widespread rain arrives Wednesday morning. All sites have a chance
of thunderstorms through the period, but the confidence in any
particular site having a thunderstorm is too low to include in the
TAFs at this time. Steady rain should move east of INT/GSO by
Wednesday afternoon, although scattered showers will continue
through the TAF period. However, steady rain is expected through the
rest of the TAF period at eastern terminals.

Outlook: Rain showers and IFR/LIFR conditions will persist east of
INT/GSO through Thursday morning. Isolated TSRA are also possible
Wednesday and Thursday. VFR conditions will return from west to east
Thursday afternoon and evening and continue into Sunday. Gusty winds
of 20-30 kts are expected each day from Thu into Sat, from the N on
Thu, from the W/NW on Fri, and from the SW on Sat.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...Danco
SHORT TERM...Hartfield
LONG TERM...Swiggett
AVIATION...Green


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