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000
FXUS62 KRAH 250012
AFDRAH

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
710 PM EST Fri Jan 24 2020

.SYNOPSIS...
Low pressure will track across the west-central Carolinas to south-
central VA this evening. A trailing cold front will sweep east
across central and eastern NC through Sat morning. High pressure
will then build from the lower MS Valley eastward across the
Southeast through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 445 PM Friday...

A closed mid-upr low centered over the cntl IL/IN border this
afternoon will wobble newd into swrn MI by 12Z Sat. An elongated
axis of vorticity around the base of the low, including an observed
~90 kt mid level jet at SHV and JAN at 12Z, will stream newd and
overspread the srn Appalachians and wrn Carolinas tonight, with
related strong height falls (60-120 m)/forcing for ascent focused
over cntl NC between 06-12Z Sat.

At the surface, an occluded low over the nrn IL/IN border at 21Z
will move slowly nwd across Lake MI tonight, generally beneath the
aforementioned mid-upr low. Meanwhile, an elongated, 1012 mb low
along an in situ cold air damming/wedge front from Forsyth and Davie
Co. sswwd across w-cntl SC and e-cntl GA, will consolidate while
tracking newd across the wrn and nrn NC Piedmont, into s-cntl VA,
through 06Z. The trailing cold front and elongated low will sweep
ewd across cntl NC through 08-09Z.

A strongly confluent llj and related band of convection across the w-
cntl Carolinas and swrn VA, still entirely devoid of lightning at
2145Z, will intensify beneath the strengthening forcing aloft and
low level frontogenesis, while shifting east across cntl NC tonight.
Previous timing and intensity thoughts remain relatively unchanged -
across the srn and wrn Piedmont through 02Z, the Sandhills and ne
Piedmont between 03-06Z, and the Coastal Plain between 06-08Z.

A shallow plume of modified EML, sampled in the 850-700 mb layer by
the BRO RAOB last evening, has nosed from the nrn GOM newd into srn
GA this afternoon, per both RAP-based (SPC) Mesoanalysis and GOES 16
wv satellite (7.3u) data. The models indicate this EML plume, and
relatively steeper mid level lapse rates, will advect newd into the
ern Carolinas roughly coincident with the foregoing convective line
and contribute to mostly elevated instability of up to 500-750 J/kg
of MUCAPE over the Sandhills and srn Coastal Plain between 03-06Z.
And while low and deep layer shear will be strong, enhanced by the
arrival of the exit region of the mid level speed max noted above,
related convective organization/rotation will likely remain rooted
above a shallow layer of stability near the surface. Nonetheless
point forecast soundings suggest this stable layer will be sensitive
to even subtle changes to surface theta-e, so surface-based (or
nearly so) cells --and related surface wind hazards (e.g. damaging
wind/isolated tornado)-- cannot be ruled out early tonight. This
threat will be roughly from MEB to FAY to GSB and points south,
where surface dewpoints are likely to maximize in the upr 50s to
around 60 degrees and contribute to parcels rooted nearer the
surface, with a relative minimum of CINH.

Additional rainfall amounts are expected to range from around an
inch over the nw Piedmont (where around a half an inch fell this
morning), along the track of the surface wave and where deep forcing
for ascent will be strongest and longest, to a half an inch in the
srn and cntl Coastal Plain. Individual convective elements will race
nnewd (motion ~200/45-50kts) and briefly train within the parent
band that will edge more slowly ewd. Locally heavy rain and minor
flooding may result, primarily in urban/areas, since the brunt of
the rain will fall in just a couple of hours time.

Lastly, areas of low overcast and fog --some dense-- may develop and
expand from the Foothills to the Piedmont of NC overnight, beneath
clearing skies aloft, with low temperatures mostly in the 40s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 250 PM Friday...

Sat: A closed mid-upr low will wobble newd across MI Sat, while a
negative tilt trough at the base of the trough, initially over the
Carolinas, will pivot off the middle Atlantic coast. Height rises
will consequently overspread the srn Appalachians and Carolinas,
with related subsidence, through 00Z Sun.

At the surface, a cold front along the srn middle Atlantic coast at
12Z Sat will move offshore, while a lagging occluded front will
cross the ne Piedmont and nrn Coastal Plain through 14Z. Appalachian-
lee troughing will otherwise persist beneath cyclonic, wly flow
aloft influenced by the features noted above.

While there may be a few shallow showers along the occluded front
during the morning, the day should be dry. Otherwise, after
lingering low overcast and areas of fog focused over the srn
Piedmont during the morning, a scattering of flat cumulus at the
base of a developing subsidence inversion will yield partly to
mostly sunny conditions - and mild ones, with high temperatures in
the 50s, to near 60F in the Coastal Plain.

Sat night through Sun night: Westerly flow and a brief period of
cold advection will set in Saturday night, while modified high
pressure migrates along the gulf coast.  Broad westerly flow aloft
and limited moisture between the exiting system and next in a series
of shortwaves moving through the southern US will keep skies mostly
clear Sunday.  The airmass change behind the early weekend system is
minimal, and LL thicknesses on Sunday support highs rebounding back
in the lower 50s and near normal lows in the low to mid 30s Saturday
and Sunday nights.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 250 PM Friday...

The forecast for the upcoming week is fraught with uncertainty as
low amplitude shortwaves move through a broader longwave trough
before perhaps carving out a deeper longwave trough by next weekend.
Early in the week a pair of shortwaves look to phase over TN valley
to SE US on Monday, with weak cyclogenesis along the polar front
across FL.  However, models have trended stronger with the shortwave
dynamics and have some qpf blossoming across the Carolinas,
particularly near the arctic front which should lie across VA. Per
forecast soundings most of the moisture is mid-level, but a period
of showers are possible Monday afternoon. Have lowered highs a few
degrees given the expected cloud cover and possible showers and
virga as the shortwave passes overhead.  The arctic front will trail
on Monday night with temps falling into the upper 20s and lower 30s.

Another shortwave is forecast to cross the region
Wednesday/Thursday, but models have been all over the place with the
amplitude of this wave and potential for precip.  Most recent runs
have been weaker with limited moisture, so will keep the forecast
mostly dry with just a flight chance on Wednesday night.  The ECWMF
squeaks out a few hundredths of qpf, and thermal profiles are a bit
cooler and supportive of frozen precip with the frontal zone to our
south, but forcing and moisture look to be too limited at this time.
Have kept temps mostly near normal in line with LL thicknesses
around 1300-1310m, though Wednesday could be another cooler day
given increase mid and high clouds.

Finally the next and deeper system forecast for the weekend has the
potential to bring more substantial rain with a digging trough and
coastal low by Saturday.  Forecast confidence is low at this time
given run to run inconsistencies, but the signal is certainly there
in the deterministic runs and GEFS/EPS means.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 710 PM Friday...

Restrictions have already developed at INT/GSO/FAY as a front moves
into the region with showers and lower ceilings. A band of heavy
showers with an isolated thunderstorm possible will move from west
to east. Have included a tempo group for each terminal when the most
intense rain is expected as well as the possibility of mixing down
some stronger wind gusts. Once the rain departs the Triad,
conditions should briefly rise to MVFR before IFR conditions become
predominant until sunrise. At RDU, conditions should remain steady-
state, MVFR, for a few hours after the rain. Meanwhile, FAY/RWI
should both see conditions improve quickly after rain departs. All
terminals are expected to return to VFR by 15Z, with clouds
scattering out.

Outlook: A passing mid to upper level disturbance will result in a
chance of light showers and MVFR ceilings on Mon. Mainly VFR
conditions are otherwise expected through mid next week.

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...MWS/BS
LONG TERM...BS
AVIATION...Green/MWS