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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 181448
AFDRAH

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
950 AM EST Sat Jan 18 2020

.SYNOPSIS...
High pressure extending into the area from the north will slide off
the Mid Atlantic coast this morning, as a storm system approaches
from the west. This system will cross the region late today through
tonight, with a cold front pushing offshore early Sunday. Much
colder air will pour into the area late Sunday through Tuesday as
Arctic high pressure builds in from the northwest.

&&

.NEAR TERM /TODAY THROUGH TONIGHT/...
As of 950 AM Saturday...

Little changes needed to the forecast for the morning update. Better
matched the current forecast to in-situ observations, and continuing
to see a more delayed trend in the rainfall arrival time. Should see
POPs increase later this afternoon (Triad) and evening (Triangle
east) as previously expected.

Previous valid discussion...

Primary forecast changes this morning included a noteworthy upward
bump in near term temps and a slight delay in precip chances until
lunchtime at the earliest. The latest surface map shows the chilly
high extending from SW Quebec down into the Carolinas, while the
diffuse warm front extends from the FL/GA line W and N into the Ohio
Valley and W to strong low pressure over SW IA, all associated with
a progressive strong mid level low crossing the Great Lakes. Mid and
high clouds associated with SW-NE passage of the elevated warm front
continue to stream across the area, and this will remain the case
through daybreak. Starting mid morning, increasing moist upglide at
285-300K will result in stratus spreading in rather quickly from the
SSW, arriving first over the S and SW CWA before expanding over all
of central NC through early afternoon. Models agree on depicting
several dry layers through the column during this time, however, and
the significant rise in PW as the surface high pushes offshore and
the warm frontal zone moves northward will be delayed until later
this afternoon. We`ll spend the first half of the day with no
tangible forcing for ascent beneath the slowly exiting mid level
ridge, and this lift is unlikely to arrive until early to mid
afternoon. All recent CAM runs agree on delaying chance pops until
after 18z. So, have delayed the onset of pops, with just a slight
chance in the Triad around lunchtime before increasing pops to
chance/likely and expanding them eastward across central NC in
tandem with the arrival of weak height falls, a strengthening wind
field, and increasing upper divergence. Given this delay, and given
that the current temps (and wet bulb temps) in the W Piedmont are
running above statistical guidance with relatively warm ground
temps, the potential for any freezing or frozen precip this morning
is infinitesimal, so have removed this mention. But we should still
see neutral or slightly stable air in the low levels as the
weakening wedging ridge lingers in the NW Piedmont. Expect highs
today in the low-mid 40s NW of Highway 1 with upper 40s to mid 50s
along and SE of Highway 1 (where precip will be last to fall). Rain
chances should peak 21z-03z over the NW CWA and 03z-09z in the SE,
although it looks like amounts will be light, mostly under a quarter
inch for the event. A downturn in pops and partial clearing is
expected late tonight in the NW as the cold front pushes SE through
the region, initiating a drying WNW low level flow. With this
timing, pops should end over the SE CWA just before daybreak with a
flattening mid level flow and drying column, prompting clearing late
from NW to SE. Lows from the upper 30s NW ranging to around 50 SE
(where the cooler post-front air will be last to arrive). SW winds
will strengthen with increasing gustiness this afternoon into this
evening. -GIH

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
As of 400 AM Saturday...

The initial cold front will push well to our SE early Sun, with a
secondary reinforcing front and corresponding mid level shear axis
tracking SSE through central NC late Sun. While thicknesses are
projected to drop through the day, the real Arctic air is likely to
hold off until passage of the secondary front later in the day into
early evening. We`ll see abundant sunshine and good mixing, so
expect to see highs from the upper 40s to near 50 in the Triad
ranging to the mid 50s to lower 60s over the rest of the area. As
thicknesses continue to plunge Sun night, reaching values 40-45 m
below normal by Mon morning with falling dewpoints well down into
the teens, we should see lows in the 20s areawide. -GIH

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 150 AM Saturday...

The extended forecast period will largely be dry an cool, with cool
high pressure building over the area and lingering through at least
Thursday/Thursday night. Aloft, a trough will swing through the area
early in the week, with high pressure ridging northward into the
region mid-week. In a change from this past week, temperatures will
be well below normal through Wednesday moderating to near normal
Thursday. Highs in the upper 30s to mid 40s and lows in the low to
mid 20s expected. Normal highs for this time of year range from 48-
55 degrees and normal lows from 29-34 degrees.

The next weather system will develop over the Plains on Thursday and
moving into the region late in the week/early weekend. There is
still quite a bit of uncertainty as the medium-range models vary
greatly. Generally expect an increase in chances for precipitation
Friday/Saturday, with temperatures continuing to moderate back above
normal for Friday.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
As of 645 AM Saturday...

VFR conditions will hold through daybreak over central NC as broken
to overcast mid and high clouds continue to streak across the area
ahead of the approaching storm system. Lower level moisture evident
over S MS early this morning will stream N and NE into western NC
including the Triad terminals starting after 14z, when cigs are
expected to drop to MVFR at INT/GSO. These MVFR cigs will then
spread into RDU after 16z and FAY/RWI after 18z. Light precip will
lag these lower clouds by an hour or two, moving into INT/GSO toward
17z, RDU around 18z, and RWI/FAY around 20z. Vsbys in this light
rain will be mostly VFR, although a few hours of MVFR vsbys and
brief IFR cigs are possible 00z-09z. Conditions should improve to
VFR after 08z at INT/GSO/RDU and after 09z at RWI, while FAY may
retain an MVFR cigs through 12z. Surface winds will be mainly under
10 kts all sites through 18z, however winds will strengthen this
afternoon out of the SSW at 10-16 kts gusting to 18-25 kts through
this evening. There is a good chance of LLWS at all sites after 22z
as a strong SW 40-50 kt jet just aloft, near 2000 ft AGL, develops
over central and E NC.

Looking beyond 12z Sun, any remaining sub-VFR conditions at FAY
(mainly cigs) will improve to VFR with clearing skies around 15z
Sun. Surface winds will decrease a bit and swing around to W and NW
with this clearing Sun morning, although winds may stay gusty. VFR
conditions will dominate Sun through Wed beneath chilly high
pressure. -GIH

&&

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

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...JJM/Hartfield
SHORT TERM...Hartfield
LONG TERM...KC
AVIATION...Hartfield