Area Forecast Discussion
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FXUS62 KRAH 220755
Area Forecast Discussion
National Weather Service Raleigh NC
255 AM EST Sun Jan 22 2017
A potent low pressure system will track northeast from the Deep
South into the Carolinas this afternoon into tonight, linger over
the area on Monday, then track offshore the Mid-Atlantic coast on
.NEAR TERM /TODAY AND TONIGHT/...
As of 300 AM Sunday...
...Dense Fog Advisory in effect until 10 am for the Triangle,
Northern Piedmont and NE Coastal Plain...
...Severe Weather Possible late this Afternoon and Evening...
Unseasonably rich moisture continues surging N/NE from the GOMEX
into the Carolinas this morning as low-level flow backs/strengthens
in response to height falls in advance of a potent upper level low
progressing east from the lower MS river valley into the Deep South.
Significant moistening has occurred over the past 24 hrs, as
evidenced by PWAT values near 1.25" on the 00Z GSO RAOB (roughly
double the PWAT observed on the 12Z Saturday GSO RAOB). An MCS
upstream over AL/GA at 06Z is expected to progress rapidly E/NE into
the Carolinas this morning, the northern portion of which should
cross central NC between 12-17Z (roughly from sunrise to noon).
Dense fog will erode from SW-NE between roughly 7-10 am as the
aforementioned MCS (or remnants thereof) progresses across central
NC. In the wake of the departing MCS, expect a lull in precipitation
during the early/mid afternoon as a dry mid-level airmass /modified
elevated mixed layer/ advects northeast into central NC.
Chances for convection will increase from SW-NE by late afternoon as
small amplitude waves rounding the base of the upper low eject NE
from the Deep South into the Carolinas amidst diffluent flow aloft
and increasingly favorable thermodynamics as rich low-level moisture
advects poleward underneath a modified elevated mixed layer
characterized by H7-H5 lapse rates on the order of 7-8 C/km. A slow
moving warm front is expected to bi-sect central NC from SW-NE or
WSW-ENE (i.e. along or south of CLT-RDU-RWI) this afternoon. If
sufficient forcing is available to break the cap at the base of the
EML in the warm sector along/south of the front this afternoon, the
thermodynamic/kinematic env would favor supercells capable of
producing all severe weather hazards. Thus, a conditional potential
for severe weather will exist during the mid to late afternoon.
Temperatures may range from the low/mid 70s south of the warm front
to the mid/upper 50s north of the warm front.
A squall line is expected to develop in AL/GA this afternoon, along
a cold front assoc/w a rapidly deepening sfc cyclone tracking NE
from the Deep South into the western Carolinas, in advance of a
potent upper level low tracking ENE through the Deep South. The
aforementioned squall line is expected to propagate E/NE through
portions of the Carolinas this evening (00-06Z Mon). Thus, the
primary severe weather threat is expected to unfold this evening (00-
06Z Mon) as the aforementioned squall line propagates across the
Carolinas. While damaging straight line winds will be the primary
threat with the squall line, a few tornadoes will be possible in the
warm sector along the coast and in vicinity of the warm/occluded
front further inland over portions of central NC. Expect lows
tonight ranging from the upper 40s in the NW Piedmont to the lower
50s elsewhere. -Vincent
.SHORT TERM /MONDAY AND MONDAY NIGHT/...
As of 320 PM Saturday...
To be posted shortly.
.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 230 PM Saturday...
The departing upper low will give way to height rises on Tuesday,
with a brief stint of high pressure at the surface. The ridging
aloft will quickly give way to increasingly cyclonic flow aloft as a
broad trough develops over the eastern US through the end of the
week. A shortwave moving out of the Southwest is forecast to lift
and shear across the Midwest States Wednesday/Thursday, resulting in
limited moisture/lift over our region as the cold front crosses the
area early Thursday. The GFS and ECWMF are in pretty good agreement
on the timing of the front, but the GFS brings a secondary wave
through the base of the trough, resulting in anafrontal precip on
Thursday. Confidence in the longwave pattern and trend from above
normal temps Tuesday/Wednesday toward below normal is high, but the
details of the midweek precip are still uncertain.
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
As of 215 AM Sunday...
24-HR TAF Period: Conditions ranging from MVFR to VLIFR were present
across central NC at 06Z this morning. The worst conditions were
located at the INT/GSO/RDU/RWI terminals across the Northern
Piedmont and NE Coastal Plain, north of a warm front extending SW-NE
across portions of the Sandhills and SE Coastal Plain. As the warm
front pushed north of the FAY terminal early this morning,
conditions improved to MVFR. Expect conditions to remain relatively
steady state this morning. Although dense fog will begin to lift as
precipitation overspreads the area from SW-NE after ~12Z, ceilings
are likely to remain in the IFR/LIFR category at the INT/GSO/RDU/RWI
terminals through this afternoon as morning precip helps to
reinforce an in-situ CAD wedge along and north of the Hwy 64
corridor. The FAY terminal will be situated south of the warm front
and should see MVFR ceilings prevail today, though periodic IFR
conditions will be possible during precipitation later this morning.
A Squall line is expected to develop upstream this afternoon, then
track E/NE across central NC terminals late this evening, between 00-
06Z. Isolated severe thunderstorms will be possible during this time
frame, particularly at the FAY terminal. Some improvement will be
possible by the end of the TAF period (06-12Z Monday) as low-level
flow veers to the SW in the wake of the squall line.
Looking Ahead: Any improvement late tonight and early Monday will be
short-lived, however, with showers increasing in coverage and
IFR/MVFR ceilings returning as a potent vertically stacked low
rotates slowly eastward across the Carolinas. Gusty NW winds will be
possible on the back side of the system Monday evening/night.
Conditions are expected to improve /return to VFR/ sometime late
Monday night or early Tuesday as the aforementioned system tracks
offshore the Carolina/Mid-Atlantic coast. -Vincent
Dense Fog Advisory until 10 AM EST this morning for NCZ007>011-