Area Forecast Discussion
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FXUS62 KRAH 231147
Area Forecast Discussion
National Weather Service Raleigh NC
645 AM EST Mon Jan 23 2017
A potent low pressure system over the southern Appalachians will
track east-northeast through the Carolinas today, then track off the
Mid-Atlantic coast on Tuesday.
.NEAR TERM /THROUGH TONIGHT/...
As of 335 AM Monday...
Through daybreak: In advance of the vertically stack cyclone over
Northern GA, low-topped convection within the mid-level dry slot
will pivot northward across the area as the occluded front along the
NC/SC state line lifts north into Central and Eastern NC through
daybreak. Elevated instability of 500 to 1000 J/Kg of MUCAPE will
develop briefly across the area between 06 to 12z as tongue of 850-
700mb moist warm air advection lifts north into the area, and
further aided by the proximity of the cold temperatures aloft and
relatively steep mid-level lapse rates of 7.5-8.0 C/km. This may
lead to a slight uptick in coverage and intensity, with some
isolated elevated thunder possible across the NC Piedmont.
Today: Upper low will track eastward across southern NC through 00z,
and off the NC coast tonight. In the wake of the occluded front
lifting north into Virginia, we could see some breaks develop in the
low clouds across the central and eastern zones during the mid to
late morning hours, before the approach of the cold core aloft(-22
to -24C)and steep lapse rates aloft(7-7.5C/km) will support the re-
development of scattered showers across the area, with best coverage
and best chance for thunder across the far SE where stronger diurnal
heating is expected. Given cold temps aloft, could see some small
hail with any decent updraft. Highs ranging from mid 50s NW to lower
Tonight: Drier air filtering into the area with the departure of the
system should lead to SW to NE clearing late tonight into Tuesday
morning. Lows in the lower 40s NW to mid 40s elsewhere.
.SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
As of 400 AM Monday...
In the wake of the vertically stacked low progressing offshore the
Mid-Atlantic coast, a shortwave ridge aloft will build eastward over
the Carolinas and Mid-Atlantic Tue afternoon/evening, progressing
offshore by Wed morning as an upper level trough (moving ashore the
Pacific coast today/tonight) digs/expands across the Intermountain
west/Rockies and shortwave energy rounding the base of the trough
(in vicinity of the 4-corners region) ejects northeastward through
the Central Plains into the Upper Great Lakes, establishing
southwest flow aloft downstream along the Gulf/Southeast Coast and
Eastern Seaboard. A cold front assoc/w a sfc cyclone attendant the
aforementioned shortwave energy ejecting NE into the Upper Great
Lakes will slowly approach the Appalachians from the west Wed
aft/eve. Expect dry conditions through this period, with a breezy NW
wind gusting 20-30 mph on Tue and a breezy SW wind gusting 20-30 mph
on Wed. Highs near 60F on Tue will fall into the upper 30s to lower
40s Tue night, then rebound into the upper 60s on Wed. -Vincent
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 400 AM Monday...
Wed Night-Thu: The aforementioned cold front is expected to slowly
track east across the Carolinas/Mid-Atlantic Wed night/Thu morning.
With the parent shortwave/sfc cyclone tracking rapidly NE away from
the front at this latitude, the NAM suggests the front will progress
through central NC with little more than a few sprinkles. However,
both the GFS/ECMWF suggest a SW-NE oriented swath of light rain may
develop along/behind the pre-frontal trough in association with low-
mid level frontogenesis. At this time will indicate a 30% chance of
rain across central NC Thu morning through early afternoon.
Fri-Sun: The latest long range guidance suggests Fri and the
upcoming weekend will be dry albeit a little chilly with highs
generally in the mid/upper 40s, lows in the upper 20s to lower 30s,
and a brisk W to WNW breeze during the aft hours each day. -Vincent
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
As of 645 AM Monday...
24-Hour TAF period: Showers focused along a zone of strong 850-700mb
warm moist air advection lifting north into Virginia will exit the
area in the next hour or two. The widespread IFR ceilings could
improve to MVFR/VFR during this dry period. However, as the upper
low moves east through the area during afternoon, we could see
another round of scattered low-topped convection. Cannot rule out
some isolated elevated thunder at KFAY this afternoon, in closer
proximity to the upper low. MVFR ceilings will linger into the
evening before drier air begins to filter into the area from the
southwest between 06 to 12z, bringing a return to VFR by Tuesday
Looking ahead: Ridging aloft and at the surface will produced VFR
conditions Tuesday and Wednesday. A cold front will cross the region
late Wednesday night/early Thursday, bringing with a chance of
showers and sub-VFR ceilings to the area. VFR conditions should
return late Thursday afternoon/evening.