FXUS62 KRAH 170834

Area Forecast Discussion
National Weather Service Raleigh NC
330 AM EST Tue Jan 17 2017


Cool high pressure over the area will move offshore this morning. A
warm front will push northward into the area today, and will be
followed by a warm southwest flow late today into early Wednesday.
The front will push back southward as a cold front Wednesday
afternoon, with high pressure again building in for Wednesday night
through Thursday. 


As of 330 AM Tuesday...

Water vapor imagery this morning showing moisture moving into the
area from the southwest and a low pressure system moving through the
Ohio Valley with a frontal system extending through the Tennessee
Valley and into the deep south. As a result of this moisture
increase we are starting to see some pockets of dense fog across the
southwest Piedmont. Models are mixed on the progress this fog will
make to the northeast but will monitor and issue products as needed.
As the front hangs northwest of the area today, the NW Piedmont and
northern tier will be the most likely to see any kind of
precipitation today as some weak isentropic lift over the
deteriorating wedge front remains in place through the afternoon and
pre-frontal precipitation begins to creep into the area from the
northwest. Indications are that we should begin to scatter or lift
out by later in the afternoon and while this may ultimately
determine max temperatures, expect highs in the 60s across the area
with warmest temps in the southwest. Some wind gusts are possible
after the wedge lifts out late in the afternoon but nothing more
than 15-20 kts.


As of 330 AM Tuesday...

The lingering frontal system to the northwest will finally be pushed
across the area as an upper level low develops moves southeastward
out of the great lakes. This should push precipitation through the
area by late Wednesday afternoon and maybe some drying after that.
Until then, expect periods of rainfall and fairly warm temperatures
as max temps rise into the mid 60s to low 70 with highest temps
across the southwest. After precipitation moves out of the area to
the east, a surface high moving in from the NW will take over the
weather pattern drying things out but also cooling temperatures.
Lows Wednesday night in the low 40s.


.LONG TERM /Thursday through Monday/... 
As of 330 AM Monday...

This time frame will feature above normal temps and alternating wet
and dry periods. Polar air will hold well to our north, affecting
only northern and eastern Canada into Maine, leaving NC in a mild
pattern with low level thicknesses staying well above seasonal
normals. A very wavy and progressive flow across the southern CONUS
will bring bouts of unsettled weather reminiscent more of early
spring than of the heart of winter.

Thu/Thu night: A brief dry period is expected as the front settles
just to our south and a weak continental high builds over the area
from the west, beneath a prominent mid level ridge in the wake of
Wednesday's potent shortwave trough swinging out over the Atlantic.
Expect fair to partly cloudy skies Thu, with increasing clouds late
Thu into Thu night as the next shortwave trough (now over Baja
California) pushes east then lifts NE, approaching NC from the SW as
it takes on a negative tilt. As this trough moves in, falling mid
level heights and a preceding low level jet nosing into central NC
will foster deepening of moisture and an increasing chance of rain
overnight, affecting the western CWA first. Highs 55-60 and lows in
the mid-upper 40s. 

Fri/Fri night: Rain is likely early Fri morning, particularly over
the northern and western forecast area, as the combination of upper
divergence, mid level DPVA and height falls, and low level moisture
transport appears to peak around 12z Fri. As the negatively tilted
and deamplifying shortwave trough shift to our NNE, the front to our
south should shift back northward as a warm front, as another round
of shortwave ridging follows, persisting through Fri night. Expect
rain chances to decrease SW to NE Fri afternoon as drying aloft
punches in from the WSW, with dry weather but low clouds likely Fri
night. Expect highs Fri from the mid 50s north to mid 60s south,
where the northward-moving warm front will first arrive. Lows 45-50. 

Sat into Mon: Expect fair and warm weather Sat as the mid level
ridge shifts overhead and over the East Coast. Thicknesses are
projected to be well above normal, perhaps by as much as 40 m,
although shallow mixing may mean that the thickness values could be
overestimating the warming realized at the surface. Expect highs of
60-67. By Sun, attention turns to quickly deepening low pressure
over the southern Plains, within the active and progressive southern
stream. As this low shifts through the Mid-South and NNE into the
Ohio Valley, a strong negatively tilted trough will approach our
area from the W and SW. The GFS and ECMWF remain in remarkably good
agreement on timing and evolution of this feature as well as with
the corresponding surface frontal configuration, with a primary low
tracking into the Ohio Valley, an occluded low moving into the
western Carolinas, and a trailing front shifting E then NE through
GA and the Carolinas Sun night. There remains the threat for a few
strong storms late Sun into Sun night in our area, with this risk
supported by a highly energetic and strengthening system featuring
vigorous upper divergence, intense DPVA, strong kinematics with a
sweeping curved hodograph, and abundant moisture with PW over 1.5".
Will mention isolated thunder, with minimal CAPE values and subdued
lapse rates limiting the coverage. Will trend the high pops down
from SW to NE Sun night into Mon morning as the dry slot arrives,
but will keep scattered showers late Mon as the trough axis shifts
through the area. Highs in the upper 50s NW to mid 60s SE Sun, then
around 60-65 Mon. -GIH


AS OF 100 AM Tuesday... 

24 Hour TAF period: A mix of aviation conditions at this hour as
ceilings have dropped below VFR levels in most locations. There is
model disagreement this morning whether or not dense fog will occur.
At this point have not included it in the TAFs as the HRRR had
already depicted fog in the area which has not yet occurred. Low
ceilings should then be the main threat to aviation conditions with
everything down to LIFR possible. After sunrise, ceilings are
eventually expected to break out although it may take until the
afternoon to do so. Some gusty winds are possible up to 20 kts or so
this afternoon.

Long term: A frontal system will move through the area on Wednesday.
High pressure returns on Thursday for a brief stay before the next
system moves in Thursday night through Friday night. High pressure
then returns once again for the weekend.






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