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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 161428
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1030 AM EDT Mon Apr 16 2018

.SYNOPSIS...
A deep upper level low over the lower Great Lakes will produce
blustery and cool conditions across central NC today and tonight. An
area of high pressure over the northern Gulf will drift eastward
Tuesday and Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 1030 AM Monday...

A much drier but still somewhat unsettled day ahead. We`ve see a few
light showers rotate through northern sections of the CWA this
morning, in response to waves of DPVA rotating around the large/deep
mean mid level trough/low and oriented along one of several surface
troughs pinwheeling around the low over the Northeast. These showers
have mostly lifted northeast and out of the area, on pace with RAP
output. A lull in shower chances is expected until late afternoon,
when another vorticity max swinging through the trough base over the
Carolina should spur development of another round of isolated
showers, mainly across southern and eastern sections, late afternoon
into early evening. Winds will remain blustery with frequent gusts
into the afternoon, although the MSLP gradient over NC will slacken
a bit today. The 25-35 kt 925 mb winds will diminish to 15-20 kts
for awhile through mid afternoon, but will strengthen again to 25-35
kts toward evening, so the occasional gustiness should persist into
this evening, as we should remain mixed. Have gone slightly under
guidance for highs with the periodic cloudiness and cold air
advection today, 58-65. -GIH

Earlier discussion from 330 am: 06Z meso analysis depicts a sfc low
in proximity of Danville, VA with a trailing sfc cold front
extending from the low across central NC. West-SW flow behind the
boundary advecting a drier air mass into our region has evidence by
sfc dewpoints in the 40s across the southern Piedmont and western
Sandhills versus dewpoints in the 60s across the coastal plain and
northeast Piedmont. This sfc boundary projected to lift newd and
exit our northern coastal plain counties by sunrise. A sfc trough
extending from the sfc low will cross central NC later this morning
and through the afternoon. As the atmosphere destabilizes later
today due to heating, lift along this boundary interacting with
available residual moisture may produce a few showers. Aloft, a deep
upper level low will drift ewd across the lower Great Lakes today
and tonight. Weak perturbations in the cyclonic flow around this
feature will cause periods of cloudiness across our region through
this tonight.

The westerly low level flow will advect a cooler air mass into
central NC as the 850mb thermal trough will lie immediately west of
our region. This should result in a lower than normal diurnal
temperature recovery, with high temperatures later today about 10
degrees warmer than early morning lows. Tonight, the 850mb thermal
trough settles overhead. The cool dry air mass will yield overnight
temperatures in the mid-upper 30s. Potential for spotty light frost
over portions of the Piedmont though a light westerly sfc wind and a
relatively dry air mass may inhibit frost from developing. Will
refrain from mentioning patchy light frost for now though if it
appears that the sfc wind will decouple, a frost advisory would be
necessary for sections of the Piedmont.
-- End Changed Discussion --

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
As of 330 AM Monday...

Relatively quiet weather pattern for much of the work week. The deep
upper level low over southern New England early Tuesday lifts nwd.
This will subside/abate the cyclonic flow over our region. A sfc
high to our south-southwest Tuesday will drift eastward and be  off
the FL peninsula by Wednesday. This will turn our low level flow to
a more swly direction, advecting a warmer air mass int our region.
Thus, after highs Tuesday in the low-mid 60s, highs Wednesday will
jump well into the 70s to around 80.

A sfc cold front associated with a s/w crossing the northern Mid
Atlantic , will drop across central NC late Wednesday night through
Thursday morning. The frontal passage will be pretty much uneventful
as the atmosphere appears too dry and stable to support anything
more than a few clouds. The cooler air associated with the front
will likely not take hold of our region until later Thursday, behind
the passage of the 850mb trough. Thus, it will remain mild over most
of the region Thu with afternoon highs ranging from the lower 70s NW
to around 80 southeast.

Overnight temperatures through the period will vary as well with 40s
expected Tuesday night, mild 50s Wednesday night ahead of the front,
and cooler 40s anticipated Thursday night.

Finally, the difference in sfc pressure between the high off of the
Southeast U.S. and an area of low pressure to our north will
maintain breezy conditions. Expect wind gusts 20-30 mph Tuesday
through Thursday. These breezy conditions along with low afternoon
relative humidity may result in slightly elevated fire danger
parameters.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 255 AM Monday...

The upper-air pattern on Friday morning will feature a trough with
an embedded closed low over New England with another trough and
closed low over the four corners area with narrow ridging in
between. Central NC will experience a northwest flow aloft for
Friday and most of Saturday which typically features cooler than
normal conditions and a generally dry pattern. At the surface, high
pressure centered over the upper Midwest on Saturday will shift east
in the northern Great Lakes on Saturday as it extends into the
region. The result for Friday and Saturday will be dry weather,
mainly clear skies, and temperatures generally about 5 degrees
cooler than average.

Confidence decrease significantly when the pattern begins to change
on Sunday as the closed low over the southern Rockies shifts east
into the southern Plains and the ridge axis moves over the
Carolinas. Not surprisingly, NWP guidance is struggling with the
handling of the closed low. The operational GFS moves the system
eastward faster than the EC but the available ensemble means are in
closer agreement and provide a middle of the road compromise. Will
follow the compromise for now and keep the forecast dry for Sunday
morning with a chance of rain Sunday on afternoon and Sunday night,
especially across the south and southwest. Given the placement of
upper low and the surface reflection, central NC is currently
progged to be on the cooler and more stable portion of the storm
system. Morning lows on Sunday will range in the mid 40s with highs
in the mid 60s to around 70. -Blaes

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
As of 740 AM Monday...

While aviation conditions will improve southwest-northeast across
central NC this morning, a series of perturbations in the cyclonic
flow aloft will result in periods of cloudiness through tonight with
a few isolated showers possible. Expect ceilings bases to gradually
lift through the morning hours, then hover between 3500-5000ft this
afternoon. It will remain blustery with frequent gusts in the 25-
30kt range through late this afternoon.

While VFR parameters will dominate through the work week, it will
remain quite breezy for this time of year with wind gusts in the 20-
25kt range expected each day Tuesday through Thursday. A dry cold
front will cross the region late Wednesday night into Thursday
morning with just a smattering of clouds anticipated with the
frontal passage at this time.

&&

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

&&

$$
SYNOPSIS...WSS
NEAR TERM...Hartfield/WSS
SHORT TERM...WSS
LONG TERM...BLAES/Ellis
AVIATION...WSS