Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 171821

Area Forecast Discussion
National Weather Service Raleigh NC
220 PM EDT Tue Apr 17 2018

An area of high pressure will drift east from the northern Gulf
today to a position off the FL peninsula on Wednesday. Meanwhile, a
series of strong low pressure systems will track from the upper
Midwest into New England. The difference in pressure between the
high to our south and the lows to our north will create breezy
conditions across central NC through Thursday.


As of 220 PM Tuesday...

Skies have largely cleared out under the influence of subsidence
behind the departing mid level vorticity max and trough axis
shifting to our NE. A surface warm frontal zone approaching from the
SW will continue to become more defined far N and NE NC through the
rest of the day, and low level flow will back from WNW to uniform
WSW. A weak surface low and trough will develop over SW NC through W
NC respectively, and as this passes through this evening, with the
low tracking along the front along the NC/VA border, surface winds
will decrease, and we`ll finally see an abatement of the winds
toward nightfall, with a shift of light surface winds to a NE
direction over our NE and far N sections. Skies will stay generally
clear through the rest of the afternoon into the mid evening, but
then a layer of moisture around 850-800 mb spreading over far N and
NE sections (atop areas along and N of the surface front) late
tonight will bring a trend to partly to mostly cloudy skies in these
areas from late evening through much of the night. These clouds
should start to decrease toward daybreak as the 850 mb frontal zone
lifts NNE. Expect lows from 40 NE to the upper 40s/around 50 SW
(where SW winds S of the front will draw in milder air), although if
the clouds come in more numerous or earlier than expected, NE
sections may stay a few degrees warmer. -GIH


As of 330 AM Tuesday...

Wednesday through Thursday, the atmosphere will remain relatively
dry and stable, leading to a dry forecast. The stout sw flow
Wednesday will usher a much warmer air mass into the region. Aloft,
heights will be rising as the upper level low over New England lifts
into southern Quebec. The modifying air mass will lead to
temperatures slightly above normal, ranging from the upper 70s north
to the lower 80s south. While sfc winds will generally be less than
10 MPH int he morning, a tightening sfc pressure gradient should
yield sfc wind 10-15 MPH later in the afternoon with gusts around 25
MPH. These winds in conjunction with minimum RH values in the upper
20s-lower 30s across the southern counties may lead to enhanced fire
danger conditions.

A dry cold front will move sewd across central NC late Wednesday
night-Thursday morning, being propelled aloft by a s/w crossing
southern New England. The breezy conditions will continue Wednesday
night into Thursday, drying the fine fuels even more. While cooler
air will overspread the region from the NW Thursday, lower dewpoints
will lead to minimum RH values in the afternoon close to 25 percent.
The low RH combined with gusty winds between 25 and 30 mph will lead
to another afternoon of enhanced fire danger. High temperatures Thu
will vary from the upper 60s/around 70 NW to the upper 70s SE. Sfc
winds will subside Thursday evening under clear skies as high
pressure builds into central NC from the west. Min temps in the low-
mid 40s.


As of 250 AM Tuesday...

The upper-air pattern at the beginning of the long term period on
Friday features a broad trough over New England with another trough
and closed low over the four corners region with ridging in between
across the Plains states. The eastern U.S. trough axis will be
pushing off the mid Atlantic coast on Friday morning and central NC
will experience a northwest flow aloft for Friday into Saturday.
This pattern typically supports dry weather and cooler than normal
temperatures. The surface pattern will feature a cool 1034MB surface
high pressure system centered over the northern Plains on Friday
that will shift east into the eastern Great Lakes on Saturday and
then ridge into the Mid-Atlantic. The resulting sensible weather on
Friday and Saturday will include mainly clear skies, dry weather,
and temperatures between 5 and 10 degrees below normal.

The upper trough and embedded closed low over the southwestern U.S.
pushes east and reaches the southern Plains on Sunday and the Deep
South on Monday as the narrow ridge axis reaches the Carolinas late
Sunday and early Monday. NWP guidance is in better agreement with
the overall pattern and timing which is a little slower than
guidance from previous days. This should result in dry conditions on
Sunday and through a good part of Monday. As the surface high to our
north shifts off the New England coast, a weak surface low
associated with the upper-trough will push east across the Deep
South/Gulf Coast region late Sunday and Monday. This will allow an
easterly flow to develop across the Carolinas on Sunday into Monday
with a breezy and cool northeast winds expected by Monday. Given the
placement of the surface low, central NC will remain on the cooler
and more stable portion of the storm system. The resulting sensible
weather will feature increasing clouds on Sunday with mostly cloudy
conditions expected by late afternoon with considerable cloudiness
persisting into Monday. Dry weather is expected on Sunday with a
chance of showers arriving across the southwest and southern areas
Monday morning with rain chances increasing slightly and spreading
north on Monday night. At this point, the greatest precipitation
chances and amounts through Monday night will be located to our
south in SC, GA, and FL. Morning lows on Sunday will range in the
mid 40s with highs in the mid 60s to around 70. Lows on Monday
morning will be moderated by the cloud clover and stirring wind with
lows in the upper 40s to lower 50s and highs in the lower to mid
60s. -Blaes

As of 1250 PM Tuesday...

VFR conditions are likely at all central NC terminals over the next
24 hours. A warm front approaching from the SW will shift into NC,
stalling out across far N and NE sections of the state through Wed,
before lifting to our north Wed evening/night. A passing disturbance
aloft tracking to the ESE along the frontal zone tonight will bring
a period of cloudiness across far N and NE portions of the forecast
area, including RDU/RWI, but cloud bases will be VFR. Otherwise,
skies will be mostly clear. Surface winds from the W and WNW early
in the period will shift to SW this afternoon, and will stay
southwesterly through Wed. Expect sustained speeds of 10-15 kts
gusting to 23-28 kts this afternoon, dropping to sustained 3-8 kts
this evening/tonight, then increasing again Wed morning to sustained
10-16 kts gusting to 20-25 kts. At FAY, there is a risk of low level
wind shear tonight 03z-09z as a 35-40 kt low level jet from the WSW
passes overhead.

Looking beyond 18z Wed, VFR conditions are very likely through late
week, with high confidence in VFR lasting through next weekend.
Winds may prove problematic through Thu, however, especially for
small aircraft. The threat will peak on Thu, along and behind
passage of a mostly dry cold front, when sustained values of 15-20
kts with frequent gusts to 25-30 kts are anticipated. -GIH





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