Area Forecast Discussion
Issued by NWS Blacksburg, VA

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869
FXUS61 KRNK 251318
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
918 AM EDT Mon Sep 25 2017

.SYNOPSIS...
A strong high pressure area will remain over the Mid-Atlantic
region through midweek, then diminish and shift eastward.
Meanwhile, Hurricane Maria will remain off the SC/NC coast while
drifting northward. A mainly dry cold front will finally move
into the region by the end of week bringing much cooler
temperatures.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 915 AM EDT Monday...

Fair and warm weather to start the workweek this Monday.
Patchy fog will continue to dissipate this morning leaving
us with sunshine filtered through a veil of cirrus clouds.

Previous discussion...

Continued unseasonably warm, dry weather across the forecast
area through midweek as a 590+ dm ridge slowly drifts eastward
across the northern Mid-Atlantic region. 850mb temperatures will
hover in the +18C to +20C range. Temperatures will again
average 10-15F degrees above normal maximum readings ranging
from the upper 80s Piedmont to the upper 70s western mountains.
Minimum temperatures will be well above normal as well in the
mid 50s west to the mid 60s Piedmont. The outer cirrus shield
of Hurricane Maria will drift over the region with periods of
thicker cirrus, but this should only reduce heating a few
degrees, mainly keeping the Piedmont from reaching 90 degrees.
Model soundings do not support much if any CU, and the cirrus
may limit heating enough to further prevent much CU development,
especially across the Piedmont. However, there is always some
threat with an increasing upslope easterly flow for some CU/SC
to develop.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
As of 230 AM EDT Monday...

During this portion of the forecast, Hurricane Maria is expected to
be heading north in the western Atlantic, east of the coasts of
South and North Carolina. Concurrently, a persistent upper ridge of
high pressure will be parked overhead until Thursday. On Thursday, a
fairly dry cold front is expected to cross the region.

While any precipitation associated with Maria is expected to remain
east of the region, cyclonic flow around the system will advect
marine based air into the region on Tuesday, prompting the arrival
of increased cloud cover, especially across east sections of the
region. As we progress into Wednesday, the flow will back more
northerly, and then northwesterly by Thursday, post-cold front. The
result will be less cloud cover on Wednesday as compared to Tuesday.
On Thursday, isolated showers and increased cloud cover will be
confined to southeast West Virginia, and potentially the
neighboring tier of counties of southwest Virginia.

Temperatures Tuesday through Wednesday night will continue to be
very mild for this time of year, averaging some ten to fifteen
degrees above normal. Thursday, readings will be a little cooler in
the west with increased cloud cover with the front over the area,
but still about five to ten degrees above normal, with eastern areas
still ten to fifteen degrees above normal. Temperatures will trend a
little cooler Thursday night and less humid, but still average about
five degrees above normal.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 133 PM EDT Sunday...

Stronger shortwave with another front could trigger a few showers
Saturday, but overall very low chance. After one more warm day
Thursday with highs in the mid to upper 70s west, to mid 80s east,
highs should return to normal Friday-Sunday with mid 60s to lower
70s west, mainly 70s east.

&&

.AVIATION /13Z MONDAY THROUGH FRIDAY/...
As of 740 AM EDT Monday...

With the exception of patchy late night/early morning, which is
somewhat more questionable than usual, looking for VFR
conditions through the TAF valid period at all sites. The cirrus
shield from Hurricane Maria, well off the Atlantic seaboard,
will thicken with time over the forecast area as the hurricane
moves north well off the coast. Soundings and time-height cross
sections of RH suggest limited CU development during the day,
but enough moisture in the 045-060 layer to consider FEW-SCT.
This may be more prevalent in the areas further west with less
cirrus.

The cirrus shield, dry surface air mass, and light northeast
wind flow around the extreme outer periphery of the hurricane
may inhibit fog development again tonight/Tuesday morning, but
cannot completely rule out some patchy fog development in areas
that decouple, especially in valleys of the western mountains.
Have limited this to LWB with this TAF set.

The large circulation around Hurricane Maria will keep a
northeast flow over the area through the period, mainly in the
040-080 range, except at BLF where it will be more in the
090-120 direction. Speeds will increase to 8-10kts after 14Z,
with some low end gusts possible mainly across the Piedmont,
decreasing to 4-6kts again after 00Z.

Extended Aviation Discussion...

Overall persistence forecast through the first half of this week as
strong high pressure aloft slowly drifts across areas just to
our north. The upper high will gradually weaken and allow a
mainly dry cold front to move through the region late in the
week. Late night/early morning fog can be expected through the
week as low-level moisture slowly increases in advance of the
front. For the most part, VFR conditions are expected to
continue through the week and into the weekend.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...RAB
NEAR TERM...MBS/RAB
SHORT TERM...DS
LONG TERM...DS/WP
AVIATION...RAB



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