Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 231945

Area Forecast Discussion
National Weather Service Wilmington NC
345 PM EDT Tue May 23 2017

Waves of low pressure will continue to move along stalled cold
front producing a good chance of showers and thunderstorms
through mid week. Another cold front trailing from a deep low
pressure system over the Ohio Valley on Thursday will cross the
area, bringing the final round of showers to the area. High
pressure will build in late Thursday into Friday maintaining
quieter weather for much of the weekend. Low pressure may affect
the area early next week producing more unsettled weather.


As of 300 PM Tuesday...Convective coverage has solidly
increased over the last few hours ahead of a wave of low
pressure. This wave will be moving NE along a stalled font with
its main impacts being felt across our area during the eve hours
with widespread showers and thunderstorms expected. The heavy
rain potential will continue, thus a Flash Flood Watch remains
in effect. Precipitable water values are at record levels for
this time of year, 2 inches. Thus, training thunderstorms will
have the potential to bring excessive rainfall. We are
forecasting 1 to 3 inches of additional rainfall through Wed
with amounts locally in excess of 4 inches. This may lead to
significant ponding in many low-lying an poor drainage areas and
even the risk for flash flooding, although the flash flood risk
should be more localized. Urban areas will be the most
susceptible to flooding.

Low level jetting increases this eve and SPC has the area in a
slight risk for severe weather. There is a non zero risk for
damaging wind gusts in a wet microburst or even a brief tornado. The
limiting factor for severe weather will be marginal lapse rates/
marginal instability as cloud cover has been extensive today.

Once this wave moves by, there should be an overnight lull which
should persist into Wed morning. Then another low pressure wave
later Wed and Wed eve should bring an increase in showers and
thunderstorms. Expect extensive clouds to dominate the period with
low stratus overnight and Wed morning.


As of 300 PM Tuesday...Deep moisture associated with cold front now
progged to get shunted offshore more quickly than previously thought
early Wednesday night and this period should mark the end of
appreciable rainfall. Light shower activity will persist but in a
more spotty fashion thereafter as increasingly strong PVA and height
falls impinge from the west. In fact, the coverage and intensity
should pick up midday Thursday as the fairly impressive 32 s-1 vort
and -21C trough axis swings through at 500mb. In fact this energy
swings through so quickly that the low level CAA shuts off Thursday
night but not before dropping enough to support some lows in the
upper 50s with low 60s along beaches.


As of 300 PM Tuesday...Plenty of dry air will move in with deep
westerly flow on the back end of exiting low pressure system on
Fri. Pcp water values drop down to .75 inches or below early
Fri but do creep back up over an inch by late Friday. Overall
expect a sunny dry day on Friday with temps reaching into the
mid 80s.

High pressure ridge to the south will reach up into the
Carolinas maintaining pleasant weather through much of the
weekend. A shortwave rides across the top of the ridge over the
weekend mainly remaining north of the forecast area. This could
produce some clouds or a spotty shower late Sat into Sat night,
mainly over NC. The GFS builds the ridge a little farther north
and therefore holds any weather farther to the north with a deep
warm southerly flow and sunnier weather overall all weekend. A
deeper mid to upper trough digs down late in the weekend and
could produce an increase of clouds and showers Sun through Tues
timeframe. Will have to see how the models evolve. For now,
will keep chc of shwrs north of area through Sat night but will
include Pops for Sun through Tues.

The building ridge and westerly downslope flow through the mid
levels will produce above normal temps through much of the
period with temps reaching above 90 in spots especially over
the weekend.


As of 18Z Tuesday...Much of the TAF period will be dominated by
convection with MVFR and IFR ceilings and visibility. One wave
will bring widespread convection into the later eve hours. Then
there should be a decrease in the number of thunderstorms, but
ceilings should remain near or within the IFR category if not
lower overnight. The coverage of showers and thunderstorms will
again increase on Wed, most likely after 18z. As low level
jetting increases this eve, the risk for wind shear will
increase. At this time, have included wind shear at KFLO.

Extended Outlook...Reduced flight categories will be possible
in periodic showers and thunderstorms into Thursday.


As of 300 PM Tuesday...A Small Craft Advisory is in effect for all
waters through the period and beyond. Wind speeds will be up to 20
to 25 kt with gusts up to 30 kt. The highest wind speeds during this
period will be tonight. However, although wind speeds will slacken
during the first half of Wed, they are expected to increase to
similar levels during Wed afternoon and eve. The wind direction will
be SW through the period. Seas will build to 5 to 7 ft tonight, then
perhaps subside a foot or so before building to similar levels
during the later stages of Wed afternoon. Bouts of showers and
thunderstorms with heavy rain will drop visibility to a mile or
less. The most widespread coverage during this forecast period will
be tonight.

As of 300 PM Tuesday...Solid small craft advisory conditions
Wednesday night in not only a moderately pinched gradient but also
an environment characterized by increased wind fields aloft leading
to vertical momentum transfer. So now peak wind gusts may attain
35kt but at this time they do not appear to be near frequent enough
to warrant Gale Warning. Frontal passage comes early Thursday
leading to a veering to the west and a gradual decrease in sustained
wind speeds. The upper trough meanwhile may persist the gustiness
factor into the early afternoon. Winds may tick up a category in
speed in the CAA Thursday night, likely continuing the Advisory.

As of 300 PM Tuesday...A stronger off shore westerly flow on
Friday will diminish and back around to the W-SW through the day
as low pressure system exits farther off to the east and high
pressure builds up from the south. Seas of 3 to 5 ft will
diminish to 2 to 4 ft through Friday and down below 3 ft by Fri
night in weakening offshore flow.

High pressure south of the area waters will shift east through
the weekend into early next week producing a persistent SW
return flow. Initially winds will only be 10 kts or so but low
pressure moving by to the north Sat night into Sun and an
approaching cold front late in the weekend into early next week
may produce an increase in SW winds. Seas less than 3 ft
Saturday in lighter winds will rise up to 3 to 5 ft in
increasing SW winds Sat night into Sun.


SC...Flash Flood Watch through Wednesday evening for SCZ017-023-024-
     Beach Hazards Statement until 8 PM EDT this evening for SCZ054-
NC...Flash Flood Watch through Wednesday evening for NCZ087-096-099-
     Beach Hazards Statement until 8 PM EDT this evening for NCZ106-
MARINE...Small Craft Advisory until 8 AM EDT Thursday for AMZ250-252-



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