Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 161850

Area Forecast Discussion
National Weather Service Raleigh NC
250 PM EDT Mon Jul 16 2018

A southerly flow, around high pressure offshore, will bring a hot
and more humid air mass into the region through Tuesday. A cold
front will approach from the northwest late Tuesday, drop through
the area Tuesday night, and then stall just south of the region
Wednesday through Thursday.


As of 230 PM Monday...

Convection has begun to fire on differential heating and a lee
trough which is barely visible in the observations at this time,
mainly in the form of speed convergence. With good mixed layer cape
of about 1000-1500 J/KG across the west and some high low-level
lapse rates, cells have been quick to grow initially before slowing
down with mid-level lapse rates only in the 5-5.5 deg/KM range. A
few lightning strikes have been observed but otherwise showers and
storms have remained well below severe criteria. With little shear
and organization present, that should continue to be the case but
can`t completely rule out the threat of an isolated microburst. Much
of the activity should be confined to the western half of the
forecast area as a layer of dry air at 700 mb remains very prominent
in the east. If you could get a storm to fire here it would have a
better chance of becoming severe with DCAPE values north of 1000
J/KG thanks to that drier air.

Temperatures are tricky due to the breaks in the clouds with most
locations still in the mid to upper 80s but sites like RDU have
already busted through forecast highs with a reading of 93 degrees
at 18z. Wouldn`t expect anywhere to top out much higher than that
this afternoon. Overnight tonight expect some low stratus to form in
the west, particularly in areas hit by afternoon convection. Lows in
the low to mid 70s.


As of 230 PM Monday...

For Tuesday, a frontal system will make its way towards central NC
from the northwest, but won`t arrive until evening. Until then, the
same airmass remains in place with a more invigorated lee/pre-
frontal trough in place. There will be plenty of instability once
again from temperatures close to if not above 90 degrees but more
cloud cover in the area could keep those numbers down. High
resolution models show more coverage than this afternoon with
instability driven convection, followed by a more organized linear
feature when the front comes through, closer to 00z Wednesday in the
Triad and pushing through the CWA by 9z with some convection
possibly remaining in the far southeast as the front slows and
begins to stall out along the coast and near the NC/SC border. Again
the threat for severe weather looks minimal but with more forcing
the chances on Tuesday of seeing an isolated damaging wind event are
greater than they are this afternoon. Highs near 90 and lows near 70
in the Triad with mid 70s in the southeast.


As of 250 PM Monday...

The cold front will be progressing southeast across the area, and
associated showers will be ending across the southern tier counties
Wednesday morning. Skies will be clear or clearing quickly with a
decrease in humidity in drier northerly flow behind the front. Highs
will be near normal...85 north to around 90 south. The high pressure
building in behind the front will be progressive, moving across the
mid Atlantic and offshore later Thursday. The ridge builds down the
Appalachians in typical fashion, to maintain dry weather with
seasonable temperatures in the mid and upper 80s Thursday and
Friday. Lows will be in the mid and upper 60s both mornings.

All this while, the front which pushed south of the area in the mid
week will be stalled southeast of the area. This front will lift
back to the north on Saturday as a warm front as the surface high
lifts out to the northeast. This will produce both moisture and
modest warm air advection, and highs will edge up to mainly upper
80s with some lower 90s in the south through the weekend. The chance
of rain will be on the uptick, as there will also be a transition in
the upper flow towards an amplified omega blocking pattern featuring
ridging over the far west and a trof stretching out of the Great
Lakes into the eastern CONUS. Details are not really resolvable at
this range, but the pattern looks wet and should follow the diurnal
cycle. We will remain unsettled into early next week as the blocked
stationary upper trof axis gradually shifts east over the area. Will
maintain generally chance PoPs given the low confidence timing for
more active convective periods.


As of 200 PM Monday...

24 Hour TAF Period: Convection starting to pop up already between
the Triangle and the Triad which is a little ahead of schedule.
Chances for vicinity thunder are possible at all sites except KRWI
over the next several hours. Convection is not expected to be severe
but cant rule out the possibility of an isolated microburst. Outside
of thunderstorms, conditions should remain VFR for much of the
period. There is a chance for some MVFR stratus developing in the
west from 9-12Z. Another round of convection can be expected
Tuesday, initiating near the end of the TAF period.

Outlook: Thunder will be possible on Tuesday and Tuesday night at
all terminals as a cold front moves through the area. Periods of
sub-VFR conditions are possible, particularly during the overnight
areas. Conditions return to mainly VFR for the end of the week
before rain chances pick up again for the weekend, along with the
threat of adverse aviation conditions.





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