Scientific Forecaster Discussion
fxus62 krah 200753
Area forecast discussion
National Weather Service Raleigh NC
250 am EST Wed Nov 20 2019
a strong upper level disturbance will move across the Carolinas
early this morning. Surface high pressure will build into the region
later today and Thursday. A cold front will move into the region
late Friday and linger into Saturday when a storm system and an
associated cold front moves across the region.
Near term /through tonight/...
as of 245 am Wednesday...
A potent short wave trough with a belt of strengthening 80+ kt winds
at 500 hpa will continue to move east across the Carolinas and
offshore by mid morning. Behind this system, a relaxing
northwesterly flow aloft is expected today and tonight. As the
upper trough axis moves offshore, heights will rise today and
tonight as a short wave ridge axis reaches the Appalachians by
Thursday morning. At the surface, high pressure centered over
the Tennessee Valley this morning will shift east and settle
over the Carolinas and Virginia by daybreak Thursday.
Areas of lingering low clouds and areas of fog early this morning
will give way to increasing sunshine after daybreak. A corridor with
areas of dense fog in a region from the western/southern Piedmont
into the sandhills and possibly into the coastal plain this morning
may persist a little longer but should dissipate by mid morning.
With rising heights and subsidence, expect mainly clear skies late
this morning and afternoon with some patches of cumulus clouds
possible this afternoon, mainly across the northern Piedmont.
Statistical guidance is in good agreement with highs in the 58 to 63
range today, pretty close to normal for this time of year. A
northwest wind at around 10 mph is expected today with some gusts of
15 to perhaps 20 mph possible.
Mainly clear skies are expected tonight although there will be an
increase in some high clouds late as upper level moisture
spills over the ridge axis. With the surface high settling into
the region overnight, conditions for good radiational cooling
should become established. Will need to monitor the amount of
high clouds which could offset the radiational cooling, but for
now have adjusted minimums down slightly, -blaes
Short term /Thursday through Thursday night/...
as of 250 am Wednesday...
Thursday will be a quiet weather day as weak upper ridging
transitions to zonal flow and high pressure begins the day parked
over the Carolinas. The high will slowly drift southeast and
offshore during the 24 hour period. High clouds will gradually move
into the area from northwest to southeast during the afternoon.
Highs will be a few degrees below normal while lows will be a few
degrees above normal as clouds roll in and southerly wind develops.
Long term /Friday through Tuesday/...
as of 250 am Wednesday...
The main weather maker during the extended forecast continues to
come from a complex system ranging from Canada all the way into
Texas. Low pressure over Quebec will have a cold front extending
into Texas, off of which another wave of low pressure will develop.
Today's wrinkle in the forecast is that the Canadian low appears to
move more easterly than northeasterly on Friday, which will result
in a more east-west orientation of the cold front as it sags across
Virginia and North Carolina. This will slightly increase pops during
the day along the Virginia border, while diminishing pops south of
Raleigh. The second wave of low pressure should reach Tennessee by
Saturday morning, pass over West Virginia Saturday evening, and
reach New York City by Sunday morning. The best chance for rain will
come Saturday afternoon and evening as the cold front sweeps across
the region. Slightly raised pops, but did not have enough confidence
to go with categorical pops. The GFS ensemble remains insistent that
some showers will linger into Sunday morning, but have stuck with
the deterministic models that show drier air moving in by sunrise.
High pressure will follow the cold front, allowing for dry weather
Monday and Tuesday. Clouds will be on the increase late Tuesday in
advance of the next approaching system. The warmest day should be
Friday while the region is in the warm sector, then temperatures
will fall a few degrees below normal behind the cold front for the
rest of the period.
Aviation /08z Wednesday through Sunday/...
as of 150 am Tuesday...
Adverse and varied aviation conditions are noted across central NC
early this morning with widespread MVFR and IFR conditions in areas
of fog and overcast conditions. An upper level disturbance producing
some enhanced clouds and even some spotty light rain will move
offshore before daybreak. Behind this system, skies will clear after
daybreak. High confidence that VFR conditions with mainly clear
skies will arrive by mid morning with some patchy cumulus clouds
this afternoon across the north and some patchy high clouds tonight.
Very light to calm winds early this morning will give way to mainly
northwest wind at around 10kts with some gusts of 15 to 20kts this
afternoon. Winds will become light northerly tonight.
Looking beyond 06z Thursday, VFR conditions are expected to continue
through early Friday with increasing high clouds. A cold front will
move into the region later on Friday and then stall as an area of
low pressure develops and moves across the mid Atlantic on Saturday.
Periods of adverse aviation conditions are possible during this
period, especially Saturday afternoon and evening. Mainly fair
weather is expected on Sunday and into Monday. -Blaes