FXUS62 KRAH 190853

Area Forecast Discussion
National Weather Service Raleigh NC
452 AM EDT Tue Mar 19 2019

Continental polar high pressure will extend across the middle
Atlantic states through Wednesday. Coastal low pressure will
strengthen while tracking along the coast of the Carolinas
and Virginia Wednesday night through Thursday.


As of 415 AM Tuesday...

Downstream of a split flow pattern over wrn NOAM, which includes a
blocking ridge over wrn Canada, a srn stream shortwave trough now
evident in WV satellite imagery over w-cntl TX will migrate ewd
across the Gulf Coast today, then pivot newd off the coast of the
sern US tonight. Meanwhile, a strong nrn stream shortwave trough
over the nrn Plains will dig sewd into KS through the same time.

At the surface, 1031 mb, continental polar high pressure centered at
08Z over wrn WV will build/extend across the middle Atlantic states
through tonight.

Nnely low level will continue to draw an area of low stratus and fog
from sern VA, sswwd into the nrn Coastal Plain and nern Piedmont of
NC this morning, but this regime should quickly disperse between 8
AM and 10 AM. Otherwise, periods of mainly thin high level moisture
will stream overhead in wswly upr level flow, downstream of the
aforementioned srn stream trough; and a scattering of 4-6 thousand
ft stratocumulus will develop with heating this afternoon. The
foregoing nnely low level flow around the cP high will also provide
for cooler, below average temperatures ranging from lwr 50s north
to upr 50s south today.

While skies should be mainly clear for most of the night, in the
prsence of continued thin cirrus/cirrostratus, the influence from
the passing srn stream shortwave trough will result in moistening in
the 5-10 thousand ft layer overnight; and this may manifest as the
development/expansion of an area of altocumulus from offshore the
coast of the Carolinas, nwwd into the Coastal Plain by Wed morning.
Low temperatures will be mostly in the lwr to mid 30s, with some upr
20s likely in rural nrn/wrn Piedmont locations - away from the
possible altocumulus and in closest proximity to the surface ridge


As of 445 AM Tuesday...

The nrn stream shortwave trough over KS at the start of the period
will amplify into the TN Valley/srn Appalachians vicinity through
early Wed night, then lift newd across the Carolinas through 12Z
Thu. Meanwhile, a trailing nrn stream shortwave trough will
amplify/dig sharply across the Great Lakes through the same time.
The increasing and increasingly focused QG forcing for ascent
accompanying these two, strong shortwave features will overspread a
strengthening coastal front/baroclinic zone off the coast of the
Carolinas and promote the spin-up/development and deepening of a
coastal low that will subsequently track nwd along the coast of the
Carolinas, and into ern NC, through early Thu.

The sensible weather result in cntl NC will be the continued
blossoming/nwwd expansion of multi-layer overcast and rain into the
srn and ern half of cntl NC on Wed, then areawide Wed night.
Additionally, the combination of strong QG forcing for ascent
coupled with strengthening low-mid level frontogenesis may
contribute to the development of a narrow/mesoscale precipitation
band capable of producing one half to one inch of rain through early
Thu in the US Highway 1 to I-95 vicinity. The presence of increasing
clouds and developing rain will likely hold temperatures in the lwr
to mid 50s again Wed, with lows ranging from upr 30s to mid 40s Wed


As of 430 AM Tuesday...

Model guidance for the mid term has continued to change to a wetter,
and therefore slightly cooler solution for Thursday. The two pieces
of energy responsible for the Thursday precipitation can already be
seen on water vapor this morning. The first piece of energy is a
weak mid-level shortwave over Texas. This energy is forecast to
slowly push off the coast of Florida Tuesday into Wednesday inducing
surface pressure falls off the coast of South Carolina. The second
piece of energy is located over the Midwestern United States and is
pushing south around the western edge of a broad upper level trough
axis. This piece of energy will be approaching North Carolina from
the west Thursday morning. The wave will actually begin to take on a
negative tilt and the associated DCVA will allow surface low
pressure to strengthen near Wilmington, NC. The surface low pressure
is forecast to pull north towards Sampson County with precipitation
spreading across the Coastal Plain. The latest runs of the NAM and
GFS show a deformation zone and resultant Fgen band setting up
northwest of the surface low. The ECMWF and CMC also show a similar
set up. There still remains differences in the timing, placement and
strength of the low, but given the clear trend of global and high
res models towards low pressure forming, the Thursday forecast has
been trended significantly wetter than the last couple of forecasts.

Thursday afternoon the next shortwave is also much quicker and
absorbs the aforementioned shortwave in the paragraph above. This
allows the synoptic cold front to now cross the zones early Friday
morning. Behind this front precipitation will come to an end.
Temperatures behind the front will only be near normal though as the
wave quickly heads northeast. A secondary shortwave will dive
southeast out of Ontario Friday morning and will quickly deepen over
New England Friday evening. This wave will push another reinforcing
cold front through the area Friday evening. Given the faster
progression of the initial two waves, this stronger wave now wraps
up further west than previously forecast. What does this mean for
central NC? This means that the colder air will be slightly further
west and south than previously forecast. Due to this have trended
temperatures down a bit Friday into Saturday.

Sunday high temperatures will moderate back above normal as the deep
vertically stacked low over New England heads east and heights rise.
Both Saturday and Sunday are dry for now with subsidence on the back
side of the upper level low. Monday, the upper level low over the
western United States will start to open up as another closed low
over Quebec dives southeast. Exactly how quickly the low from Quebec
dives south will determine when the next chance of precipitation
arrives. The GFS appears to open up the wave to quickly, while the
ECMWF and CMC are generally slower. For now have kept mention of
slight chance PoPs in for Monday, but this could easily be pushed
later given support from the CMC and ECMWF. Temperatures Monday will
be near normal.


As of 220 AM Tuesday...

Nnely low level will draw an area of low stratus and fog over sern
VA, sswwd into the NC Coastal Plain through 12Z; and this will
result in a risk of LIFR ceilings and visibility restrictions this
morning near and especially just northeast of RWI - toward IXA, ETC,
and ASJ. Otherwise, periods of high level moisture will stream
overhead in wswly upr level flow, and with a scattering of 4-6
thousand ft stratocumulus with heating this afternoon. Surface winds
will be generally light from the northeast, with perhaps a few gusts
into the teens kts mainly at FAY between 15-19Z.

Outlook: Low pressure will develop off the coast of the sern US on
Wed, then track nnewd in the vicinity of the coastline of the
Carolinas Wed night through Thu. An area of rain and sub-VFR
conditions will likely, consequently blossom nwwd into cntl NC late
Wed and particularly Wed night, then linger through Thu. The passage
of a trailing mid to upr level disturbance will then result in a
chance of light VFR rain or sprinkles, mainly from mid level
ceilings, throughout cntl NC Thu afternoon into early Thu night.




LONG TERM...Haines
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