Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Raleigh NC
1015 am EDT Friday Apr 18 2014
Synopsis...strong high pressure centered over New England will
extend south through the Carolinas today. Meanwhile...low pressure
will develop over the northeastern Gulf of Mexico...drift across The
Big Bend of Florida tonight...then meander along the southeast US coast
through the weekend.
Near term /through Saturday night/...
as of 1015 am Friday...
Current visible satellite shows high clouds continuing to move up
toward central NC from the south...in advance of a closed middle level
low and surface low moving east across the deep south and NE Gulf Coast
regions. Current regional radar shows rain spreading north across
central Georgia...and has just recently reached Georgia/SC border. The 12z
gso sounding came in quite dry between 500 and 900 mb. Looking
farther south...even the 12 chs sounding showed a dry layer between
600 and 800 mb. Thus it still looks like it will take until middle-
evening or so before the lower troposphere moistens enough to allow
rain to begin across our area. In the meantime...for the rest of this
morning and afternoon across central NC...you can expect increasing
clouds...perhaps some dim sunshine filtered by high clouds...and high
temperatures in the lower 60s. Current forecast on track and no major
changes this morning.
Previous near term discussion as of 256 am Friday...
surface high pressure will extend down the East Coast during the
day Friday. A shortwave in the southern stream will move eastward
along the Gulf Coast...closing off late in the day... as a surface
low develops in the vicinity of the Florida Panhandle. Significant upper
level cloudiness...already visible on satellite imagery just to our
southwest... will keep high temperatures suppressed in to the middle
50s to low 60s. Precipitation will begin to try to spread in to the
area from the south by around 00z Saturday...however it may take the
several hours to saturate the dry low levels... and the deeper
isentropic lift will arrive after 06z Saturday. With thick cloud
cover and precipitation... temperatures will not fall off much and
lows will be in the middle to upper 40s.
Stacked low pressure will continue to track slowly eastward over
northern Florida on Saturday... before exiting the East Coast Saturday
evening. Continued below normal temperatures in the middle 50s.. with
northeast flow... cloud cover... and precipitation. Expecting a good
soaking through the day Saturday... with total quantitative precipitation forecast of about 0.75-1.5
inches... greatest in the southeast. Precipitation will end
generally from west to east as the system begins to pull away from
the coast... and isentropic lift diminishes in the west after 12z...
and in the coastal plain after 00z. Lows in the middle and upper 40s.
Short term /Sunday through Monday/...
as of 255 am Friday...
The southern stream coastal gyre will drift only slowly east and
away from the coast of the Carolinas Sunday. Continued overcast -
low ones in the coastal plain and more middle level ones over the
western Piedmont - with northeasterly low level flow in association
with renewed polar high pressure extending south from New
England...will result in cooler temperatures than earlier
anticipated. Temperatures will likely display an atypical
distribution...with warmer temperatures in the middle 60s in the
southern and western Piedmont as clearing occurs during the middle-
afternoon...and 50s for most of the day...with periods of lingering
light rain early...in the coastal plain.
Clearing will then overspread all of central NC behind the departing
low Sun night-Mon...with the exception of brief low overcast...in
continued NE low level flow...Monday morning. The much anticipated -
and now well-delayed - warm-up will finally arrive Monday...when the
high over New England succumbs to warmth building over the plains
and MS valley. Highs Monday in the upper 60s to lower 70s. Lows 50 to
Long term /Monday night through Thursday/...
as of 305 am Friday...
The northern stream...held at Bay across the northern tier of states
during through the short term...will buckle/amplify southeastward
from the upper Midwest to the NE quarter of the nation through early-
middle next week. The sharpening trough aloft will send an associated
surface cold front through the middle Atlantic and Carolinas Tuesday
afternoon-evening...at which time scattered to numerous showers and
thunderstorms...fueled by destabilizing surface temperatures in the
upper 70s (to around 80) and dewpoints around 60 degrees...are
expected. Cooler but generally clear conditions will follow in brief
surface ridging from the Ohio Valley/Great Lakes Wednesday. Frontogenesis
will then occur from the upper Midwest to the central Appalachians
Wednesday night-Thu...leading to a warmer southwest low level flow beneath
a building ridge aloft over the southeastern US...late week.
Aviation /12z Friday through Tuesday/...
as of 745 am Friday...
Polar high pressure centered over New England will extend south and
maintain VFR conditions for most of the taf period...with two
exceptions. The first will be a brief period of around 1000 feet
stratus through 15z...while the second will be later tonight as
clouds thicken and lower and result in the development of light
rain - and eventually MVFR-IFR ceilings toward the end or just beyond the
12z taf period - to the north of an area of low pressure forecast to
develop from the NE Gulf of Mexico to the southeast US coast.
Otherwise...6-12 knots NE surface wind today will increase into the 10-
15 knots range...especially at kfay as the mean sea level pressure gradient
Outlook: moisture associated with the aforementioned developing low
pressure area will continue to spread north late tonight and early
Saturday...and consequently result in the development of rain
throughout central NC during that time. However...ceilings will be
progressively higher from southeast to northwest...such that IFR-
MVFR ones will be likely at southeastern terminals...trending higher
to the west at krdu and triad terminals...the latter of which may
remain VFR despite periods of light rain.