Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
320 PM EDT Monday Mar 10 2014
Synopsis...beneath dry westerly flow aloft...a weak surface trough
will linger over the Carolinas through Tuesday.
Near term /through Tuesday/...
as of 305 PM Monday...
Through tonight: moisture in deep layer west-northwest flow will be remain
limited over central NC...unlike over much of Virginia where widespread
orographic cirrus and virga has kept cloudy and cooler conditions in
place today. Some additional thinner cirrus will stream
southeastward from the Ohio Valley and across NC tonight...but any
orographic enhanced at our latitude should be short-lived before the
flow aloft backs to a more westerly component. Despite occasional SW
stirring in the presence of the Lee/Piedmont trough...bufr soundings
still indicate the development of a strong surface-based inversion
supportive of at least some periods of calm...and consequent modest
radiational cooling tonight...into the lower to middle 40s.
Tuesday: westerly/zonal flow aloft will develop downstream of a
southern stream closed middle-upper low forecast to migrate and
deamplify from the Rio Grande to the central Gulf Coast states. The
westerly flow and associated downslope component will maintain Lee
surface troughing across the Piedmont of the Carolinas...on the
northern periphery of a modified Pacific high over the Gulf Coast
and southeast states. The combination of downslope warming and
consequent southwesterly surface flow in vicinity of the Lee trough will
result in further warming temperatures into the 72 to 78 degree
range...per forecast thickness values of 10-12 meters above those of
Short term /Tuesday night through Wednesday night/...
as of 300 PM Monday...
Split flow pattern is evident during the short period as a closed
low located over Texas Monday night opens up as it moves eastward
and deamplifies Tuesday night and continues to do so on Wednesday as
it moves off the southeast coast. At the same time a northern stream
short wave dives into the northern plains states and swings through
the Ohio Valley on Wednesday evening. The northern stream wave
induces cyclogenesis along the Ohio River on Wednesday with the
surface wave moving into New England on Wednesday night. This
pattern will keep central NC in the warm sector and will mercifully
preclude any winter weather ptype issues with this system. Expect
moisture to increas quickly Tuesday night in the increasingly moist
southerly flow resulting in thickening clouds and increased
precipitation chances. Nwp guidance differs with the arrival time of
the precipitation with the GFS/European model (ecmwf) faster with precipitation arrival and
the NAM delaying the precipitation arrival until after daybreak
Wednesday. Will slowly ramp up probability of precipitation beginning after midnight with
precipitation chances increasing after daybreak Wednesday and
reaching likely probability of precipitation for Wednesday afternoon as the combined forcing
from the northern stream wave and the approaching cold front produce
fairly widespread showers. There should be sufficient instability
for at least a few thunderstorms but the instability is rather
limited with MLCAPE values around 500 j/kg and modest lapse rates.
So will include a mention of thunder but expect the threat of severe
weather to be limited. Precipitation chances will quickly end from
west to east as the cold front pushes east and reaches the coast a
little after 00z. Low temperatures Wednesday morning will be
modified by the southwesterly flow ahead of the approaching cold
front and the cloud cover. Lows in the lower to middle 50s look
reasonable. High temperatures Wednesday afternoon should warm into
the 68 north to 74 South Range...if the precipitation is more
limited and there are some breaks in the overcast...these temperatures will
be underdone. Much colder and blustery conditions are expected on
Wednesday night as cold advection arrives behind the front with lows
in the upper 20s to lower 30s. -Blaes
Long term /Thursday through Monday/...
as of 320 PM Monday...
The extended range features a rather persistent West Coast ridge
with periods of eastern Continental U.S. Troughing. Thursday will feature cold
and blustery conditions with the eastern Continental U.S. Trough axis located
across the East Coast. Despite lots of sunshine...highs on Thursday
will only reach the middle 40s. Fair weather and moderating
temperatures are expected on Friday as weak short wave ridging
arrives and a return flow develops on the backside of the departing
cold high. High temperatures Friday will reach the middle to upper 50s.
The next shortwave trough with the associated cold front approaches
the region on Saturday with increasing amounts of moisture. The
operational GFS suggests a chance of precipitation while the European model (ecmwf)
is essentially dry. Many of the gefs ensemble members are also dry.
So will increase cloud cover but hold off on precipitation chances
for now. A southerly flow will result in additional warming with
highs in the middle 60s on Saturday.
Confidence in days 6 and 7 is very low with a very complicated
pattern that suggest a digging northern stream trough along with
some southern stream energy could result in a storm system that
moves across the southeast coast. The calendar and nwp guidance
suggests that the threat of any wintry precipitation should be
limited but this has not been a typical winter and the colder air
will not be too far away. For now for now will introduce chance probability of precipitation
for Monday and Monday night with near seasonable temperatures.
Aviation /18z Monday through Friday/...
as of 200 PM Monday...
Mainly VFR...aside from a persistence forecast of a little radiation
fog late tonight at kfay and especially at krwi. Otherwise skies
will be clear or mostly so...with just some passing cirrus through
tonight. The presence of a Lee surface trough will maintain west-southwest
surface flow...which after subsiding to calm or light at less than
5 kts after sunset...will once again increase into the 6-11 knots range
Outlook: breezy southwest winds...showers...and mostly MVFR ceilings
and visibility restrictions...will accompany a passing low pressure
system Wednesday-Wednesday evening.