Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
1240 am EDT Wednesday Mar 12 2014
moisture will increase tonight ahead of a system moving northeast
from the Gulf of Mexico and a cold front from the west. The front
will be moving through the midlands and csra late Wednesday. It
will be much cooler behind the front Thursday and Friday. Freezing
temperatures will likely occur Thursday night.
Near term /until 6 am this morning/...
an area of low pressure over the southern/Central Plains will
track into the Ohio Valley this evening. This will open the
forecast area to Gulf moisture and increasing clouds. Moisture
will increase across the area tonight as the middle/upper flow
becomes southwest and moisture flux increases across the area.
Current 88d regional composite shows light showers have already
developed quickly out ahead f the main system and have moved
across the Savannah River into the midlands. Expect the main area
of showers to follow in the next 3 to 4 hours. Models show
increasing isentropic lift and moisture convergence across the
area between 06z and 12z. Clouds and rainfall will give way to
above normal overnight low temperatures in the middle to upper 50s.
Short term /6 am this morning through Thursday night/...
Wednesday and Wednesday night...low pressure will be stretched
across the Ohio Valley Wednesday morning and track northeastward
through the day reaching eastern PA/western New Jersey Wednesday evening.
Swath of Gulf moisture will start the day across the forecast area
and quickly progress eastward through the day and offshore during
the afternoon. High temperatures Wednesday afternoon will be in the
lower to middle 70s at most locations. The cold front associated
with the low will move through the forecast area Wednesday evening
with breezy northwest winds pushing much cooler air back into the
region. Although winds will remain breezy through the night with
clouds quickly diminishing and cold air advection overtaking the
region temperatures will drop steadily through the night. Overnight
lows Wednesday night will range from around 32 in the western
midlands to the middle and upper 30s over the central and eastern
Thursday and Thursday night...high pressure will build into the
region Thursday and be centered over the region Thursday night. As
the high builds into the area Thursday the pressure gradient will
relax and the winds will diminish through the day. Thursday night
will be excellent for radiational cooling with clear skies and light
winds. With temperatures struggling to reach 50 across the northern
midlands and the middle 50s elsewhere for afternoon highs expect the
temperatures to drop into the middle 30s by 11pm. Through the early
morning hours temperatures will continue to cool with overnight lows
reaching the middle 20s across the northern and western midlands with
upper 20s to around 30 elsewhere. Currently expect most locations to
see conditions near to below freezing for 6 to 7 hours.
Long term /Friday through Tuesday/...
uncertain and low confidence forecast in the extended this period.
A brief transition to a more zonal upper pattern is expected on
Friday into Saturday which will allow temperatures to moderate and
rebound a bit from the well below normal temperatures on Thursday.
Friday morning low temperatures will be in the 20s across the region
but near full sunshine and warming 850mb temperatures should support
maximum temperatures on Friday in the low to middle 60s.
The forecast confidence decreases significantly over the weekend
into early next week due to poor run to run model consistency and
significant differences among the operational runs of the
GFS/ECMWF. Both the GFS/European model (ecmwf) made large shifts from their 11/00z
runs with the European model (ecmwf) previously showing shortwave energy diving into
the lower Mississippi Valley and closing off over Mississippi then
moving across the southeast states early next week. The GFS is a bit
more progressive and shows a weak system crossing the area on
Saturday followed by a brief break...then brings a positively tilted
trough along the Gulf Coast states early next week.
Regardless of model choice...it appears that the weather pattern
will become unsettled by the end of the forecast period with a more
substantial system moving through the southeast early next week
compared to the system on Saturday/Sat night.
Temperatures through the period will generally be near or slightly
below normal Friday/Sat and likely to be below normal sun-Tue. Will
add chance probability of precipitation to the forecast Saturday into Sunday and continue
the previous forecast probability of precipitation through the remainder of the extended
forecast due to low confidence.
Aviation /06z Wednesday through Sunday/...
latest high resolution model data brings rain NE into the dnl/ags
vicinity by 05z...and into the other terminals around 07z. Models
suggest about a 6 hour period of rainfall in the morning...during
which ceilings are expected to decline. Latest guidance generally
keeps visibilities and ceilings in the MVFR category. Once this system and
associated precipitation moves of to our east...expect a lull in
the precipitation and some rise in ceilings. The pressure gradient
will tighten up ahead of an approaching cold front as low pressure
develops to our north. Breezy to windy conditions expected
Wednesday afternoon. The cold front is prognosticated to roll through
around or after 00z Thursday. There may be a band of scattered
showers along the front...with winds shifting to northwest behind the
front. This is just beyond the current 24 hour taf forecast
Extended aviation outlook...breezy conditions may continue through
Thursday morning. No significant impacts to aviation expected
Thursday afternoon through early Saturday. Restrictions possible
with the next system late Saturday and Sunday.