Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
738 am EDT sun Mar 16 2014
surface low pressure will move across the Gulf Coast states today
as a warm front develops just south of the forecast area. Well
below normal temperatures on Monday and Tuesday with unsettled
weather impacting the region today through Tuesday as low pressure
moves across the area and redevelops off the Carolina coast late
Monday. High pressure will build back over the region for midweek
as temperatures moderate through the end of the week.
Near term /through tonight/...
surface low pressure to the west will move eastward today as the
upper level positively tilted trough amplifies with some of the
energy at the base of the trough cutting off over south Texas by
late tonight. A warm front is expected to develop just south of
the forecast area today extending eastward from the surface low.
Increasing deep southwesterly flow ahead of the approaching low is
already resulting in moisture advection off the Gulf northeastward
into the region with isentropic lifting also increasing. Regional
radar already showing widespread rain extending across northern
MS/Alabama and developing over eastern Georgia. Precipitation will
continue to develop along and north of the developing warm front
this morning and move over the forecast area becoming widespread
by this afternoon as a 35-40 knot 850mb jet aides in continued
moisture transport while upward vertical motion increases due to
the proximity of a 130 knot upper jet positioned to the northwest
of the forecast area.
Instability forecasts by operational models remains very low across
the forecast area as we remain on the north side of the warm front
in the more stable airmass and widespread rainfall should help
maintain a stable atmosphere this afternoon and evening.
However...very strong wind shear is expected with helicity values
exceeding 500 m2/s2 this afternoon into early evening and if any
instability does develop this would provide a favorable environment
for possible severe weather. Despite the lack of instability...the
0-3km sherb parameter...an indicator of favorable high shear Low
Cape environments...reaches the critical value of 1 during the
18z-03z time frame. Will continue to advertise possible convection
across the southern half of the forecast area and carry very high
categorical probability of precipitation today and tonight as precipitable water values
continue to increase to a peak over 1.5 inches around 00z-03z before
shifting eastward towards the coast.
Temperatures today will be impeded by increasing clouds and
precipitation and will feature a gradient from middle 50s northwest to
middle 60s southeast over the area today. This evening the surface low
approaching from the west will transition across the state and
redevelop as a coastal low off the Carolina coast by 12z Monday.
During this transition strengthening northerly low level flow will
occur and cold advection in the boundary layer will commence. At
this point temperatures should remain warm enough above freezing to
prevent any wintry weather through Sunday night.
Short term /Monday through Tuesday night/...
active weather continues this period with the positively tilted
upper trough moving through the southeastern states culminating in
the development of a coastal low off the Carolina coast which will
shift northeastward away from the area on Tuesday. Leaned toward a
preferred blend of GFS/European model (ecmwf) as the NAM solution continues to be an
outlier showing upper trough become negatively tilted contributing
to a much slower timing and lifting the coastal low northward over
inland eastern North Carolina late Tuesday. The NAM solution has
also continued to be much colder than the other operational models
regarding the lowest levels and surface temperatures...showing
possible freezing rain in the northern midlands on Monday morning
and again Monday night into Tuesday morning.
The upper low at the base of the upper trough will track eastward
across the northern Gulf of Mexico on Monday and Monday night before
opening up and accelerating northeastward across southern Georgia
and eastern South Carolina on Tuesday. Persistent
north-northeasterly low level flow across the area during this
period will keep The Wedge locked into place further supported by
the overrunning of moist southwesterly flow atop the cad layer.
While there is expected to be a break in the heavier precipitation
Monday into Monday afternoon with the main baroclinic zone east of
the forecast area...areas of drizzle are possible along with patches
of light rain. The next wave of precipitation will move up with the
upper trough Monday night and Tuesday...and expect the best rainfall
to occur across the eastern midlands into the coastal plain where
better deeper moisture will exist. Bumped up probability of precipitation to
categorical/likely Monday and Monday night with decreasing probability of precipitation
Tuesday through the day as the system departs to the northeast.
Temperatures during this period will be well below normal...with
highs some 20-25 degrees below normal with highs on Monday ranging
from the lower 40s northern midlands to middle 50s in the southern csra.
Long term /Wednesday through Saturday/...
little change made to the extended forecast. Generally a dry weather
pattern forecast Wednesday-Friday with surface high pressure building over
the area and zonal westerly flow aloft. Temperatures expected to
moderate during the period back to near or slightly above normal
values by the end of the week. A cold front may move into the
region on Saturday bringing another chance for rain.
Aviation /12z Sunday through Thursday/...
all models indicate VFR at the beginning of the taf period with
conditions deteriorating to MVFR by 15z as the airmass becomes
saturated and rain continues over the taf sites. High confidence
for IFR after 18z with widespread rain and fog. IFR/LIFR expected
to continue tonight as cold air damming develops.
Extended aviation outlook...a prolonged period of rain with IFR/LIFR
conditions into Tuesday as a cold air damming event persists.