Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1048 am EST Monday Feb 8 2016
a series of reinforcing cold fronts will cross the region through
middle week. High pressure Thursday will give way to an Arctic cold
front late in the week...which could bring some of our coldest
weather of the season into early next week.
Near term /through tonight/...
ahead of an approaching cold front...much of the day will feature
sunshine...a gusty southwest breeze and near normal high
temperatures 60-65f at most locations...highest near the Altamaha
river. By late afternoon...clouds will begin to overspread the
area from the west...and a few showers could push into inland
Meanwhile...an amplifying longwave upper trough easily evident on
water vapor imagery will drive a strong surface cold front toward
the region today. Despite a dry air mass in place across the
region....latest guidance continues to depict strong forcing for
ascent supporting showers developing along/ahead of the cold
front and pushing through the forecast area mainly early this
evening. Per guidance trends...delayed the onset of showers until
late afternoon/early evening then raised probability of precipitation to some degree
across the region especially during the 5-6 PM to 9-10 PM time
frame. Given dry air ahead of the front...capped probability of precipitation at 40-50
percent...but some high resolution guidance including the hrrr
suggests that higher probability of precipitation could eventually be required. In any
case...rainfall amounts exceeding 0.10 inch should remain highly
localized. Also of note...strong forcing for ascent and
steepening middle level lapse rates promoted by the approaching upper
trough could support a few lightning strikes...thus added a slight
chance of thunderstorms to forecasts for the evening. The
potential for any severe weather remains very low...less than 10
percent...but subtle inverted-v sounding signatures and rapid
cooling aloft could support a strong wind gust and/or hail in
an isolated thunderstorm.
Later this evening and overnight...a few showers may linger
through middle- evening along the coast and adjacent coastal
waters...but overall rainfall chances will be on the decrease. The
band of thicker clouds along the front will shift offshore and
mainly scattered clouds will linger through the night. Winds will
remain elevated through the night in the cold advection...consistently
in the 15-20 miles per hour range...so it will definitely not be a radiational
cooling night. As the much colder air rushes in...lows will fall
into the low 30s away from the beaches.
Lake winds...a strong cold front will push across Lake Moultrie this
evening and winds will increase behind the front through the
overnight. Frequent gusts to 25 knots could occur and a lake Wind
Advisory may eventually be needed.
Short term /Tuesday through Thursday/...
Tuesday through Wednesday...a broad and deep layered trough will
evolve over the eastern states while occasional weak cold fronts
and/or surface troughs pass through the area within deep westerly
flow throughout the atmosphere. These fronts/troughs will have
little moisture to work with...but with some perturbations aloft on
Tuesday and low level confluence there might be a few sprinkles in
spots. Otherwise the weather pattern is one that features a
continued supply of cold Canadian air...with deep mixing and a tight
pressure pattern to result in breezy to windy conditions into middle
Temperatures both Tuesday and Wednesday will be similar and around 12-15f
below normal given 850 mb temperatures that area as cold as -8 to -9c.
Tuesday night will be cold with a freeze everywhere inland from the
intra-coastal...but it/ll be even colder Wednesday night with a hard
freeze to occur west of US-17 and freezing temperatures all the way to the
Winds will peak at 20-30 miles per hour with gusts near 35 miles per hour both Tuesday and
Wednesday...probably just short of Wind Advisory thresholds. There
is enough wind both Tuesday night and Wednesday night to generate
wind chills down in the upper teens/lower 20s Tuesday night and into
the teens most communities Wednesday night. This might could
potentially lead to a Wind Chill Advisory for parts of the area.
For Thursday the large scale trough in the east lifts into the
Atlantic with decent height rises and some warm advection. But given
the bitterly cold start to the day our maximum temperatures won't be too much
different than the previous two days...and again well below normal.
Lake winds...colder air moving atop the relatively warmer waters of
Lake Moultrie will likely be strong enough to result in a lake Wind
Advisory Tuesday and again on Wednesday.
Long term /Thursday night through Sunday/...
a quasi-zonal flow will prevail aloft into Friday before an
anomalous eastern trough re-establishes itself this weekend. We
get a break from the colder weather Friday in advance of an Arctic
cold front that sweeps through late in the week and opens the door
for a penetration of what may turn out to be our coldest air of
the season for early next week.
Precipitation chances are slim in advance of the Arctic front late in the
week...and for now it looks to be liquid rather than anything else.
Otherwise it/S dry through the bulk of the extended periods.
At present the consensus of the guidance is that 850 mb temperatures will
plunge to as cold as -6 to -10c Saturday...-10 to -14c Sunday as a
1040 mb or greater high builds out of the northern Great Plains. Our
forecast might not be cold enough...but for now we have temperatures as
much as 15-20f below normal and night time lows as much as 10-15gf
below seasonal levels.
Aviation /15z Monday through Friday/...
low probability for brief flight restrictions in showers and even
isolated thunderstorms this evening. Otherwise...VFR through Tuesday.
SW and west winds will become stronger and quite gusty late this
morning into tonight...with the highest winds reach around 25-30
knots in advance of a cold front that moves through this evening.
Extended aviation outlook...VFR conditions will prevail.
this afternoon...as a strong cold front approaches the region
from the northwest the pressure gradient will tighten and southwest
winds will ramp back up into the Small Craft Advisory range
through the afternoon for all marine areas. Advisories go into
effect through the afternoon with differing start times and
frequent gusts to 25 knots are expected...with even some 30 knots gusts
possible over the SC waters.
Tonight...winds will continue to ramp up and become more west-
northwest with time. High end 25-30 knots Small Craft Advisory
conditions will be widespread through the night as colder air rushes
in behind the front. In fact...there is a chance for marginal gales
over the outer Georgia waters tonight. Confidence isn/T high enough
to hoist a gale watch...though subsequent forecast updates may need
to eventually go with a Gale Warning for a period of time.
Regardless...hazardous marine conditions will continue through the
Tuesday through Wednesday...a deep trough of low pressure will
supply the coastal regime with a continued influx of colder air and
a tight pressure pattern...resulting in a long duration of elevated
winds and seas. We/re easily looking at small craft advisories on
all waters...but indications from sounding profiles support the
potential for gales and this will be included in the hazardous
Thursday through Saturday...much quieter conditions are anticipated
as weak high pressure develops into early Friday...allowing for
winds and seas to remain below any advisory criteria. But any
improvement is limited as winds and seas will climb again behind an
Arctic cold front late in the week...perhaps again resulting in
advisory conditions for the weekend.
Marine...Small Craft Advisory from 2 PM this afternoon to midnight EST
Tuesday night for amz330.
Small Craft Advisory from 4 PM this afternoon to 5 am EST
Thursday for amz352.
Small Craft Advisory until 5 am EST Thursday for amz350.
Small Craft Advisory until 11 am EST Thursday for amz374.
Small Craft Advisory from 6 PM this evening to 5 am EST
Thursday for amz354.