946 
fxus62 kcae 212317 
afdcae 
area forecast discussion 
National Weather Service Columbia SC 
617 PM EST Sat Nov 21 2009 


Synopsis... 
a low pressure system in the northwest Gulf of Mexico will move 
slowly northeast to the Florida Panhandle tonight...then reform 
along the Carolina coast Sunday night. High pressure will wedge 
into the Carolinas from the north. This pattern will bring clouds 
and rain to the area through Monday. 


&& 


Near term /through tonight/... 
closed upper low over East Texas will Delaware-amplify overnight as it 
moves northeast. Surface low over the northern Gulf of Mexico this 
afternoon will slowly move east as high pressure wedges into the 
Carolinas from north. Skies expected to become cloudy tonight as 
isentropic lift begins. Rain spreading north from the Gulf Coast 
states may reach the Savannah River area by daybreak Sunday. Went 
with consensus lows...ranging from the middle 40s north to near 50 
south. 


&& 


Short term /Sunday through Tuesday/... 
models finally in agreement with strong isentropic lift over the 
area Sunday afternoon into Sunday night. Weakening short wave 
moving out of Texas tonight will cross Georgia into the Carolinas 
Sunday night. Low pressure developing on an inverted trough off 
the SC coast. Kept categorical probability of precipitation for Sunday into Sunday night. 
Rainfall amounts ranging from one half inch to around one inch. 
The surface low will move away from the coast Monday with rain 
chances decreasing. Kept chance of drizzle in for Monday night 
into Tuesday. 


Since wedge pattern expected Sunday through Tuesday...should see 
plenty of clouds. Kept daytime temperatures below guidance. Highs 
in the low to middle 50s (which may be on the high side). Little diurnal 
change in temperatures expected. Lows in the middle to upper 40s. 


&& 


Long term /Tuesday night through Saturday/... 
medium range models depict a series of middle/upper level lows moving 
across the upper Midwest to the eastern Great Lakes and 
southeastern Canada Tuesday night into Saturday. All in all, 
slight upper ridging over the southeast part of the country 
Tuesday is replaced by a large upper trough over the eastern 
United States Wednesday through Friday. Upper trough finally moves 
off the East Coast Saturday. Surface high pressure centered over 
southeastern Canada Tuesday night ridging into the area from the 
north. Surface low pressure crossing the Great Lakes region on 
Thanksgiving day will drag a cold front across the area. Moisture 
appears limited since the best isentropic lift remains south and 
east of the forecast area. Any chance for rain (which is slight) 
looks like Wednesday into Thursday morning. Cool high pressure 
builds in for Friday and Saturday. Will keep the extended forecast 
dry. Seasonably mild maximum temperatures Wednesday and Thursday cool 
a few degrees below normal for Friday and Saturday. Nighttime lows 
in the 40s middle-week cooling to the middle and upper 30s by late next 
week. 


&& 


Aviation /00z Sunday through Friday/... 


High pressure over the Middle-Atlantic States will move offshore as a 
low pressure system over the Gulf of Mexico moves northeast. This 
low will track over the southeast states on Sunday bringing rain with 
MVFR/IFR conditions to the area. The taf period will start out VFR 
with MVFR ceilings developing by around 12z-14z with some sprinkles 
possible by then. Conditions become IFR by late in the taf period as 
precipitation spreads across the region Sunday afternoon. 


Extended aviation outlook...widespread MVFR or IFR conditions will 
continue late Sunday into early Monday as the low pressure system 
moves through the area. Conditions will improve to VFR by Monday 
afternoon as the low moves out of the area. 


&& 


Cae watches/warnings/advisories... 
SC...none. 
Georgia...none. 


&& 


$$