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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
247 am EST Sat Nov 22 2008 


Synopsis... 
cool high pressure will continue over our region through the 
weekend. As the high moves off the Carolina coast Sunday and 
Monday...a more southerly flow will warm temperatures a bit ahead of 
the next cold front. This front should cross our area Monday 
night...followed by high pressure again through Thanksgiving. 


&& 


Near term /through tonight/... 
high pressure will build into the region today. High clouds will be 
on the increase...especially over the NC zones...ahead of a 
weakening short wave...but that/S about the only feature of note. 


The short wave will pass just north of the region tonight. The NAM 
and GFS have good q-vector convergence and some upward vertical velocity/S with the 
low...but the lowest 10kft of the atmosphere are so dry that the 
only thing we should see is a little virga. It will be another cold 
night...though the high clouds and modest recovery in the low level 
thickness should keep mins 5 degree or so warmer than this morning. 


&& 


Short term /Sunday through Tuesday/... 
as of 205 am Saturday...dry/cool weather will continue through 
Sunday night...as high pressure remains largely in control. 
However...most of the area should find itself on the backside of the 
surface high by Sunday evening...so some slight modification to the 
airmass can be expected. 


Overnight Sunday...a SW trough moving out of the Southern Plains 
combined with an upper low diving out of the Canadian prairie will 
carve out a substantial lw trough across the eastern states by the 
end of the period. The associated cold front will cross our region 
on Monday. Deep layer forcing and moisture advecting around the 
periphery of the surface ridge should be sufficient to warrant 
likely probability of precipitation across the mountains...with chances to the east. Due to a 
cool start to the day...and the very dry airmass that will be in 
place ahead of the front...p-type will be a bit of a concern across 
the mountains at the onset of precipitation. However...it appears that precipitation 
should begin late enough in the day that any wintry mix should be 
relatively brief. 


Gusty northwest winds along with strong cold advection will result 
in yet another round of northwest flow snow across the mountains 
beginning Monday night and continuing through at least Tuesday. 
Based on the anticipated duration and the coldness of the airmass... 
this could be the most significant event of the season thus far. 


&& 


Long term /Tuesday night through Friday/... 
as of 2 am Saturday...the period begins 00z Wednesday with a well defined 
surface cyclone making its way NE over New England and well past our 
area. Latest 00z long range model runs continue to show some return 
flow moisture along the NC/tenn border counties and generate some 
light quantitative precipitation forecast for about the first 12 hours of Wednesday. With temperatures well below 
freezing during this period...I kept a solid chance of snow showers 
for the northernmost counties. Moving into Thursday...an amplified surface 
ridge slowly pushes its way across the central Continental U.S. And eventually 
builds over the Carolinas by the end of the week. By day 7...the 
models depict another low forming over the Southern Plains with the 
European model (ecmwf) being more aggressive with its development at this time. Both 
models have slowed the development of this feature down with respect to to the 
previous runs. So I reduced probability of precipitation to just a slight chance for the 
later part of Friday with low level moisture values not increase until afterwords. 
Temperatures were tweaked a bit in order to emphasize what looks to be 
diminished cloud cover on Thursday and Friday resulting in a slightly more 
diurnal pattern. So...maximum temperatures were bumped up a degree or two and 
min temperatures were lowered by the same amount. 


&& 


Aviation /08z Saturday through Wednesday/... 
a large ridge of high pressure will settle into the region today. 
Winds will either be calm or light out of the north this morning. By 
afternoon most sites should develop a light SW wind...though winds 
should stay out of the north-northwest through the day at kavl. 


Outlook...VFR conditions are expected across the region Sat night 
through sun. As high pressure moves off the coast...a cold front will 
move through the area Monday with a chance of showers and associated 
ceiling/visibility restrictions. Gusty winds likely behind the front through 
the day on Tuesday...with possible MVFR conditions at kavl into the early 
part of the day. 


&& 


Fire weather... 
relative humidity red flag warning criteria continue to look like a slam dunk today 
in NE Georgia and the warning will be kept in effect as is. Relative humidity/S will 
also fall to between 18 and 23 percent across much of the rest of 
the forecast area...but both NC and SC require 30 miles per hour wind gusts in order to 
meet criteria...values we won't be close to this afternoon with a 
sprawling high overhead. 


&& 


Gsp watches/warnings/advisories... 
Georgia...red flag warning from 9 am this morning to 7 PM EST this 
evening for gaz010-017-018-026-028-029. 
Fire Weather Watch Sunday afternoon for gaz010-017-018-026-028- 
029. 
NC...none. 
SC...none. 


&& 


$$ 
Synopsis...deo 
near term...McAvoy 
short term...jdl 
long term...jpt 
aviation...McAvoy 
fire weather...McAvoy