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fxus64 khun 120118 aab 
afdhun 


Area forecast discussion...updated 
National Weather Service Huntsville Alabama 
818 PM CDT Sat Oct 11 2008 




Discussion...evening surface analysis shows a large high centered 
across New England and extending southwest through the 
Appalachians. A trough was oriented off the southeastern coast and is the 
surface reflection of a pesky upper low near Savannah. Broken-overcast deck 
of low clouds have been trying to move westward across Georgia and 
into central/northern Alabama this evening...but overall progress has been 
relatively slow so far. Based on most recent trends and latest 
model guidance...expect several more hours of clear to partly 
cloudy skies before clouds begin to thicken from east to west 
after roughly 0900 UTC. 


Temperatures are currently running in the upper 60s to lower 70s with 
dewpoints around 60f. Winds have decoupled across northern/western zones this 
evening...but expect winds to pick up slightly overnight as surface 
gradient begins to tighten. Would not be shocked to see some 
light/patchy fog development but with an increase in low clouds 
and tightening gradient...don't expect it to be a major issue. 
Overall...current forecast in good shape. Have already updated grids 
for evening trends and made minor changes to temperatures and cloud 
cover. Will issue quick update to adjust sky cover wording in text 
products as well. 


&& 


Previous discussion... /issued 623 PM CDT Sat Oct 11 2008/ 


Aviation...weak isentropic lift at 305k associated with a low 
pressure system in Georgia is creating MVFR conditions at this 
time. This will begin pushing west into northern Alabama between 3z and 
6z...and become entrenched after 6z along and west of I-65. This 
will bring temporary MVFR ceilings at khsv between 3z and 6z. Then 
expect MVFR ceilings to become prevailing after 6z at both taf 
sites. Winds and mixing should keep fog from developing. 


Discussion...the upper low parked off the Georgia/SC coast just won't 
go away. It continues to have a profound influence on area 
weather...having pumped quite a bit of low /mid-level cloudiness into the 
area for most of the morning hours...but this has now pushed 
through...and the eastern 2/3rds of the area is now at least partly 
cloudy. A larger area of stratus persists across the I-85 corridor 
and promises to advect into the area later today. 


Forecast for the next few days will hinge upon the impacts of that upper 
low. Models are in good agreement on retrograding the low back along 
the northern Gulf Coast...shearing it apart as it moves westward. Isentropic 
lift and low-level moisture transport forecasts suggest more of the same 
over the next several days...but as we have seen today...that does 
not guarantee overcast conditions. Still believe conditions will be 
mainly mostly cloudy and will increase sky cover grids. Whether any 
of this translates to precipitation remains uncertain...with the GFS and NAM 
showing typical wet and dry biases. Tend to think that lift and 
moisture will not be quite sufficient for precipitation generation...but a 
few sprinkles or a rogue shower certainly cannot be ruled out 
especially in Cullman/Marshall/DeKalb counties. Anticipating the 
increased cloud cover...have trended a degree or two warmer at 
night...and a degree or two cooler during the day. 


Long term...Tuesday through Saturday... 
anomalously strong upper high will build just to our NE for Tuesday 
and Wednesday...resulting in a dry but warm forecast /roughly 5 degrees 
above climo/. By mid-week...a trough from the upper Midwest will 
make a run at breaking down the ridge...and should erode it enough 
to transition to a zonal pattern by late week. At this point models 
diverge sharply...with the European model (ecmwf) bringing in another deep trough 
which cuts off along the Atlantic coast...and the GFS building the 
ridge right back over the Gulf Coast. 


Either way...the front expected to approach the area in the Thursday/Friday 
time frame will not be proceeded by much deep southerly flow...so 
rain chances do not look particularly impressive. There appears to 
be enough for a 20 pop over a couple of periods but this is done 
with low confidence. Have trended with a model blend for 
temperatures...generally staying with persistence...but this could be too 
warm for the European model (ecmwf) solution. 


&& 


Hun watches/warnings/advisories... 
Alabama...none. 
Tennessee...none. 
&& 


$$ 


Discussion...15 
aviation...20