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fxus61 Kiln 030540 
afdiln 


Area forecast discussion 
National Weather Service Wilmington Ohio 
1240 am EST Wednesday Dec 3 2008 


Synopsis... 
high pressure will build into the Ohio Valley briefly tonight and 
Wednesday. A cold front will move across the region Wednesday 
night bringing the chance for rain...possibly ending as light snow 
showers early Thursday as colder air rushes in. Below normal 
temperatures are expected Thursday into the weekend. 


&& 


Near term /until 6 am this morning/... 
the latest RUC surface analysis indicates high pressure centered over 
the southeastern Continental U.S.. a cold front extends across the upper MS valley 
from a low over the southern Hudson Bay. Locally...the Ohio Valley 
remains under high pressure which has built in from the south. At 
the mid-levels...as a short wave exits the mid-Atlantic...a deep 
positive tilted 500 mb trough is beginning to dig into the northern plains. The 
Ohio Valley is under wrly flow in between the two features. Temperatures 
this evening ranged from the middle to upper 20s...with cirrus 
approaching the County Warning Area from the northwest and a SC deck exiting the eastern 
County Warning Area. 


Overnight...skies will be clear or mostly clear across the County Warning Area as 
high pressure remains the dominant feature. The challenge this 
evening is determining overnight lows with warm air advection and mostly clear 
skies. It appears that many areas across the western half of the County Warning Area 
have already reached their overnight lows...and will see a gradual 
increase in temperatures by sunrise. For the eastern County Warning Area...and especially the 
southeastern zones...temperatures should drop into the low to middle 20s before 
recovering into the upper 20s by dawn. Adjusted temperatures down a few 
degrees to account for clearing and latest temperature trends which are 
running below guidance...especially across the southeastern County Warning Area. 


&& 


Short term /6 am this morning through Thursday night/... 
middle level ridging will be centered across Ohio Valley Wednesday. With continued 
srly flow funneling north into region between surface hi and appchg frontal 
boundary...will see winds become gusty particularly during the afternoon. 
Both GFS/NAM solutions indicating 50-55kt 850 low level jet rotating north ahead of 
the cold front and with sunshine through the first half of the 
day...boundary layer mixing should enable some of this to make it to 
the ground. Clouds will slowly increase from northwest to southeast during the 
afternoon as front approaches and surface hi shifts east into the western Atlantic 
Ocean. Model consensus favoring a stronger surface hi located over the 
middle Atlantic...resulting in a slower appch to frontal boundary Wednesday evening. 
Have brought low chance probability of precipitation into northwest forecast area during the second half 
of the afternoon but if current slowing trends continue to be exhibited 
on the models...Wednesday could end up being dry across entire forecast area. 


Model soundings indicating subsidence across boundary layer slow to depart Wednesday 
evening as low level winds back to S/southeast for a period. Appears forecast area 
will end up being in the split zone between surface low over the Great Lakes 
and surface low across the lower Mississippi Valley. Much of the deeper 
forcing will remain displaced north and south of the region as a 
result Wednesday night. Low level conv along and immediately behind frontal 
boundary appears to be the main forcing for precipitation across the forecast area. 
Will see widespread light -ra overspread forecast area from west to 
east during the evening and into the overnight. Have leaned towards 
12z GFS/European model (ecmwf) solution which shwng a quicker frontal passage late Wednesday night. 
Increased to Cat probability of precipitation as a result. Most of the models continue to 
be slower with crashing boundary layer thicknesses Erly Thursday...with 
result that rain will be main precipitation type for majority of this 
event. Lower levels really do not become supportive for -shsn until 
between 06 and 12z and only for a short time as deeper moisture 
associated with front already pulling away to the east. Have placed 
light accums across northwest 1/2 forecast area to the tune of a few 
tenths...but not overly confident that will see much more than a 
dusting if that. 


Passage of the cold front will usher in a reinforcing shot of 
Arctic air for Thursday as deep upper trough settles across Great Lakes/Ohio Valley. 
Drier air funnels into region fairly quickly in wake of the front 
and low level winds never really align properly to support lake effect 
induced -shsn for any length of time into region. Could see a few 
flurries but otherwise expect a mixture of clouds and sun as 
increasing amts of low level cold air advection induce plenty of SC through the day. Surface 
hi will attempt to build in Thursday night...but expect at least some 
clouds to linger all night as weak disturbance undercuts surface hi and 
drops into the middle Mississippi Valley and middle level shortwave energy dives 
across lower Great Lakes. 


Temperatures...combination of strong srly low level flow should allow for a 
nice rise in temperatures for Wednesday...ranging from the m40s north into the 
l50s across far southern forecast area. Felt mavmos guidance was a bit too 
aggressive with temperatures though and ended up undercutting by 1-2 degree. 
Temperatures will fall slowly ahead of the front Wednesday evening...with a more 
aggressive drop in temperatures with frontal passage during the second half of the 
night. Have allowed for a small rise in temperatures Thursday morning...with 
temperatures falling slowly in the afternoon as cold air advection deepens Arctic airmass 
across Ohio Valley. Very possible though that temperatures remain steady Thursday 
morning before falling with many locations remaining below 30 degree all 
day. Undercut guidance for temperatures both Thursday/Thursday night. 


&& 


Long term /Friday through Tuesday/... 
Friday...temperatures will remain well below normal despite west-southwest flow 
and dry weather as high pressure moves east of the region. Looking 
at the GFS and European model (ecmwf)...snow showers should stay just west of the 
forecast area overnight Friday night in advance of an approaching 
clipper system. 


For Saturday...high temperatures should range from the lower to upper 30s 
for the most part as the disturbance sweeps across the lower Great 
Lakes. Although low level thickness suggest the precipitation should stay 
all snow even south of the Ohio River...with the SW flow and surface 
temperatures mostly somewhat above freezing...some rain may mix in at 
times. Snow showers will linger Saturday night behind the 
reinforcing shot of colder air. Any accumulations should be rather 
light. 


Sunday...scattered snow showers will linger in the northwest flow over the Great 
Lakes region...generally with better coverage north of I-70. High 
pressure moves in briefly Monday...with a respite from snow 
showers. Temperatures remain decidedly below normal. 


Monday night into Tuesday...there are significant model differences 
as one would expect that far out. Another system dropping southeast from 
the plains interacts with a southern wave...which is particularly 
pronounced with the European model (ecmwf). Conditionally...depending on the 
track...a wintry mix...rain and/or snow will be possible at times. 


&& 


Aviation /06z Wednesday through Sunday/... 
surface high pressure will push off to the east through the 
morning hours allowing for a developing warm air advection pattern. This will 
lead to a gradual increase in mainly high clouds through the 
morning hours. As better low level moisture begins to advect in 
through the afternoon hours...expect ceilings to drop into a low VFR 
deck through late afternoon. Cold front will push into the area 
tonight and this will lead to some light rain showers and MVFR 
ceilings toward the end of the taf period. 


Outlook...MVFR ceilings likely Thursday along with scattered -shsn. Brief 
periods of MVFR/IFR visibilities will be possible with -shsn. MVFR ceilings and 
visibilities will also be possible Sat through sun. 


&& 


Iln watches/warnings/advisories... 
Ohio...none. 
Kentucky...none. 
In...none. 


&& 


$$ 
Synopsis...Ryan 
near term...woodrum 
short term...Ryan 
long term... 
aviation...jgl 

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