292 
fxus63 klmk 171858 
afdlmk 


Area forecast discussion 
National Weather Service Louisville Kentucky 
258 PM EDT Wednesday Mar 17 2010 


Short term (tonight and thursday)... 


Middle level pattern is characterized by two upper lows over the 
eastern Continental U.S....with central Kentucky in a No Mans Land of 
synoptic features tonight. The first system across the Gulf states 
should eject eastward toward the Atlantic coast overnight...with 
the only effect on sensible weather being a few cirrus flowing 
overhead from south to north. The second system currently over the 
Kansas/Missouri/ Oklahoma/Arkansas borders will continue to dig 
southward and phase/absorb into the parent low overnight. This 
will allow for upper level ridging...along with surface high 
pressure to move over southern Indiana/central Kentucky tonight 
and tomorrow. 


The result on sensible weather through the forecast period will be 
finally clearing out from north to south overnight and cool low 
temperatures in the middle to upper 30s. A few locations in the 
southern County Warning Area could hold onto 40 degrees as sky cover doesn/T look 
to clear out until just before dawn. Thursday looks to be a 
beatiful day...with any lingering low level moisture in the south 
quickly departing. Expect sunny skies with highs generally in the 
middle 60s. Generally went at or just above NAM/GFS guidance for 
highs tomorrow and at or just below guidance for tonights lows. 


Long term (thursday night - wednesday)... 


A split flow in the upper jet stream is forecast across the Continental U.S. 
At the beginning of the extended. The southern stream will lie 
across the Gulf of Mexico. A trough over Florida late Thursday 
will move well out into the Atlantic by early Saturday. The 
northern jet will lie along the US Canadian border. 500mb ridging 
across the Midwest to the south of this northern jet will bring 
mild temperatures Friday into Saturday across the western Great 
Lakes and the lower Missouri Valley. 


For our neck of the Woods...subsidence associated with this 
building 500mb ridge will bring mostly clear skies and mild 
temperatures Thursday night through probably the first half of 
Saturday. Light north winds will become calm early Friday and then 
become light southerly Friday as the axis of a surface ridge 
slides southeast across the Ohio River. Expect highs well into the 
middle 60s Friday. 


A vigorous trough associated with the northern stream of the jet 
will amplify over the northern rockies late Friday. By Saturday 
evening a deep trough is forecast to eject over the plains states 
and lead to cyclogenesis across Missouri or Arkansas. The most 
recent operational GFS and European model (ecmwf) have actually diverged on both the 
development of the surface low and the timing of the associated cold 
front as it moves towards the lower Ohio Valley. Feel that the 
models do not have a great handle early Saturday on the complex 
interaction between the northern trough and the southern jet over 
the southern rockies. 


The operational 12z GFS is well on the fast side of the GFS 
ensembles...which in terms of timing is closer to the European model (ecmwf). Prefer 
the European model (ecmwf) which attempts to partially cut off of this deep trough 
from the established westerlies over the upper Midwest. This more 
elongated trough is forecast to move slower than the GFS. 


So...using the slower European model (ecmwf)...will forecast a pre-frontal band of 
showers with possibly some embedded thunderstorms to move from west 
to east across our area late Saturday or early Sunday. Moisture 
return ahead of this band of showers is not expected to be 
robust...and will probably also be limited by an expected line of 
thunderstorms late Saturday across the western Gulf states. 
However...dynamics will likely compensate for this. Will continue 
likely probability of precipitation for late Saturday through Sunday morning. 


Much colder air will arrive behind this front. However...the 
aforementioned trough is forecast to lift quickly north of the Great 
Lakes...so cool temperatures will likely not last past Monday. High 
temperatures Sunday will likely depend on the exact timing of the 
front. However...high temperatures Monday through Wednesday should 
moderate from the lower 50s into the Lower Middle 60s under partly 
cloudy skies. 


&& 


Aviation (18z taf issuance)... 


Overcast stratocu deck will slowly erode from east to west for the 
rest of this afternoon...with instability cumulus developing where 
clearing occurs. This will result in sdf/Lex hanging on to ceilings 
between 5-6 k feet until around 6 to 8 PM. Thereafter...any 
remaining clouds should quickly dissipate due to loss of diurnal 
heating. Bwg will hold onto ceilings for much of the night and scatter 
out toward dawn. This will provide a brief opportunity for some 
reduced visibilities but will hold off on any MVFR categories until 
timing of clearing...if any...becomes more confident. Thursday 
should be a clear day with any noticeable gradient wind out of the 
north or northeast and generally less than 5 to 7 miles per hour. 


&& 


Lmk watches/warnings/advisories... 
Kentucky...none. 
In...none. 
&& 


$$ 


Short term........bjs/dk/11 
long term.........Jsd 
aviation..........bjs/dk/11