784 
fxus63 klmk 180104 
afdlmk 


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


..forecast update... 


Forecast is in good shape. We will make some minor adjustments 
tonight to the cloud cover as the current forecast is a little 
optimistic. No other changes planned. 


Short term (tonight and thursday)... 


Middle level pattern is characterized by two upper lows over the 
eastern Continental U.S.. 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. 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 overnight will be finally clearing 
out from north to south 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)... 


Thursday night through 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 (00z taf issuance)... 


Late afternoon and evening satellite pictures indicated clearing 
skies across Illinois and Indiana. This clearing trend will continue 
to work south overnight. So VFR clouds should clear by 08z at all 
locations. We will mention MVFR visibilities at bwg in the morning with the 
clear skies and calm winds. Surface and low level winds should 
remain from the north through most of the forecast period. 


&& 


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


$$ 


Update.........Ja 
short term.....Bjs 
long term......jsd 
aviation.......ja