Weather

806 
fxus63 klmk 061002 cca 
afdlmk 


Area forecast discussion...corrected 
National Weather Service Louisville Kentucky 
453 am EST Tuesday Jan 6 2009 


Short term (tda and tonight)... 


Will move the advisory 1 tier of counties farther to the north and 
end it sooner...by 9 am EST. Coordinated with pah and iln. 


Light freezing rain...mixed at times with sleet...has been confined to 
our southern Indiana counties and parts of Oldham...Henry and Trimble 
counties in Kentucky. This should not change much through sunrise...with temperatures 
steady or rising a degree or so. The most prone areas 
(bridges-overpasses) for those counties just south of the 
new advisory area...may develop some brief icing (its 31 degree at 
NWS-lmk)...but the temperature at the present is trending up...as well as 
those across the region with sensible heat flux in progress due to 
precipitation falling from a warmer layer just above the surface. 


Lead shortwave trough/vorticity maximums in southern stream forecast to phase with northern 
stream impulses and approach our forecast area today while lnwv trough axis moves 
into the plains. Stronger shortwave trough prognosticated across East Texas at 00z 
tonight...then forecast to approach and move into our forecast area by 12z Wednesday. 


Quasistnry surface boundary has begun a slight northward drift into the Tennessee Valley 
with wave development noted on the boundary across northern MS into southern 
middle Tennessee. This process will continue today with NAM/GFS indicating a 
deepening trough axis from northern Alabama into eky. With the approach of 
shortwave energy and deepening trough...ascent and low level warm moist 
advection will increase today and rain should become widespread. 


Continued deepening trough of low pressure prognosticated to be across eky/the 
virginias tonight with backlash precipitation-rain changing to or mixing with 
snow from northwest to southeast expected toward sunrise Wednesday. 


Long term (wednesday through monday)... 


Subtle but signigicant differences in models throughout this 
period...especially with respect to relative humidity fields and resultant 
probability of precipitation...and especially over the weekend. GFS has been odd man out 
with digging a 500 mb cutoff low during the weekend over the southern 
rockies and keeping it there for remainder of the forecast time frame 
while other models bring a sharp but open wave east into the central 
U.S. By Monday morning. Have opted to go with the majority solution 
on this and have used European model (ecmwf) as model of preference for this forecast 
period. 


With the above in mind...precipitation lingering Wednesday should end from 
west to east across the area as bulk of moisture races eastward with 
cold front. Trailing stream of higher relative humidity back to northern plains 
will be enough to keep some clouds around...but best dynamics will 
be east of the area when it comes in. As colder air moves in...rain 
snow mix will change over to all snow but with little accumulation. 


Probability of precipitation drop from Wednesday night through Friday...then return Friday night 
and Saturday with next frontal passage...though confidence not great on timing 
at this time due to model disagreements. Sunday and Monday should remain dry. 


No major temperature swings through the period as progressive 
pattern not allowing much time for any Big Warm ups or cool Downs. 
Maximum temperatures mainly in the 40s with mins mainly in the 20s to lower 30s. 


&& 


Aviation (06z tafs)... 


Still a rather messy taf period in store with bwg already in the IFR 
Cat for ceilings...sdf/Lex conditions will decline within the next 4 hours 
into MVFR with IFR in store for these sites near dawn. 


Again chose the 0z NAM for precipitation/temperature guidance. According to model 
soundings...bwg still may see rain with pl mixing in for the next 3 
hours. After which precipitation should remain just rain. For 
sdf/Lex...they both sit above freezing right now...but with dewpoints 
in middle 20s...expect surface temperatures will drop to freezing at onset of 
precipitation. This will allow for a period of freezing rain between about 
7z to 13z at sdf/Lex. After 13z...they will switch to plain rain. 


Conditions at all taf sites will gradually begin to improve tomorrow 
afternoon as the system moves NE. In this taf package have held on 
to IFR ceilings longer through the afternoon. Winds will switch around 
to southeast and eventually SW at the end of the taf period. 




&& 


Lmk watches/warnings/advisories... 
Kentucky...Winter Weather Advisory for Oldham...Henry...Trimble counties until 9 
am EST. 
In...Winter Weather Advisory until 9 am EST. 
&& 


$$ 


Weather.Gov/Louisville 


Short term...Kirkpatrick 
long term....jbs 
aviation.....Aml