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Area forecast discussion...updated 
National Weather Service Jackson Kentucky 
1135 am EST Sat Nov 21 2009 


Short term.../the rest of today/...updated 


A shortwave over the southern Great Lakes and upper Ohio Valley continues 
to move east...with ridging over the southeastern states and to the 
west of a trough in the Southern Plains over the Desert Southwest. At 
the surface...high pressure was centered over the middle Ohio Valley/ 
appalachian region. Middle and high level moisture has also decreased 
over the past few hours per WV imagery and this is leading to little 
in the way of cirrus at this time...especially north of the hal Rogers/Kentucky 
Highway 80 corridor. Outside of some stratus/stratocu moving through 
the Bluegrass counties...skies are mostly sunny to sunny underneath 
the cirrus free or thin cirrus. 


With this in mind...opted to decrease cloud cover based on this 
recent trend as cirrus is not expected to increase or thicken that 
much this afternoon as compared to present. With some spots a degree 
or two colder the first couple of hours after sunrise than what was 
earlier anticipated...these two should more or less balance each 
other out. The previous forecast highs still look on track and no 
changes were made there as forecast 875 mb temperatures suggest highs of 
about or within a couple of degrees of 60 with mixing. 


The previous short term forecast discussion follows... 


/today through Monday/ 


Models solutions are in reasonable agreement with evolution of upper 
air pattern. Weak short wave passing through the Great Lakes region 
will continue to track eastward. A more significant low passing 
through Texas will take aim at eastern Kentucky...passing through as an 
open wave by late Sunday or Sunday night. Model trends have been 
slower and weaker with this feature with respect to our weather. This 
system pulls off to the northeast by the end of the period. At the 
surface...low pressure center over the Gulf morphs into nothing more than 
an inverted trough over our area in response to opening wave 
traversing the Tennessee Valley region Sunday. For isc grids...leaned more 
towards the NAM for the first 24 hours...thereafter moving closer to 
a blend of the GFS and European model (ecmwf) solutions for the remainder of the 
period. 


These latest trends have a significant affect on sensible weather... 
particularly with respect to probability of precipitation and precipitation. In general had to 
trend lower with probability of precipitation through the period...and decrease quantitative precipitation forecast totals. 
Otherwise...only made some tweaks to elements to come into line with 
latest thoughts. 


Long term.../Monday night through Friday/ 


Models have been all over the board with respective surface solutions. 
However...models continue to show decent agreement with overall 
upper level pattern evolution. Weak short wave energy tracks quickly 
through the Ohio Valley region Monday night...just as a more potent 
low pressure system drops out of the intermountain region into the 
plains. This system moving out of the plains will be our next 
weather maker...most likely affecting our area from middle week through 
the Thanksgiving Holiday. The European model (ecmwf) has a slower...more southerly 
track than the GFS and swings a frontal boundary through our area 
late Wednesday...about 24 hours slower than earlier runs. The GFS 
has trended slower as well...with this front moving through our area 
Tuesday night into Wednesday morning...or about 12 hours slower. Made 
appropriate changes to the forecast to account for these latest 
trends...though confidence is overall scenario of events is low at 
best. Most interestingly...both the GFS and European model (ecmwf) show a significant 
band of wrap around moisture affecting our area behind the main 
systems departure on Thanksgiving. The GFS column profiles support 
the potential of some snow late Thursday into Thursday night. 
However...the European model (ecmwf) is quite a bit warmer. At this time preferred the warmer 
European model (ecmwf) solution and will leave any mention of the white stuff out of 
the forecast. 


&& 


Aviation.../18z to 18z/...updated 


Aside from patchy MVFR fog in the deepest valleys between 8z to 13z 
in locations such as 1a6...VFR conditions will be the rule through 
the taf period. High pressure is expected keep the area clear below 
12k feet through at least 15z near the Tennessee and Virginia border...and likely 
through the end of the period at the taf sites and north. As for the 
taf sites...sme could possibly drop to the upper end of the MVFR 
range with br near sunrise. Although sme and loz will probably have a 
period of calm winds overnight...winds are expected to generally be 
light through the period. The prevailing direction will be northeast 
through 12z...and then east through the end of the period. 


&& 


Jkl watches/warnings/advisories...none. 


&& 


$$ 


Short term...ray/jp 
long term....ray 
aviation...jp