Weather

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fxus63 kjkl 080701 cca 
afdjkl 


Area forecast discussion...corrected 
National Weather Service Jackson Kentucky 
300 am EDT Monday Sep 8 2008 


Short term.../today through Wednesday/...updated 


At 2 am high pressure was centered over southern Ohio. This should 
help keep the area dry today. Model soundings indicate any convection 
that fires today in the higher terrain should be east of our County Warning Area. 
Soundings over our County Warning Area show some capping...and convective temperatures are 
higher than to the east. Moisture begins to increase tonight ahead of 
an approaching cold front. Low level jet also begins to kick in. 
Decent elevated instability is also evident...with showalter indices 
dropping to around -4. Increased probability of precipitation to high chance...especially 
late tonight...with all of these factors in mind. Strong elevated 
thunderstorms will be possible. Also depicted higher wind speeds on 
the ridge tops tonight with low level jet. Tuesday the cold front 
should be slowly crossing eastern Kentucky. Went with likely probability of precipitation 
with the combination of moisture...dynamics...and instability across 
the area. Preferred a solution closer to the WRF and srefs...which is 
slower than the GFS with frontal passage. A few strong storms will be possible 
again as the front moves through. Lingered probability of precipitation into Tuesday 
night...with the highest in the southeast...and dry in the northwest 
portions of the County Warning Area. Should be a good moisture and temperature 
gradient across the County Warning Area Tuesday night...with drier and cooler air 
working into the northern portions. Model soundings show some cooler 
low level air moving in on Wednesday...and went a little closer to 
sref 2m temperatures than other guidance. There is still some lingering 
moisture in the far southeast on Wednesday...and carried a 20 probability of precipitation in 
that area. Removed probability of precipitation from the rest of the area. For temperatures...used a 
blend of h10-800 mb schemes and 800 mb temperatures for today...and at or a little 
above raw 2m sref temperatures Tuesday through Wednesday. Also made 
adjustments for local terrain effects. 


Long term.../Wednesday night through Sunday/...updated 


Made a few minor adjustments in the early portion of the long term 
period. Removed probability of precipitation from Wednesday night with models in better 
agreement keeping precipitation south and east of the area. Models also 
showing an increase in instability on Thursday...and added some 
thunder to the forecast. Also adjusted temperatures down a little on 
Thursday...and up a little for Thursday night with increased moisture 
creating less of a diurnal temperature difference. Plenty of uncertainty 
still exists in past Thursday...and no changes were made at this time. The 
rest of the earlier extended forecast discussion is below. 


The next question past Thursday is how quickly warm air advection 
will bring a return of moisture...especially deep moisture. The European model (ecmwf) 
is persistent at bringing it back over the area on Wednesday night. 
The GFS is persistent in holding deeper moisture off until Thursday 
night or Friday. Have continued to use minimal probability of precipitation of 20 percent 
Thursday through Thursday night as a compromise. 


By Friday...the GFS and European model (ecmwf) do not agree at all on the timing of 
upper level features and a surface low which sends a cold front 
south toward US. Despite this...both models do indicate deep 
moisture present in the local area in the warm air advection pattern 
along and ahead of the approaching cold front. We then stay in or 
near the deep moisture through Sunday. Hurricane Ike is another big 
variable which also puts a lot of uncertainty in the forecast. 
Various model runs and GFS ensemble members show a huge range of 
possibilities. It may bring precipitation either directly...or indirectly 
through an increased supply of moisture as it is eventually sheared 
apart. Any influence is likely to be during or near next weekend. In 
light of all this have included chance probability of precipitation for the Friday through 
Sunday period. Think there will likely be some rain during this 
time...but at this point it is just impossible to nail down when 
higher probability of precipitation would be appropriate. 


&& 


Aviation.../06z to 06z/ 


The only concern for aviation interests this period will be the 
potential for MVFR and IFR br at the taf sites over the next couple 
of hours and through dawn. With the sunshine of yesterday expect a 
drier boundary layer to keep the fog from becoming dense at all but 
the deeper river valleys. This fog will then burn off quickly Monday 
morning with just a smattering of high and middle level clouds. Winds 
will be light and variable through Monday morning before switching to 
the south at around 5 kts for the afternoon. 


&& 


Jkl watches/warnings/advisories...none. 


&& 


$$ 
Short term...wjm 
long term...hal/wjm 
aviation...greif