Scientific Forecaster Discussion

NWS Discussion
			
				area forecast discussion 
National Weather Service Louisville Kentucky 
1251 PM EDT Sat may 25 2013 


..updated aviation discussion... 


Forecast update... 
issued at 1225 PM EDT Sat may 25 2013 


Current forecast remains on track through the afternoon, although 
have made a few minor tweaks. The most extensive cloud cover will 
continue to track southeast along a line from Louisville to London, 
Kentucky. Areas to the east of this line will see partly to mostly cloudy 
skies through the remainder of the day and temperatures will likely 
be held to the upper 60s or around 70. Southwest of this line, skies 
should stay mostly clear, where solid mid 70s and maybe a few upper 
70 degree readings will be possible. 


Upstream radar returns continue to fall apart as they enter the 
Wabash and Ohio River valleys. With dry low levels in place across 
the County Warning Area think any returns over our area will be virga. Will continue 
to leave any light rain chances out of the forecast until this 
evening and overnight when deeper moisture arrives from remnant mesoscale convective system 
over the upper Midwest. 


&& 


Short term (now - sunday)... 
issued at 300 am EDT Sat may 25 2013 


Surface high pressure ridging in from the north will shift very 
slowly to the east through Sunday. Aloft the region will remain in 
northwesterly flow through this period. 


Today will start out on the cool side with temperatures in the 40s 
in most locations, with a few upper 30s in sheltered areas possible. 
Some valley fog is showing up on area webcams this morning. This 
should dissipate quickly once the sun rises. Today should be dry 
across the area. A few models are trying to develop some 
precipitation this afternoon over northern portions of the area. 
However, with very dry air aloft, it looks like the moisture 
streaming in will mainly enhance cloudiness. Some virga may be 
possible as well. 


Chances for some measurable precipitation increase tonight and 
tomorrow, though it still does not look to be widespread. The 
atmosphere will become more saturated by tonight and a couple 
of weak waves will move southeast through the flow aloft. However, 
am still not really certain as to how much precipitation we will see 
through this period. Thunderstorm chances look fairly limited as 
soundings indicate a decent cap will remain in place at least Sunday 
morning. Will only mention isolated thunderstorms on Sunday. 


Temperatures today will range from the upper 60s in the northeastern 
portions of the forecast area to the mid 70s near the Tennessee/Kentucky border. 
Lows tonight will be a bit warmer in the lower 50s. Tomorrow's highs 
will top out in the lower to mid 70s areawide. 


Long term (sunday night - friday)... 
issued at 317 am EDT Sat may 25 2013 


Sunday night through Monday night... 


Surface warm frontal boundary will be located somewhere across the 
Ohio Valley at the start of the forecast period. With a 
northwesterly flow aloft, several mid-level waves will likely move 
down along the upper trough axis. These waves will likely lead to 
several rounds of mesoscale convective system activity passing close to the region. The 
models still have a large spread across the region with the American 
GFS and NAM being more on the wetter side of the guidance envelope 
and the European trending more drier. For now, plan on keeping 
isolated to scattered storm chances in for Sunday night and into 
Monday. Still does not look to be a washout by any means, but the 
best threats of rainfall would likely be more favored over northern 
areas. Surface warm front will slide to the north of the region 
Monday night ending the threat of rainfall. Lows Sunday night will 
be in the mid-upper 50s in the north with upper 50s in the south. 
Highs Monday look to warm into the upper 70s to around 80 in the 
north and lower 80s in the south. Lows Monday night will cool into 
the upper 50s to around 60. 


Tuesday through Friday... 


Not much change to the ongoing forecast through this portion of the 
forecast period. The latest suite of deterministic and ensemble 
guidance continues to show relatively good agreement with the 
overall synoptic pattern. All of the guidance agrees that a 
strengthening area of high pressure and ridging aloft will develop 
over the eastern US. With a strong high pressure system anchored 
over the western Atlantic, we should see a good, sustained southerly 
fetch coming north off of the Gulf. With the good southerly flow 
and plenty of insolation, it will certainly feel like Summer around 
the Ohio Valley as temperatures warm into the middle to upper 80s. 
Generally went close to multi-model consensus for temperatures here, 
but given the strength of the ridging and high sun angles, the 
models...in particular the statistical guidance is probably lagging 
on temperatures a little bit. So it would not be out of the 
question that an increase in Max temperatures may be required with 
subsequent forecasts. Overnight lows through the period will be in 
the upper 60s to around 70. 


&& 


Aviation (18z taf issuance)... 
issued at 1251 PM EDT Sat may 25 2013 


VFR conditions are forecast through this taf period, although will 
have gradually lowering ceilings through the late afternoon and 
evening hours. Broken ceilings (~10k feet) will overspread sdf/bwg 
by 4-5 PM EDT, and will gradually lower to ~5k feet around midnight 
EDT tonight. Meanwhile, Lex will see an already broken ceiling 
gradually lower as well. There may be some sprinkles or light 
showers falling around midnight or after at the taf sites, however 
expect no impacts to flight operations at this point so will only 
mention vcsh. Ceilings around 4-6 k feet will linger through the end 
of the forecast with scattered rain showers also possible 
throughout. Surface winds will remain light and variable with any 
noticeable gradient wind likely out of an easterly direction. 


&& 


Lmk watches/warnings/advisories... 
in...none. 
Kentucky...none. 
$$ 




Update...........bjs 
short term.......eer 
long term........mj 
aviation.........Bjs