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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Monday
• 
• High: 88 °
• Low: 68 °
• Partly Cloudy

• Tuesday
• 
• High: 84 °
• Low: 66 °
• Chance of T-Storms

• Wednesday
• 
• High: 73 °
• Low: 63 °
• T-Storms

• Thursday
• 
• High: 77 °
• Low: 55 °
• Partly Cloudy

• Friday
• 
• High: 70 °
• Low: 50 °
• Chance of Rain

area forecast discussion 
National Weather Service Louisville Kentucky 
642 am EDT Monday may 20 2013 


..updated aviation discussion... 


Short term (now - tuesday)... 
issued at 309 am EDT may 20 2013 


The biggest concern for the early morning hours continues to be 
patchy fog formation, however steady southerly winds will likely 
keep this potential confined to sheltered valleys and spots that 
received rainfall yesterday. Will only keep patchy fog wording in 
the zones for now. Otherwise expect a dry, mostly clear, and mild 
overnight in the mid and upper 60s. 


An upper level ridge axis is in place over the Ohio Valley and will 
remain that way today. Meanwhile, central Continental U.S. Trough and its 
associated features will continue to produce severe weather across 
the eastern plains into the Great Lakes. Will keep the forecast dry 
over our region as there will be no real trigger for convection. A 
couple of concerns Worth noting, however. First of all, forecast 
soundings do not show as much of a subsidence inversion as had been 
forecast in past days. Secondly, the generally uncapped environment 
will be quite unstable as temperatures in the upper 80s and dew 
points in the upper 60s combine with steep low and mid level lapse 
rates. There is potential that differential heating (from upstream 
convective debris) or a remnant outflow boundary (also from upstream 
convection) could set off a few thunderstorms. The higher resolution 
20/00z Storm Prediction Center WRF model shows this, but has not done well over our area 
recently. Anything that is able to go in our environment will likely 
go big due to the instability. After collaboration with surrounding 
offices, have decided to keep the forecast dry as there is a low 
probability of this occurring and coverage is expected to be less 
than 20 percent. Will have to watch for areas of moisture 
convergence and cu development this afternoon. If any storm does go, 
large hail, cloud to ground lightning, and heavy rainfall would be 
the main threats. 


Temperatures are expected to be even warmer today under partly 
cloudy skies and steady southerly flow. The forecast temperature for 
Louisville (90) is expected to fall just 1 degree short of the old 
record (91 set in 1934). A few spots will likely be right around the 
90 degree mark, although the majority of locations will settle for 
the upper 80s. Much will depend on cloud cover, especially if 
upstream convective debris makes it this far east. 


As we move into tonight and Tuesday, the upper level ridge over 
our area will break down as the trough axis moves into the eastern 
plains and upper Midwest. With stronger westerlies aloft and a 
strongly unstable airmass in place, upstream convection is expected 
to survive into the Ohio Valley. Tonight's chances will only be 
across southern Indiana, however by Tuesday much of the County Warning Area will 
have solid storm chances (40-50%). This will begin an active period 
of weather as the associated cold front hangs back to our west for a 
couple of days. Storm Prediction Center has placed areas along and west of a Bowling 
Green to Frankfort line in a slight risk. This makes sense given the 
increase in 0-6 km bulk shear around 25-30 knots and the strongly 
unstable airmass. Multicell clusters with heavy rainfall and cloud 
to ground lightning, along with isolated instances of large hail and 
damaging winds will be the main threats. 


Tonight's temperatures will again be mild in the upper 60s and low 
70s. Tuesday will see a warmup to the upper 80s in most spots. 


Long term (tuesday night - sunday)... 
issued at 306 am EDT Mon may 20 2013 


Thunderstorms will erupt from Illinois to Texas around the beginning 
of the long term and will push east into our region overnight 
Tuesday night. While severe weather looks likely out to our west, 
the storms will become increasingly elevated as they head eastward 
as shown on sounding progs advertising a strong nocturnal inversion 
setting up around 925hpa. So, while the low level jet does crank up 
from Memphis to Indianapolis overnight, most of those winds should 
stay off the surface. Wet bulb zeroes look to be a little too high 
for anything more than isolated marginally severe hail. The best 
chance for any strong storms will be along and west of Interstate 65. 


Wednesday remains complicated. Surface low pressure will move from 
Illinois to Michigan and will drag a cold front into the Mississippi 
Valley. We'll be under the entrance region of the upper jet and 
additional convection is likely. However, how strong the storms 
will be is still a question mark. Surface based instability may be 
hampered depending on how much cloud and shower activity there is 
from the previous night's rain. Total totals in the upper 40s and 
sweat index around 300 are marginal for any severe storms (and are 
actually lower on Wednesday than Tuesday night). Wet bulb zeroes do 
lower some on Wednesday, though, supporting a little more of a hail 
risk. 


Scattered storms will remain in the forecast Wednesday night and 
Thursday until the aforementioned low pulls off into New England and 
drags a secondary cold front through here Thursday evening. 
Canadian high pressure will then move in from the north and keep US 
dry through at least Saturday. 


The forecast for Saturday night-Sunday is almost nil confidence, 
with the GFS keeping US dry and the European model (ecmwf) bringing in widespread 
shower/tstorm activity. Will lean toward the generally more 
reliable European model (ecmwf) this far out in the forecast, and even the drier GFS 
has a warm front in the Ohio Valley during this time period, further 
supporting the idea of a chance of rain. Will keep pops very low. 


Will go for high temperatures on Wednesday around 80, though the 
prevalence of clouds/precip will have a big effect on that. Highs 
should then be in the 70s for the rest of the forecast period. 


&& 


Aviation (12z taf issuance)... 
issued at 641 am EDT Mon may 20 2013 


There is still a small window for some briefly reduced visibilities 
at bwg/Lex, however with the sun beginning to rise the window is 
rapidly closing. Have removed mention from the tafs. VFR conditions 
will prevail today as an upper level ridge of high pressure holds 
overhead. Expect a few cu around 3-4 k feet and some upper level 
clouds. Southerly winds will increase to between 10 and 15 mph by 
late morning with occasional gusts up around 20 mph. Scattered 
storms may move into southern Indiana by late evening, however will 
stay north of sdf. 


&& 


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




Short term.......bjs 
long term........13 
aviation.........Bjs