Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
709 PM EDT Tue Jun 2 2015
..updated aviation discussion...
Short term (now through Wednesday night)...
issued at 245 PM EDT Mon Jun 2 2015
Upper low has moved along the Kentucky/Tennessee border today and made it as far
east as the I-75 corridor. Low-level moisture has persisted over the
Ohio Valley, keeping a low stratus deck in place and limiting temps
to the lower/mid 60s in most places, and a few spots in the
Bluegrass region have not gotten out of the 50s.
Tricky forecast as models are often too quick to scour out low-level
moisture, especially when we would normally expect June sun to be
strong enough to do so. Once we get into evening, expect to maintain
status quo with cloud cover through the night, so it will be a
partly to mostly cloudy forecast. Fog is certainly on The Table
anywhere that we clear out, but not enough confidence in clearing to
For Wednesday, the models remain optimistic but it will still be
tough going with the 850mb thermal trof remaining over central
Kentucky. Will err on the side of a cloudy forecast, and keep the
Max temp forecast in line with the cooler NAM MOS. If we stay
overcast all day, even the mid/upper 70s would be a generous
forecast. Also have limited afternoon pops to just a slight chance
over east-central Kentucky, and removed the mention of thunder as
the cloud cover will keep US stable. Ridging aloft finally becomes
enough of a factor Wednesday night that cloud cover should scatter
Long term (thursday through tuesday)...
issued at 235 PM EDT Tue Jun 2 2015
By Thursday, the stubborn closed low is expected to have wobbled
over to North Carolina, allowing a period of upper level ridging to
move over the lower Ohio Valley. With more sunshine, temperatures
are poised to climb back to near seasonal normals. Instability
builds somewhat in the afternoon, mainly across south-central and
eastern Kentucky where afternoon/early evening diurnal showers and
storms may develop. Environment isn't too favorable so pops were
kept at slight chance. A similar setup is expected for Friday as
well, dry in the morning with a slight chance of afternoon showers
or storms. Highs both days look to top out in the low/mid 80s and
plan on morning lows in the 60s.
By Friday night into Saturday a weak frontal system approaches the
area as northwest flow aloft sets up. This front stalls or hangs
across the area during the day Saturday, but with less than
favorable dynamics, precipitation coverage is likely to remain
scattered. Pops were kept in the 30 to 40 percent range.
A break between weather systems continues to look likely Saturday
night into the first half of Sunday before a more significant cold
front arrives by early next week. 02.12z deterministic and ensemble
guidance points to a frontal passage that would bring a round of
showers and thunderstorms to much of the region late Sunday night or
Monday morning. While the 12z data trended toward a similar
solution, there remains some timing differences to work out for a
day 6/7 forecast. For now, sided with a model consensus of 40 to 50
percent pops, which looks appropriate at this time.
Aviation (00z taf update)...
updated at 707 PM EDT Tue Jun 2 2015
The pesky stratus deck continues to hang around at all sites this
evening as moisture remains trapped under a Stout low-level
inversion. Klex and kbwg remain solidly under this deck, but ksdf
seems to be on the edge of a more scattered deck. Despite guidance
continuing to suggest this deck will scour out, see no reason it
will given the loss of daytime mixing and no significant dry air
advection. Therefore, will keep all terminals within at least MVFR
stratus overnight, with klex the most likely to dip into the IFR
range. 925mb flow is forecast to turn more to the east-southeast through the
overnight, so even if ksdf briefly scours out in the next few hours,
think stratus is likely to slowly return northwest overnight. If
any terminal does manage to scour out for an extended period
overnight, then fog could become more of an issue towards sunrise
than is currently anticipated.
Otherwise, clouds should slowly erode and lift tomorrow as daytime
mixing commences, but they very well could hold on even longer than
this forecast implies. Winds will be light out of the east-northeast.