Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Louisville Kentucky
622 am EDT Tuesday Sep 1 2015
..updated aviation discussion...
Short term (now through wednesday)...
issued at 302 am EDT Tuesday Sep 1 2015
Persistence is the key to the short term forecast as both the upper
level and surface weather pattern remain largely unchanged from the
past few days. The dog days of September are upon US it seems.
Light/variable winds combined with some boundary layer moisture this
morning is producing patchy fog across the favored locations. This
should burn off quickly after sunrise. Plan on another seasonably
warm and muggy day as readings top out right around 90 under mostly
to partly sunny skies. A weak upper level shortwave spinning over
central Indiana will be the focus for a stray shower or storm this
afternoon. Models show this feature dropping south a bit...so will
continue to carry a slight chance across southern Indiana during
Look for another muggy night with patchy fog possible and lows right
around 70. Wednesday will be a Carbon copy...mainly dry conditions
with highs near 90.
Long term (wednesday night through monday)...
issued at 323 am EDT Tuesday Sep 1 2015
In the long term period, the latest models continue indicate a
highly amplified upper level pattern. This is one is a bit
different that the one that we've typically seen this Summer in that
the eastern U.S. Will be under a developing ridge while upper
troughing remains out to the west. High pressure at the surface
beneath the upper level ridge will keep precipitation suppressed
across our region with temperatures remaining near seasonal normals.
With the developing ridge over the eastern U.S., We'll have to keep
a watch for several waves that will migrate around the periphery of
the ridge. Previous model runs had several weak disturbances moving
near the region. However, the latest runs have strenthened the
ridge somewhat and these disturbances look to have less of an impact
on our weather. However, we could see some isolated storms as close
as southeastern in, or southwest Ohio Thursday afternoon/eve.
As we head into the Holiday weekend, the upper level ridge looks to
remain in place across the eastern US. The global deterministic and
ensemble models do hint at a bit of upper level troughing developing
over the southeastern US by Sunday. With an area of surface high
pressure to the east, a southerly flow may get re-established and
attempt to transport deeper Gulf moisture back into the region.
There remains considerable spread in the ensembles regarding the
evolution of the pattern at that time period. Thus, a persistence
forecast of dry conditions looks more likely at this point.
However, a stronger signal suggests that moisture may be plentiful
enough by Monday to spark a stray shower or storm...especially
across southern Kentucky. This will be something to watch over the coming
Highs during the the period will range from the upper 80s in the
north to the lower 90s in the south. Overnight lows will generally
range from the upper 60s to the lower 70s. It is interesting to
note that some of the raw model guidance continues to suggest that
we'll see middle 90s by late week and into the weekend. However, 850
temperatures are not warming more than 1-2 degrees over what we're seeing
right now...and we've been hard pressed to hit 90 in the last few
weeks. Should also note that the models have been exhibiting a warm
bias on surface temperatures. The consall blends and the bias-
corrected models have been whipping up on the deterministic
solutions here. Thus, have stuck close to the superblend guidance
which is very similar to previous forecast. Some slightly cooler
readings are possible by late in the period due to increased cloud
cover and isolated convection, if the southern Gulf moisture gets up
into the region.
Aviation (12z taf update)...
issued at 620 am EDT Tuesday Sep 1 2015
Some light fog will continue at bwg through about 12-13z...then plan
on VFR conditions at all the taf sites through the period. Weak
upper level system spinning over Indiana may spark showers/storms
later today but those should stay well north of sdf/Lex.
Overall...winds will be light and variable with high pressure nearly
overhead. Look for patchy light fog again late tonight at bwg...in
the typical 9-13z window.