Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 290705
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
305 AM EDT Wed Jul 29 2015
.SHORT TERM (Now through Thursday)...
Issued at 305 AM EDT Wed Jul 29 2015
Juicy and boundary-rich air mass remains in place over the Ohio
Valley, but some fairly substantial changes are on the way as a cold
front pushes ESE from the Upper Mississippi Valley. Showers and
storms over northern Illinois and now over northern Missouri have
not gotten organized into any southeastward-diving MCS, so not too
excited about our precip chances too early in the day. However,
can`t rule out a renegade shower or T-storm in this environment, so
will see slight chance POPs area-wide before noon.
Later in the day our precip chances really start to ramp up with the
approach of the cold front. Believe that storms will still struggle
to organize, but plenty of instability and just enough forcing to
support marginally severe wind gusts and torrential rainfall out of
the strongest storms this afternoon and evening.
Heat will likely be a bigger story today, with temps climbing into
the lower 90s, and dewpoints solidly in the mid-70s as moisture
pools over southern Indiana and generally west of I-65 in Kentucky.
Heat index values in this area will reach 100-103F, so will cover
this in a Special Weather Statement.
The cold front and its associated convection should push south and
east of the area overnight, but could hang up just enough to give us
an isolated T-storm across south central Kentucky Thursday morning.
Mainly expect relief from the soupy air mass as lower dewpoints
filter in from the north.
.LONG TERM (Thursday night through Tuesday)...
Issued at 246 AM EDT Wed Jul 29 2015
A generally benign long term period looks to be in store for the
Ohio Valley as surface ridging takes control for the end of the week
into the first part of the upcoming weekend. A couple of weak
systems may attempt to make a run at the region late this weekend
into the upcoming week, but high model spread leads to some
uncertainty in that part of the forecast.
High pressure will build into the region Thursday night into Friday
night, allowing slightly cooler but seasonably dry air to infiltrate
the Ohio Valley. Highs on Friday will be in the mid to upper 80s,
but dewpoints in the low to mid 60s will make those readings feel
much more pleasant than they have of late. With generally light
winds and clear/partly cloudy skies expected both nights, overnight
lows should be able to dip into the mid and upper 60s.
A weak front will approach from the north on Saturday. Moisture
return ahead of this front will be rather unimpressive, with very
little in the way of upper-level support as the main PV anomaly
diving through the NW flow aloft will pass well to the north of the
region. Therefore, will continue with a dry forecast, but can`t
completely rule out an isolated shower or storm within the weak
frontal convergence Saturday afternoon into Saturday night,
especially in the northern Bluegrass region of KY.
There are signals that the NW flow regime will become a bit more
active as we head into early next week. However, there seems to be
rather poor consistency both spatially and temporally with these
potential systems. The 29/00Z GFS is advertising a weak front
pushing through on Monday with some associated convection, but the
GEFS/GEM/ECMWF are not on board so will leave Monday dry for now.
Will go ahead and bring in pops Tuesday as yet another front
attempts to make southern progress into the Ohio Valley. Several
waves may ride along this front which may keep precipitation in the
forecast through the middle/end of next week, outside the scope of
this official forecast.
.AVIATION (06Z TAF Update)...
Updated 100 AM EDT Tue Jul 28 2015
Steamy conditions will persist overnight, with fog potential being
the biggest near-term question. Rainfall Tue afternoon/evening was
fairly unimpressive near the terminals, and visibilities didn`t drop
too hard in the morning anyway. Temp/dewpoint spreads remain
slightly wider than advertised by models, so it seems that MVFR
should cover the visibilities around daybreak. Best chance of any
IFR restriction seems to be in LEX, as cirrus should keep any fog at
BWG in check.
Next challenge is timing and impact of any convection as a cold
front moves in late in the day. Morning should be high and dry as
the storms over Iowa and northern Missouri struggle to organize into
any kind of MCS that could dive at us early in the day. Hi-res
models all point to mid/late afternoon for any T-storms, and there
remains a hint that some of the are could get gapped. If a storm
does directly affect an airport, there will be MVFR vis in rain, if
not briefly IFR. Will carry a PROB30 group for that into early