Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 041917
Area Forecast Discussion
National Weather Service Louisville KY
317 PM EDT WED MAY 4 2016
.SHORT TERM (Now through Thursday Night)...
Issued at 300 PM EDT Wed May 4 2016
The synoptic pattern early this afternoon features an anomalous
upper-level low across the Great Lakes region. This feature will dig
southeast and amplify significantly through the short term period,
bringing continued cool and dreary conditions to the Ohio Valley.
A strong PV anomaly is diving south into the region his afternoon.
The seasonably cold core of this system (500mb temps around -24 to
-26C) is combining with just enough surface heating to cause MLCAPEs
around 250-500 J/kg. Given freezing levels around 6-8 thousand
feet, we will continue to see some small hail out of these showers
and scattered thunderstorms. We`ve already received a few reports
of pea-sized hail across southern IN. Don`t expect a whole lot of
lightning with this activity given the shallow depth of the storms
and non-impressive charge separation, but there have been enough
strikes to continue with thunder wording.
Convection will wane this evening as the sun sets and surface
heating is lost. However, guidance is suggestive another PV anomaly
will dig southeast through the region late tonight, helping to one
again enhance shower coverage. Forecast soundings show moisture
saturation will be generally shallow, so will not go overly high
The final wave rotating around the upper-level low will move through
mainly areas east of I-65 on Thursday. This should once again
enhance shower coverage in the eastern CWA. The western edge is a
bit in question, but for now will keep shower mention along/east of
I-65. Do think we will see quite a bit of stratocu, especially
across the eastern CWA. These clouds combined with steady cold air
advection should keep temperatures into the 50s through much of the
day. Areas along/west of I-65 may benefit from some late afternoon
sunshine attempting to peak through which should push temperatures
into the low/mid 60s.
Thursday night will finally turn mainly dry as the low shifts to the
east. Overnight lows will still be chilly, in the low to mid 40s.
.LONG TERM (Friday through Wednesday)...
Issued at 316 PM EDT Wed May 4 2016
The synoptic pattern at the start of the long term period will
feature an omega block across the CONUS. This regime will slowly
break down beginning this weekend as a kicker PV anomaly dives into
the Great Lakes region. Therefore, expect a return to a warmer,
more convectively active period this weekend into next week.
Friday continues to look like the pick day of the next seven. The
upper-level low will be far enough east that we should see mainly
sunny skies and temperatures warming back into the low/mid 70s as a
A few sprinkles will be possible late Friday night into early
Saturday morning within weak isentropic ascent, but the first part
of Saturday is shaping up to be nice. Expect a mix of clouds and
sunshine with temperatures climbing into the lower 80s. However,
things become a bit more dicey as we head into early Saturday
evening and into Saturday night. Guidance has continued to trend a
bit stronger with the kicker wave mentioned above, now digging
deeper into the Great Lakes region. This results in a further
south/quicker push of a surface cold front into southern IN by early
Saturday evening. Guidance is suggestive that enough moisture will
return ahead of this front to give us ample instability (about 800-
1000 J/kg from the GFS - which is typically underdone at these
timeframes). Deep-layer flow will help push 0-6km shear to around
40-45 knots which could foster a few stronger storms pushing in from
the north on Saturday evening. This is something we will have to
continue to monitor over the next couple of days as timing could
certainly change, but those with outdoor plans early Saturday
evening into Saturday night along and north of the I-64 corridor
should continue to monitor the latest forecasts.
Otherwise, the upper-level flow will turn more southwesterly by
early next week. This will make for a more active pattern and will
keep showers/storms in the forecast Monday, but especially into
Tuesday and Wednesday.
.AVIATION (18Z TAF Update)...
Updated at 130 PM EDT Wed May 4 2016
Steady rain was still moving through BWG/LEX as of 1730Z
occasionally reducing flight conditions to IFR or MVFR. This line
of showers will exit BWG/LEX within the next few hours. Behind the
line, a cold front and multiple other boundaries exist which will
provide focus for showers and sct storms this afternoon. Due to
lower coverage and low confidence in a t-storm hitting a TAF site,
will continue VCSH through this evening. A wind shift with the
front will occur this afternoon from SW to NW. Winds could also
become gusty especially behind the front up to 20-25 mph this
afternoon or evening.
Tonight VFR conditions should prevail for a good portion of the
overnight period. However, low clouds will move back into the
region with perhaps some stray showers as well especially toward
sunrise. Will include MVFR for tomorrow morning.