Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 201725

Area Forecast Discussion
National Weather Service Louisville KY
125 PM EDT MON JUN 20 2016

...Updated Aviation Discussion...

.SHORT TERM (Now through Tuesday)...
Issued at 310 AM EDT Mon Jun 20 2016

The new work week begins with quiet weather, but the pattern will
certainly become more active Tuesday through Thursday across the
area with a several rounds of thunderstorms possible.

Currently, infrared satellite imagery shows some mid-level clouds
over the southern half of Indiana and parts of central Kentucky,
caught within an eastward extension of a sprawling ridge over the
central and southwest U.S. Model cross-sections suggest these clouds
and diurnal cumulus clouds later today will result in a partly sunny
sky. Surface high pressure over the Gulf Coast states will create a
southwest breeze this afternoon around 10-15 mph. Marginal
instability will develop and can`t preclude an isolated brief shower
here or there during peak heating, but model soundings generally
show a capping inversion, so most if not all areas should remain dry
today. Expect high temperatures in the upper 80s/around 90.

Currently a complex of thunderstorms is occurring over the western
Great Lakes moving east associated with a shortwave embedded within
unusually strong upper-level westerly flow (e.g., 100-120 kts at 300
mb along the North Dakota-Minnesota border with Canada). This axis
of thunderstorms will redevelop later today and tonight over the
eastern Great Lakes and Ohio Valley, mainly to our north, along and
ahead of a cold front. However, models suggest that some storms may
move southeast into south-central Indiana and perhaps north-central
and east-central Kentucky late tonight/Tuesday morning. Although
instability would be expected to diminish nocturnally Monday night,
model soundings do show enough some elevated instability that could
still support scattered storms, as the anomalous jet streak aloft
dives southeast into the Ohio Valley in northwest flow aloft.

Convective trends Tuesday are a bit tricky depending on evolution
early Tuesday. Most 00 UTC models suggest that the front will sag
into central Kentucky and become somewhat diffuse with time. This
would suggest that thunderstorms Tuesday afternoon will be most
prevalent over central and south-central Kentucky, with a lower
chance over southern Indiana and then north-central Kentucky late in
the day. The NAM is typically slowest with the front, keeping a good
chance of storms over northern areas as well. Will side with the
GFS/ECMWF with highest POPs in central/south-central Kentucky. Low-
level convergence should weaken somewhat Tuesday with veered low-
level flow. Thus, organized severe storms may not occur, although
with the predicted level of instability and stronger winds at higher
altitudes, some strong storms and isolated severe are possible. High
precipitable water values also suggest high rainfall rates with the
stronger storms. Clouds may hold afternoon highs Tuesday a little
lower in the mid and upper 80s.

.LONG TERM (Tuesday Night through Sunday)...
Issued at 330 AM EDT Mon Jun 20 2016

...Strong to severe storms possible Wednesday and Thursday...

We will be watching closely synoptic and mesoscale evolution in the
middle of this week as a few rounds of strong to potentially severe
thunderstorms could occur.

Scattered to numerous thunderstorms Tuesday afternoon/evening over
central Kentucky should weaken out Tuesday night. However, the
boundary over central Kentucky will extend northwestward and be more
prominent over Illinois and Iowa. All models are pointing to
potential development of a mesoscale convective system (MCS) roughly
over Iowa Tuesday night which would then propagate and develop
southeastward in swift northwest flow aloft into the lower Ohio
Valley by Wednesday morning. Low-to-mid-level warm air advection/
isentropic lift is expected along and north of this boundary/warm
front. At 300 mb, a continued anomalously strong jet streak around
100 kts will power southwest out of the Great Lakes into Ohio,
placing MCS development clearly in an area of upper-level divergence
in the right entrance region.

Forward propagation should bring the MCS into or very close to our
northwest counties by Wednesday morning, although the Canadian is a
little slower. Although strong/isolated severe storms certainly are
possible, much of the MCS should be elevated just north and east of
the warm front, meaning less strong surface wind potential but very
heavy rain and possibly some hail. Nevertheless, any cells right
along the warm front would have to watched for severe potential if
the MCS materializes as suggested by model guidance.

Weather conditions Wednesday will be highly dependent on development
and evolution of this MCS. Wednesday appears to be the best day for
severe weather across much of the Ohio Valley with some significant
wind damage not out of the question. Where this axis sets up is
still to be determined. Right now, the best corridor for severe
would appear to be central or northern Illinois to Ohio, coincident
with SPC`s Day 3 "Enhanced" risk ahead of a developing surface low.

Nevertheless, south-central Indiana and north-central and east-
central Kentucky could also see some severe storms. Assuming an MCS
develops as suggested and moves our forecast area early Wednesday,
this could leave a tangible outflow boundary somewhere in our area
which could cause renewed robust thunderstorm development Wednesday
afternoon/evening, vs. having the warm front lift far enough north
to take most of the storms to our north. Actually, the 00 UTC GFS
hints at this with its instability and surface temperature forecast.
The most intense cells could produce wind damage, hail, and
torrential rain. There would be a gradient in high temperatures
Wednesday afternoon with lower 80s far northeast to lower 90s

Will continue with a good chance of thunderstorms Wednesday night
over the Bluegrass area with least chance in west parts of south-
central Kentucky away from the area of forcing. On Thursday, another
cold front will sag south across the Ohio Valley. This front will
work on a potentially very unstable air mass resulting another round
of strong to possibly severe storms.

Finally, conditions should quiet down Thursday night and especially
Friday as the front clears the area. However, dry weather and
slightly lower humidity should be short-lived as isolated to
scattered thunderstorm potential will return Saturday and Sunday,
although a wash out these days is certainly not expected with
a number of dry weather periods as well.


.AVIATION (18Z TAF Update)...
Issued at 125 PM EDT Mon Jun 20 2016

Generally VFR conditions are expected through the valid TAF period.
Diurnal cu will continue to blossom this afternoon, with bases at 4-
5k feet.  Can`t completely rule out a stray shower at SDF this
afternoon or along northern approach routes, but coverage will
remain very sparse and not worth a mention.

Uncertainty remains rather high for tonight as convective coverage
along a cold front is in question.  The best potential for scattered
convection will be at SDF and LEX early Tuesday morning.  Will
continue with VCTS wording at these sites until confidence increases
in coverage and timing. BWG will likely see precip after this valid
TAF period. Any storm will have the potential to bring gusty and
variable winds along with IFR cigs/vsbys.


.LMK Watches/Warnings/Advisories...


Short Term........TWF
Long Term.........TWF
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