Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 161721

Area Forecast Discussion
National Weather Service Louisville KY
121 PM EDT Wed May 16 2018

.Forecast Update...
Issued at 922 AM EDT Wed May 16 2018

Widespread rain with embedded thunder has been falling along the
lower Ohio Valley in an area of low/mid level convergence along a
broad surface boundary, in a corridor of max precipitable water
around 1.6 inches, and beneath some weak upper level divergence.
Radar presentation has been indicating a slow weakening of most of
the activity, but we did a quick update to significantly increase
PoPs and QPF for the next few hours where rain has moved into
western sections of southern Indiana and central Kentucky.

Issued at 620 AM EDT Wed May 16 2018

Indeed the wave now over central Missouri is starting to spark off
storms in a band along the Ohio River in western Kentucky. This
gives some credence to the earlier models thinking our southwest
Indiana counties should go first with activity this morning...then
firing off further scattered storms to the east and southeast. Have
trended the forecast to the latest hi-res guidance that most closely
matches this thinking. That raises the chances into the likely range
for our eastern will issue a zone update shortly.


.Short Term...(Today and tonight)
Issued at 325 AM EDT Wed May 16 2018

After our record warm first half of May, today we back off to
somewhere roughly halfway between normal and those records...with
highs in the low to mid 80s. A weak trough of low pressure at the
surface is partially to blame, as it will keep in some cloud cover
as well as good rain chances. Another cause is a couple of areas of
low pressure aloft, one to our west and one to our southeast that
will slowly merge together.

Expect with lower convective temperatures today that we should have
an earlier onset of storms. Isolated cells could pop up at anytime,
as they still are just to our north in IND`s area and another now in
Marion county, KY. Some of the high-res guidance is focusing on our
northwest counties, such as Dubois County, IN, for initiation by
late morning. The RAP picks up on this potential likely because of a
shortwave moving into western Missouri at this hour. These storms
could then set the stage for more scattered to numerous activity
areawide by mid afternoon. Storms will be slow moving today, with
main push being from outflow boundaries from other storms. Once
again, we will have to watch for localized flooding, especially in
areas that receive multiple rounds of storms.

Tonight, convection will be slow to wane, but should become isolated
in nature by midnight. Expect lows a few degrees colder than this
morning, as we do end up with a slight northerly component of the
surface wind.

.Long Term...(Thursday through Tuesday)
Issued at 340 AM EDT Wed May 16 2018

Thursday into early next week will feature a stretch of warm and
unsettled weather. Upper troughing will continue to develop and
propagate across the region Thursday into Saturday. The 500 mb low
is forecast to pivot right over the forecast area Friday into

So we`ll have upper level support in place for at least chance PoPs
in multiple periods, but the upper level flow will remain weak
overall. On Thursday, the atmosphere will remain warm, moist, and
somewhat unstable. Compared to recent days, lower thicknesses and
copious cloud cover will limit surface heating/destabilization.
Afternoon highs should only reach the upper 70s to around 80.
Scattered thunderstorm development is likely during the afternoon
hours. Low-level convergence is weak and uncertain, and leftover
outflow boundaries from Wednesday night may provide a source of

Weak low-level boundary lifts north on Friday, supporting at least
chance PoPs and a slight chance for a storm with the upper low
overhead as well. The whole system takes on a negative tilt and
pivots northeast of the area Friday night into Saturday. Highest
precip chances for Saturday are across the eastern forecast area. A
relative lull in rain is expected starting either Sat morning or
afternoon and continuing through Saturday night. Highs Saturday
should reach the low to mid 80s.

A low pressure system forecast to track through the Midwest and
Great Lakes will bring additional rain and thunderstorm chances to
the area Sunday and Monday. PoPs increase from northwest to
southeast Sunday-Sunday night as a cold front approaches. Sunday
will likely be the warmest day in the long term, with highs in the
mid to upper 80s. But temperatures won`t fall all that much behind
the front next week. The front actually weakens quite a bit and
slows/stalls over the area Monday-Monday night. If this scenario
plays out, this would bring a good chance for additional
thunderstorms Monday afternoon as the boundary layer heats up.
Forecast for Tuesday is uncertain, but will hold on to chance PoPs
across the south for now with highs in the low to mid 80s.


.Aviation...(18Z TAF Issuance)
Issued at 121 PM EDT Wed May 16 2018

A humid, stagnant atmosphere will support scattered pop-up showers
and storms this afternoon and early this evening. Where ever a cell
does form, locally heavy downpours can be expected, but they won`t
last long in any one spot.

Convection will wane this evening with quiet conditions overnight.
Some light BR/HZ may form by morning.

Tomorrow will be more of the same with scattered storms popping up,
especially in the afternoon.




Short Term...RJS
Long Term...EBW
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