Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 251137

Area Forecast Discussion
National Weather Service Paducah KY
637 AM CDT MON APR 25 2016

Issued at 637 AM CDT Mon Apr 25 2016

The AVIATION section has been updated for the 12Z TAF issuance.


.SHORT TERM...(Today through Wednesday night)
Issued at 345 AM CDT Mon Apr 25 2016

A majority of guidance still keeps the area dry today and tonight,
but later Tuesday and Tuesday night it will start to get wet. It
will remain wet through at least Wednesday. The severe weather
threat is still there, especially over the western half of the
area Wednesday, but concern is increasing for more of a heavy
rainfall threat Tuesday night and Wednesday.

By Tuesday, the dominant feature on the weather map will be a
large and deep upper low over far eastern Quebec. This will serve
to block the flow of systems through our region, and therefore,
complicate the forecast for the middle of the week. Our weather-
maker for Wednesday will emerge from the Rockies into the high
Plains late Tuesday night, but it will not make much progress
eastward, and may even interact with another storm system that is
diving south through California.

Our chance of severe weather will be tied to increased shear
associated with an impulse that is expected to eject out of the
base of the larger-scale trough and over our region on Wednesday,
but it will be lifting more north than the northeast.

At the surface, a cold front will drop southward just to the north
of the area by early Tuesday, and then sag into our region Tuesday
night into Wednesday. It will lift back north as the upper-level
impulse rotates through the area. The 00Z NAM and GFS each develop
lots of surface-based instability south of the front Tuesday, but
soundings indicate that the depth of moisture may not be quite
enough to tap it.

Best guess at this time is that storms will fire on the cold front
Tuesday afternoon, in a pretty unstable airmass, but with weak
shear due to a weak upper ridge over the area. The consensus of
00Z guidance develops QPF south southeast through much of our
forecast area Tuesday night. With little steering flow, the storms
that initiate on the cold front are likely to just propagate
southward into the unstable air, which may continue through much
of the night.

Given the instability available, cannot rule out a few strong
pulse storms with some potential for hail late Tuesday and Tuesday
night, but the overall severe threat will be quite low due to the
lack of shear. However, the presence of a nearly stationary
boundary with a continuous fetch of moisture into it supports a
heavy rainfall threat.

As the main impulse rotates north northeast through the region on
Wednesday, the wind fields will improve significantly. The
question is how much the airmass will be able to recover ahead of
the impulse? Figure that recovery will be most likely over
southeast Missouri, and possibly into southern Illinois. This is
also where the strongest wind fields are expected. Severe storms
with damaging winds and large hail will be possible, especially in
SPC`s slight risk area.

Another concern are storms that may develop on the surface
boundary, which will be more of a warm front on Wednesday. If a
storm gets going on the old boundary and rides along it, the
deviant storm motion may lead to some non-zero tornado threat. Of
course, heavy rainfall will continue to be a concern.

There are a lot of moving parts synoptically and convectively
ahead of and through this potential severe weather event, so we
will have to ultimately wait and see what happens through Tuesday
night before having increased confidence in the severe weather
forecast for Wednesday. Most of the 00Z guidance pushes the
convective activity north and east of the area by 00Z Thursday, so
Wednesday night may end up dry for much of the region.

.LONG TERM...(Thursday through Sunday)
Issued at 345 AM CDT Mon Apr 25 2016

The upper-level flow pattern during the long-term period will be
nearly identical to the short-term. A series of 500 mb shortwaves
will track northeast from the southern Rockies across the central
Plains to the Great Lakes. This pattern favors a continuation of
warm and wet conditions.

As far as the daily details, Thursday will be the start of a short
drying trend between systems. A surface cold front will exit to the
east of our region in the afternoon. There is a small chance of
lingering showers and storms east of the Mississippi River. The
models have trended a bit faster with the arrival of a mid-level
ridge and its associated dry air. This should limit convective
coverage along the front. Winds will be slow to veer into the
northwest, which should allow temps to reach the model consensus
highs of around 80. Thursday night will be dry as a high builds in
at the surface and aloft.

Friday still looks like a mainly dry day east of the Mississippi
River as the deep-layer ridge axis passes overhead. Late in the day,
850 mb southerly return flow and associated moisture could result in
some showers reaching southeast Missouri. Will continue chance pops
west of the Mississippi, with a buffer zone of slight chances in
southern IL and far west KY. Highs should be limited to the lower
and mid 70s due to increasing clouds and northeast surface winds.
The coverage of showers will increase Friday night as warm moist
advection increases.

On Saturday, a surface warm front will likely lift north across our
region. The models are in good agreement that widespread showers and
storms will develop near the front as a 500 mb shortwave rotates
northeast from the southern Plains. The parent 500 mb closed low is
forecast to move into the central Plains on Sunday. There are
surprisingly no major model differences at this time range at 500
mb. For surface features, the forecast follows the 00z ecmwf, which
takes a surface cold front or occluded front east across our region
Sunday. This entire setup looks quite similar to our mid-week
system, and therefore not a whole lot of difference is expected in
sensible weather elements.


Issued at 637 AM CDT Mon Apr 25 2016

Plenty of 4-6kft clouds are expected to stream over the region
through the entire forecast period. Toward Tuesday morning, they
will lower close to 3kft and should definitely be ceilings. Opted
to leave MVFR conditions out of these forecasts. Otherwise, south
southwest winds will gust over 20kts at times this afternoon.


.PAH Watches/Warnings/Advisories...


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