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Area forecast discussion
National Weather Service Paducah Kentucky
935 PM CDT Wed Mar 29 2017

Update...
issued at 935 PM CDT Wed Mar 29 2017

Thunderstorms continue to increase in coverage and intensity across
the Ozarks this evening. A surface warm front extended from the
southern border counties of Kentucky back westward into the Ozarks
of Missouri. The storms over Missouri are forecast to gradually
develop eastward across the lower Ohio Valley as the warm front
moves northward overnight. The new 00z NAM and rap models indicate
the strongest instability will remain over Missouri the rest of
tonight. Though MUCAPES will generally remain under 1000 j/kg, shear
will increase as a 500 mb jet streak pivots northeast from the
Arkansas Ozarks. Therefore, an isolated tornado threat will persist
much of the night, mainly in se Missouri.

The 500 mb jet streak of 65 to 75 knots will progress across western
Kentucky on Thursday as diurnally driven storms increase during the
day. Shear and instability parameters suggest the tornado threat
will increase during the day Thursday as the cold front moves east
into our region.

&&

Short term...(tonight through Friday night)
issued at 239 PM CDT Wed Mar 29 2017

Main story will be severe weather potential late tonight and again
Thursday afternoon and evening. The remainder of the short term
forecast period (friday & Friday night) should see slowly decreasing
cloudiness with temperatures slightly below normal.

Initial elevated pre-warm frontal convection has lift out of the
area late this morning and into the afternoon hours.

The next round of convective activity will likely move into extreme
western sections of the weather forecast office pah forecast area (carter, Ripley,
Wayne, and Butler co. In southeast missouri), between 8 PM and 9 PM
CDT. However, the severe potential is not likely increase until
closer to midnight for the aforementioned counties. The 12km NAM
and 13km rap, and in some sense the esrl hrrr guidance have been
suggesting an instability plume with increased winds aloft over
southeast Missouri, especially between midnight and 500 am/6 am
CDT/. The primary concern would still be winds and hail during this
time period, but could not rule out embedded circulations (qlcs)
within the line that may produce a brief tornado. Although included
in the Storm Prediction Center day 1 severe weather outlook for severe potential, am
concerned that southwest Illinois could see some severe potential as
well before daybreak. Will wait and see what happens with later
outlooks from Storm Prediction Center.

The convective activity during the morning hours may contaminate and
slow the progress of the next plume of instability and shear for the
weather forecast office pah forecast area, especially the western half of the County Warning Area. At
this time, have focused any mention of severe thunderstorm to west
Kentucky, southwest Indiana, and southwest Illinois for Thursday
afternoon and evening, mainly between noon and 8 PM CDT. All modes
of severe weather, hail, damaging winds, and tornadoes, as well has
heavy rain will be likely. Greatest concern for some stronger
tornadoes will be in southern sections of west Kentucky, outlooked
by Storm Prediction Center as moderate risk in the day 2 severe weather outlook.

Long term...(saturday through wednesday)
issued at 239 PM CDT Wed Mar 29 2017

Moderate forecast confidence exists through the extended portion
of the forecast, as we remain in a very active pattern.

We will be in a progressive zonal flow aloft with two strong storm
systems moving east northeast through or region. The first storm
system will take a more southern track, with the upper low passing
just to our south over or right through our region. The 12z models
have some differing ideas on how fast we may begin to see
precipitation with the system, but the consensus emphasizes Sunday
night and Monday for widespread showers and storms.

The 12z GFS brings showers into the region late Saturday night
into Sunday, while the European model (ecmwf) keeps the area mostly dry for that
period. Likewise, the GFS lingers quantitative precipitation forecast into Tuesday, where the
European model (ecmwf) and CMC do not. Bottom line is we will have pops over about
a 72 hour period, but the main action will be Sunday night through
Monday evening. With the upper low passing over or to the south
of the region, organized severe weather is not likely with this
system. The cold core aloft could result in some small hail, but
the wind fields will not be conducive to organized severe storms.

The second storm system is expected to track north of our area,
potentially situating US in a better position for some more severe
weather. There is some variability in the timing of this system,
but it should be a bit more of a quick hitter sometime Wednesday
through Thursday. Wind fields should be more supportive of
organized severe storms, depending on the amount of moisture and
instability available.

Temperatures will remain on the mild side through the extended
forecast.

There are some signs of a pattern shift late next week, as
troughing develops over the northeast Pacific. This will likely
lead to downstream ridging over the West Coast, and potentially
more of a northwest flow over our region. Of course that would
make Gulf input less readily available, and hopefully lead to a
less active convective regime. We will see.

&&

Aviation...
issued at 630 PM CDT Wed Mar 29 2017

VFR cigs this evening, primarily, will yield to MVFR bases as the
first wave of convection moves in toward midnight. Another late
night wave may offer more restrictions, to both ceilings and vsbys, as
atmosphere moistens/destabilizes. A brief early to mid morning
pause, will then be followed by the potentially strongest storms
for the PM hours. Winds really get cranking by then too, so these
were the additions to the inherited forecast, esp for the planning
period.

&&

Pah watches/warnings/advisories...
Illinois...none.
MO...none.
In...none.
Kentucky...none.

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