Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 211715 CCA
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1105 AM CST Tue Feb 21 2017

.UPDATE...
Issued at 1105 AM CST Tue Feb 21 2017

Just completed a late morning update to short term grids from now
through midnight to reflect precipitation moving through the WFO
PAH forecast area. Deformation zone enhanced precipitation along the
I-57/I-64 corridor should gradually dissipate this afternoon as the
northern stream flow becomes decoupled from the steady state closed
low along the LA/AR border. Mid-Upper level forcing should also
continue to diminish through noon over Southeast Missouri, lessening
the chance for more rain this afternoon. Marginal vorticity
advection and lift will still keep some precipitation moving
northeast from the Lower Mississippi Valley into parts of Southern
Illinois, Southwest Indiana, and West Kentucky during the afternoon
and evening hours, gradually shift east with time into the Pennyrile
region of West Kentucky before midnight.

With the abundant cloud cover, temperatures closer to the closed
low will hold into the lower 60s, with middle 60s likely in
eastern sections of the WFO PAH forecast area where there are
occasional breaks in the clouds through midday.

Will issue gridded, tabular, text forecast updates shortly.

UPDATE Issued at 559 AM CST Tue Feb 21 2017

Looking at the latest radar trends, it appears that the rains will
come to an end in the far west from south to north in the next
hour or two. Farther east, shower activity will be increasing over
the Purchase Area. Overall coverage is diminishing as expected.

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

&&

.SHORT TERM...(Today through Thursday night)
Issued at 337 AM CST Tue Feb 21 2017

The primary signal in the 00Z guidance and later CAM output is
that the current north/south oriented band of showers will rain
itself out over southeast Missouri, leaving only scattered showers
for this afternoon, mainly east of the Mississippi River. Tried to
show these basic trends in the hourly PoP/Wx grids. There may be
some lingering shower activity this evening, mainly in the
southeast. No thunder is forecast, and QPF for this event will
range from 1/4"-1/3" over the western four counties in southeast
Missouri to a tenth of an inch or less east of the Mississippi
River.

With light winds expected tonight, more fog will be possible late
tonight in areas that receive rainfall today and are able to
clear out tonight. Not real confident in the clearing trend, but
did throw in some patchy fog over all but the far southeast
portion of the area.

Zonal flow aloft will establish itself over our region Wednesday,
and this will allow south winds to develop. Clouds may linger for
much of the day, especially in the east, until the zonal flow
takes over. We should be able to climb back into at least the
lower 70s over much of the area Wednesday afternoon.

South winds will increase Thursday into Thursday night as a strong
storm system takes shape over the central Plains. With the flow
aloft ahead of the system becoming west southwesterly over our
region, a nice elevated mixed layer (EML) will overspread the
area. This should effectively cap deep convection, however,
cannot rule out some lighter showers as the boundary layer deepens
beneath the cap Thursday afternoon and night, mainly along and
north of I-64. Ended up mentioning thunderstorms Thursday night
along I-64 in southern Illinois to blend with my neighboring
forecast offices, but figure any deep convection will be well
north of our region.

As for temperatures, cloud cover and rainfall will hold readings
down over much of the area today. However, records may still be in
play where the sun breaks through for an hour or two. Clouds could
be an issue Wednesday as well, but we should be able to test, if
not break, records that are only in the upper 60s to lower 70s.

Tried to go on the warm side of guidance Wednesday night through
Thursday night. Some areas may not drop below 60 Thursday night.
Thursday`s record max min may be in jeopardy. Once again if we see
plenty of sunshine, record highs on Thursday will be possible,
despite the records being in the mid 70s throughout the area.

.LONG TERM...(Friday through Monday)
Issued at 337 AM CST Tue Feb 21 2017

Forecast confidence in the long term starts off higher than average
Friday and Saturday with increasing model consistency. Confidence
falls to below average early next week with greater model
variability.

A fairly active weather pattern is expected late this week into
early next week with at least a couple chances for thunderstorms.
Starting with Friday, low pressure is forecast to be centered over
Iowa at daybreak, with a cold front trailing from the low into
Missouri. The low is forecast to track east to Lake Michigan by the
end of the day, with the cold front bisecting the forecast area by
Friday evening.

As the cold front encounters an increasingly warm, humid, and
unstable air mass, showers and thunderstorms are forecast to develop
along and ahead of the cold front by Friday afternoon. The main
limiting factor appears to be deep-layered moisture, which may limit
the overall coverage of convective activity. Severe storms are at
least a possibility with at least marginal surface-based instability
and modest deep-layered shear for storm organization. Main concerns
should be damaging winds and possibly some hail. Outside of
thunderstorms, the strong pressure gradient will result in windy
conditions as some wind gusts top 30 mph.

The chance for showers and thunderstorms will taper off in the
evening over the eastern half of the area as the cold front sweeps
to the east. In the wake of the front, much cooler and drier air
will filter into the region on Saturday as high pressure builds in.
After highs in the upper 60s to mid 70s on Friday, Saturday will be
much colder with highs only in the mid to upper 40s. Temperatures
will begin to moderate on Sunday as the high shifts to the east
and southerly winds develop at the surface.

More uncertainty enters the picture late in the weekend as forecast
models begin to diverge. While both the Canadian and ECMWF maintain
dry conditions Sunday and Sunday night, the GFS indicates the
possibility for some light rain as a fast moving weak upper level
wave moves through. A better chance of showers and eventually
thunderstorms arrives by Monday and Tuesday as the next storm system
approaches in fast zonal flow aloft. Temperatures will respond as
well as highs move back into the upper 50s and lower 60s by
Monday.

&&

.AVIATION...
Issued at 559 AM CST Tue Feb 21 2017

The latest guidance continues to overestimate the low-level
moisture, so will we will continue with VFR conditions at all
sites through most of the day. Will have a few hours of MVFR rain
potential at KCGI to begin the forecast, but otherwise, the
coverage of showers should scatter out quickly this morning, as it
attempts to spread north and east through the area. Will go with a
VCSH in lieu of trying to pin-point shower activity at the TAF
sites for the remainder of this event.

MVFR ceilings are expected to eventually develop over the area
from west to east late this afternoon through the evening.
Guidance is advertising dense fog or VLIFR ceilings overnight, but
not confident enough to go for it at this time, especially given
the low bias guidance has already displayed with this system.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

UPDATE...Smith
SHORT TERM...DRS
LONG TERM...RJP
AVIATION...DRS



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