Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 200720
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
120 AM CST Fri Jan 20 2017

.UPDATE...
Issued at 119 AM CST Fri Jan 20 2017

Interim discussion to address cancellation of Dense Fog Advisory.
The evening precipitation and warm frontal boundary moved much
quicker than anticipated through short term, high resolution model
guidance this evening. With mixing expected across most of
Southeast Missouri and Southwest Illinois through the night, the
probability of visibilities dropping at or below criteria will be
low. The only area that will still have some potential will be
parts of Ripley, Carter, Wayne, and Butler County in Southeast
Missouri. Will leave these counties in the Dense Fog advisory
through expiration.

Also updated rain chances for the rest of tonight through Friday.
There may be enough instability in the faster flow around the base
of the broad trough to warrant an isolated shower or two, so kept
a token mention over the area earlier in the day on Friday.

UPDATE Issued at 1120 PM CST Thu Jan 19 2017

Updated for 06Z aviation forecast discussion.

&&

.SHORT TERM...(Tonight through Saturday night)
Issued at 313 PM CST Thu Jan 19 2017

The warm frontal return into Southeast Missouri will be somewhat
slower than expected this afternoon and through most of the night
following the passage of the rain and the surface low that passed
through the Tennessee Valley earlier today.

Given the super-saturated atmosphere, weak wind fields and lift
ahead of the warm front, will have to issue a Dense Fog Advisory
for late this afternoon and most of the night for Southeast
Missouri. This Dense Fog Advisory will be expanded along and west
of a line from I-55 and I-57 in Southeast Missouri and Southwest
Illinois for tonight. Depending on the progress of the warm front
northward by daybreak on Friday, part of the Advisory in Southeast
Missouri may be cancelled earlier. The GLAMP MELD and HRRR
numerical guidance seems to have a decent handle on the temporal
and spatial coverage of the dense fog tonight.

An Special Weather Statement for locally dense fog is already in
effect for part of Southeast Missouri at this time.

As the warm front spreads east late tonight and Friday, most of
the precipitation should cut off. There will be the potential for
some warm advection/isentropic shower development early Friday
morning with the passage of a vorticity lobe. Otherwise, dry
conditions should prevail through the rest of Friday/Friday night
as the WFO PAH forecast area becomes fully covered in the warm
sector.

The next wave in the broad U.S. trough work up through the Lower
Mississippi Valley into the eastern section of the WFO PAH
forecast area Saturday morning. As energy quickly rotates around
the base of the trough, an area of low pressure will develop and
deepen over Arkansas and move east across the Lower Mississippi
Valley through Saturday evening. Given the instability present
with this low, added a mention of thunderstorms during the
afternoon and evening hours on Saturday.

Rainfall amounts are still somewhat uncertain with respect to
impact associated areal flooding potential. Will mention the
potential in the Hazardous Weather Outlook, but will hold off any
consideration of a Flood Watch, given the dry time on Friday to
allow for drainage of surface water.

.LONG TERM...(Sunday through Thursday)
Issued at 313 PM CST Thu Jan 19 2017

Medium confidence in the extended.

Two systems are expected to move through during the extended. The
first is expected to move through to our south with the latest model
runs. Previously the models had the low taking a more northerly
path. The Canadian still does have a more northerly path but the GFS
and ECMWF both agree it pass through central AR and TN into the
Smokies. Even though there is still some surface based instability
in the forecast soundings albeit low with LI`s negative one or two
and CAPE values aloft and surface based averaging around 500 j/kg2.
There is also some elevated instability with K index values around
30c. However Showalters stay positive. Thus will keep a slight
chance of thunder going...considered going scattered but will wait
for better continuity before increasing thunder chances for now. It
will be a bit breezy Sunday night into Monday as the low passes. The
next system will pass through about mid week and appears to be weak
at this time. It will approach the northwest coast then rotate
through the southwest before lifting northeast into the great lakes
region. With its origin from the Pacific it will not have a great
deal of cold air with it. It will cool down to around normal for
this time of year but for now will not introduce thunder with this
system.

Temperatures will remain well above normal for this time of year at
least until late in the work week.

&&

.AVIATION...
Issued at 1120 PM CST Thu Jan 19 2017

The rain has pretty much ended at KCGI and it should be slowly
moving out of the rest of the area over the next 3-4 hours. Cigs
will be IFR or lower for the most part. KPAH is running VFR attm
but should drop back to IFR closer to sunrise. Vsbys have been all
over the place as well due to varying winds and precipitation.
Believe sites will be MVFR for the most part with dropping down to
IFR at times, especially if the wind drops off. Slowly improving
cigs and vsbys will be the rule during the day Friday...with VFR
conditions looking like a good possibility just beyond this TAF
period, at least wrt cigs. Winds will be aob 10 kts from the
south.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...Dense Fog Advisory until 8 AM CST this morning for MOZ100-
     107>109.

IN...None.
KY...None.
&&

$$

UPDATE...Smith


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