Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 270951
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
351 AM CST Sun Nov 27 2016

.SHORT TERM...(Today through Tuesday night)
Issued at 350 AM CST Sun Nov 27 2016

Main forecast concern in the near term is dense fog potential
early this morning. Then we turn our attention to the next storm
system slated to bring our next chance of precipitation tonight
into Monday night. Forecast confidence is relatively high through
the period with good overall synoptic model agreement.

Starting with this morning, areas of fog have developed across
much of the region. For the most part, visibilities have generally
remained in the 3 to 5 mile range. However, visibilities over
southern Missouri have dropped to 1/4 mile at both West Plains and
Poplar Bluff. As a result, we will be issuing a Dense Fog Advisory
for the westernmost 6 counties west of a line from Greenville to
New Madrid. More counties may be added if needed later on.

Once the fog burns off by mid morning, sunshine will become
increasingly filtered by high clouds on the increase ahead of the
next storm system. Dry conditions are expected through the day
with high temperatures reaching the mid to upper 50s.

Upper level energy currently over the southwestern U.S. is forecast
to generate the development of a deep low pressure system over the
Upper Midwest by Monday. Increasing moisture and lift coincident
with a strengthening southwesterly flow pattern will result in an
increasing potential for showers from west to east tonight and
Monday. Rainfall totals with this initial round of rainfall should
average no more than one or two tenths of an inch through early
Monday.

The bulk of the rain event is expected to occur from late Monday
morning through Monday evening as a strong mid level shortwave
rounds the base of the central U.S. trough and streams into the
Mid Mississippi Valley. Blended model guidance continues to
suggest the potential for 1 to 2 inches of rain across much of the
forecast area, with locally higher totals possible. This could
lead to the formation of standing water on roadways and in low
lying areas.

Enough elevated instability also exists to warrant at least a
slight chance mention of thunderstorms Monday and Monday evening.
The strength of wind fields aloft and resultant strong low level
helicity values is at least some cause for concern. However,
forecast MUCAPE values remain rather weak, so much of the focus
for severe weather should remain south of the immediate forecast
area.

The precipitation is expected to quickly come to an end Monday
night as drier air works in from the west. Tuesday still looks dry
and unseasonably warm with low pressure parked over the Upper
Midwest and the region still in southwest flow. For that matter,
highs Tuesday are forecast in the lower to mid 60s.

.LONG TERM...(Wednesday through Saturday)
Issued at 350 AM CST Sun Nov 27 2016

Confidence in the long term a little higher due to slightly better
model agreement.

At the beginning of the long term period a short wave ejecting
northeast out of a huge long wave trough centered over the central
US will induce a low/wave on a frontal boundary just to the south
and east of our CWA. This scenario (forcing through the column) will
tap into a stream of deeper moisture from the Gulf and produce
overrunning precipitation mainly over the southeast third of the CWA
Wednesday into Wednesday evening.

Late Wednesday night into Thursday should be dry as the front and
upper troughing move off to the east. This puts our region in zonal
flow aloft with the Gulf moisture cut off as high pressure at the
surface overspreads the area.

Beyond Thursday an interesting pattern develops across the country.
As the aforementioned upper troughing continues to shift eastward, a
short wave diving almost due south across the western US is forecast
to deepen into a cutoff low by 12Z Friday along the NV/UT border.
The low is forecast to continue moving southward and expected to be
over the Baja Peninsula by the end of the period.

This scenario puts our region between the two systems, consequently
there are no frontal boundaries, zonal flow aloft with little to no
upper level energy, very little moisture to work with, and high
pressure at the surface. All of this translates to little to no
chances for precipitation through the end of the period. Will have
to monitor subsequent model runs closely for any synoptic changes.

Temperatures the first couple of periods are near normal, then drop
to below normal through the rest of the period.

&&

.AVIATION...
Issued at 1145 PM CST Sat Nov 26 2016

Complicated fog/low cloud forecast tonight. KPAH has already
developed dense fog on ASOS, but that seems to be a gross
overstatement of the conditions based on visual evidence at the
forecast office. The temperature at KPAH has dropped well below
guidance and the cross-over temperature, so a decent fog is
certainly a possibility overnight. However, there is some prospect
for light south winds to develop toward daybreak, and the air has
not been totally still to this point. All sites could end up in
this same situation. KCGI has the added issue of an expanding
mass of IFR ceilings to their west that could eventually
overspread that area. Of course that would likely limit the fog
potential there. Whatever happens will dissipate by around 15Z
and VFR conditions are then expected through the remainder of the
forecast.

The consensus of the 00Z guidance is to keep any shower activity
to the west of KCGI and the other sites through 06Z Monday.
Although they will be overspreading much of the area by 12Z
Monday. South winds will kick in a bit through the afternoon and
should not drop off much, if at all, after sunset.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...Dense Fog Advisory until 9 AM CST this morning for MOZ100-
     107>110-114.

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

$$

SHORT TERM...RJP
LONG TERM...JP
AVIATION...DRS



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