Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 251120
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
620 AM CDT MON JUL 25 2016

.SHORT TERM...(Today through Wednesday night)
Issued at 315 AM CDT Mon Jul 25 2016

The cold pool from the small MCS (Mesoscale Convective System)
along the Mississippi River in the Saint Louis Metro area is a
little more pronounced in the last couple of hours, but appears to
be modeled well by the CR version of the HRRR guidance at of 08z
(3 am CDT). The interaction of the MCS with the current pre-
frontal trough convection/outflows will suggest minor convection
leading into and along the Interstate 64 corridor before 7 am
CDT. May still need to do some last minute PoP/Weather adjustments
with convection as the NAM-WRF (NMM version) also seems to have a
good handle on the convection, but also develops a secondary zone
of convective activity in Southeast Missouri this morning in a
deeper plume of moisture. Can`t totally discount this modeling,
since satellite difference channels showing some new cloud
development over Southeast Missouri in the vicinity of the LAPS
theta-e maximum.

The aforementioned shower and thunderstorm activity will slowly
work southeast across the WFO PAH forecast during the rest of the
morning and into the afternoon today, with a relative minimum
(PoP-wise) during nighttime periods. The effective increase in
cloud cover and precipitation should mitigate significant heating
over parts of Southeast Missouri and Southwest Illinois, lessening
heat index values at or below 100 degrees. There will still be
heat index values in the 100-103 degree range over West Kentucky
and Southwest Indiana today, but given the scattered nature of
these "hot spots" will just address through the hazardous weather
outlook and other communication venues. Beyond today, heat
concerns should be mitigated through Wednesday.

The surface frontal boundary will slowly shift east-southeast
across the WFO PAH forecast area through Wednesday. Given the
variability in lift and shear through this area, kept most of the
thunderstorm activity within the chance probability category, but
used coverage wording through at least Tuesday to reflect the
higher confidence of the precipitation.

.LONG TERM...(Thursday through Sunday)
Issued at 315 AM CDT Mon Jul 25 2016

Forecast confidence is high for the overall synoptic pattern through
the extended, but as usual, the day to day convective details and
the resultant impact on cloud cover and temperatures will be
difficult to pin down.

The 00Z models continue to develop a weakness in the upper ridge
right overhead Thursday and Friday. This will lead to good coverage
of convection, lots of clouds, and possibly high temperatures a
degree or two below normal both days. 50-60% PoPs may not be high
enough depending on how organized the convection becomes. Figure on
locally heavy rainfall and lightning as the main concerns, but the
flow aloft will be increasing which would support a non-zero severe
threat.

The 00Z ECMWF develops a closed upper low over the upper midwest
Friday and then pushes it through the Great Lakes by Sunday morning.
This is by far the most intense trough, as compared to the GFS and
GEM, and would result in better shear and a better chance of a few
severe storms Thursday and especially Friday. At this point, it is
just something to keep in the back of our minds.

The other effect of the stronger ECMWF solution is the possibility
of a drying trend Saturday. However, it brings another weaker upper-
level disturbance through the region Sunday into Monday, so the
drying would likely be short-lived. Will not be able to remove PoPs
on Saturday with little model agreement, but will be able to go with
lower chances Saturday through Monday.

In the absence of convection and related cloud cover, temperatures
will generally be near normal levels with less humidity than we have
enjoyed over the last week.

&&

.AVIATION...
Issued at 620 AM CDT Mon Jul 25 2016

With the approach of a diffuse frontal boundary, it was a little
difficult to pin down mean wind direction changes associated with
any convection nearby each TAF location during the 24 hour
forecast period. Switched from mean southwest wind flow to
variable or calm winds in the vicinity of the frontal boundary.

Likewise, with the exception of MVFR ceilings in the 12z-16z time
frame, kept VFR ceilings in place for most of the forecast period
for each TAF location. A mention of showers was added when
guidance suggested a higher probability occurrence.

&&

.PAH Watches/Warnings/Advisories...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

SHORT TERM...Smith
LONG TERM...DRS
AVIATION...Smith


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