Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 222308
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
608 PM CDT Tue Oct 22 2019

.UPDATE...
Issued at 608 PM CDT Tue Oct 22 2019

Updated aviation discussion for the 00 UTC TAF issuance.

&&

.SHORT TERM...(Tonight through Friday Night)
Issued at 313 PM CDT Tue Oct 22 2019

An enhanced surface pressure gradient will stay in place over the
PAH forecast area through midweek, as one low departs to the north
away from the Great Lakes, and another moves into the upper Midwest.
In the deep South, the center of high pressure will move eastward.
Meanwhile, our region will be under cyclonic flow aloft. This
pattern will provide mostly clear conditions for much of the time,
with a substantial southwesterly breeze Wed afternoon. Temperatures
are expected to be a bit variable, and at or a little below
seasonable averages through the short term period.

Thu/Thu night, isentropic lift ahead of a mid level shortwave in the
southern Plains should bring moisture across mainly the northwestern
third of our region. How much moisture is in question, along with
how much lift will occur, because of differing scenarios between the
ECMWF/CMC and the GFS. For now, we will go with a slightly modified
blend for the forecast, with slight and chance PoPs for parts of
southwestern IL and southeastern MO for showers. At this time frame,
the ECMWF/CMC solution was drier because of anticyclonic flow ahead
of the southern Plains shortwave (depicted as a cut-off low), while
the GFS showed the shortwave and cold front punching through on Fri.

The 1st model solution keeps Fri mostly dry, then ramps up PoPs Fri
night as warm advection rains start up ahead of the ejecting low.
The 2nd model solution has our area dry after Fri afternoon. Our
blended forecast yielded a compromise...a dry Fri and limited PoPs
near the AR/TN state line late Fri night.

.LONG TERM...(Saturday through Tuesday)
Issued at 313 PM CDT Tue Oct 22 2019

The weekend forecast continues to be problematic on many levels
with both the deterministic and ensemble guidance split on
precipitation solutions (wet vs. dry).

The ECMWF and GFS model suite experienced some issues last week
in resolving the evolution of weather this past weekend, before
centering on a solution within approximately three days of the
event.

For this upcoming weekend, the GFS/GEFS guidance favors a faster,
open shortwave moving through the intermountain region Wednesday
into Thursday, while the Canadian (CMC-NH) and European (ECMWF)
guidance are eerily similar in favoring a sharp deepening of the
trough into a closed low over the Four Corners region of the
Desert Southwest by early afternoon on Thursday. Both of these
aforementioned numerical models actually continue to close off and
deepen the low over southwest Missouri by early afternoon on
Saturday. The orientation of this low, combined with its
ageostrophic response from the Gulf of Mexico/Lower Mississippi
Valley (in the form of an inverted trough at the surface),
suggest rapid warm/moist advection bodily through the low/middle
atmospheric layer. The ECWMF`s depiction of a 60-100 knot entrance
region 250 mb winds around the low suggest some rapid lift
potential as the low moves into and through the WFO PAH forecast
area Saturday evening. Would not be surprised to see some
isentropically-lifted precipitation break out much faster than
expected late Friday going into Saturday.

Given the continued model variance and forecast uncertainty,
adjusted rain chances upward with collaborative limits with
surrounding NWS offices. Once the next shortwave is amply sampled
within the remote sensing fields of WSR-88d Wind fields upper air
soundings later tonight and Wednesday, the forecast solution may
become more refined. At this point in time, should the ECMWF/CMC
pan out as advertised, later forecast shifts may need to bump up
PoPs and weather on Saturday and potentially shorten the duration
of time for precipitation over the weekend. Although a very short
term duration potential on Saturday, if the Canadian and European
solutions pan out, could see a brief potential for strong to
possibly severe storms during the late morning or early afternoon
on Saturday. Will wait and see.

All of the guidance keeps southwest flow aloft under ridging near
the surface into early next week, so dry conditions may be
maintained Sunday through early Tuesday. Another system is
forecast to enter the WFO PAH forecast area around the end of this
forecast period, but for now, kept rain chances low given
uncertainty on timing and location of the next system. The flow
aloft may limit the potential for temperatures dipping to freezing
or below for any measurable length of time.

&&

.AVIATION...
Issued at 608 PM CDT Tue Oct 22 2019

The TAFs are VFR. Overnight, expect clear skies and west-
southwesterly winds of 5-7 kts. Winds will increase again by late
morning into the afternoon hours, becoming southwesterly at at 10
to 15 kts with gusts up to 25 kts possible. Isolated mid-level CU
is possible in the afternoon. Winds will subside in the late
afternoon.

&&

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

$$

UPDATE...DWS
SHORT TERM...DB
LONG TERM...Smith
AVIATION...DWS


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