Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 150537
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1137 PM CST Thu Dec 14 2017

.UPDATE...
Issued at 1132 PM CST Thu Dec 14 2017

Late evening grid update focused on cloud cover and temperatures.
Latest satellite and observations show low clouds persisting back
through southern and central Missouri. Therefore less optimistic
of a clearing, and given recent model trends have sided with the
clouds sticking around through the night. Temperatures have also
been nudged up a degree or two due to the cloud cover.

&&

.SHORT TERM...(Tonight through Saturday night)
Issued at 239 PM CST Thu Dec 14 2017

Surface high pressure will keep the region relatively calm and
cool tonight and Friday, as a weak upper-level trough moves east
through the region. The low clouds are still expected to hang
around for most of the night before clearing overnight. There will
be some higher clouds associated with the upper trough over the
region when the low clouds dissipate, but they too should clear
early Friday morning. Plenty of sunshine, west winds and a dry
airmass expected Friday should allow for nearly 10 degrees of
warming compared to today.

Ridging aloft will build over the region Saturday. Southerly winds
will develop late Friday night and increase and become gusty
Saturday. The warming trend will definitely continue into Saturday
with most locations climbing well into the 50s or several degrees
above normal. Tried to lean toward the warm side of guidance both
days.

An upper-level trough will eject out of northern Mexico Saturday
night, as more substantial energy drops into its place. This will
result in the system dampening as it rides up the west side of the
upper ridge. This system will tap some moisture, but how much
forcing is left as it reaches our area will determine how much
rain we will get.

There will be a ton of dry air to overcome, but most of the 12Z
guidance does bring some modest rainfall at least into southeast
Missouri by 12Z Sunday. The NAM is the slowest and keeps the
entire area dry, while the GFS is the most aggressive and brings
the rain through the Purchase Area and the southern tip of
Illinois. The 12Z ECMWF is in the middle ground spreading the
rains through much of southeast Missouri. NAM and GFS soundings
agree that the freezing line will be near 700mb with plenty of
warm air to keep the precipitation all rain. There will be no
instability to work with, so this should be a stratiform rain
event.

.LONG TERM...(Sunday through Thursday)
Issued at 239 PM CST Thu Dec 14 2017

Fairly high confidence in the storm system bringing rain and warmer
temperatures this weekend.

The models have been locked onto this system for numerous cycles.
There are some minor strength differences among the deterministic
models but too small to be of concern. This system is generally a
weak perturbation in the southwest flow with a warm front as a
surface reflection. With temperatures expected to be in the 40s and
50s with this system...all liquid is expected. Also with little to
no CAPE combined with positive LI`s and K index values less than
30...we do not anticipate thunder at this time. I do think we will
be able to narrow the longevity of the pops with this system as it
nears. The models start to diverge with what I would call the main
trough lifting out of the southwest and through the region early
next week. Currently the blend lingers a pop into early next week.
Although confidence is not very high with this scenario...will
embrace the light pops of the blend at this time. For the most part
temperatures will be above normal through the extended. The models
are trying to bring in yet another system for the end of the
week...but its mostly outside the valid time of the current
forecast. Will monitor closely to see how this evolves with future
runs.

&&

.AVIATION...
Issued at 1128 PM CST Thu Dec 14 2017

A large mass of low clouds over the lower Ohio and mid Mississippi
Valleys is proving very difficult to dislodge. Computer model
moisture profiles suggest drying will be very slow to occur.
Therefore, the 06z tafs have been made more pessimistic. Broken to
overcast low clouds should persist for much of the period. Cloud
bases will be mainly vfr, though some pockets of mvfr cigs are
possible. As winds become southwest Friday evening, dry air should
finally arrive from the southern Plains. No vsby restrictions are
anticipated. Winds will gradually back from northwest to southwest
over the next 24 hours.


&&

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

$$

UPDATE...SP
SHORT TERM...DRS
LONG TERM...KH
AVIATION...MY


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