Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 222140

Area Forecast Discussion
National Weather Service Saint Louis MO
340 PM CST Sun Jan 22 2017

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 339 PM CST Sun Jan 22 2017

Wound up low pressure system over the Deep South continues to sling
moisture back up into the Mid Mississippi Valley.  295K isentropic
surface shows a well developed cyclonic turning moist conveyor belt
over northern Arkansas and Missouri matching up well with a
deformation zone. Present indications are that the moisture will
drop further south by late this afternoon and early evening, and the
deformation zone will weaken as well.  Did hold on to some slight
chance PoPs over our southern counties until 02Z as the moisture
will hang on over southeast Missouri longest.  Remainder of the
night should be cloudy but dry with temperatures falling into the
30s.  A weak ridge will build over the area on Monday ahead of the
next storm system over the Great Plains.  Think clouds will be slow
to clear, but we may see some sunshine late in the day.  With
stubborn clouds and northwest flow, temperatures will be a little
cooler than they`ve been recently, but still well above normal in
the mid and upper 40s.


.LONG TERM...  (Monday Night through Next Sunday)
Issued at 339 PM CST Sun Jan 22 2017

A weak RIDGE will sneak thru our region Monday night, followed
quickly by another strong Pacific storm system approaching late
Tuesday.  The track of the storm center heading into Tuesday night
remains more or less the same to our north thru IA, but the
strengths of the system depicted by the various models continues to
vary widely.  The NAM, for instance, has an open upper wave, while
the GFS has a closed, much deeper, system.  The end result for our
region doesn`t look to change much, however, with pretty weak lift
to the south of the system and low PoPs continuing for the period
from Tuesday afternoon thru Wednesday evening.  Pcpn-types of
what does fall should be mostly rain as temps remain above average
here, but may mix with snow at times in the northern regions.

Heading into Thursday and thru next weekend, models continue to
show additional weak upper level disturbances sliding down into our
region from the resultant northwest flow aloft as a longwave TROF
carves into the eastern CONUS early in this period and then
persists.  Confidence on pcpn from any one of these individual
disturbances is low, but this is typical for a northwest flow
scenario and do not expect to get a decent handle on any one of
these until we get within 36hrs or closer of the event.  So don`t
be surprised that the dry late week and weekend forecast has PoPs
introduced at some later date.

Otherwise, temperatures are expected to remain above average until
the middle of the week when the longwave TROF develops, with
temperatures more appropriate for late January for late week
and into next weekend.



.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1147 AM CST Sun Jan 22 2017

An area of mainly IFR ceilings along the I-44/I-55 corridor
should slowly dissipate this afternoon which should leave the area
with VFR ceilings into the evening. Expect the lower clouds over
northwest Missouri and Iowa to eventually move over our area
during the mid to late evening. Expect low-end MVFR and IFR
ceilings to then prevail through Monday morning. While these
general trends look sound...exact timing and ceiling heights are
low confidence.


Watching IFR ceilings at Lambert. Current satellite trend is to
clear out the low clouds, but confidence on timing is low right
now. Once the low clouds clear out, Lambert should stay VFR until
sometime during the late evening or early overnight hours. Again,
the timing on lowering ceilings is uncertain, but I leaned
pessimistically and brought ceilings down earlier than guidance
suggested. Once ceilings drop, expect low end MVFR or potentially
IFR to prevail through Monday morning with improving conditions in
the afternoon.





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