Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 180946

Area Forecast Discussion
National Weather Service Saint Louis MO
346 AM CST Thu Jan 18 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 326 AM CST Thu Jan 18 2018

The sfc ridge, currently centered over srn AR, will gradually build
east today. This will allow sfc winds to remain swly thru tonight,
while 850mb flow will remain wly. Mdls agree with the region
remaining largely free of clouds today, with cirrus across nrn
portions of the U.S. dissipating as they move south.

This is a great setup for a warming trend today, however, some
uncertainty remains as to how warm today will be. Mdls disagree
regarding how deep mixing will be today. There is still snow on the
ground across much of the area. A local climo study suggests
approximately a 20 degree rise from temps this morning based on
parameters mentioned above. Overall, made only minor changes to the
prev forecast, generally trending twd the cooler guidance. However,
did trend warmer across srn portions of the CWA where forests have
lower albedo.

As for tonight, have continued a cool trend with MOS generally being
too warm overnight.


.LONG TERM...  (Friday through Wednesday)
Issued at 345 AM CST Thu Jan 18 2018

The warming trend will continue with persistent south-southwesterly
surface winds Friday through most of the weekend.  Plenty of solar
insolation expected on Friday will also lead to above normal highs,
about 10 to 15 degrees above normal.  Rising surface dew points over
the cold ground may lead to advection fog late Friday night and
Saturday. Low-mid level warm air advection along with increasing low
level moisture may also lead to patchy drizzle Saturday and Saturday
night with weak upward vertical motion and shallow low level
moisture.  Despite increasing cloud cover highs on Sunday should
peak at about 20 degrees above normal.  More significant rain is
expected Sunday afternoon and night as an upper level low and
associated deepening surface low and trailing cold front move
through the region.  The models continue to trend a little slower
with the storm system with the ECMWF model still slower than the
operational GFS and also a tad further south with the track of the
surface low.  Either model solution still places our forecast area
in the warm sector of the low pressure system with a possible line
or band of showers and embedded storms moving through our forecast
area Sunday night.  The dry slot south of the upper level low will
shut down most of the precipitation on Monday, except for the
possibility of deformation zone light rain or snow over northeast MO
and west central IL in the wrap around moisture on the backside of
the surface low.  Colder air will advect into our area on Monday
after the passage of the surface low and trailing cold front.  The
chance of precipitation should end over the entire forecast area by
late Monday night with temperatures down to near normal levels by



.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1111 PM CST Wed Jan 17 2018

VFR conditions and SW surface winds are expected at the TAF sites
thru the valid period. Winds will strengthen somewhat during the
late morning and afternoon hours, with some potential for a brief
gust pushing 20kts possible.

SPECIFICS FOR KSTL: Other than above, surface wind direction
should remain above 210 for the first half of the valid period
with a more definitive slide to below 210 during the mid-late
afternoon and into Thursday evening.



Saint Louis     42  26  50  34 /   0   0   0   0
Quincy          37  23  46  32 /   0   0   0   0
Columbia        40  25  49  34 /   0   0   0   0
Jefferson City  42  24  51  34 /   0   0   0   0
Salem           35  21  44  32 /   0   0   0   0
Farmington      42  22  47  34 /   0   0   0   0




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