Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 241953

Area Forecast Discussion
National Weather Service Saint Louis MO
253 PM CDT Sat Mar 24 2018

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 248 PM CDT Sat Mar 24 2018

A great example of a classic mature cyclone setup is ongoing now
across our region, with a moderately strong surface LO over
southeast MO, with a warm front extending SE from this LO into
central TN and a cold front extending southwest from this LO into
northern AR.  The system is tilted to the northwest, where the
strong upper level system resides over central IA.  The LO has been
tracking along the preceding warm frontal path with a tight
temperature gradient along it, separating upper 30s and low 40s to
the north from mid 70s to the south.  Precipitation has diminished
significantly from what was there this morning, with one final swipe
of solid pcpn moving thru southwest IL, parts of STL metro and
southeast MO, and the pcpn much more spotty elsewhere.

Both the upper level and surface components of this storm system
will track southeast this evening, with the entire area returning to
the cold sector and clouds filling back in to portions of southeast
MO that had seen partial clearing.  Spotty pcpn will continue to
persist into this evening with deep cyclonic flow and some upper
level support in the north.  The pcpn heading into the night will
increasingly favor a drizzle setup, and as temperatures continue to
slip thru the 30s in the northern CWA, could see the pcpn end as a
brief period of freezing drizzle.  Warm surfaces and temperatures
right at the freezing mark should limit any ice accretion and
impacts. but it will need to be monitored over the next several
hours.  Otherwise, cloudy skies will persist with min temps only
dropping into the 30s.

Drier air from an increasingly influential high pressure system
centered over the Great Lakes will attempt to clear the clouds out
from the east, but this clearing may never be fully realized heading
further west into Missouri before the next pcpn producing system
arrives Sunday night.  Look for another cool day for most areas,
with max temps in the 40s.


.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 248 PM CDT Sat Mar 24 2018

Main focus for the remainder of the forecast period is still the
precipitation chances through Wednesday.

Still some difference in the models on timing of main cold front
that will begin to move through region Monday night. In the meantime
ahead of system, will see decent low level jet from the southwest
bringing in plenty of moisture with several waves along warm front.
PW values still between 1.25 and 1.50, and with some convection in
the mix, most of the area will see between 1 to 3 inches with
locally higher amounts possible for this event.

Showers and isolated storms to develop over western MO and slide
east across region beginning early Monday morning. By Monday night,
GFS is still a bit faster with frontal movement through region and
wetter, will keep blend which is between the GFS and slower NAM
solutions. Monday night through Tuesday will be the wettest period,
then taper off Tuesday night/Wednesday morning as front finally
exits region.

Secondary system on back side to slide through Wednesday night/
Thursday with scattered showers developing. Finally surface ridge
builds in with drier wx Thursday night through Friday night.
Extended models showing another system approaching in northwest flow
aloft, but differences in timing. For now just kept low chance pops
on Saturday.

As for temperatures through this period, near normal temps through
Wednesday, though will need to keep eye on this depending on
location of warm front, clouds and precipitation. Beyond that,
cooler than normal conditions expected into early next weekend.


.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1235 PM CDT Sat Mar 24 2018

IFR conditions will prevail at the TAF sites to begin the valid
period, with gradual improvement to VFR or MVFR from northeast to
southwest beginning tonight and continuing into Sunday. East to
northeast surface winds will prevail thru the valid period.
Otherwise, rain showers or drizzle will gradually diminish this
afternoon and this evening, possibly ending briefly as some
freezing drizzle or snow for the KUIN terminal this evening.

SPECIFICS FOR KSTL: IFR to prevail thru much of tonight with
gradual improvement into VFR between late tonight and Sunday
afternoon. There is a small possibility that the improvement will
be stunted to only MVFR conditions but steady east flow and this
is where the higher CIGs will approach from, have remained
optimistic. Otherwise a brief period of rain showers early this
afternoon otherwise rain showers or drizzle in the area thru this


Saint Louis     34  48  38  56 /  30   5  10  80
Quincy          29  43  33  52 /  40   0  10  80
Columbia        33  48  39  58 /  20   5  30  90
Jefferson City  33  49  40  59 /  10   5  40  90
Salem           35  48  37  57 /  40   5   5  80
Farmington      34  47  37  57 /  20   5  20  70



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