Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 230946
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
446 AM CDT Mon Mar 23 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 346 AM CDT Mon Mar 23 2015

Surface low over north central Missouri will move southeast today
and should be in the vicinity of the STL Metro area around 18Z.  Low
level warm advection and moisture convergence ahead of the low is
producing isolated to scattered showers and even a clap of thunder
or two across northeast Missouri.  Expect this activity to continue
to spread southeast into the CWFA today.  Not really sure how far
south it will progress...but scattered showers producing a few
hundredths of an inch of rain look likely generally along and north
of I-70 today with decreasing chances for measurable precip further
south.  Temperatures are going to be tricky today...actually
temperatures are going to be tricky pretty much through Wednesday.
Decent warm advection ahead of the cold front today will likely be
offset somewhat by clouds and light precip.  Regardless, there will
probably be around a 20 degree temperature spread between Quincy and
Farmington.  In this kind of setup, highs are pretty much guaranteed
to be wrong across much of the area.  I just tried to minimize the
damage using a blend of guidance which yielded mid 40s across
northern zones to low-mid 60s along the I-70 corridor to near 70 in
southern zones.

Carney

.LONG TERM:  (Tonight through Sunday)
Issued at 446 AM CDT Mon Mar 23 2015

Guidance is in good agreement that the surface cold front will make
it through the entire CWFA and down into southwest Missouri by 12Z
Tuesday morning.  The strong high pressure currently over the Great
Lakes region will funnel some fairly chilly air on east-northeast
flow into the region and MOS guidance is in pretty good agreement on
lows tonight with temps ranging from the low to mid 30s across
northern zones.  Still looks like good warm advection aloft late
tonight into Tuesday morning.  Timing may be a bit of an issue for
official PoPs tonight as rain will likely be arriving across
northern zones sometime between 10Z and 14Z.  However, since models
tend to be a little slow with warm advection precip, have stuck with
likely/categorical PoPs from central Missouri through west central
Illinois.  Temperatures will again be basically impossible to get
right on Tuesday as the surface boundary lifts back to the north as
a warm front.  Latest guidance suggests that it might get as far
north as the I-70 corridor or perhaps into northeast Missouri/west
central Illinois, although clouds and precipitation may make this
difficult.  SPC moved the slight risk for Tuesday afternoon/evening
further to the southwest where short-range models are indicating
greater instability.  Can`t say this is an unreasonable move;
however am still concerned that there will be considerable deep
layer shear and as much as 1000-1200 J/kg MLCAPE in central Missouri
along with some eye-popping values of 0-1km helicity in the 200-400
m2/s2 range.  Given these parameters I wouldn`t be surprised to see
some supercells with locally damaging winds and perhaps some
tornadoes.

Should have a break in the storms overnight Tuesday night into
Wednesday morning.  However the surface cold front which was
supposed to drop across the eastern Ozarks behind Tuesday evening`s
storms doesn`t quite make it that far south according to the latest
model runs.  In fact, it now looks like it won`t even make it
through the STL Metro area...and this will set the stage for another
round of potential severe weather.  Latest Day 3 Outlook from SPC
encompasses the entire southern 2/3 of the CWFA in a slight risk.
Greatest instability looks like it will stay south of the I-44
corridor with MLCAPE once again exceeding 1000 J/kg according to
both the GFS and the NAM.  Think the NAM CAPE values are probably
too high due to higher boundary layer temperatures/dewpoints.  Not
sure it will be quite as warm and moist as the NAM says since it
tends to be too aggressive in these situations; and I prefer the
more conservative GFS for now.  Still, another round of severe
thunderstorms looks likely, with the potential for large hail and
damaging winds, and possibly some training and heavy rain until the
front finally pushes through after 06Z.

Thankfully, the remainder of the forecast for Thursday through
Sunday looks quieter...if chilly.  A blast of Canadian air will move
into the Midwest behind Wednesday night`s FROPA and temperatures
look to fall well below normal.  Highs will drop from the 50s on
Thursday into the 40s for Friday and Saturday.  A hard freeze looks
possible...if not likely for Saturday morning with lows dipping into
the low to mid 20s.  Should have a warm up on Sunday as the Canadian
high moves down into the southeast CONUS and south-southwest flow
develops over the mid Mississippi Valley.

Carney

&&

.AVIATION:  (For the 06z TAFs through 06z Monday Night)
Issued at 1146 PM CDT Sun Mar 22 2015

Present indications are that VFR flight conditions should prevail
through 12z with a general increase in clouds from 5,000-7,000 ft
overnight. Still appears a cold front will progress across the
region on Monday accompanied by scattered showers, maybe an isolated
thunderstorms Monday morning. Maintaining the mention of showers
into the TAFS. While there is currently no visibility restriction
mentioned, that is more a reflection of the uncertainty in
coverage and intensity. MVFR flight conditions/CIGS should settle
into the terminals in the wake of the cold frontal passage and
persist through the end of the valid TAF period.

Specifics for KSTL:

Still thinking that VFR flight conditions should prevail through
12z with a general increase in clouds from 5,000-7,000 ft overnight.
A cold front is on track to move across the region on Monday
afternoon accompanied by scattered showers. Maintaining the mention
of showers into the TAFS. While there is currently no visibility
restriction mentioned, that is more a reflection of the
uncertainty in coverage and intensity. MVFR flight conditions/CIGS
should settle into the terminal in the wake of the cold frontal
passage at 21z and persist through the end of the valid TAF
period.

Glass

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     60  41  63  50 /  30  40  70  70
Quincy          47  35  52  45 /  40  70  90  80
Columbia        62  44  67  45 /  20  60  70  70
Jefferson City  64  45  69  46 /  20  50  70  70
Salem           57  39  61  51 /  30  20  60  70
Farmington      66  46  70  50 /  20  20  40  60

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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