Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 141756

1256 PM CDT Mon Apr 14 2014

Issued at 1243 PM CDT Mon Apr 14 2014

Minor update to going forecast to lower temps slightly. Cu field
shud remain bkn thru the afternoon limiting any heating. This will
also increase chances of SN across much of the region. However,
have kept RA/SN mix mentioned as DZ shud persist thru much of the
afternoon before the SN begins. Precip may also begin briefly as
RA before ice crystals are introduced.

Mdls are conflicting as to exactly how precip will move thru the
region. The HRRR/local WRF and to some degree the 12z 4km NCEP WRF
suggest the ongoing area of SN will lift newd without much ewd
progression. Have not changed POPs much as even if the RA/SN does
not move across the entire CWA this afternoon, the entire area
shud see DZ at times for much of the day.



.SHORT TERM:  (Through Late This Afternoon)
Issued at 304 AM CDT Mon Apr 14 2014

Cold front continues to push southeast across the CWA early this
morning.  FROPA has just occurred at STL, and at the current speed
front should clear our far SE counties before 12z.

Interesting spring forecast for today as unseasonably cold air
surges into the mid-Mississippi Valley.  There should be a bit of a
lull in the wet weather this morning as the region is between
shortwaves, but expect precipitation to ramp back up later this
morning and especially into the afternoon as shortwave enters the
bottom of the trof and pushes into the area.

There will be some ptype issues today as the cold air deepens across
the area.  Critical thickness values drop fairly rapidly over the
northwest half of the CWA already this morning, but forecast
soundings indicate that the morning lull in precip will allow for a
slight moderation in surface/low level temps as well as a slight
increase in the freezing level. However, the next round of afternoon
precipitation will produce some evaporative cooling that will cause
low level temps to drop once again.  Will take the mention of snow
as far east as a PPQ-VIH line this afternoon, but bottom line is
that ptypes will be messy due to the localized effects of
evaporative cooling on low level thermal profiles...especially this

Temps in our far SE counties will likely fall all day today as
they are just now getting into the heart of the CAA. Our NW
counties may see temps rebound several degrees this morning with
the lull in precip, but will likely fall once again this afternoon
as round 2 of the precip develops.


.LONG TERM:  (Tonight through Sunday)
Issued at 304 AM CDT Mon Apr 14 2014

There are three primary forecast issues for the extended forecast:
a hard freeze tonight, a rapid warm-up on Wed, and a possible
frontal system during Fri-Sat.

Hard freeze tonight...Expect some lingering precipitation before
midnight tonight due to a vort max in the base of an upper level
trough as the trough moves east of the region. BUFKIT profiles
suggest that some of the precip may fall as snow (possibly mixed
with rain), but no accumulation is expected because the ground is
still warm. Temperatures are expected to fall into the mid 20s to
lower 30s due to the unseasonably cold air mass. Temperatures are
expected to remain several degrees below freezing for at least 4-6
hours, therefore a Freeze Warning is warranted because the
growing season has started with the recent warm weather.

Warm-up on Wed...Winds turn southerly by 12z Wed around the back
side of a high pressure center, and the pressure gradient will
tighten ahead of a developing surface low over SD/NE with a
secondary surface low taking shape over the OK/TX panhandles. The
tightening pressure gradient will produce breezy south winds on Wed,
contributing to a rapid warm-up. Went a few degrees warmer than
guidance since guidance has not been warm enough on days with
favorable warming signals. The frontal system discussed below
would tend to keep temperatures warm through Thu.

Possible frontal system late in the week...The upper vort max
associated with the aforementioned northern surface low will quickly
lift toward the Great Lakes on Wed night and Thu. Models depict a
cold/quasistationary front stretching from northern KS through
extreme northwest MO into central IA towards WI with very little
southwestward progress due to the absence of upper forcing once the
system has lifted to the northeast. This front then lifts north as a
warm front once another vort max crosses the Rockies over CO/NM and
the entire southern system lifts northeastward. Models continue to
disagree on how much interaction occurs between a vort max over
southern Canada/northern Plains and the southern system as it lifts
into the central Plains. Chance PoPs look reasonable for now.



.AVIATION:  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1208 PM CDT Mon Apr 14 2014

Area of SN continues to move ewd. Have made some slight changes to
the prev TAFs based on latest RADAR trends and mdl guidance.
Confidence is higher that precip will be all SN at COU/UIN early
this afternoon. With ample cloud cover across the region, believe
temps will remain cold enuf for all SN at SUS/CPS late this
afternoon. However, with some uncertainty and since main focus
shud be nw of sites, will leave precip as a RA/SN mix for now.
Beyond precip, cigs shud lift quickly and remain VFR thru the
remainder of the TAF period.

Specifics for KSTL: With clouds expected to remain in place,
precip this afternoon has a better chance of being SN. However,
with placement of precip wrt the terminal, precip may remain as a
very light RA or more likely DZ. Beyond precip this afternoon,
cigs shud lift quickly to VFR and remain VFR thru the remainder of
the TAF period.



MO...FREEZE WARNING from 11 PM this evening to 9 AM CDT Tuesday FOR
     Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Knox MO-Lewis
     MO-Lincoln MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-
     Montgomery MO-Osage MO-Pike MO-Ralls MO-Reynolds MO-Shelby
     MO-St. Charles MO-St. Francois MO-St. Louis City MO-St.
     Louis MO-Ste. Genevieve MO-Warren MO-Washington MO.

IL...FREEZE WARNING from 11 PM this evening to 9 AM CDT Tuesday FOR
     Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-
     Greene IL-Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe
     IL-Montgomery IL-Pike IL-Randolph IL-St. Clair IL-
     Washington IL.



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