Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 140809
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
309 AM CDT Mon Apr 14 2014

.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
afternoon.

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.

Truett

.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.

Kanofsky

&&

.AVIATION:  (For the 06z TAFs through 06z Monday Night)
Issued at 1028 PM CDT Sun Apr 13 2014

Cold front extending from a surface low over northwestern IL
southwest through UIN and COU will move sewd through the St Louis
metro area just after 06z Monday. The more significant showers and
storms will shift east of the taf sites by 06z Monday, but there
may be lingering patchy light rain or isolated light showers til
around 08z Monday. Surface winds will veer around to a nwly
direction after fropa, and will be relatively strong and gusty late
tonight and Monday due to a tight surface pressure gradient. The
wind will gradually diminish Monday night as a surface ridge
approaches and the surface pressure gradient relaxes. Ceilings
will likely fall into the IFR catagory behind this front, down to
around 1000 ft or slightly lower late tonight and early Monday
morning. The cloud ceiling will gradually rise Monday afternoon,
becoming VFR Monday evening. There will be some light rain mainly
Monday afternoon as an upper level disturbance moves through the
area, possibly mixing with or changing to light snow in UIN and
COU as colder air continues to filter sewd into the area.

Specifics for KSTL: The cold front will move southeastward through
STL just after 06z Monday. The more significant showers and
storms will shift east of STL by 06z Monday, but there may be
lingering post frontal patchy light rain or isolated light showers
until around 08z Monday. The surface wind will veer around to a
nwly direction late tonight after fropa. The wind will remain
strong and gusty through Monday, then diminish Monday night. The
cloud ceiling will lower into the IFR catagory late tonight and
early Monday morning after fropa. The cloud ceiling will gradually
rise into the MVFR catagory Monday afternoon, VFR Monday evening,
then finally clearing out completely late Monday night. Periods
of light rain can be expected Monday afternoon, possibly changing
to a little light rain/snow mix before ending early Monday evening.

GKS

&&

.CLIMATE:

RECORD LOWS FOR 4/15:

STL - 27 IN 1928
COU - 25 IN 1928
UIN - 24 IN 1928
FAM - 24 IN 1928


&&

.LSX WATCHES/WARNINGS/ADVISORIES:
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.

&&

$$

WFO LSX






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