Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 270840
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
340 AM CDT WED APR 27 2016

.SHORT TERM...  (Through Late This Afternoon)
Issued at 339 AM CDT Wed Apr 27 2016

A strong upper level storm system was centered over western KS early
this morning with a RIDGE axis over our region.  The surface
reflection was located over central KS, showing that it had not yet
become occluded, with a frontal boundary that has become nearly
stationary stretching eastward to near the I-70 corridor in MO and
IL.  Temps were in the 50s and low 60s across our region with what
was a band of severe TSRA but has since weakened moving towards our
region from western MO.

The storm system center is expected to track northeast to the mid-MO
river valley by late this afternoon, and with the RIDGE axis over
our way slow to yield ground, will result in the TROF associated
with the storm itself to become increasingly negatively-tilted, with
the TROF axis anticipated to be over our region during the afternoon
hours.  At the surface, the low center will become occluded by
this afternoon with a new triple point likely just NW of STL metro,
with the old east-west quasistationary boundary extending east from
this, and a cold front extending south from the new triple point.

With all of this in mind, it appears the leading more active
convective edge currently from central to south-central MO will
become increasingly detached from the enhanced stratiform pcpn
behind it early this morning as it gradually dissipates, but
the leading edge convective elements should still sweep thru much
of the forecast area in the process accompanied by gusts of 30-
40mph.  This round is expected to exit into eastern IL by late
morning.

A brief period of quiet wx for midday looks likely before the
approach of the upper TROF and increasing instability should set
off numerous TSRA by mid-afternoon areawide.  The synoptic setup
will be such that if things can de-stabilize enough for the
afternoon, there will be a tornado threat, namely near and just
northeast of the quasi-stationary east-west frontal boundary that
will probably be just north of STL by this time.  Otherwise, the
environmental shear will be sufficient for storms capable of large
hail and damaging winds, notably along the edge of the approaching
dry slot from the west.  Maintained likely and categorical PoPs for
this afternoon.

Temps are going to be tricky again, with a lot of conditions being
set on pcpn development and cloud cover, so stayed within the
boundaries of MOS, with 60s north of the front and 70s elsewhere.

TES

.LONG TERM...  (Tonight through Tuesday)
Issued at 339 AM CDT Wed Apr 27 2016

Focus for the short term will be convection and severe potential.

Forecast for tonight is conditional on how storms today unfold.
Believe there will be two main areas of storms at the beginning of
the period. One area shud be across ern portions of the CWA where
storms developing this afternoon near the triple point move ewd.
These shud exit the area mid to late evening. The second area of
convection is expected across nrn portions of the CWA under the
better upper level support. What severe threat develops this
afternoon, will linger into the evening, but out of the region by
Midnight.

Mdls are in fairly good agreement over the remainder of the short
term. The upper low lifts nwd on Thurs, leaving zonal flow over the
region. Can not rule out precip across far nrn portions of the CWA,
but believe the bulk of the precip will remain N of the fnt on
Thurs. With the sfc ridge building into the region, the remainder of
the week, and thru the weekend, is expected to be seasonably cool.
There is still some question of temps for Thurs as the 850mb fnt is
progd to be across srn MO/IL. The going forecast may still be too
warm, however, with deeper mixing expected and some uncertainty,
believe trend is in the right direction.

Looking into the extd, the deep trof over the Rockies is still
expected to eject into the Plains on Fri, with precip spreading into
the area Fri night and continuing thru much of the weekend. The
system this weekend has similarities to the current system impacting
the area. There is differences among guidance and any severe threat
will be conditional on location of sfc features and therefore a low
probability attm.

With a sfc ridge building into the area Mon and thru the remainder
of the forecast period, chances for precip are small. Temps are
expected to be aob seasonal average thru mid-week.

Tilly

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1230 AM CDT Wed Apr 27 2016

Pockets of IFR are showing up here and there in observations
around the STL Metro area. Earlier guidance hinted at this and
subsequent runs continue to develop and expand IFR ceilings across
much of the area before daybreak. More confidence in this now
since it`s actually developing. Otherwise, expect waves of showers
and thunderstorms across the area over the next 24 hours...likely
ending early to mid Wednesday evening. Any thunderstorm will be
capable of lowering flight conditions to IFR. Hail and gusty winds will also be a continuing
threat.

Specifics for KSTL:

Looks like Lambert will be in and out of IFR ceilings for a few
hours and likely prevailing IFR by 09-11Z. The first wave of
showers and thunderstorms should be moving into the vicinity of
the terminal by 10Z. And then another wave of storms is likely
after 18Z Wednesday.  Strength of the storms is uncertain at this
time, but any storm could produce brief periods of IFR conditions
in heavy rain. Hail and gusty winds will also be a continuing
threat.


Carney

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     76  57  76  50 /  80  70  10  10
Quincy          67  52  69  45 /  80  70  20  10
Columbia        74  51  72  47 /  60  40  10  10
Jefferson City  77  52  75  48 /  60  30  10  10
Salem           75  59  77  50 /  80  70  10  10
Farmington      75  55  79  50 /  70  30   5  10

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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