725 
FXUS63 KLSX 060503
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1203 AM CDT Fri Jun 6 2014

.UPDATE:
Issued at 910 PM CDT Thu Jun 5 2014

Making some changes to the forecast for the rest of tonight.
Primarily to PoPs. Looks like focus for convection will be down
across southern Missouri and that the storms up in Iowa which
might have threatened parts of northeast Missouri/west central
Illinois have pretty much died out. With the shortwave moving
rapidly east through the Upper Mississippi Valley, I think
regeneration is unlikely. Latest RAP and HRRR still indicate that
some of the southern convection could clip the far southern
portions of our CWFA overnight, but it looks like the vast
majority of our area should stay dry.

Carney

&&

.SHORT TERM:  (Through Late Tonight)
Issued at 256 PM CDT Thu Jun 5 2014

Unsettled weather is expected to continue over the next several
days due to multiple shortwaves interacting with a quasistationary
front as it sloshes back and forth across the region.

Tonight...There are two areas where precipitation is possible this
evening and overnight. The first area is across the northern CWA
within a zone of ascent ahead of an elongated mid/upper trough
moving through the northern plains. Afternoon SHRA/TSRA have
already developed along an upstream surface trough/front in NE/KS
aided by ascent from this trough, and the precip could move
eastward into northeast MO/west central IL if it persists.
However, the H5 trough axis is forecast to move quickly eastward,
and upstream SHRA/TSRA may not persist long enough to reach the
LSX CWA in the absence of upper level support. 

The second area is across the far southern CWA where a developing
LLJ should interact with a quasistationary front across southern
MO, leading to another MCS tonight. The position of the synoptic
scale quasistationary boundary has been pushed farther south by a
mesoscale outflow boundary from the large MCS which moved across
southwestern MO earlier today. Initial thoughts are that today's
MCS will have pushed the effective boundary far enough south that
the main precip threat from an MCS during the overnight hours
should be south of the CWA, although there is uncertainty about
the location of scattered WAA pcpn. This fits reasonably well with
forecasts from the local WRF, GFS, and ECMWF regarding placement
of MUCAPE and H7-H85 moisture convergence. The areal coverage of
likely PoPs has been reduced accordingly, although it may still be
too high depending on where the MCS forms.

Kanofsky

.LONG TERM:  (Friday through Next Thursday)
Issued at 256 PM CDT Thu Jun 5 2014

Friday through Sunday...There may be a brief break in the
precipitation on Friday due to shortwave ridging aloft across most
of the area. Scattered SHRA/TSRA remain possible across the
southern CWA due to the presence of a boundary and weak
shortwaves. 

High pressure moving out of Canada will push a cold front into the
northern and central plains on Fri night and Sat, but this
boundary appears to remain distinct from the quasistationary
front/developing warm front located farther south, at least
initially. In any event, precipitation should spread across the
area on Sat/Sat night due to a combination of factors associated
with an approaching shortwave, starting with a developing H85 LLJ
on Fri night which will interact with the quasistationary boundary
across MO/KS, leading to increasing precipitation chances by
daybreak as the shortwave progresses eastward. Isentropic ascent
also increases along the 305-315 K surfaces during the day on Sat
as the boundary starts to lift north as a warm front. Models have
been consistently showing that this shortwave also induces a
surface low along the western part of the stalled boundary (which
may have been reinforced by the cold front dropping south out of
the northern plains) which then tracks northeastward through MO
into IL. Forecast PW values of 1.8-2" on Sat are at +2 SD for June
across this part of the country, suggesting that locally heavy
rainfall is possible. The precipitation should taper off on late
Sat night with the passage of the shortwave. Another shortwave may
or may not approach the area on Sunday, but it is difficult to
discern whether this feature is a shortwave or the result of
convective feedback.

Monday through Wednesday...Compared to the 04/12z runs and the 
05/00z runs, the 05/12z model runs have come into astounding
agreement regarding the large scale pattern during Mon-Wed.
ECMWF/GFS/GEM all show a closed low developing over the central
CONUS after two vort maxes become phased over MO/AR/IL. Despite
the remarkable agreement between models, I am hesitant to buy into
this solution right away because it seems unlikely that all of the
models are accurately capturing the timing and placement of weak,
unsampled, and occasionally ill-defined shortwaves this far in
advance and in the presence of convective feedback issues. Due to
low confidence, this forecast package generally followed the
recommended CR initialization for Mon-Wed.

Kanofsky

&&

.AVIATION:  (For the 06z TAFs through 06z Friday Night)
Issued at 1155 PM CDT Thu Jun 5 2014

Latest surface analysis shows convective generated outflow
boundary continues to extend from north-central Oklahoma through 
far northwest Arkansas then southeast into northern Alabama. This
front will begin to move northeast late Friday evening and early
Saturday morning.  

Specifics for KSTL: Clear skies will give way to lower
visibilities in light fog after 0900 UTC Scattered to borken layer
of stratus around 010 kft may form after 0900 UTC. Stratus clouds
will give way to scattered clouds above 030 kft after 1400 UTC.
Winds will be light and variable. 

RP

&&

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

$$

WFO LSX