Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 300027
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
727 PM CDT Mon Jun 29 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 347 PM CDT Mon Jun 29 2015

Isolated convection has formed over the last hour in a narrow
north-south band along the Mississippi River from near Quincy to
near St Louis. Could be a bit more development over the next
several hours, and then anticipate that this activity will quickly
dissipate with loss of heating.

However, upstream shortwave currently fueling convection over
eastern MN and nw WI will be dropping south overnight, and this
may return a low shower/thunderstorm threat to areas along and
north of I-70 in the midnight-daybreak time frame.

Truett

.LONG TERM:  (Tuesday through Next Monday)
Issued at 347 PM CDT Mon Jun 29 2015

(Tuesday-Thursday)

Weak ripples in the upper level NW flow will continue a threat of
showers and a few thunderstorms into the day on Tuesday.  Have
attempted to reflect a bit of a diurnal trend to the PoPs with
afternoon heating and instability leading to a bit more of a
threat/coverage, but this trend may certainly be altered by the
arrival of the difficult to time shortwaves.   At this point I`ve
only made modest tweaks to going forecasts, and will likely have to
save any major adjustments to the nowcast time frame.

Unfortunately, it appears that several rounds of convection...and
more heavy rain...are in the offing as we head into midweek. 12z
runs are maintaining trends of previous solutions in forecasting a
slight eastward shift of the upper level trof during this time,
which willl allow baroclinicity over the plains to work back to
the east. Deep UVV is progged to develop across the FA on Tuesday
night due to strong shortwave in the NW flow sweeping into the
mid-Mississippi Valley, with resultant low level WAA producing
strong isentropic ascent over eastward advancing baroclinic zone.
Resultant strong lift and rapid eastward advection of lower
tropospheric moisture should cause elevated convection to develop
during the late evening over western MO and then grow into an MCS
which will then work its way east-southeast late Tuesday night and
early Wednesday morning. This round of convection should then be
followed by more storms late Wednesday and Wednesday night as yet
another shortwave in the NW flow propagates into the region, with
both the GFS and NAM suggesting nearly persistent WAA/theta-e
advection over the southern half of the CWA in this time frame.
Both the GFS and the NAM are progging PWATS of over 2 inches in
our area heading into midweek, so storms should be efficient rain-
makers...again... It does appear that the heaviest rainfall may be
located over the southwest or southern half of the CWA (avoiding
the critically water-logged northeast half of the FA), but in
reality no spot in our CWA needs any more wet weather. Have
mentioned this heavy rain potential in a hydrologic outlook
issued earlier this afternoon.

A chance of thunderstorms will certain carry into Thursday, but it
does appear that the barrage of shortwaves in the Tuesday night-
Wednesday night time frame...along with the convection they
produce...will cause a southward and westward displacement of the
low level baroclinicity, lessening the heavy rain threat by that time.

(Friday-Monday)

Medium range solutions maintain ridging over the western CONUS and
a mean trof over the northeast U.S.,which places mid-Mississippi
Valley in the heart of the NW flow regime throughout the period.
With shortwaves rippling through this NW flow it appears that
there will be a chance of showers and thunderstorms throughout the
Friday-Monday time frame. There should be lots of dry time and
certainly don`t see any all-day rains at this point, but for now
no solution really offers any significant rain-free period.

Truett

&&

.AVIATION:  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 709 PM CDT Mon Jun 29 2015

Specifics for KCOU, KUIN: Generally VFR through the period,
although light fog is possible overnight at KUIN due to the
additional moisture near the airport from late afternoon rainfall.
Initially northwest winds will back and become westerly overnight,
then veer again and become northwesterly during the day on
Tuesday.

Specifics for KSTL, KSUS, KCPS: Isolated SH/TS near the St. Louis
metro area will affect all 3 terminals for the first 0-2 hours of
the TAF period. SH/TS should dissipate with the loss of daytime
heating. Winds will remain northwesterly to westerly through the
period. There is an increased chance of fog tonight at any
terminal which receives rainfall during the late afternoon and
early evening hours.

Kanofsky

&&

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

$$

WFO LSX






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