Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 230457

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1157 PM CDT Thu Jun 22 2017

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 349 PM CDT Thu Jun 22 2017

Just a few showers are currently moving across southeast Missouri
into south central Illinois.  These are occurring on the northern
periphery of Tropical Depression Cindy.  Moisture and showers
associated with Cindy will be confined to the southeastern part of
the CWA while an shortwave trough moves across Iowa into Illinois in
the mid-level flow. This will in turn cause the cold front that is
currently over the Upper Midwest to drop south across the region
late tonight and on Friday at the same time the remnants from Cindy
moves northeast across Arkansas and Kentucky.  Have kept high
chance/low likely PoPs for showers and thunderstorms late tonight
through early afternoon on Friday before the rain moves southeast of
the area by late in the afternoon.

Agreeable MOS guidance looks good for lows tonight.  Highs tomorrow
will be closer to the SREF mean MOS temperatures.


.LONG TERM...  (Friday Night through Next Thursday)
Issued at 349 PM CDT Thu Jun 22 2017

Much cooler and drier weather will be the rule beginning Friday
night and lasting through the weekend and at least through early
next week.

Longwave trough will carve out across the eastern 2/3 of the CONUS
this weekend and early next week with northwest flow aloft across
the mid-Mississippi Valley. There looks to be at least a few
reinforcing shots of cooler air behind individual shortwave troughs
and associated cold fronts. The end result should be 4 days of well
below normal temperatures along with dry weather. While the
possibility of isolated instability showers cannot totally be
ruled out during the afternoon hours Sunday or Monday, better
chance of this activity will be further to the northeast where
stronger mid/upper level forcing will reside.

Very strong surface high (~1025 hPa) will settle into the bi-state
area early next week. This high will slowly slide to the east
Tuesday into Wednesday. Return flow around this high will bring
warm/moist advection which will bring an increasing threat for
showers and thunderstorms, mainly focused on the Wednesday/Thursday



.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1142 PM CDT Thu Jun 22 2017

An are of IFR ceilings developed over Illinois earlier in the
evening and is trying to spread very slowly westward. This area of
IFR ceilings may get into the STL Metro area later tonight, but
current model guidance is not very excited about this possibility.
Another area of MVFR ceilings developed over the eastern Ozarks
and is expected to spread slowly north through the remainder of
the night. A cold front over central Iowa will drop southeast
across the area from around 11Z through 17Z. Expect showers and
thunderstorms along and ahead of the front through the morning
hours. Also expect MVFR ceilings to move through with the
front...lifting and scattering out during the late morning and
afternoon from northwest to southeast.


IFR ceilings over central Illinois will try to build westward
toward the terminal...but model guidance is not showing that the
low ceilings will make it to Lambert. Otherwise, expect VFR
conditions to prevail until the cold front moves into the vicinity
of the terminal. Widely scattered showers and thunderstorms will
likely be in the vicinity of the terminal as the front moves
through. Expect an MVFR ceiling to move in with the front and
stick around through most of the morning before lifting and
scattering as drier air moves in behind the front.





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