Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 252009

Area Forecast Discussion
National Weather Service Saint Louis MO
309 PM CDT Tue Jul 25 2017

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 308 PM CDT Tue Jul 25 2017

A few isolated showers and thunderstorms may be ongoing first thing
this evening in close proximity to stalled frontal boundary. Most
(if not all) activity should stay south of the area before
dissipating by mid-late evening hours. Rest of tonight is expected
to be dry with a light southeast wind. Seasonably warm minimum
temperatures are expected tonight due to an increase in sky cover
overnight in addition to high dewpoints. Forecast low temperatures
tonight should be in the low to mid 70s for most locations.

An area of showers and storms will likely be ongoing across the mid-
Missouri Valley on Wednesday morning. This area however should
dissipate or at least weaken substantially by mid-late morning. Only
effects for portions of our area will likely be an increase in
cloudiness across portions of mainly northeast Missouri. Heat will
be the big concern for tomorrow as 859-hPa temperatures increase to
around +20C. That factor combined with plentiful sunshine, deep
mixing, and seasonably high dewpoints should yield peak heat index
values of 103-107F for most of the area. Will therefore expand the
heat advisory to include these locations. Only area within the CWA
that looks to escape the advisory will be across portions of
northeast Missouri and west-central Illinois where slightly cooler
high temperatures (low 90s) are forecast.


.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 308 PM CDT Tue Jul 25 2017

An active period initially over the area will lead to unseasonably
cool weather this weekend into early next week over the area. A
short wave currently moving along the Canadian border along the
Washington  and Idaho state line will help to flatten out the ridge
and move it west to the southern Rockies by Wednesday night. This
will allow for northwest flow to setup over the area providing a
chance for severe weather over parts of northeast Missouri and
western Illinois on Wednesday night into early Thursday. The threat
will be associated with an elongated MCS projected to form in
southern Iowa Wednesday afternoon before moving southeast over
northeast Missouri and western Illinois.

The primary hazard will be damaging winds. A secondary threat will
be heavy rain with PW values over 2 inches over the area could lead
to a localized flash flood threat from I-70 north. This will be
dependent on speed of the MCS or if an outflow boundary becomes
stationary over the area allowing training of storms to occur over
the same area on Thursday. It should also be noted that soils are
excessively dry from I-70 northward.  The cold front moves south
providing additional chances for showers and thunderstorms on
Thursday along and ahead of the front.

The boundary will exit the area by late Thursday night. Afterwards,
the region will be wedged between a trough over the northeast and a
broad ridge over much of the west. A series of shortwaves within the
flow will provide some clouds and dry weather. The pattern will
allow for unseasonably cool air over the region this weekend into
early next week.



.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1229 PM CDT Tue Jul 25 2017

Stalled frontal boundary will produce some isolated showers and
thunderstorms but they should stay south of the terminals this
afternoon. Light east/southeast winds will become out of the
south/southwest late Wednesday morning as the aforementioned front
moves back northward as a warm front.


Dry/VFR expected through Wednesday afteroon. Could be some
isolated showers/storms Wednesday afternoon however as warm front
moves through the area. Winds will be primarily out of the
east/southeast prior that that frontal passage, and
south/southwesterly afterwards.



Saint Louis     78  99  77  88 /   0  10  50  50
Quincy          70  92  72  84 /   0  20  70  50
Columbia        71  94  73  85 /   0   5  60  50
Jefferson City  73  95  75  86 /   0   5  60  50
Salem           70  93  75  87 /   0  10  40  50
Farmington      72  94  75  88 /  10  10  30  50


MO...Heat Advisory from noon to 8 PM CDT Wednesday for Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-
     Montgomery MO-Osage MO-Reynolds MO-Saint Charles MO-Saint
     Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Warren MO-Washington MO.

IL...Heat Advisory from noon to 8 PM CDT Wednesday for Bond IL-
     Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Randolph IL-Saint Clair IL-Washington IL.



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