Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 220422
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1122 PM CDT THU JUL 21 2016

.UPDATE...
Issued at 1120 PM CDT Thu Jul 21 2016

MCS to our north continues to move south towards our region.

Western periphery has only recently begun to forward propagate to
the south, and have added this into latest forecast thinking,
adding PoPs for what essentially is the remainder of our forecast
area for late tonight and into Friday morning.

Still looks like heat and humidity will build in force for the
afternoon but how fast that happens and how much of the afternoon
that dominates looking more in doubt, now.

Severe potential continues to be minimal with lack of warnings
currently and as we head into the late night.

TES

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 323 PM CDT Thu Jul 21 2016

Isolated showers and thunderstorms began developing earlier this
afternoon within the region enhanced diurnal cu across eastern MO
and southwest IL where SBCAPE is 4000+ j/kg.  Warmer air aloft
compared to previous days and lack of any forcing mechanism has
limited both coverage and longevity. There will remain a threat of
short-lived isolated showers and thunderstorms through late
afternoon/early evening. Attention then turns to the overnight
period and potential for shower and thunderstorm activity to our
north to impact the area. The main focus tonight should remain
across the upper Midwest and into the Great Lakes region. North-
northwest flow aloft on the eastern periphery of the upper high
merits close watching of this activity. However, the aforementioned
warm air aloft featuring mid level temps of 13+ degC prevalent
across northern MO into west central IL should prove detrimental to
organized convection. Warm and humid conditions tonight will remain
the key story.

Glass

.LONG TERM...  (Friday through Next Thursday)
Issued at 323 PM CDT Thu Jul 21 2016

Still looks like Friday and Saturday will be the hottest days during
this heat wave. Models have been consistent with 850 temps in the 22
to 25C range, giving us highs in the 95 to 100+ range both days.
With dewpts in the 70s, will continue to see heat index values well
over 105. As for precipitation chances on Friday they are very low
due to strong capping, so kept slight chance pops for southern
portions of forecast area, depending on where any boundaries may
trigger isolated activity similar to today. As for Friday
Night/Saturday, models are indicating more MCS development along
boundary to our north, which may track a bit more to the south or
southeast, so have slight chance pops mainly for areas along and
east of Mississippi River for Friday night and most of forecast area
on Saturday. SPC has placed areas to the east of Mississippi River
in a marginal risk for Saturday.

With the slower movement of this frontal boundary, the update to the
Heat Warning still looks good with it going til 8 pm Sunday. Will
see increasing chances of showers/storms on Sunday, mainly over
northeast MO, west central/southwest IL.

Front to begin moving into forecast area by 00z Monday and stalling
out just south of forecast area by Monday evening. Best chance of
storms will be Sunday night and Monday before tapering off Monday
night. Will see temps near normal for rest of forecast period with
next best chance for rain Wednesday night and Thursday.

Byrd

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1116 PM CDT Thu Jul 21 2016

MCS to our north looks like it will affect much of the forecast
area to varying degrees late tonight and Friday morning, with UIN
the most likely, COU the least likely, and STL metro sites
somewhere in the middle as it stands now. Will handle with at
least a wind shift/gust front and VC for now and may introduce
TEMPO into UIN. Confidence is low on how long this will last at
each site, but initial guess will be 2-3 hours on VC handling.

TES

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Excessive Heat Warning until 8 PM CDT Sunday for Audrain MO-
     Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
     Gasconade MO-Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln
     MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-
     Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Charles MO-
     Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Shelby MO-Warren MO-Washington MO.

IL...Excessive Heat Warning until 8 PM CDT Sunday for Adams IL-Bond
     IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-
     Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-
     Montgomery IL-Pike IL-Randolph IL-Saint Clair IL-Washington
     IL.

&&

$$

WFO LSX



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