Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 232046
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
346 PM CDT SAT JUL 23 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 320 PM CDT Sat Jul 23 2016

A few short-lived showers have developed this afternoon within the
area of enhanced cu across east central/south central MO. Warm
air aloft and weak shear has limited coverage and longevity. There
will remain potential for isolated short-lived showers and storms
through early evening within this area of enhanced cu. Otherwise
the main convective action tonight is expected to be focused from
the northern Plains across the Upper MS Valley and into the Great
Lakes region in proximity to the quasi-stationary front and
residual outflow boundaries. A decidely more westerly component to
the mid-upper flow tonight compared to several nights ago in
conjunction with a veering LLJ "should" result in forward
propagating systems. The other feature of interest is a trailing
vort max currently embedded in the weak flow aloft in eastern KS.
This feature has quite a bit of mid cloud with it and could
produce some spotty high-based precipitation as it moves east
tonight. I have mentioned slight chance pops across the far
northern CWA to account for this.

Glass

.LONG TERM...  (Sunday through Next Saturday)
Issued at 320 PM CDT Sat Jul 23 2016

The dangerous heat and humidity will be in full swing on Sunday
and this could possibly be one of the hottest days of this
prolonged heat wave. A more westerly component to the low level
flow and continued presence of the pronounced thermal ridge would
support hotter temps than today. A cold front will begin moving
into northeast MO and west central IL during the afternoon. The
heat and humidity will continue to fuel a very unstable air mass
across the region during the afternoon and this frontal boundary
combined with a weak impulse tracking across the MO/IA border
should aid in the development of scattered thunderstorms. Deep
layer shear is weak, and any severe threat would appear to be
downburst winds associated with pulse type storms or where
multicell storms could produce merging cold pools and hence
something with a bit more organization. Further south we may
continue to see the spotty type showers and storms like those of
today in the afternoon.

The east-west oriented cold front will continue to sag southward
on Sunday night in response to a short wave trof digging from the
upper MS Valley into the western Great Lakes. The front should
extend roughly from northern IN into the St. Louis area into
southern KS at 12z Monday, with the front then moving south of the
CWA by early Monday evening...ending the current heat wave. A
series of weak impulses within the flow aloft in addition to the
frontal convergence and that associated with outflows will support
clusters of thunderstorms along/ahead of the front from Sunday
night through Monday. The front eventually stalls by early Tuesday
from AR into the TN valley region with pops generally confined to
the frontal zone including portions of southern MO and southern
IL. The GFS appears to be a bit too far north with the extent of
precpitation during this time frame.

The upper air pattern within the extended forecast period
features an upper high near the southern portion of the Great
Basin with a broad upper trof from the upper MS Valley through the
Great Lakes into the NERN states. The resultant west-northwest
flow aloft will feature a series of short waves and weaker low
amplitude disturbances traversing the Upper-Mid MS Valley. These
features combined with the frontal boundary wavering first north
and then south will keep an extended chance of showers and
thunderstorms in the forecast and largely near average temps. The
Wed-Thurs period would appear to have the highest chance of
thunderstorms during the day4-7 forecast period.

Glass

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 134 PM CDT Sat Jul 23 2016

VFR conditions expected through forecast period. Any storms that
develop will be widely scattered, so kept tafs dry at this time.
As for winds, light south to southeast winds to veer to the
southwest by mid morning on Sunday at KUIN as cold front
approaches area.

Specifics for KSTL:
VFR conditions expected through forecast period. Any storms that
develop will be widely scattered, so kept taf dry at this time.
As for winds, light southeast winds to veer to the south by 01z
Sunday and then to the southwest and pickup by 18z Sunday at KSTL.

Byrd

&&

.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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