Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240448
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1148 PM CDT SAT JUL 23 2016

.UPDATE...
Issued at 933 PM CDT Sat Jul 23 2016

Current IR satellite imagery depicts a complex of showers and
thunderstorms near the Chicagoland area propagating to the
southeast. Unlike a couple of nights ago...this complex should
stay well to the NE of the CWA as Corfidi vectors are much more
easterly compared to two days ago. A midlevel cloud deck extended
further to the southwest and is now across northern portions of
the CWA. Updated cloud cover trends through the night increasing
clouds for the NW third of the CWA while also boosting low
temperatures a couple of degrees due to this cloud cover. Looking
upstream...very strong cap across the mid-Missouri Valley with
700-hPa temperatures of aoa +14C. HRRR does try and develop storms
up that way which seems suspicious. It typically is very very
difficult to get convective initiation with that much
capping...particularly with a lack of very strong forcing like
tonight. Long story short...expect a dry night tonight so reduced
the schc PoPs across NE MO and W/C IL overnight tonight.

Gosselin

&&

.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 06z TAFs through 06z Sunday Night)
Issued at 1142 PM CDT Sat Jul 23 2016

Strong capping across the mid-Missouri Valley should prevent
thunderstorms from initiating. Consequently...am expecting a dry
forecast for the terminals for the rest of tonight and into at
least early on Sunday. Scattered thunderstorms are expected to
develop along the cold front by afternoon and slowly sag
southward. Have added a VCTS group at each terminal to account for
this. In addition...could also see some isolated diurnal type
thunderstorms within the warm sector on Sunday afternoon/very
early evening...particularly across the eastern Ozarks. This
activity will likely stay south of the terminals however. Front
expected to be through KUIN by late Sunday evening and KCOU and
the metro terminals likely after this valid TAF package. Winds
behind the front will veer from the south to the northwest.


Specifics for KSTL:

Dry and VFR for rest of tonight and early Sunday. Cannot totally
rule out an isolated storm affecting terminal on Sunday afternoon
but probability too low to mention in TAF. Did add a VCTS group in
for expectation of scattered showers/storms along the approaching
cold front for Sunday evening. Frontal passage looks to be late
Sunday night toward the end of the forecast period with winds
switching from a southerly direction to the northwest behind the
front.

Gosselin

&&

.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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