Special Weather Statement, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
642 AM CDT WED JUL 6 2016

.SHORT TERM...  (Through Late This Afternoon)
Issued at 357 AM CDT Wed Jul 6 2016

Ongoing MCS to our north with its eastern section moving thru
northern IL dropping to the south-southeast.  Current indications
are that this should hold together long enough to impact our far
northern CWA and much of the CWA in Illinois during the early to mid
morning hours.  Severe threat should be minimal with this but will
continue to monitor.

Another MCS over in KS also bears watching, with the MCV from this
activity expected to track eastward into our region later this
morning and thru the afternoon. HRRR and our local WRF models
picked up on this feature the best and supports likely PoPs or
greater for much of our region from late morning thru much of the
afternoon as it tracks west to east.

Temperatures will be very conditional on the rain and become
increasingly uncertain with time but should peak in the eastern CWA
around midday or early afternoon with dropping temps with the
increasing clouds and approaching rain, while will be stunted in the
west this morning with some recovery in the mid to late afternoon.
Favored max temps on the cool side of MOS.  Heat index values look
to edge around 100F for many areas near and south of Interstate 70 at
some point today but not enough for an Advisory given what looks to
be the very brief likelihood of the attainment of these heat index
values and uncertainty.

TES

.LONG TERM...  (Tonight through Tuesday)
Issued at 357 AM CDT Wed Jul 6 2016

Tonight - Thu

Precip assoc with MCV should exit sthrn IL this evng with much
of the overnight prd dry. Subtle short wave embedded in the zonal
flow will move out of the nthrn Plains this aftn and into IA/MN
this evng. This should initiate TSTM dvlpmnt to our NW. This
activity will drop SE overnight and may approach the nthrn FA well
after midnight. The eventual sthrn extent of this activity and
assoc outflow bndry will determine convective trends on Thu since
the area will be largely void of any other forcing mechanisms. Any
activity that does dvlp is expected to be sparse due to a substantial
cap with 700mb temps of +13C to +15C. A dvlpng short wave across
the Dakotas will be our next WX maker for the end of the week.

Thu should be the hottest day of the week. 850mb temps of +22C to
+25C support high temps in the mid 90s to near 100. I think plenty
of BL moisture will help keep temps from getting out of hand and
am expecting highs in the low/mid 90s...though there is the
potential for temps to be a category higher. Regardless...highs in
the 90s and Dps in the mid 70s will produce HIs above 100 across
the entire area and possibly 105+. A headline may very well be
needed.

Thu Night - Fri Night

Any convection that was able to dvlp drng the aftn should fade after
00Z. The aforementioned short wave will track from the Dakotas on
Thu to the wrn Grt Lks Thu night into Fri mrng. This feature will
lift a SFC low from IA Thu night to the Grt Lks by Fri night. A cold
front assoc with the SFC low will drag thru the FA from Thu night
thru Fri. There are timing differences...but the general scenario is
for convection to fire along the front to our N/NW drng the late
aftn and evng and then sink S/SE along with the front or at least
what will become the effective front. Expect this activity to move
into the wrn/nthrn CWA around midnight. Convection should continue
to move SE drng the early mrng and then should slowly fade away
towards 12Z. Front should progress to the I44 corridor in MO and I70
in IL by 18Z before addntl convection dvlps drng the aftn. Front is
expected to clear the far sthrn zones across SE MO Fri evng...tho
precip chances will continue for SE MO due to proximity to the bndry.
SFC high centered across Hudson Bay builds into the region
overnight.

Temps on Fri could be tricky depending on evolution of mrng
convection. Residual cloud cover...outflow bndrys and frontal timing
will play an important roles.

Sat - Sat night

Fri's FROPA will introduce a cooler and drier air mass for the wknd.
Upper heights begin to rise as a ridge progresses E from the Plains.
This will cause the front to stall along the AR/MO border over the
wknd so shtrn zones will continue to have diurnally driven precip
chances. Guidance has come into better agreement depicting what
appears to be an MCV traversing sthrn MO Sat. There is still some
discontinuity on exact track of vort max but it appears to have
shifted S/SW some.

Potential clouds and precip may limit high temps...esp across the
far sthrn CWA on Sat.

Sun -  Tue

Upper ridge will be well established early next week. Sthrly flow
will begin by Sun. This will allow normal summer time conditions to
return as the air mass slowly modifies with limited chances for
diurnally driven convection.

2%

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 642 AM CDT Wed Jul 6 2016

First batch of storms from the north edging UIN currently and
ability to edge the STL metro sites looking more doubtful with
western edge eroding as it pushes south. Will need to be monitored
but due to it being in doubt currently, have no mention for this.

Second batch of storms from the west are filling in a bit more of
late and are still on track to move thru COU between 15-18z and
STL metro sites between 17-20z, with UIN again being on the
northern edge.

After this, storm chances look small, small enough to preclude
mention in the TAFs, but indications continue to favor another
storm complex dropping from the northwest at the very end of the
valid period or just beyond.

Otherwise, southerly surface winds and mainly VFR conditions will
prevail at the TAF sites thru the valid period.

TES

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

WFO LSX

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ST LOUIS MO
454 AM CDT WED JUL 6 2016

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-071000-
GREENE IL-MACOUPIN IL-MONTGOMERY IL-BOND IL-FAYETTE IL-CLINTON IL-
MARION IL-WASHINGTON IL-RANDOLPH IL-ADAMS IL-BROWN IL-PIKE IL-
CALHOUN IL-JERSEY IL-MADISON IL-SAINT CLAIR IL-MONROE IL-KNOX MO-
LEWIS MO-SHELBY MO-MARION MO-MONROE MO-RALLS MO-PIKE MO-BOONE MO-
AUDRAIN MO-MONITEAU MO-COLE MO-OSAGE MO-CALLAWAY MO-MONTGOMERY MO-
LINCOLN MO-GASCONADE MO-WARREN MO-SAINT CHARLES MO-FRANKLIN MO-
SAINT LOUIS MO-SAINT LOUIS CITY MO-JEFFERSON MO-CRAWFORD MO-
WASHINGTON MO-SAINT FRANCOIS MO-SAINTE GENEVIEVE MO-IRON MO-
MADISON MO-REYNOLDS MO-
454 AM CDT WED JUL 6 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN AND
CENTRAL MISSOURI AS WELL AS WEST CENTRAL AND SOUTHWEST ILLINOIS.

.DAY ONE...TODAY AND TONIGHT

A FEW STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE ACROSS
NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS THIS MORNING. THE
GREATEST THREAT WILL BE DAMAGING WIND GUSTS.

ADDITIONAL SEVERE THUNDERSTORMS ARE POSSIBLE ACROSS THE ENTIRE
AREA THIS AFTERNOON. THE PRIMARY THREAT WILL BE DAMAGING WIND
GUSTS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

HEAT INDEX VALUES WILL BE NEAR 105 DEGREES FOR MUCH OF THE REGION
THURSDAY AFTERNOON.

STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE MAINLY FOR LOCATIONS
ALONG AND NORTH OF INTERSTATE 70 ON THURSDAY AND THURSDAY NIGHT.
THE PRIMARY THREAT WILL BE DAMAGING WIND GUSTS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE THIS AFTERNOON.

2%

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ST LOUIS MO
830 AM CDT WED JUL 6 2016

ILZ069-074-098>101-MOZ052-061-063-064-061415-
WASHINGTON IL-MADISON IL-CALHOUN IL-CLINTON IL-JERSEY IL-
ST. CLAIR IL-ST. LOUIS CITY MO-ST. CHARLES MO-ST. LOUIS MO-
LINCOLN MO-
830 AM CDT WED JUL 6 2016

...SIGNIFICANT WEATHER ADVISORY FOR WASHINGTON AND CLINTON COUNTIES
IN SOUTH CENTRAL ILLINOIS...NORTHERN ST. CLAIR...SOUTHERN MADISON...
SOUTHWESTERN JERSEY AND SOUTHEASTERN CALHOUN COUNTIES IN SOUTHWESTERN
ILLINOIS...NORTHERN ST. LOUIS...ST. CHARLES...AND SOUTHEASTERN
LINCOLN COUNTIES IN EAST CENTRAL MISSOURI AND ST. LOUIS CITY UNTIL
915 AM CDT...

AT 827 AM CDT...DOPPLER RADAR WAS TRACKING A GUST FRONT PRODUCING
WIND GUSTS TO 40 MPH WELL AHEAD OF A LINE OF SHOWERS AND
THUNDERSTORMS.  THESE WIND GUSTS WILL AFFECT THE ST. LOUIS
METROPOLITAN AREA BETWEEN 830 AM AND 915 AM.

LOCATIONS IMPACTED INCLUDE...
  ST. LOUIS...ST. CHARLES...ST. PETERS...FLORISSANT...CHESTERFIELD...
BELLEVILLE...UNIVERSITY CITY...GRANITE CITY...WENTZVILLE...
O'FALLON...KIRKWOOD...MARYLAND HEIGHTS...EAST ST. LOUIS...
HAZELWOOD...COLLINSVILLE...EDWARDSVILLE...WEBSTER GROVES...
FERGUSON...CREVE COEUR AND FAIRVIEW HEIGHTS.

LAT...LON 3825 8915 3853 9025 3880 9094 3914 9094
      3883 9005 3861 8915
TIME...MOT...LOC 1327Z 337DEG 32KT 3915 9098 3878 9002 3858 8916

CVKING