Special Weather Statement, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
539 AM CDT Mon Apr 10 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 332 AM CDT Mon Apr 10 2017

A weakening MCS will move eastward through northeast MO and west
central IL early this morning.  Additional, more scattered
convection will develop late this morning and this afternoon as an
upper level low over northwest Nebraska early this morning moves
east-northeastward into the Great Lakes region tonight and sends a
cold front southeastward through our forecast area today and
tonight. There may be isolated severe storms this afternoon across
east central and southeast MO and southwest IL as the atmosphere
destabilizes ahead of the front. High temperatures will be slightly
cooler today than the previous day due to the increased cloud cover,
albeit still well above normal. Most of the convection should shift
southeast of our forecast area by late tonight as a surface ridge
over the northern Plains builds southeastward into the region behind
the cold front. Low level cold air advection behind the cold front
along with a clearing sky and lowering surface dew points will lead
to much colder low temperatures tonight, close to seasonal normals.

GKS

.LONG TERM...  (Tuesday through Sunday)
Issued at 332 AM CDT Mon Apr 10 2017

This period will open with a rare quiet stretch of wx until
Wednesday evening.

The surface cold front should be southeast of the CWA by 12z/Tue
with high pressure dominating the remainder of Tuesday.  This high
pressure will represent the outer fringe of a Canadian airmass
centered much further to the north and therefore will only be able
to cool us to near normal for one day.

Clear skies on Tuesday night along with a light east wind should
give us the coolest night of the week with min temps in many
locations in the lower 40s.  A few favored valley areas should drop
into the 30s and this will need to be watched for any need to
mention frost, but for now, it looks like any potential will be
very isolated.

High pressure will begin losing its influence on Wednesday with
winds returning from the southeast and daytime temps creeping back
into the 70s for most locations.

From Wednesday night onward, it looks to be a more typical active
springtime pattern with the chance for showers and storms each day.

An upper level disturbance ahead of a surface front will provide the
next round of storms Wednesday night and this will continue into
Thursday as the surface front sinks into the CWA and stalls.  At
this point, there is some model spread concerning mid level flow
which will determine how long the front stalls before retreating
northward as a warm front.  The GFS lingers the front the longest
over our region (into Friday) while the EC and CMC are quick to yank
it back north by Friday morning.  Went conservative on reducing PoPs
Friday, instead leaning toward more of a hedge climo value, which is
30% this time of year.

For Friday night and Saturday, there is better agreement on a warm
sector setup for much of the CWA, and went for a brief period of dry
wx for most locations save northern MO and central IL.

The spread increases further between the CMC/EC/GFS concerning on
whether or not to bring a cold front thru the region next weekend,
with the GFS not even dropping it thru at all.  Again leaned towards
a climo PoP approach when some models were bringing the front thru
Saturday night and into early Sunday until confidence can increase.

Concerning temps, after Tuesday, southerly surface flow is expected
to prevail for virtually the remainder of the week and into next
weekend.  So a prolonged stretch of above average temps continues to
be forecast, highlighted by what should be the warmest day on
Saturday with decent consensus on the warm sector setup, with highs
reaching into the 80s again in some areas.

TES

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 522 AM CDT Mon Apr 10 2017

Cluster of showers and thunderstorms moving eastward through UIN
early this morning. Most of this activity will shift east of UIN
by 12Z Monday, and most of it will remain north of the St Louis
metro area taf locations. A cold front will move southeastward
through the taf sites today and this evening. Scattered showers
and storms will develop along and ahead of the front this
afternoon as the atmosphere destabilizes. The convection should
shift southeast of the St Louis metro area by early evening.
South-southwesterly surface winds will veer around to a
northwesterly direction tonight after the passage of the cold
front.

SPECIFICS FOR KSTL: Cluster of showers and thunderstorms moving
eastward through northeast MO and west central IL early this
morning. Most of this activity will remain north of the STL area
this morning. A cold front will move southeastward through the STL
area this afternoon and this evening. Scattered showers and
storms will develop along and ahead of the front this afternoon as
the atmosphere destabilizes. The convection should shift
southeast of the STL area by early evening. South-southwesterly
surface winds will veer around to a northwesterly direction by
late tonight after the passage of the cold front.

GKS

&&

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

WFO LSX

Hazardous Weather Outlook
National Weather Service Saint Louis MO
405 AM CDT Mon Apr 10 2017

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-111200-
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-
405 AM CDT Mon Apr 10 2017

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

Isolated severe thunderstorms are possible this afternoon and
early this evening for the Saint Louis metro area and areas to the
south and east as a cold front moves through. Large hail and
damaging winds are the main severe threats.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is possible this afternoon and early this
evening for the Saint Louis metro area and areas to the south and
east.

TES

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Special Weather Statement
National Weather Service St Louis MO
955 AM CDT MON APR 10 2017

MOZ060>063-101545-
St. Louis MO-St. Charles MO-Franklin MO-Warren MO-
955 AM CDT MON APR 10 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN ST. CHARLES...
NORTHEASTERN FRANKLIN...WEST CENTRAL ST. LOUIS AND SOUTHEASTERN
WARREN COUNTIES UNTIL 1045 AM CDT...

At 954 AM CDT, Doppler radar was tracking a strong thunderstorm over
Washington, moving northeast at 55 mph.

Nickel size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
O'Fallon, St. Peters, Chesterfield, Wildwood, Wentzville, Lake St.
Louis, Washington, Dardenne Prairie, Weldon Spring, Cottleville, St.
Paul, Spirit of St. Louis Airport, Marthasville, New Melle, Augusta,
Weldon Spring Heights, Dutzow, Defiance and Matson.

This includes Interstate 70 in Missouri between exits 214 and 219.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3846 9107 3858 9113 3885 9072 3870 9054
TIME...MOT...LOC 1454Z 232DEG 46KT 3854 9104

Byrd