Tornadoes and Damaging Wind in Missouri, June 27, 2020

Area Forecast Discussion
National Weather Service Saint Louis MO
314 PM CDT Sat Jun 27 2020

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 312 PM CDT Sat Jun 27 2020

Challenging convection forecast for this afternoon and tonight.  An
MCV left over from last night's convection over Kansas and Nebraska
is moving east across Missouri this afternoon.  This MCV combined
with what's left of a cold front is expected to produce another
round of thunderstorms later this afternoon and tonight...the
beginnings of which may be developing in central Missouri at this
time.  Current thinking is that the showers currently forming will
continue to expand in coverage and strengthen through the afternoon.
The HREF ensemble paintball plot shows that the majority of the
members blow up convection along and about 40 miles north and
south of I-70 by late this afternoon. The area of convection
pushes south, likely due to outflow, and then starts drifting
north again as the warm front gets pushed northward by the low
level jet. If the RAP is right, there will be just enough
instability available for these storms to produce marginally
severe hail and wind, although any severe storms should be fairly
isolated and will probably weaken after sunset. Forecast
precipitable water approaching 2 inches and potential for back-
building/training storms is concerning for heavy rain and
flooding. Have decided not to issue any hydro watches at this time
as antecedent conditions are rather dry. Sunday should be quieter
than today with warming temperatures. There may be some lingering
showers/storms along the warm front as it continues moving
through Illinois...primarily during the morning.

Carney

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 312 PM CDT Sat Jun 27 2020

Little has changed in the forecast for next week. Upper level
pattern becomes highly amplified with large cut off lows over the
eastern and western CONUS, and ridge extending from the deep south
north throuigh the Mississippi Valley. This blocky pattern holds
into next weekend. Both the GFS and ECMWF ensembles show fairly
low standard deviation in the upper pattern, so confidence is high
in this forecast. This translates to a period of warm and humid
weather for the Mid Mississippi Valley with highs in the upper 80s
to low and mid 90s. Medium range guidance has been consistently
pushing a short wave into the upper ridge on Monday where it cuts
off and gets stranded over the Mid Mississippi Valley Monday night
into Tuesday. According to all of the guidance, this compact low
will be enough forcing to allow convection to develop each day
through the week despite the larger scale upper ridge. Have
therefore kept PoPs in the forecast through next Saturday.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1244 PM CDT Sat Jun 27 2020

An upper level disturbance over Missouri combined with a weak
surface front is expected to provide a trigger for additional
thunderstorm development this afternoon. However, confidence in
where and when the storms will develop is not high. Model guidance
has not been handling the morning storms very well up to this
point. Additionally, there is a lot of cloud cover left over from
this morning's storms, so developing enough energy for additional
storms may be problematic. Regardless, there is the potential for
storms across the entire area this afternoon and into tonight.
Some storms may produce locally heavy rain and reduce the
visibility to 1SM or less. Ceilings will likewise be reduced to
low MVFR or possibly IFR with these storms. Elsewhere and
otherwise, the current MVFR ceilings across parts of eastern
Missouri and and southwest/central Illinois area expected to
continue to break up and rise. VFR conditions are expected to
prevail outside of thunderstorms.

SPECIFICS FOR KSTL:

Thunderstorms are likely in the vicinity of the terminal later
this afternoon into the evening. However, guidance has not been
performing very well with today's storms up til now. Therefore,
the VCTS timing in the TAF is low confidence. There is a weak
surface front in the vicinity of STL and once the thunderstorms
start, they may continue for quite some time. Heavy rain is
possible so IFR flight conditions are another possibility with any
storms that form

Carney

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     73  95  78  95 /  60  40  10  40
Quincy          70  90  73  90 /  60  40  20  50
Columbia        71  91  73  90 /  60  20  10  40
Jefferson City  72  92  74  92 /  50  20  10  40
Salem           72  90  73  93 /  70  50  20  40
Farmington      73  91  73  91 /  50  20  10  30

&&

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

WFO LSX

Hazardous Weather Outlook
National Weather Service Saint Louis MO
317 PM CDT Sat Jun 27 2020

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-282030-
Adams IL-Audrain MO-Bond IL-Boone MO-Brown IL-Calhoun IL-Callaway MO-
Clinton IL-Cole MO-Crawford MO-Fayette IL-Franklin MO-Gasconade MO-
Greene IL-Iron MO-Jefferson MO-Jersey IL-Knox MO-Lewis MO-Lincoln MO-
Macoupin IL-Madison IL-Madison MO-Marion IL-Marion MO-Moniteau MO-
Monroe IL-Monroe MO-Montgomery IL-Montgomery MO-Osage MO-Pike IL-
Pike MO-Ralls MO-Randolph IL-Reynolds MO-Saint Charles MO-
Saint Clair IL-Saint Francois MO-Saint Louis City MO-Saint Louis MO-
Sainte Genevieve MO-Shelby MO-Warren MO-Washington IL-Washington MO-
317 PM CDT Sat Jun 27 2020

This Hazardous Weather Outlook is for portions of eastern and
central Missouri as well as west central and southwest Illinois.

.DAY ONE...Tonight.

Thunderstorms are likely across much of the area tonight. Some
storms may be strong to severe this evening. The primary threats
will be damaging winds and large hail. Some of the storms may also
produce locally heavy rain.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

The chance for thunderstorms continues across parts of the area from
Sunday through Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this this evening. Spotters are
encouraged to report any severe weather or flooding, if observed, to
the National Weather Service.

Carney