Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 131744

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1244 PM CDT Sun May 13 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 340 AM CDT Sun May 13 2018

An upper ridge will remain across the region today and tonight. At
the surface, a quasistationary boundary in northern MO is expected
to lift slightly northward to the MO/IA border by this afternoon.
BUFKIT profiles depict a capping inversion between H7 and H8 which
will limit SHRA/TSRA development today south of the boundary in
MO/IL. That said, isolated SHRA/TSRA invof the boundary cannot be
entirely ruled out.

Little air mass exchange has occurred, therefore yet another day of
unusually warm May temperatures are expected today. The normal highs
for this time of year are in the 70s while the normal lows are in
the 50s. Highs ranging from the upper 80s to low 90s look
reasonable, although there is a standing concern that convective
cloud debris could keep temperatures a few degrees cooler than
forecast. Lows tonight should range from the mid-60s to around 70


.LONG TERM...  (Monday through Saturday)
Issued at 340 AM CDT Sun May 13 2018

Upper RIDGE that has dominated our region this weekend will hang on
thru Monday.  This scenario aloft will combine with the frontal
boundary buckling back to the north some with all or nearly all of
the forecast area expected to be to the south of it.  Rain chances
should be confined to areas near the front or areas principally in
northern MO and central IL.  Convective debris clouds have been an
issue the past 2-3 days in keeping temps slightly below forecast
values and Monday may end up being not too different, but also looks
to have the best chance of seeing the least amount of convective
debris clouds.  Cautiously preserved much of the max temp forecast
for Monday afternoon with most areas only about a degree or two less
than what it looked like a couple days ago.  We are still
forecasting max temps in the upper 80s and lower 90s for most areas,
edging towards mid 90s in the STL metro area.  This should threaten
record maxes this day--see CLIMATE section below.  Max heat index
values will not be much higher than the ambient temps, but should
still see some upper 90s in STL metro on Monday.

An upper level disturbance, currently over the far western OK
panhandle, is expected to wobble northeastward and should be in a
position to affect our weather on Monday night.  This should be the
organized convection that the models have been hinting at for this
time period and combined with the environmental shear and
instability has resulted in a Slight Risk for severe storms for Day
2--an upgrade from the previous outlook for Day 3.

The pattern will shift heading into Tuesday into more of a split
flow regime, and continue more-or-less thru the rest of the week. An
upper LO currently over the Great Basin is ejecting out
disturbances, and these disturbances will wear down the RIDGE over
our region.  By Tuesday, this is expected to have made enough of an
impact for the RIDGE to significantly breakdown with these
disturbances then continuing to wobble eastward into our region on
subsequent days, further being reinforced by a new strong storm
system coming onshore later in the week.  Overlaying this outcome
with the gradual southward progression of the surface cold front
thru our region on Wednesday and Thursday should result in PoPs that
are above climatological values of 30% for this time of year, but
will be hard to go likely for now due to the scattered convective
nature of what is expected.

By Thursday and Friday, the surface frontal boundary is expected to
be south of the forecast area and despite continued intrusion of
upper level disturbances, favors mentionable PoPs but those that are
generally below climatological values.  Another front is expected to
approach by Saturday to continue what should be a week filled with
numerous rain chances.

Temps should slip back closer to average but split flow regime aloft
and lack of any fronts of decent strength should still favor above



.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1238 PM CDT Sun May 13 2018

Terminals are expected to stay south and east of any convection
through the valid TAF period. VFR conditions are likely with
west/southwest winds backing to the south tonight before veering
to the southwest by mid morning on Monday.


Lambert Field is expected to stay south and east of any
convection, and therefore, dry/VFR conditions are expected through
the valid TAF period. Primary wind direction of WSW through
afternoon before backing to the SSW tonight. Winds will veer back
to the southwest Monday morning.




Record highs and record warm lows for St. Louis:
May 13th: 91 (1915), 73 (1886)
May 14th: 93 (2013), 73 (1915)
May 15th: 94 (1944), 72 (2013)

Record highs and record warm lows for Columbia:
May 13th: 91 (1940), 68 (1970)
May 14th: 90 (1987), 67 (1941)
May 15th: 90 (1944), 71 (1941)

Record highs and record warm lows for Quincy:
May 13th: 92 (1940), 68 (1933)
May 14th: 94 (1915), 66 (1932)
May 15th: 93 (1944), 69 (1962)




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