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Area forecast discussion 
National Weather Service St Louis MO
425 am CDT Tuesday Jul 28 2015

Short term: (through wednesday)
issued at 309 am CDT Tuesday Jul 28 2015

Oppressively hot and humid conditions will persist today beneath
an upper level ridge axis. The presence of outflow boundaries
within a nearly uncapped atmosphere has been sufficient for
isolated to scattered sh/ts over the last couple of days, and
since neither the air mass nor the forecast 700 mb temperatures have
changed significantly from the last few days, a similar precipitation
scenario is expected today. Generally followed 700 mb temperatures as
a proxy for capping to determine placement of schc probability of precipitation.

A low pressure system moving along the US/Canada border will send
a cold front through the plains today/tonight. Since the upper
flow becomes northwesterly behind the low pressure system in
response to a building ridge over the West Coast, odds are good
that this cold front will move through MO/Illinois on Wednesday/Wednesday night and
bring relief from the recent heat/humidity for a couple of days.
Sh/ts may accompany the front on Wednesday but precipitation should taper
off across the County Warning Area by Wednesday night.

Kanofsky

Long term: (thursday through monday)
issued at 309 am CDT Tuesday Jul 28 2015

Thursday and Friday look spectacularly drier and less humid within
the Post-frontal air mass. The building ridge over the western
Continental U.S. Will keep northwest flow in place over MO/Illinois through the weekend.
Both the 12z and 00z runs of the GFS/European model (ecmwf) disagree on the extent
of the northwest flow, however-- the ec is farther north with a low
pressure system in Canada which keeps the flow nearly quasizonal
but the GFS is farther south with the low in Canada which leads to
a sharper northwest flow solution. A couple of disturbances moving
through the flow could support periods of sh/ts late this weekend
and/or early next week, but such features are too poorly resolved
this far in advance to have confidence in probability of precipitation greater than schc-
chance. Temperatures will moderate to seasonably warm upper 80s to
lower 90s.

Kanofsky

&&

Aviation: (for the 06z tafs through 06z Tuesday night)
issued at 1048 PM CDT Monday Jul 27 2015

Only isolated thunderstorms and rain remains across southeast MO. Short wave lifting
north as the ridge builds across the region. One would think this
would produce a mostly dry day Tuesday as any development should
be well north of MO. However models continue to fire up scattered
thunderstorms and rain in the afternoon mainly across eastern MO and western Illinois. It
will not take much in this hot, humid, unstable air mass. A
vicinity for uin, sus and cps would will be the best I can do for
now. Expect some morning fog again as well.

Specifics for kstl: isolated thunderstorms and rain has pushed south and should stay
there. What lift that is left appears to be better across
southeast MO. Models again develop isolated thunderstorms and rain across eastern MO
for Tuesday afternoon. Will throw in a vicinity to cover.

Jpk

&&

Lsx watches/warnings/advisories:
MO...excessive heat warning until 9 PM CDT this evening for Boone MO-
Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-
Montgomery MO-Osage MO-Reynolds MO-St. Charles MO-St.
Francois MO-St. Louis city MO-St. Louis MO-Ste. Genevieve
MO-Warren MO-Washington MO.

Heat advisory until 9 PM CDT this evening for Audrain MO-Knox MO-
Lewis MO-Marion MO-Monroe MO-Pike MO-Ralls MO-Shelby MO.

Illinois...excessive heat warning until 9 PM CDT this evening for Calhoun
Illinois-Jersey Illinois-Madison Illinois-Monroe Illinois-Randolph IL-St. Clair Illinois.

Heat advisory until 9 PM CDT this evening for Adams Illinois-Bond Illinois-
Brown Illinois-Clinton Illinois-Fayette Illinois-Greene Illinois-Macoupin Illinois-Marion
Illinois-Montgomery Illinois-Pike Illinois-Washington Illinois.

&&

$$

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