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Area forecast discussion 
National Weather Service St Louis MO
339 PM CDT Tuesday Jul 7 2015

Short term: (tonight through Wednesday night)
issued at 320 PM CDT Tuesday Jul 7 2015

The front continues to sag southeastward and extends from the Ohio
Valley across southern Illinois and southeast MO into eastern OK at middle
afternoon. The majority of the heavy rainfall has shifted south of
the region at this time, but a broad persistent southwesterly low level jet
continues to generate showers well to the north of the surface
front. I don't anticipate major changes into the evening with
showers and maybe some drizzle the dominant precipitation and a
better threat of showers and any thunderstorms confined to the far
southern County Warning Area in the immediate vicinity of the quasi-stationary
front. Overnight however things will change as the short wave
currently centered through western OK lifts east northeast. In
response the western portion of the front will lift northward as
the associated surface low tracks northeast along it, and low and
middle level flow will back and strenghthen. This should lead to the
spread and development of more continous showers and thunderstorms
with heavy rain back into the area from the southwest.

Wednesday into early Wednesday evening still appears to be the
period of heaviest rainfall and flash flood potential. The overall
scenario remains the same with the surface low tracking east
northeast prompting the front to lift northward, and continued
strengthening and backing of the southerly low level jet producing strong
lift/mcon along and north of the front and surface low. Present
indications are that the axis of highest rainfall totals should be
centered in the vicinity of a Jefferson City to Litchfield axis,
although precipitation will be widespread. Have leaned the
forecast towards the GFS/ECMWF, which is a bit faster than the
NAM, but still has a threat of showers and thunderstorms and
heavy rain during the evening across far eastern MO into Illinois.
Accordingly I extended the Flash Flood Watch in this area until
06z Thursday. There could also be a conditional severe weather
threat across the southeast half of the County Warning Area Wednesday afternoon/evening
depending on the amount of destabilization which can occur as low
level shear will be favorable along and in advance of the surface
low.

Glass

Long term: (thursday through next tuesday)
issued at 320 PM CDT Tuesday Jul 7 2015

The front will sag back into southern MO and southern Illinois by
Thursday morning in the wake of the departing surface low and the
best threat of the scattered showers and storms will be across the
far southern County Warning Area in the vicinity of the front. The final hurrah
will be Thursday night into early Friday morning as the final
disturbance aloft tracks east northeast out of the plains
resulting in the same sequence of a migratory surface low and
lifting front with showers and thunderstorms likely along and
north of the front. This front and the threat of precipitation
should be north of the area by Friday afternoon. Thereafter heat
and humidity will dominate the area late Friday into the weekend
as heights rise aloft in association with a large upper high/ridge
building into the Lower/Middle MS valley. This upper high continues
retrograding to the west by early next week bringing a return of
troffing in the east, northwest flow aloft for US, and another
frontal passage in the Monday/Tuesday time frame with a threat of showers
and thunderstorms.

Glass

&&

Aviation: (for the 18z tafs through 18z Wednesday afternoon)
issued at 1241 PM CDT Tuesday Jul 7 2015

Cold front has sagged just south of the St Louis metropolitan area early
this afternoon. Patchy Post frontal light rain or drizzle will
continue to impact cou and the St Louis metropolitan area this afternoon
and this evening. Uin cloud ceiling should scatter out with their
haze dissipating later this afternoon...or at least their ceiling
should rise into the VFR catagory. Should see the ceiling rise
into the MVFR catagory later this afternoon or early this evening
in cou and the St Louis metropolitan area. More significant rain or
showers should move back into our area late tonight and Wednesday
morning as a surface low moves northeastward into southwest MO
Wednesday morning with the ceiling and visibility dropping again.
Northerly surface wind will gradually veer around to an east-northeasterly
direction tonight.

Specifics for kstl: periods of light rain or drizzle can be
expected this afternoon. The cloud ceiling should gradually rise
to at least 1000 feet later this afternoon or this evening. More
significant showers with a few thunderstorms will move back into
the area Wednesday morning with the ceiling and visibility
dropping again. Northerly surface wind will gradually veer around to a
northeasterly direction tonight...and to an Ely direction Wednesday
afternoon.

Gks

&&

Lsx watches/warnings/advisories:
MO...Flash Flood Watch through Wednesday evening for Audrain MO-Boone
MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
Iron MO-Knox MO-Madison MO-Moniteau MO-Monroe MO-Montgomery
MO-Osage MO-Reynolds MO-Shelby MO-St. Francois MO-Ste.
Genevieve MO-Warren MO-Washington MO.

Flash Flood Watch through late Wednesday night for Jefferson MO-
Lewis MO-Lincoln MO-Marion MO-Pike MO-Ralls MO-St. Charles
MO-St. Louis city MO-St. Louis MO.

Illinois...Flash Flood Watch through Wednesday evening for Randolph Illinois.

Flash Flood Watch through late Wednesday night for Adams Illinois-Bond
Illinois-Brown Illinois-Calhoun Illinois-Clinton Illinois-Fayette Illinois-Greene Illinois-
Jersey Illinois-Macoupin Illinois-Madison Illinois-Marion Illinois-Monroe Illinois-
Montgomery Illinois-Pike IL-St. Clair Illinois-Washington Illinois.

&&

$$

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