Scientific Forecaster Discussion
Area forecast discussion...updated aviation
National Weather Service St Louis MO
632 PM CDT Sat Jul 4 2015
Short term: (through late tonight)
issued at 330 PM CDT Sat Jul 4 2015
Tranquil night on tap for the area with pleasant early July
temperatures. High pressure system centered in the Ohio Valley
will slowly retreat east overnight with light southeast surface
winds developing. The current diurnal cumulus will dissipate with the
loss of heating, while some cirrus will spread into the area
ahead of a plains shortwave. Overall skies will range from clear
to partly cloud and a tad hazy, with some patcy fog development
Long term: (sunday through next saturday)
issued at 330 PM CDT Sat Jul 4 2015
High pressure over the Ohio Valley will continue to retreat east
while surface pressures begin to fall across the plains, and this
will lead to increasing southerly low level flow and attendant
warm advection and moisture return Sunday into Sunday night.
Accordingly, the high temperatures on Sunday will be warmer and
closer to average. Precipitation chances during this period appear
to be focused well to our northwest across the northern plains
into the upper MS valley.
The dry period however will come to an end on Monday and especially
Monday night into Wednesday. Troffing aloft will evolve across the
northern tier of the Continental U.S. As a series of short wave troughs dig
east southeast from western Canada. This will ultimately bring a
northeast-southwest oriented cold front into the area. The models
differ some on timing with the NAM the slow outlier and the more
progressive GFS/sref/ECMWF solutions followed - bringing the
front into northwest MO on Monday afternoon and into northern
sections of the County Warning Area Monday night with a wavy frontal boundary from
southern Illinois into southeast Missouri by Tuesday afternoon.
The area well ahead of the front from central into east central MO
and southwest Illinois should see another warm day on Monday with
highs around 90, while showers and thunderstorms will move into
northwest sections of the County Warning Area by early Monday evening. A seasonably
moist air mass with surface dew points in the upper 60s/lower 70s
and 850 mb dew points in the teens along with favorably deep low
level convergence will support widespread showers and thunderstorms
along and ahead of the front as it progresses southeastward. Given
this scenario and the aforementioned moisture content /pws near 2
inches/ and overall slow wind speeds aloft, we could see another
widespread 2-4 inch multi-day rainfall event.
Weak quasi-zonal flow aloft will persist during the later half of
next week with embedded weak disturbances. These combined with the
front wavering about the area will result in an unsettled pattern
with continued thunderstorm chances into at least late Friday.
Aviation: (for the 00z tafs through 00z Sunday evening)
issued at 622 PM CDT Sat Jul 4 2015
Hazy evening cross much of the area...although only one site
(khae) is reporting visibilities less than 6sm. Expect the visibilities to
slowly drop through the evening, and there may be times when smoke
from fireworks sharply limits visibilities for short periods. Think that
MVFR visibilities will be fairly widespread across the area before
sunrise, and pockets of IFR may be possible, but perhaps not as
prevalent as this morning due to a bit more southeasterly flow.
Remainder of Sunday should be VFR with increasing southeast flow.
Specifics for kstl:
Hazy conditions at Lambert will likely slowly deteriorate through
the evening and overnight hours. Additionally, smoke from
fireworks may sharply limit visibilities for a short period this evening.
In general though, slightly increased wind from the south-
southeast may help to keep fog from reducing the visibility as
much as this morning. Remainder of the day should be VFR with
increasing southeasterly flow.
Weather forecast office lsx