Scientific Forecaster Discussion
Area forecast discussion...updated aviation
National Weather Service St Louis MO
646 am CDT Wednesday Aug 5 2015
Short term: (through tonight)
issued at 340 am CDT Wednesday Aug 5 2015
Primary concern for the today/tonight period will be on possibility
of heavy rainfall. Latest guidance has come in more in line with the
old European with respect to track of upper-level impulse coming
down from the middle-Missouri Valley and its associated low-level
cyclone transversing the baroclinic zone. This results in a track of
the system further south and several hours faster than what it
looked like 24 hours ago. As a result...main changes were to lower
quantitative precipitation forecast amounts...particularly along and north of the I-70 corridor...as
well as reduce probability of precipitation for late tonight. Have therefore elected to trim
northern extent of the Flash Flood Watch including the cities of
Columbia and St. Louis. In addition...have Flash Flood Watch now
expiring at 9z instead of 12z to match up better with pop forecast
for late tonight. Still have concerns that many counties in the
northern portion of the existing watch may not receive overly heavy
rainfall with forecast rain amounts through tonight only around one
inch but did leave some wiggle room in case the heavy rainfall axis
shifts back to the north and east a bit. Heaviest rainfall through
tonight likely to be across the far southern portion of the
County Warning Area...I.E. Reynolds/Iron/Madison counties in Missouri with up to two
inches of rain possible where strongest low-level forcing will
reside this evening. Another concern regarding through tonight
is that there may not be an abundance of convective activity
typically necessary for heavy rainfall rates both this morning as
well as overnight tonight as some model guidance suggests little to
no MUCAPE well north of the surface front.
Temperatures will not move much through tonight with low diurnal
ranges due to a lowering cloud deck....precipitation...and an
easterly component to the surface wind. Highs are expected to be in the
upper 70s to near 80 degrees for most areas which is a degree or two
below MOS. For lows tonight...seasonable temperatures are expected.
Long term: (tonight through tuesday)
issued at 340 am CDT Wednesday Aug 5 2015
(thursday - tuesday)
System will depart early on Thursday with just some schc/chance probability of precipitation
confined to the southeastern edge of the County Warning Area with middle/upper level
subsidence setting in behind the shortwave trough. Clouds should
linger however over much of the area which will result in a cooler
than normal day with highs in the low to middle 80s.
A midlevel anticyclone will strengthen over the Southern Plains
beginning on Friday putting the middle-Mississippi Valley on the
northeastern periphery of the ridge axis through Monday.
Temperature/probability of precipitation forecasts appear difficult in this time frame as
timing of individual ridge-runner shortwaves is near impossible at
this range. Have schc/chance probability of precipitation each day/night with near normal
temperatures...in other words climatology for temps/pops. Probably
not a bad guess this far out given the pattern.
One final chance of showers/storms on Monday as a cold front looks
to push south of the area with the ridge axis aloft shifting further
westward. Drier and cooler air appears likely for Tuesday given this
Aviation: (for the 12z tafs through 12z Thursday morning)
issued at 618 am CDT Wednesday Aug 5 2015
Widespread showers and scattered thunderstorms are expected over
the area today with accompanying MVFR conditions. Main timing will
be with the first area of showers and scattered thunderstorms
this morning and then expect a second area of showers and
thunderstorms later this afternoon and this evening. MVFR ceilings
may linger after the rain ends through the end of the taf period.
Specifics for kstl: showers and scattered thunderstorms will move
through eastern Missouri this morning have left predominant -shra
in the forecast with MVFR ceilings. Do expect some lull in the
precipitation early this afternoon before more showers and
possible thunderstorms move back into the area later this
afternoon and this evening. Expect MVFR ceilings to linger after
the rain ends through middle morning Thursday.
MO...Flash Flood Watch through late tonight for Cole MO-Crawford MO-
Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Madison MO-
Moniteau MO-Osage MO-Reynolds MO-St. Francois MO-Ste.
Genevieve MO-Washington MO.
Illinois...Flash Flood Watch through late tonight for Monroe Illinois-Randolph Illinois-
St. Clair Illinois-Washington Illinois.
Weather forecast office lsx