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Area forecast discussion
National Weather Service Saint Louis MO
326 PM CDT Thu Sep 19 2019

Short term... (through late Friday night)
issued at 325 PM CDT Thu Sep 19 2019

Isolated to scattered storms have developed once again this
afternoon, with the higher coverage along an old outflow boundary
currently near a kkl>>kuin line. Both these storms as well as the
isolated showers/storms further south should weaken and eventually
dissipate by late this evening with loss of daytime instability.

Precipitation coverage and timing on Saturday will likely be
similar to the past 24-48 hours where isolated to widely scattered
showers and thunderstorms peak in coverage during the late afternoon
hours. Spatially, areas west of the Mississippi River will remain
favored for this primarily diurnally-driven convection. Any
thunderstorm that does occur however will have the capability of
producing brief heavy downpours.

There were concerns that tropical storm imelda's remnants may
possibly (directly) affect portions of the County Warning Area Friday night, but
those possibilities appear to have waned. The NAM yesterday was the
outlier bringing widespread showers/storms to parts of the County Warning Area but
has come more in line with the rest of the guidance which completely
dissipates imelda's remnants in Arkansas. Chances of showers and
storms do increase slightly late Friday night however as the
mid/upper level ridge continues to breakdown and shift to the

Seasonably warm conditions are forecast to continue over the next 24-
36 hours with little to no change in the ambient airmass. Low
temperatures both for tonight and Friday night are forecast to be in
the upper 60s to low 70s which is around 10 degrees above normal for
mid/late September. High temperatures on Friday will also be near
persistence values in the upper 80s to near 90 degrees. The one
exception is likely to be across portions of southeast Missouri
which should top out in the mid 80s due to increasing mid/high level


Long term... (saturday through next thursday)
issued at 325 PM CDT Thu Sep 19 2019

(saturday - Sunday night)

The first in a series of midlevel disturbances is expected to travel
through northwestern Missouri Saturday morning. This will help force
a round of showers and thunderstorms ahead of a cold front, but the
focus will likely be northwest of the County Warning Area closer to Kansas City and
Des Moines. Isolated to widely scattered diurnal storms are also
possible further east on Saturday afternoon/early evening across
much of the bi-state area.

The main period of concern continues to be from Saturday night
through Sunday night. The synoptic cold front will slowly near a
kcou>>kuin line by early Sunday morning and exit the County Warning Area overnight
Sunday night. Widespread showers and thunderstorms are expected with
this slow-moving cold front, aided by moderately strong low-level
moisture convergence and forcing for ascent associated with the
parent shortwave trough. Heavy, efficient rainfall remains the
concern due to very high precipitable water values (nearing 2.00
inches) and deep warm cloud depths. This efficiency combined with
the slow progression to the southeast of the cold front could yield
isolated flash flooding, most likely in parts of northeast Missouri
where the highest rainfall totals are likely to be located. In
addition to the flash flood potential, the Missouri River is likely
to observe renewed minor river flooding due to the combination of
this rainfall event along with elevated stages due to upstream dam
releases from Gavins Point. Outside of these potential problems, by
and large the 1-3" of rain over 1-2 days should be very beneficial
due to the very dry weather observed so far this month.

At least a brief period of drier and cooler weather is likely Monday
into early Tuesday behind the cold front. There is still a high
degree of uncertainty thereafter as the GFS is much more progressive
with a shortwave trough that moves out of The Four Corners region.
The European model (ecmwf) continues to close this system off and then cut it off
from the mean flow farther to the north. Consequently, this system
never really affects the mid-Mississippi Valley leaving our area dry
through the middle of the week. Continue to blend these two
different model solutions for now due to the high uncertainty which
results in another chance for showers and eventually thunderstorms
for Tuesday through next Thursday.



Aviation... (for the 18z tafs through 18z Friday afternoon)
issued at 1224 PM CDT Thu Sep 19 2019

Similar to the past couple of days, isolated showers and
thunderstorms are expected this afternoon into the early evening
hours. The probability of any of the terminals being directly
affected by these storms is on the low side so no mention in the
tafs. Otherwise, dry/VFR conditions are expected to continue along
with light south/southeasterly winds.

Specifics for kstl:

An isolated shower or storm may try and develop near the terminal
this afternoon and again Friday afternoon but the probability
appears too low right now to mention a thunderstorms in the vicinity group. Dry/VFR
conditions are expected to continue through Friday afternoon along
with light southerly winds.



Lsx watches/warnings/advisories...

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