Scientific Forecaster Discussion
Area forecast discussion...updated aviation
National Weather Service St Louis MO
1208 am CDT Wednesday Aug 5 2015
Short term: (through this evening)
issued at 236 PM CDT Tuesday Aug 4 2015
Isolated to scattered thunderstorms are expected to develop late
this afternoon and early this evening near the front that is
stalled just south of Interstate 70 and is being reinforced by an
outflow boundary that is moving south from the convection that
developed and crossed northern Missouri into west central
Illinois. Mesoscale convective vortex and associated light rain shield in southeast
Kansas is also moving northeast and will be near central Missouri
for the evening hours. Will have to monitor trends and increase
probability of precipitation if they can focus into a line/cluster.
Long term: (overnight through next tuesday)
issued at 236 PM CDT Tuesday Aug 4 2015
A lead shortwave moving east-northeast from Kansas/Oklahoma in
concert with a developing low level jet intersecting a nearly
stationary surface boundary should result in numerous showers and
thunderstorms developing and propogating across the County Warning Area from
southwest to northeast tonight and Wednesday morning. Despite
model quantitative precipitation forecast differences...mass fields are in good agreement.
Utilized the bullseye of moisture convergence for highest probability of precipitation and
quantitative precipitation forecast through Wednesday morning.
Meanwhile...the main shortwave/vorticity maximum currently located across
Wyoming will travel southeast tonight across the plains and into the
lower Missouri River valley on Wednesday. This will provide
additional synoptic lift and aid in reintensifying the low level jet
by Wednesday afternoon across the County Warning Area. There is a conditional threat
of severe thunderstorms that is highlighted by the day 2 convective
outlook...but the main hazard appears to be locally heavy rainfall
and flash flooding.
Storm total quantitative precipitation forecast from tonight through Thursday morning will likely
range from 1 inch in the far northern reaches of the County Warning Area to around 3
inches from Interstate 70 and points south. Locally higher amounts
will occur with training of thunderstorms. As I stated
yesterday...the ground has recovered some from the record rainfall
of June and early July and flash flood guidance is relatively high.
That being said...widespread rainfall amounts of three inches over
24 hours could lead to some local flash flooding...especially across
the Eastern Ozarks. Have coordinated a Flash Flood Watch for 12z
Wednesday through 12z Thursday to highlight this threat.
Rain will come to an end on Thursday from west to east as the
shortwave and low level jet focus thier attention toward the Ohio
River valley and temporary subsidence ensues.
Front is not expected to travel far and therefore the threat of
showers and thunderstorms will continue through the weekend as we
remain on the northeast periphery of the building upper level ridge.
Aviation: (for the 06z tafs through 06z Wednesday night)
issued at 1201 am CDT Wednesday Aug 5 2015
Main area of rain filling in over southwest MO currently and it
now looks like much of the I-70 taf sites...cou and stl
metropolitan...will be on the northern edge of this rain through much of
Wednesday. Have maintained a rainy forecast with minimal
restrictions, but a slight turn more to the south of this system
could keep these areas now mostly dry. Uin may miss much of this
system other than the outlow generated rain showers moving their way over
the next few hours. Still looking at a break midday into early
afternoon with new development 4-5 hours later heading towards
early evening. Light easterly flow expected for much of the valid
period. VFR conditons will give way to MVFR at most sites late
tonight and Wednesday.
Specifics for kstl: should be quiet and VFR until late tonight
when the next round of rain with perhaps some thunderstorms and rain moves in. A
this will probably continue until midday when it exits and a new,
initially more scattered, round develops late afternoon and
continues into the evening. Light easterly flow through the period
with MVFR ceilings prevailing more on Wednesday.
MO...Flash Flood Watch from 7 am CDT this morning through Thursday
morning for Boone MO-Callaway MO-Cole MO-Crawford MO-
Franklin MO-Gasconade MO-Iron MO-Jefferson 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.
Illinois...Flash Flood Watch from 7 am CDT this morning through Thursday
morning for Bond Illinois-Clinton Illinois-Madison Illinois-Marion Illinois-Monroe
Illinois-Randolph IL-St. Clair Illinois-Washington Illinois.
Weather forecast office lsx