Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 302313

612 PM CDT TUE JUN 30 2015

.SHORT TERM...  (Through Late Tonight)
Issued at 358 PM CDT Tue Jun 30 2015

Most of the period will be fairly benign before an anticipated
upstream MCS approaches central MO well after midnight.

A weak cold front edging southward through central IL has a few
isolated cells along it that are mainly diurnally driven. A few of
these could graze a few of the central IL counties prior to sunset.
Otherwise, expect a smoke-filled cloud cover through the evening.

Model consensus continues to point towards a nocturnal MCS forming
over eastern NE/western IA late this evening as a southwesterly
low-level jet ramps up over the Central Plains. The cross flow over
a h8 thermal gradient should provide strong moist ascent and provide
the necessary fuel for the developing MCS. Under a northwesterly
steering flow this activity is expected to track southeast and enter
the central MO counties after midnight...probably closer to 09z.



.LONG TERM... (Wednesday through Next Tuesday)
Issued at 358 PM CDT Tue Jun 30 2015

A couple rounds of active storms with attendant MCS will be the
primary concern Wednesday into Thursday. With PWs ramping up to
well over 2"(lying between two standard deviations above normal
and the 99th percentile) plus a veering low level jet a northwest-
southeast corridor of central MO counties lies within a favored
region for repeated rounds of convection. The first one will be
ongoing Wednesday morning. Some debate as to how the MCS will
evolve Wednesday as model qpf consensus points to the MCS turning
more east towards STL. However, with the likelihood of a cold pool
forming and becoming dominant under a northwesterly flow the
heaviest rains should tend to push more south than east.

As the above MCS weakens during the day under a weakening h8 jet
there should be a lull in the action until later Wednesday evening
when we rinse, wash and repeat as the nocturnal low-level jet
reforms. Another MCS is expected to form over central MO, just where
is likely dependent on where any outflow boundaries end up. Central
MO is the most likely region. So, based on the above have gone with
a Flash Flood Watch for parts of central MO.

From Thursday through Sunday shortwave troughs dropping down the
front side of an upper ridge over the Rockies will remain a nuisance
generating off and on threats of convection. Temperatures are
expected to be below normal early in the period before gradually
warming late in the holiday weekend.



.AVIATION... (00z TAF set through 00z Thursday)
Issued at 610 PM CDT Tue Jun 30 2015

Main concern remains with evolution of convective complex to the
northwest. Latest SREF guidance trending a bit further north than
the NAM, with the HRRR a bit further west, but general indications
are that the development should be near the Iowa/Nebraska border
before tracking southeast. KCOU continues to be favored for greater
impacts by about 08z or so, with this area most likely for
widespread thunderstorms. A few showers/storms may be approaching
the metro TAF sites by about 08-09z but currently think the more
significant shower activity should be closer to 10-11z.

Effective placement of the frontal boundary near the I-70 corridor
will likely be influenced by the track of the MCS remnants Wednesday
morning, which will weaken as the low level jet focuses further
east. Afternoon convection will be more diurnally driven, and have
mentioned VCTS at all sites.

Specifics for KSTL:
Most significant impacts with convective complex expected to be a bit
further west of KSTL, but have MVFR visibilities at times by about
10z or so with the heavier showers arriving. Convection expected to
be more scattered by afternoon, before increasing late with the
development of another convective complex. Models indicating more
widespread MVFR ceilings/visibilities developing after 00z Thursday.



MO...FLASH FLOOD WATCH from Wednesday morning through Thursday
     morning FOR Crawford MO-Franklin MO-Gasconade MO-Iron MO-
     Jefferson MO-Madison MO-Montgomery MO-Reynolds MO-St.
     Francois MO-Ste. Genevieve MO-Warren MO-Washington MO.

     FLASH FLOOD WATCH from 1 AM CDT Wednesday through Thursday
     morning FOR Boone MO-Callaway MO-Cole MO-Moniteau MO-Osage


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