Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 040857
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
357 AM CDT Mon May 4 2015

.SHORT TERM: (Today and Tonight)
Issued at 330 AM CDT Mon May 4 2015

There are 2 main areas with precipitation potential this morning.
The first is from southeast/east central MO eastward into IL where
low-mid level warm advection has resulted in spotty showers within
the last few hours. The GFS and recent runs of the HRRR suggest
this potential will persist until around mid morning. The other
area is across northeast MO/west central IL extending into parts
of central MO. The frontal convection has in general become less
organized one area from eastern IA into northern IL and another
cluster in NW MO. Both regions have generated a pre-frontal cold
pool and outflow boundary, but its the western-most area in NW MO
that bears the most watching. General movement has been to the
southeast and some of the hi-res WRFs want to bring this cluster
along with some additional development into north-central/central
MO this morning. The current cluster is within a region of
moisture convergence along the northern terminus of a 40+ kts
southwesterly LLJ and weak elevated CAPE. It should encounter a
less favorable enviroment as it moves southeast this morning,
primarily after 12z, however forcing may be sufficient for
scattered showers and thunderstorms within the area highlighted by
the hi-res guidance. Otherwise clouds should thin across the
entire area during the later half of the morning and into the
early afternoon and when combined with the present WAA regime and
temps aloft, this should result in another warm day with well
above normal highs in the 80s.

There are some discrepencies in the guidance on the southward
position of the front this afternoon and evening with the RAP and
ECMWF showing a bit more southward position into the northern part
of the CWA by 00z, while the remainder of the models keep it near
or just south of the MO/IA border. I think it will ooze south into
the far northern part of the CWA by late afternoo. Present
indications are that heating and continued low-level moistening
late morning into afternono will result in moderate instability
along the frontal zone. Good low level convergence along the
boundary combined with lift associated with a migrating short wave
moving across southern IA/northern MO should result in extensive
convective development during the later half of the afternoon spanning
from KS across northern MO/southern IA into central IL. I am still
thinking that the broad and veering southwesterly LLJ will maintain
numberous thunderstorms/clusters during the evening with a decided
eastward motion. Although the models suggest the front will shift
slightly northward overnight I am not so sure this will happen
with rain cooled air maintaining its position. However increased
ridging aloft both in the low-mid levels suggest that the forecast
of a northward shift in the convection overnight is reasonable.
The only noticeable change to the pops tonight is to expand the
area of slight chances southward a bit to I-70. The GFS and ECMWF QPFs
are a bit far south and well into the warm sector and I would
think the majority of the convection will reside along the front
and northward into the cool air.

Glass

.LONG TERM: (Tuesday through Sunday)
Issued at 330 AM CDT Mon May 4 2015

Not much has changed in thinking from 24 hours ago with respect to
the Tuesday through weekend period. The front will make a decided shift
northward on Tuesday as ridging aloft continues to build from the
lower TN Valley into the upper MS Valley, while across southern
sections of the CWA we continue to see the models generate some
light QPF. I`m still not sold on it but will maintain low pops in
the slight range given the uncertainty. Tuesday still looks to be
another day of above normal temps with highs in the 80s.

Flow aloft becomes more south-southwest on Wednesday and a lead
impulse within this flow will traverse the western CWA prompting
an increased threat of showers and thunderstorms across western MO
into central MO. Flow aloft becomes southwesterly by Thursday and
this regime persists into the weekend ahead of a upper trof/low
migrating from the western U.S. and into the central U.S.. The threat
of showers and thunderstorms Thursday into the weekend gradually
ramps up and spreads west to east due to the active southwest flow
aloft with embedded disturbances, moist unstable warm sector, and
slowly encroaching cold front. Above normal temperatures should
persist through the extended period.

Glass

&&

.AVIATION:  (For the 06z TAFs through 06z Monday Night)
Issued at 1154 PM CDT Sun May 3 2015

VFR flight conditions are expected to continue to prevail across
the area through Monday evening. Scattered thunderstorms are
likely to drift south out of Iowa between 09Z-12Z, potentially
impacting the KUIN terminal. However, am not confident enough in
areal coverage to mention more than vicinity thunder in the TAF at
this time. Further south, short-range guidance is hinting that
there will be some high-based showers developing over east central
Missouri and southwest Illinois around 12Z. Showers should
dissipate by mid morning. VFR conditions with gusty southwest flow
is expected for Monday late morning through the afternoon.
Another round of thunderstorms is expected near a cold front which
will dip into northern Missouri. Coverage over northeast Missouri
and west central Illinois is again questionable, and much of the
activity may stay north of the area. Thunderstorm activity should
diminish through the evening.

Specifics for KSTL:

VFR flight conditions and south-southwest flow will prevail at
Lambert. Isolated to widely scattered high based showers look
likely to develop around 12Z Monday morning. Think impacts to the
airport will be minimal...though if a heavier shower happens to
pass over the airport it could briefly drop visibility to MVFR
range. Showers should dissipate by 14-15Z. Wind will be in the
200-220 range through much of the period, increasing to around
12kts during the afternoon with gusts to 20kts. There is a slight
chance of thunderstorms during the late afternoon, but it`s much
more likely that any thunderstorm activity will stay well north of
the terminal.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX





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