Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 290204
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
904 PM CDT Thu May 28 2015

.UPDATE:
Issued at 847 PM CDT Thu May 28 2015

Much of the shower/thunderstorm activity across central and
northeast MO as well as west central IL was gradually weakening
this evening as the atmosphere was becoming more stable. There was
an area of showers and a few storms across south central MO ahead
of a shortwave trough that will likely move into central MO later
this evening. Very little coverage of precipitation is expected
across our forecast area by midnight or shortly after. There may
be some development of showers/storms late tonight or early Friday
morning due to a modest southwesterly low level jet. This activity
would likely be across central or southeast MO. Low temperatures
tonight will be a little warmer than the previous night due to
plenty of mid-high level clouds along with at least weak south-
southeasterly winds.

GKS

&&

.SHORT TERM:  (Through Late Tonight)
Issued at 337 PM CDT Thu May 28 2015

Isolated-scattered showers and thunderstorms are expected to continue
early this evening ahead of 500-hPa shortwave trough with the best
coverage of storms across central Missouri. Combination of nocturnal
stabilization and subsidence behind aforementioned shortwave
should lead to weakening/dissipation of storms as well as a
corresponding drop in coverage late evening/early overnight. Late
tonight...sch/chc PoPs for showers/storms return to the area as
LLJ strengthens and veers from the SSW to the WSW late tonight. As
for temperatures...mild conditions are expected due to a partly to
mostly cloudy sky and a light southerly breeze. Expect lows
tonight in the mid to upper 60s areawide.


Gosselin

.LONG TERM:  (Friday through Next Thursday)
Issued at 337 PM CDT Thu May 28 2015


(Friday-Saturday Night)

Another shortwave trough will eject out toward the mid-Mississippi Valley
during the day tomorrow...similar to today just a bit further to the
northwest. PoPs will be on the increase especially Friday afternoon
for portions of central/northeast Missouri as well as west-central Illinois
as synoptic cold front associated with northern stream energy slowly sags
southeastward into region. Continued likely PoPs for showers and storms
for Friday afternoon. As for chances of severe weather...appears any
widespread strong/severe storms will be difficult due to weak deep-layer
shear values...around 20 knots. However...isolated strong to severe storms
with large hail/damaging winds does look plausible due to moderately
strong instability (1000-2000 J/kg) values.

Cold front will continue its slow southeastward progression on
Friday night and Saturday. Highest probabilities for showers and
thunderstorms continues to hone in on this period. Timing of cold
front looks to clear CWA by mid/late Saturday morning. Like Friday
...deep-layer shear/instability parameters do not look supportive
of any widespread severe weather...but a strong to severe storm is
not out of the question. Behind the front...showers (along with
some possible embedded thunder) look likely as shortwave trough
slows down and upper-level jet streak backbuilds to the southwest
putting CWFA beneath the RER.

Temperatures on Saturday look to be challenging due to frontal
timing and associated precip chances. Leaned cool (highs in the
upepr 60s to low 70s) for areas well behind the front in central and
northeast Missouri and west-central Illinois where clouds are
expected to linger along with strong low-level CAA from the north.
For areas further to the south and east...did not deviate too much
from guidance with highs in the mid 70s to near 80 degrees expected.

Tightened PoP gradient a bit on Saturday night with highest PoPs
remaining across southeast Missouri and southwest Illinois in closer
proximity to cold front. Did remove some mention of thunder well
behind the front due to lack of instability. Surface high across
the Great Lakes will begin flexing its muscle with much cooler and
drier weather beginning to filter into from the north and east.
Forecast lows are expected to dip back below seasonal norms with
lows generally in the 50s expected.


(Sunday-Thursday)

A cutoff low is still expected to develop somewhere near the
bootheel of Missouri on Sunday. Confined PoPs to far southeastern
sections of the area which will be closer in distance to this
feature as well as remnant cold frontal boundary. Instability looks
meager at best so just mentioned isolated tunder for the far
southern and eastern counties. Lingering clouds with 850-hPa dipping
to near +10C should yield a chilly day for very late May. Highs only
in the mid to upper 60s are expected on Sunday.

Cutoff low is expected to meander slowly to the south/southwest
heading into the middle of next week. Precipitation chances look low
as region will likely be too far north of aforementioned cutoff low
and too far south of main corridor of cyclones transversing the
upper Midwest. Best chance of showers/storms at the moment appears
to be on Thursday with chance PoPs as GFS suggests a trough axis may
approach the area from the west. All in all...the extended portion
of the forecast Monday through Thursday appears to be mostly dry
with moderating temperatures back above normal by Thursday.


Gosselin

&&

.AVIATION:  (For the 00z TAFs through 00z Friday Evening)
Issued at 501 PM CDT Thu May 28 2015

Thunderstorms have fired primarily along a warm front lifting
across the area. This is in response to a shortwave which will
move across by 12z. Additional thunderstorm have formed across SW
MO in the warm air in advance of the wave. This activity will
likely impact COU this evening and potentially UIN closer to
Midnight. HRRR decreases this precipitation gradually overnight,
but does fire up some new stuff primarily across SE MO as the wave
moves across eastern MO. Possible given this area has not had any
rain so far. Activity drifts into SUS and CPS area about 08z. Am
not optimistic about this so will leave out for now but will
monitor development late this evening closely. Another wave which
looks weaker moves in Friday and this will help kick off
showers/thunderstorms Friday afternoon. Timing difficult so some
VCTS will be the best forecast for now. Overall, TAFS will stay
VFR except briefly when storms move through.

Specifics for KSTL: Question is whether STL will stay dry
overnight. HRRR kills current rain that is over SW MO but forms
new stuff about 08z, most likely in response to the short wave
lifting across the area. Have doubts if the atmosphere will be
unstable enought to support this, so will leave out for now but
will watch closely late this evening. Thunderstorms will lilely
fire Friday afternoon in response to another, although weaker,
wave moving through. Timing no certain so a VCTS for a couple of
hours will suffice for now. More thunderstorms will be likely as
the cold front moves in overnight Friday night into Saturday
morning.

JPK

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     68  84  69  78 /  30  60  50  70
Quincy          65  81  65  69 /  80  70  70  50
Columbia        66  79  65  71 /  90  70  70  50
Jefferson City  66  80  66  71 /  80  60  70  50
Salem           67  84  69  79 /  20  40  40  70
Farmington      65  80  68  77 /  20  50  50  60

&&

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

$$

WFO LSX






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