Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 232044
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
344 PM CDT Mon Mar 23 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 326 PM CDT Mon Mar 23 2015

The cold front passing through the St. Louis region at this time
will continue moving southward becoming stationary from southern
KS along the MO/AR border and into the TN Valley late this evening.
This boundary will set the stage for an overrunning precipitation
event which will impact the area overnight and into Tuesday. A
stout southerly LLJ will ramp up this evening across the Plains
gradually veering to southwesterly overnight, resulting in strong
low level WAA/moisture convergence/lift north of I-70 with the
greatest focus across northeast MO and west central IL in the
09-12z period. Progged elevated instability is pretty meager this
far east, but sufficient to continue to mention thunder. Something
that will need to be monitored closely tonight is the temperatures
in this region across northeast MO and west central IL. High
pressure will be building into the area to the north of the front
and some of the guidance shows surface temps falling below
freezing while some keeps it above freezing. At this time I have
temps dropping to just above freezing, however if the air over
northern Illinois and Indiana advances this far east and/or there
is sufficient diabatic cooling we could see some freezing rain.

Glass

.LONG TERM:  (Tuesday through Next Monday)
Issued at 306 PM CDT Mon Mar 23 2015

A relatively active 2 day period will continue to unfold Tuesday
into Wednesday. The initial wave of precipitation associated with
the LLJ and a lead migratory short wave will pass to the east of
the CWA by midday with the greatest concentration during the
morning continuing across the northern half of the CWA. The second
wave of showers and thunderstorms is expected during the later
part of the afternoon and especially in the evening. A rather
impressive fast-moving and negatively tilted short wave trof will
quickly move across the region during the evening accompanied by
significant large scale ascent, strengthening low-mid level wind
fields and promoting the eastward advance of steep mid level lapse
rates. This second wave should develop from western MO southwestward
during the afternoon and spread east with the advancing upper wave
and attendant surface low and shifting LLJ. Initially during the
later afternoon the majority of the convection appears elevated,
however a weakening warm sector CAP in the evening should result
in scattered to numerous showers and thunderstorms moving across
the area. The best combination of instability and shear and hence
severe threat appears to be to the west of the CWA however there
will be at least a threat of isolated strong-severe storms during
the evening, especially across southern half of MO into southern
IL.

The surface low moves into the Great Lakes by Wednesday morning
and the front doesn`t make much southward penetration becoming
stationary across southern IL-southern MO-northern OK. This front
will then lift northward during the day on Wednesday setting the
stage for the final round of showers and thunderstorms. Moisture
and instability will be more favorable with this later round due
to continued presence of steep mid level lapse rates and
advection. This instability and rather strong westerly deep layer
shear will provide favorable conditions for organized severe
storms along and south of the cold front across the southern
2/3rds of the CWA from the afternoon and into the evening. Heavy
convective rainfall across southern sections could ultimately
prompt the need for a flash flood watch down the road in future
forecasts.

Much cooler weather is expected in the wake of the front on
Thursday with perhaps some lingering rain across southern sections
in the morning. The below average/cold temperatures will persist
on Friday and into Saturday as high pressure dominates and a deep
long wave trof temporarily elvolves over the eastern U.S.. Growers
and gardners should take notice as Saturday morning lows will be
well into the 20s. Temperatures will then warm-up on Sunday as
heights aloft rise and low level warm advection gets going with
seasonable highs expected.

Glass

&&

.AVIATION:  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1244 PM CDT Mon Mar 23 2015

Specifics for KCOU, KUIN: MVFR stratus was sinking southward on
the cool side of a boundary which stretched across MO at TAF
issuance. A weak surface low pressure center will continue moving
southeastward to eastward along the boundary today, swinging one
portion northward as a warm front and leaving a trailing cold
front behind. Stratus is expected to persist at KUIN for most of
the afternoon but there is more uncertainty with cig trends at
KCOU because of erosion on the western edge of the cloud deck.
Winds will become northerly to northeasterly after the front sinks
southward tonight, then continue veering to become easterly by
morning. Showers and thunderstorms are expected to develop over
western MO and spread eastward overnight, likely reaching the
terminals between 08-12z. Another round of SHRA/TSRA is expected
to develop beyond the end of the 24-hr TAF period.

Specifics for KSTL, KSUS, KCPS: MVFR stratus is slowly advancing
towards St. Louis metro area terminals on the cool side of a
boundary which was wavering across the region. Winds will turn
southwesterly to westerly when the warm front lifts north of the
terminals today, then become northerly to northeasterly when the
trailing cold front sinks back southward. Winds will veer
overnight and become easterly to southeasterly by tomorrow
morning. Showers and thunderstorms are expected to develop west of
the terminal and spread eastward overnight, reaching the St. Louis
metro area between 10-14z. There should be a break in the
precipitation on Tuesday afternoon before the next wave of
thunderstorms develops near or just beyond the end of the 36-hr
TAF period.

Kanofsky

&&

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

$$

WFO LSX






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