Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240857
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
357 AM CDT Tue Mar 24 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 354 AM CDT Tue Mar 24 2015

Strong shortwave now moving across the eastern Rockies is forcing
lee-side cyclogenesis over the Oklahoma pan handle.  The surface
cold front looks to be nearly stationary now over extreme southwest
Missouri at this time, but the low level jet is pouring warmer and
more moist air up over the colder air at the surface.  Warm
advection precip has spread across much of northern Missouri and
into west central Illinois at this time, as well as parts of
southwest Missouri.  Short range guidance is in good agreement that
this rain with embedded thunderstorms will continue to expand and
overspread much of the area along and north of I-44/I-70 this
morning.  The rain cooled air as well as cool easterly flow should
help to keep the front south of I-70 in Missouri and I-64 in
Illinois today even though the warm advection will continue to be
quite strong.  The front will likely lift northward across some
portion of the area though.  South of the front temperatures will
likely get into the upper 60s to low and mid 70s, while north of the
front we`ll be hard pressed to break into the mid 50s.

Severe thunderstorms still a good possibility across a portion of
the area this evening.  Latest short range guidance shows a broken
line of thunderstorms moving into the area between 23-02Z this
evening as the surface low moves into central Missouri.  There will
certainly be enough deep layer shear for severe weather across the
area with values in excess of 50kts.  Models are showing 0-1km
helicity of 300-500 m2/s2 as well.  The limiting factor will be
instability.  Latest guidance has backed off from yesterday`s runs
on CAPE values with MLCAPE barely able to crack 500 J/kg and even
MUCAPE unable to get above 1000 J/kg.  This is most likely due to
the aforementioned surface front being further south than previously
expected.  The 4km NCEP WRF looks reasonable with the broken line
moving into central Missouri around 02Z and then making it about 1/2
way to St. Louis before weakening.  Still should get some strong
thunderstorms west of the Mississippi river, with locally damaging
winds being the primary threat due to the strong kinematics.  Can`t
rule out inch hail or larger if we get some rotating storms.  And of
course there continues to be a small tornado threat due to the low
level shear/helicity...especially in the vicinity of the warm front
as it tries to lift north ahead of the surface low.

Carney

.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 06z TAFs through 06z Tuesday Night)
Issued at 1031 PM CDT Mon Mar 23 2015

Cold front has shifted south of the taf sites this evening. Post
frontal, MVFR stratus clouds has moved into UIN and will likely sag
southward into the other taf sites late tonight. A s-swly low
level jet will bring low level temperature and moisture advection
over this front leading to elevated convection late tonight and
Tuesday morning for the taf sites. Showers and embedded
thunderstorms will move into COU and UIN late tonight and into the
St Louis metro area early Tuesday morning. Surface temperatures
will likely drop to around 32 degrees in UIN around 12Z Tuesday
leading to a brief period of freezing rain.  Most of the afternoon
may be quiet, but another round of convection is expected to move
through the taf sites Tuesday evening as an upper level
disturbance and weak surface low approaches. Nely surface wind
will gradually veer around to an e-sely direction on Tuesday, and
a s-swly direction Tuesday evening.

Specifics for KSTL:Low level MVFR clouds will likely sag
southward into STL shortly after 06Z Tuesday. Showers and a few
thunderstorms should move through STL Tuesday morning, then a
break in the convection is forecast Tuesday afternoon, with
another round of convection Tuesday evening. The nely surface wind
will veer around to an ely direction Tuesday morning, then to a
swly direction by late Tuesday night.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     55  46  71  41 /  80  80  30  70
Quincy          46  40  63  34 /  90  80  20  30
Columbia        58  43  69  38 /  70  80  30  50
Jefferson City  63  43  73  39 /  60  70  40  60
Salem           54  48  69  42 /  50  70  30  80
Farmington      65  48  72  42 /  30  70  50  80

&&

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

$$

WFO LSX





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