Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KLSX 240213
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
913 PM CDT Mon Mar 23 2015

.UPDATE:
Issued at 912 PM CDT Mon Mar 23 2015

Two areas of clouds currently affecting the forecast area. The
first is an area of post-frontal low clouds that never quite
pushed as far south as originally anticipated but has nevertheless
resumed its southwestward push towards the CWA, but currently only
is over the far northern reaches. More is expected to move in
later tonight from central IL. Another area is much higher up in
elevation and the beginnings of our active wx that is in store for
this week. It has already moved past central MO and is pushing
east. One way or another, the forecast area will be cloudy at or
shortly after midnight.

Precipitation is rapidly developing over in southeast NE and
northeast KS in response to increasing and deepening lift from
several factors with this area of lift expected to expand
eastward, and should hold off on entering our forecast area until
after midnight with much of the development occurring late towards
daybreak for areas near STL metro and areas to the north and west.
Thunder chances look less now than they did but retained isolated
wording in for some areas, mainly over in central MO.

What is increasingly becoming a factor are temps in the northern
CWA, around UIN, where readings are already in the mid 30s.
With persistent low level CAA behind this front and some room to
drop due to dewpoint depressions, it now appears likely that much
of this area will drop to or just below 32F for a few hours late
tonight and Tuesday morning. This will result in some FZRA, but
thanks to temps not getting a chance to fall much below freezing
lately, surfaces should not be that cold and expected ice accums
will be minimal if any. Will have to further monitor this
overnight for any needed headlines, however.

Otherwise, rain with isolated TSRA early in the morning will
gradually push north during the morning, offering up a bit of a
break for most areas before the next round later Tuesday afternoon
fires up, where thunder composition will be more substantial.

TES

&&

.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 00z TAFs through 00z Tuesday Evening)
Issued at 549 PM CDT Mon Mar 23 2015

Cold front has shifted south of the taf sites early this evening.
Post frontal, MVFR stratus clouds has moved into UIN and may sag
southward into the other taf sites late this evening or overnight.
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. Most of
the afternoon may be quiet, but another round of convection is
expected to move through COU around 00z Wednesday and into the
rest of the taf sites by late Tuesday evening as an upper level
disturbance and weak surface low approaches. An n-nely surface
wind will gradually veer around to an e-sely direction on Tuesday.

Specifics for KSTL:Low level MVFR clouds will likely sag
southward into STL late this evening. 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 nly surface wind will
veer around to a nely direction later this evening, then to an
ely direction Tuesday morning and a sely direction by Tuesday
evening.

GKS

&&

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

$$

WFO LSX






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.