Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 121111
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
611 AM CDT Fri Sep 12 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 340 AM CDT Fri Sep 12 2014

Could not rule out a little drizzle this morning from the persistent
stratus cloud deck across most of our forecast area.  An upper level
trough, strong shortwave will move eastward through the northern
Plains today and bring measurable rain to at least northeast MO this
afternoon.  Unseasonably cool weather will continue today as the
strong surface ridge centered across the northern Rockies and
northern Plains continues to build southeastward into MO.  The
850 mb temperatures will continue to fall, ranging from only about
2 degrees C across northeast MO to around 11 degrees C across
southeast MO by 00z Saturday.

GKS

.LONG TERM:  (Tonight through Thursday)
Issued at 340 AM CDT Fri Sep 12 2014

An interesting scenario for tonight, which is a carryover from
today.  A powerful shortwave TROF will track just north of our
region this evening and early overnight with much of the good
broadscale lift also passing to our north.  But...a lobe of
vorticity will trail to the south thru our region and maintain some
presence of this broadscale lift.  This combined with similar values
for moisture and deep lift thru the column currently found over
western Kansas where there is decent coverage of rain should result
in something more than what is currently depicted by many of the 00z
run models.  Needless to say, strongly favor the wetter MET MOS PoPs
for this evening, and in some cases, going even higher.  PoPs should
rapidly taper off after midnight as much drier air and clear skies
expand.

A strong Canadian surface high pressure--the same one that delivered
the cold air that helped blanket parts of western South Dakota with
snow 24 hours ago--will then build in for Saturday and continue to
dominate our region into Sunday.  This will maintain the well below
normal temp regime and promote dry weather after tonight.  Nighttime
min temps may dip into the upper 30s in spots--first across areas in
northeast MO early Saturday morning--and then again across the
eastern Ozarks of southeast MO early Sunday morning.  Strong
sunshine which can still be seen in September, especially before the
equinox, will result in large diurnal swings.  Prefer the warmer MAV
MOS for max temps this weekend.

The chance for rain will begin to return late Sunday night and
Monday as a cold front moves thru.  The airmass behind this front is
not quite as cool as the one we`re going to get this weekend and so
the resultant daytime max temps are only slightly below normal.
Models diverge on handling of precipitation chances after this, but
with decent agreement on northwest upper flow, prefer a dry solution
at this time.

TES

&&

.AVIATION:  (For the 12z TAFs through 12z Saturday Morning)
Issued at 533 AM CDT Fri Sep 12 2014

MVFR cigs across the area with some holes in the low level cloud
deck over northeast MO and west central IL. There may be a slight
rise in the ceiling height later this morning and afternoon, but
likely remain MVFR. There will be patchy drizzle early this
morning. An upper level disturbance will bring light showers to
UIN mainly late this afternoon into the early evening. Could not
rule out a brief period of light rain further south at the other
taf sites as well. The clouds should clear out late tonight as the
upper level disturbance shifts east of the area and a strong
surface high moves southeastward into northwest MO by 12z
Saturday. Nely surface wind will back around to a nly direction
this afternoon.

Specifics for KSTL: Intermittent drizzle early this morning, then
a brief period of light rain or showers possible this evening.
Cloud ceiling around 1500 feet will rise slightly later this
morning and this afternoon, but likely remain in the MVFR catagory.
The cloud cover should finally clear out late tonight. Nely
surface wind will back around to a nly direction this afternoon.

GKS

&&

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

$$

WFO LSX






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