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Area forecast discussion...updated aviation 
National Weather Service St Louis MO
1147 PM CST Thursday Nov 26 2015

Short term: (through saturday)
issued at 333 PM CST Thu Nov 26 2015

A strong wound-up storm system over the Great Basin region of the
western Continental U.S. Is expected to move little during this period,
maintaining an active southwest flow aloft over our region, and
shooting out pieces of energy or distrbances our way as well.

The first of these disturbances is expected to arrive shortly after
Sundown this evening, with essentially a near continuous train thru
late Saturday after that. The effects of the rainfall that this
brings will be further augmented by a slow moving cold front thru
midday Friday and rich moisture from the Gulf of Mexico, some of
which will continue to overspread north of the front after it
passes, into the cold air.

Despite much cooler air ushering in behind the cold front,
temperatures are expected to stay above freezing for most areas thru
this entire period and will keep pcpn-types as all rain. The
exception is expected to be in parts of northeast MO and west-
central Illinois late Friday night and early Saturday morning, where temps
will be around the freezing mark. Fortunately, much of the pcpn by
that time should be to the south with only light spotty pcpn
currently anticipated.

Otherwise, the main concern will be the prolonged period of heavy
rainfall--especially for parts of southeast MO and far southern Illinois--
where rainfall totals may top 4 inches into Saturday. The Flood
Watch will continue, with the addition of Audrain and Lincoln
counties in MO, where similar quantitative precipitation forecast and contingency forecasts for area
rivers and streams exist. An expansion into Marion, Bond, and
Fayette counties in Illinois was also considered, with timing of onset
enough to give it one more look before making a final call. Even
though rainfall chances remain high into Saturday afternoon and into
Sunday for southeast MO and southern IL, rainfall amounts look light
enough to justify ending the flash Flood Advisory on Saturday as it currently does.

Temps will be quite mild for late November ahead of the front, but
will rapidly drop to below average for daytime maxes behind it, with
readings in some areas not getting out of the 30s. Fortunately,
plenty of warm air aloft should keep the pcpn as rain unless surface
temps can slip below 32f.


Long term: (sunday through next thursday)
issued at 333 PM CST Thu Nov 26 2015

Model solutions have come into much better agreement on mass
fields here, with the wound-up storm system ejecting into the
plains on Monday and slowly tracking east--north of our region on
Tuesday-- with northwest flow aloft to follow on Wednesday. Large
model spread then resumes for next Thursday, where the ec shows a
much deeper storm trying to take shape for the mid-MS valley than
the GFS.

Either way, pattern is very supportive of keeping the very cold air
locked in Canada. The approach of the main storm system Monday will
allow for one more decent rain chance at all locations after being
largely confined to southern MO and southern Illinois again on Sunday,
with dry wx for a change Tuesday and Wednesday as high pressure
builds in, and probably will continue into Thursday.

Temps look to be around average for the November-December interface.



Aviation: (for the 06z tafs through 06z Friday night)
issued at 1145 PM CST Thu Nov 26 2015

Frontal passage has occurred over the last hour at both kcou and KUIN, which
produced an immediate drop of cigs below 1000 feet, with a dip in
vsbys at KUIN into MVFR Cat. Expect IFR cigs to hold tough
at these locations overnight and into at least Friday morning.
MVFR vsbys in moderate to occasionally heavy rain also expected
overnight, with a slow improvement on Friday morning as the
heaviest rain shifts to the south. Meanwhile, stl Metro will
remain in the warm sector for several more hours with VFR cigs aoa
5kft as pre-frontal showers slowly work in from the west, with
low level wind shear potential due to winds just off the surface in the 40-50kt
range. However, based on latest RUC guidance expect frontal passage in the
11-13z time frame, with a rapid drop in conditions much as kcou
and KUIN experienced between 04-05z. IFR cigs and MVFR vsbys
expected for much of the day on Friday.

Specifics for kstl: expect VFR cigs for several more hours as
pre-frontal showers gradually work into the area. Looking for a
rapid deterioration in conditions around 11z as strong cold front
pushes through the taf area, with cigs immediately dropping into
the 400-700 ft range, with MVFR vsbys in moderate to heavy rain.
Expect IFR cigs and MVFR vsbys to persist for much of the day on



Lsx watches/warnings/advisories:
MO...Flood Watch through Saturday morning for Crawford MO-Franklin MO-
Jefferson MO-St. Charles MO-St. Louis city MO-St. Louis MO-
Washington MO.

Flood Watch from 6 am CST Friday through Saturday morning for
Iron MO-Madison MO-Reynolds MO-St. Francois MO-Ste.
Genevieve MO.

Flood Watch through late Friday night for Audrain MO-Boone MO-
Callaway MO-Cole MO-Gasconade MO-Lincoln MO-Moniteau MO-
Montgomery MO-Osage MO-Warren MO.

Illinois...Flood Watch through Saturday morning for Madison Illinois-Monroe Illinois-
St. Clair Illinois.

Flood Watch from 6 am CST Friday through Saturday morning for
Clinton Illinois-Randolph Illinois-Washington Illinois.



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