Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 271711

1111 AM CST Tue Jan 27 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 325 AM CST Tue Jan 27 2015

Satellite data at 08z showed the backedge of an area of clouds near
the MS river breaking apart, but a new batch of clouds was already
oozing southward from northeast IL and southeast IA.  To the west,
skies were clear, with cloudy skies covering much of our region east
of the MS river.  Temps were mild for late at night in late January,
with readings in the 30s.  Otherwise, NW flow prevailed aloft with
NW winds also at the surface, thanks to an area of weak low pressure
to the east and a weak ridge of high pressure to the west.

No upper level disturbances or fronts are expected today with weak
high pressure insteady building into the area.  With a dry
atmospheric column, the result will be dry wx.

The main forecast problem will be clouds and their impact on temps.
Flow at cloud level is expected to be out of the north this morning
with a transition to negligible wind flow in the afternoon as the
ridge builds in.  Even though the backedge of the clouds near the MS
river has collapsed, a new batch of clouds further to the north is
expected to drop south into our region and create a new backedge to
the cloud shield near the MS river again.  The afternoon should
feature some retreat of the cloud edge back to the east again as
weak subsidence from the high pressure ridge moves in.  Some
question on whether or not the surviving clouds to the east will get
moved back to the west if the ridge catches up and passes it too
fast tonight.

Max temps were forecast strongly favoring the lower MET MOS numbers
in much of southwest IL, with a MOS blend for the MS river region
and max temps at or slightly above the higher MAV MOS for central


.LONG TERM:  (Tonight through Monday)
Issued at 325 AM CST Tue Jan 27 2015

(Tonight through Thursday)

Main focus thru the period is temps with little in the way of

Mdls are generally in good agreement thru the period. However, some
differences emerge late in the period regarding the speed and depth
of the approaching trof. Mdls have come into better agreement with
thermal profiles. Have trended slightly cooler tonight with clouds
expected to clear out of the region for at least a portion of the
night. No changes to temps for Wed. While latest mdl guidance
suggests much of the region is not expected to mix above 950 mb,
mdls have struggled to warm fast enuf with these types of systems
lately. Heights lower quickly as the sfc ridge settles over the area
and have trended cooler late in the period.

Only precip expected is light precip associated with the system late
Wed night into Thurs morning. With such a strong s/w associated with
this system, enuf cold air my push in behind the system that the
precip may be SN. However, will keep p-types as RA for now until
mdls come into better agreement with precip placement and thermal
profiles with the precip.

(Friday through Monday)

As the sfc ridge remains in control thru the remainder of the week,
temps remain cooler ahead of the next approaching system. Focus
quickly turns to this system as mdl solns have finally come into
better agreement and are finally more consistent from cycle to
cycle. The leading s/w ejects into the srn Plains and spread precip
across the region on Sat as the sfc low develops ahead of the main
trof. Mdl solns are currently in very good agreement, tho some
differences in timing continue. Current track of this system shud
bring SN to at least portions of the CWA while. This system will
likely shift as it approaches and will be one to monitor. Much
colder air will move into the region behind this system as the
arctic sfc ridge builds into the area.



.AVIATION:  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1032 AM CST Tue Jan 27 2015

Low level, MVFR cloudiness across eastern IA and much of IL still
advecting southwestward late this morning. There has also been
some diurnal development of cumulus or stratocumulus clouds
further southwest which were impacting STL and CPS. This diurnal
development will likely continue this afternoon despite some
subsidence across the area, so will need at least a tempo group in
UIN and the St Louis metro area tafs for MVFR cigs at times.
Surface winds will gradually veer around to a nely direction this
afternoon, and then to an ely direction this evening due to surface
ridging strengthening across the Great Lakes and Ohio Valley
regions tonight. As these winds take on a more e-nely component it
may cause the low level cloud cover to advect back into UIN and
the St Louis metro area late this afternoon or this evening. For
now make keep prevailing conditions VFR during this time period,
but will need to keep a close eye on satellite trends. Sely
surface winds will strengthen late tonight and Wednesday morning
as the surface pressure gradient tightens due to developing low
pressure over the northern Plains.

Specifics for KSTL: MVFR clouds have develped over STL and may
continue for much of the afternoon. The more solid cloud cover
east and north of STL may also try to advect back into STL late
this afternoon and this evening. For now may keep cloud conditions
scattered tonight, but would not be surprised if it goes MVFR again
for at least part of the night. The nly surface wind will
gradually weaken and veer around to a nely direction late this
afternoon, and to an ely direction by late evening. The wind will
intensify again Wednesday morning from a sely direction.





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