Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 110555

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1155 PM CST Tue Jan 10 2017

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 349 PM CST Tue Jan 10 2017

Strong cold front to slide southeast of forecast area by 00z
Wednesday. So as weak surface ridge builds in, winds to diminish
tonight. With clearing skies and light winds, temperatures to dip
down into the upper 20s to upper 30s.

By Wednesday morning surface ridge shifts off to the east allowing
southerly winds to return once again. Decent winds aloft to mix down
to surface, so another windy day, but not quite as strong as
today`s. This will bring in warmer temps with highs in the mid 50s
to low 60s. Could even see near record highs in central and
northeast Missouri.

In the meantime, low level moisture will be on the increase as next
system approaches the region. Kept slight chance/low end chance pops
for far southern portions Wednesday morning, spreading northward
through the afternoon hours. Models showing some weak CAPE on nose
of low level jet during the afternoon hours now. So added slight
chance mention of thunderstorms with showers between 18z Wed and 00z


.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 349 PM CST Tue Jan 10 2017

(Wednesday night through Friday)

Main focus will be temps thru this period.

Mdls continue to be in fairly good agreement thru the period, tho
some temp differences do exist. Have continued higher PoPs along the
cdfnt Wed night into Thurs as a sfc wave develops and moves newd
along the fnt. After a brief lull in activity within the CWA, Thurs
afternoon into the evening, precip will gradually move back nwd. The
nwd push is due to the WAA redeveloping over the region with the sfc
ridge retreating ewd over the Great Lakes region. Expect precip to
come in waves with brief lulls between them as each s/w embedded
with the zonal flow passes thru the region. This makes timing
specific waves of precip difficult, however, have kept PoPs within
the likely range where confidence is higher.

As for temps, have generally trended twd the warmer guidance through
Thurs, then cooler for Thurs night and Fri. Still, there are
competing features that introduce uncertainty during the later half
of this period. The sfc ridge, with shallow cold air, is retreating
with WAA thru a deep column. However, ely flow and ample cloud cover
will help keep temps cooler. The good news is that where and when
the bulk of the precip is expected, sfc temps are expected to be in
the low 30s to perhaps upper 20s. With the recent warm temps, the
ground shud remain warm helping to limit ice accums to elevated
sfcs. Of course, where the colder temps are, the precip is expected
to be lighter allowing ice to accumulate more quickly.

(Saturday through Tuesday)

More uncertainty thru this period with some important differences
among mdl solns. The main difference early in this period is sfc
temps. Is fairly good agreement among GFS/GEM/DGEX with the ECMWF
being much colder. The colder soln appears to be due to a
reinforcing of a sfc ridge over snowpack across the nrn Plains
region allowing colder temps to filter back into the area. This soln
seems less likely as it is an outlier. However, did lower temps on
Sat and Sun, tho to a lesser degree, due to this colder soln.

Overall, given the marginal temps with this event, not currently
anticipating a major icing event. That said, it still appears a
warning criteria event is possible with one quarter to perhaps a
half inch of ice in spots, with higher amounts generally along and
south of Hwy 36, but north of I-70. It remains important to remember
that there is still too much uncertainty with this event as
discussed above and amounts are still likely to change. Have held
off issuing any headlines today and will reevaluate tonight and
tomorrow as needed.

Looking later in the forecast period, warming trends are expected
late this weekend into next week with precip expected to continue.



.AVIATION... (For the 06z TAFs through 06z Wednesday Night
Issued at 1131 PM CST Tue Jan 10 2017

A high pressure center was moving across the area at TAF issuance.
Winds will become southeasterly to southerly around the back side
of the departing high pressure center. Winds will increase after
11/09z due to the tightening pressure gradient, but winds will not
be as strong as they were on Tuesday. Stratus will accompany a
warm front as it lifts northward, and cigs may vary between high-
end MVFR and low-end VFR during the day before falling to MVFR
after 12/00-06z.





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