Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 290442
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1142 PM CDT Sat Mar 28 2015

.UPDATE:
Issued at 925 PM CDT Sat Mar 28 2015

This evening`s water vapor imagery indicates potent shortwave over
eastern MT and WY zipping ESE, with latest NWP runs indicating the
dynamics with this system reaching the mid-Missouri Valley by
12z. 00z 850mb data shows strong WAA already occurring over the
northern Plains in advance of this feature, and this should
increase even further overnight with the approach of the
shortwave. However, AMS over the plains is extremely dry, and
there is no obvious source of significant moisture for the
increasing southerly flow to tap over the next 6-9 hours.  While
the power of warm advection should never be underestimated,
believe the limited moisture is going to cause any measurable
precip to struggle to reach our FA overnight. Going PoP trend,
which limits mention of precip to our extreme northwest counties
in the 10-12z time frame, still looks reasonable.

Still expect a bit of an increase in clouds overnight, either from
some of the low level moisture trapped over the Ozarks sloshing
back to the east, or from high clouds in advance of the shortwave
pushing southeast during the predawn hours. Going temp trends
still look good.

Truett
&&

.SHORT TERM:  (Through Late Tonight)
Issued at 345 PM CDT Sat Mar 28 2015

Quiet weather tonight under shortwave ridging ahead of the next
shortwave trof.  Should see temperatures fall off fairly quickly
this evening under a clear/mostly clear sky and light wind.
However, think the temperature drop will be arrested overnight by
increasing mid and high clouds ahead of the shortwave and also
increasing southerly wind as the surface pressure gradient tightens
ahead of the surface wave. Stuck pretty close to blended guidance
for lows tonight, but those lows may occur a few hours before
sunrise, with perhaps nearly steady or slowly rising temperatures
through 12Z.

Carney

.LONG TERM:  (Sunday through Next Saturday)
Issued at 345 PM CDT Sat Mar 28 2015

Northwest upper level flow will prevail thru Tuesday across our
region, with mostly quiet wx and a pair of weak cold fronts dropping
thru.

The only sensible wx forecast for this stretch is for Sunday, as an
upper level disturbance edges our area to the north and west with
strong WAA on the front-end.  A band or two of showers is expected
to form from this as a result, with the highest probs to the north
and east of STL where likelys PoPs were retained, but more scattered
coverage heading into central MO and the Ozarks.

Otherwise, temps should warm up pretty well Sunday despite clouds
and rain, with at or above MOS for most sites forecasted, which
would result in 50s most areas with low 60s in central MO.

Despite a cold front moving thru late Sunday, temps on Monday are
expected to be warmer with flow already backed from the SW again.
The higher MOS values for max temps favored with decent sunshine
anticipated.

This warming trend should continue into Tuesday with another front
coming down, but not until afternoon.  Did not go as high as the MEX
MOS values, which would have had more confidence in them with a
slightly later FROPA, but nevertheless, went with max temps in the
low 70s for most areas.  There is the potential for a low confidence
shower event late Monday night into Tuesday associated with WAA, but
this is not nearly as strong as the Sunday event.  For now
maintained the dry forecast.

The Tuesday front will then linger thru much of the second half of
the work week as upper flow shifts to more from the W-SW.
Persistent shower and thunderstorm chances will reflect this period
with mild temps.  Some room to go even higher on temps south of the
front Wednesday and Thursday if confidence can be increased in rain
holding off, but very little skill in those specifics this far out.

Temps expected to return to below normal following this wet period
on Saturday with another cold front moving thru and a bit better
cool airmass moving in.

TES
&&

.AVIATION:  (For the 06z TAFs through 06z Sunday Night)
Issued at 1142 PM CDT Sat Mar 28 2015

Gradient to continue to tighten over region ahead of cold front
that will move through Sunday afternoon. Southeast to south winds
to pickup by mid morning with gusts to near 25kts at times. As for
precipitation, a lot of dry air to overcome but best chances will
be along and east of Mississippi River as system moves through.
Front to move through KUIN by 19z Sunday, KCOU by 21z Sunday and
metro area by 23z Sunday with winds veering to the west and
diminishing behind the cold front.

Specifics for KSTL:
Gradient to continue to tighten over region ahead of cold front
that will move through Sunday afternoon. Southeast to south winds
to pickup by 15z Sunday with gusts to near 25kts at times. As for
precipitation, a lot of dry air to overcome but best chances after
19z Sunday, for now just have vfr cigs/vsbys with showers. Front
to move through metro area by 23z Sunday with winds veering to the
west and diminishing behind the cold front.

Byrd
&&

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

$$
WFO LSX





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