Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240003
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
603 PM CST Sun Nov 23 2014

.SHORT TERM: (Through Monday)
Issued at 346 PM CST Sun Nov 23 2014

Main concern for tonight will be will there be any snow accumulation
over northwestern parts of the area as rain changes to snow behind a
sharp cold front. Most of the CWA has seen rain today and the
current band which is being forced by strong moisture convergence
and strong ascent ahead of ejecting shortwave trough will move
northeast of the CWA this evening. This will cause a lull in the
precipitation this evening before a second area currently over the
Plains moves into the area later this evening and overnight. This
area is being frontogenetically forced ahead of a second trough
currently over the northern Plains. Attendant cold front that
currently extends across central Iowa into far northwest Missouri
into eastern Kansas will push eastward this evening, reaching St.
Louis by midnight and east of the CWA by 3 am. Forecast soundings
suggest that the rain will mix with and then changeover to snow
after midnight before the frontogenetical band lifts out between
midnight and 6 am. Current indications are that snowfall amounts
will be less than 1 inch along and north of a Shelbina to Quincy
line given the relatively warm soil temperatures (Novelty Missouri
Mesonet 2 inch soil temperature is currently 50 degrees) and the
relative short amount of time that the accumulating snow will
fall. It will be windy late tonight into tomorrow as decent
gradient winds set up behind the cold front. However it does not
appear that we will hit advisory criteria at this time.

Do not expect much clearing tomorrow as forecast soundings show some
minimal CAPE in the lowest levels tomorrow afternoon suggesting some
isolated snow or rain showers will develop in the low level cyclonic
flow. Highs tomorrow are only a few degrees warmer than lows tonight.

Britt

.LONG TERM:  (Monday Night through Next Sunday)
Issued at 346 PM CST Sun Nov 23 2014

(Monday night through Wednesday)

Next notable trough that will move through the area will be on
Wednesday which the ECMWF and GFS both show light QPF across the
CWA. Have increased PoPs a bit across the area, with the highest
amounts over the northern CWA where current track of the surface
low will be. Temperatures will stay below normal during the period.

(Thursday through next Sunday)

Overall confidence in forecast during this period is not high as the
both operational GFS and ECMWF and their ensembles have had continuity
issues the past few days with the timing and strength of the troughs
that will move across the area later this week. Latest runs are showing
quasi-zonal flow during the period with shortwave troughs moving quickly
across the area. While the GFS is developing some QPF over the region
on Saturday, this is different than yesterday`s run, so will discount
for now. Will go dry during this period given the inherent difficulties
in timing precipitation in zonal flow.

Britt

&&

.AVIATION:  (For the 00z TAFs through 00z Monday Evening)
Issued at 531 PM CST Sun Nov 23 2014

Specifics for KCOU, KUIN: Several issues to discuss for the 00z
TAF cycle. Continual new development of RA/DZ across central and
northern MO makes it less likely to see a substantial break in the
precip at KCOU and KUIN compared to farther south and east.
Conditions should remain IFR for the near future. The next area of
precipitation to affect KCOU and KUIN was associated with an
approaching cold front. The rain is expected to mix with and
change over to snow with minor accumulations possible (one-quarter
to one-half of an inch or less) between 08-13z. A significant wind
shift will accompany the front. Winds will become west to
northwest and increase to around 20 kts sustained with gusts of
30-35 kts. It is possible that instability snow showers may
develop tomorrow afternoon due to the very cold air aloft, but
confidence is too low to include in the TAFs at this time. This
possibility will be re-examined for the 06z issuance.

Specifics for KSTL, KSUS, KCPS: Several issues to discuss for the 00z
TAF cycle. It looks like the ongoing RA/DZ will diminish over the
next few hours (vsbys should increase at least briefly), but cigs
will probably remain IFR due to the substantial low level moisture
in place. The next area of rain to affect the metro area TAF sites
is associated with an approaching cold front. It is possible that
some of the rain may mix with snow as precipitation is ending, but
confidence is too low to introduce RASN at metro area TAF sites
yet. A significant change in winds will accompany the front
between 10-14z. Winds will become west to northwest and increase
to around 15-25 kts sustained with gusts of 30-35 kts. Finally, it
is possible that instability snow showers may develop tomorrow
afternoon due to the very cold air aloft, but confidence is too
low to include in the TAF attm.

Kanofsky

&&

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

$$

WFO LSX





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