Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 250011

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
711 PM CDT Fri Mar 24 2017

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 405 PM CDT Fri Mar 24 2017

Main focus will be precip chances and potential for severe threat
thru the period.

SHRA with sct TS continues across portions of central MO this
afternoon. These will slowly propagate ewd this evening and
overnight. Ahead of theses SHRA, the area has destabilized somewhat
tho limited as dewpoints mix out into the lower 50s. This area also
remains capped with warming in the 800 mb region. There appears to
still be a limited window, in both time and space, where a severe
threat will linger late this evening. Appears the main threat will
be limited to the srn portions of the CWA with wind as the main
threat where convection can organize, or remain organized as it
propagates into the area.

Going forecast may have too much TS mentioned overnight and may
become more of a shower event thru the night.

As the stacked low continues to approach the area, expect the dry
slot to clear out precip over much of the area Sat morning. This
lull shud be brief as convection develops and fills in the area.
Still appears at least a hail threat will be exist with any storms
that develop on Sat. Can not rule out an isolated tornado threat,
but will depend on where the occluded fnt sets up. Currently, area
of most concern is nrn portions of the CWA.

The stacked low continues to fill and is expected to weaken somewhat
as it approaches the area. However, will need to monitor expected
wind speeds for Sat as an advisory may be needed. Area of most
concern are ern half to third of the CWA.


.LONG TERM...  (Saturday Night through Next Friday)
Issued at 405 PM CDT Fri Mar 24 2017

First in the series of cutoff upper lows will be over central MO as
of 00z Sunday. So for Saturday evening, will see co-located surface
low lifting northward through eastern MO and into southeastern
IA/northwestern IL. It will slowly drag the cold front through with
showers and isolated thunderstorms. Still some concern for isolated
severe due to cold core low. The latest SPC Day 2 Outlook keeps the
region in a Marginal risk, but this could be upgraded in later
forecasts as instability trends become more clear.

Showers to taper off towards daybreak on Sunday, but could still see
some isolated showers Sunday morning due to being in cyclonic flow
on back side of system. Otherwise, most locations will be dry on
Sunday before next cutoff upper low lifts out of the desert
southwest towards region Sunday night into Monday. So will see
another round of showers and thunderstorms through Monday evening.

Active pattern to persist with weak ridging building in for Tuesday-
Tuesday night before next system moves in on Wednesday. Will see
best chances of showers and thunderstorms late Wednesday night
through Thursday Night.

As for temperatures through the period, will see lows in the 40s and
highs mainly in the 60s.



.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 710 PM CDT Fri Mar 24 2017

Main forecast issue is trying to separate mainly wet periods from
periods that won`t be as wet. Looks like two periods: one with a
band of rain with some imbedded TSRA slowly sliding eastward
tonight and then another firing up of convection Saturday
afternoon with the heating of the day. VFR conditions should
prevail at the TAF sites for much of the valid period in a warm
sector setup but as the cold front slowly moves thru beginning
late Saturday afternoon and Saturday night, this should result in
lower CIGs building in from the west and deteriorating prevailing
conditions. Some surface wind issues with an outflow boundary
affecting UIN and COU, but everything should straighten out more
from the SE for much of tonight and Saturday before shifting from
the west with cold FROPA late in the valid period or just beyond.





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