Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 232041

Area Forecast Discussion
National Weather Service Saint Louis MO
341 PM CDT Thu Mar 23 2017

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 337 PM CDT Thu Mar 23 2017

A tranquil night appears to be on tap across the area. In response
to surface pressure and low level height falls centered in the
Plains, the warm front currently stretching through central MO into
southeast MO will gradually lift nortward and a stout 60+ kt south-
southwesterly LLJ will develop. This will result in the onset of
improved moisture transport through the CWA and much milder low
temps. The LLJ may also bring some stratus be parts of southeast MO
and southern IL during the predawn hours, however most of the night
is expected to be largely void of clouds.

The southwest upper low/trof will move from the Rockies into the
Plains on Friday, with a broad warm sector through the Mid MS
Valley. Height falls, and large scale ascent attendant with a lead
shortwave ahead of the upper low will contribute to the development
of a north-south band of showers and some thunderstorms in the
afternoon across western MO. The lack of steep mid level lapse rates
will result in only weak instability across eastern MO and western
IL, resulting in lesser thunderstorm chances and coverage as the
band pushes through central MO in the afternoon. Temperatures look
rather mild with highs in the 70s owing to morning sun and a good
advective component.


.LONG TERM...  (Friday Night through Next Thursday)
Issued at 337 PM CDT Thu Mar 23 2017

First closed low to lift northeast through forecast area Friday
night through Saturday evening. As prefrontal trof moves into
region, will see ongoing line of convection sliding east through
area. 12z model runs showing some timing and strength differences
between the NAM and GFS/ECMWF, so will lean more towards the
slower/stronger GFS/ECMWF solution with a band of strong low level
convergence moving out ahead of the cold front. So best chances
of showers and storms will be Friday night. With the upper low
moving over the area, there is still the potential for some modest
instability to develop near the low, and ahead of the cold front.
As mentioned in previous discussion, will need to monitor the
possibility for low-topped supercells capable of producing all
hazards near the path of the upper low with more of a hail threat
along the cold front during the day on Saturday. Latest SPC Days 2
and 3 outlooks have a marginal risk over parts of the area Friday
night through Saturday.

Then as surface low exits region, will see wrap around showers and a
few storms develop Saturday afternoon and evening.

Should see a break on Sunday as weak surface ridge builds in, before
next closed low system lifts out of southwestern US into region late
Sunday night through Monday night. Best instability with this system
will be along and south of I-70.

Upper level and surface ridges build in by Tuesday with dry wx
through mid week. Some showers are possible over central MO during
the day on Wednesday as next system approaches region. Otherwise,
better chances of showers Wednesday night through Thursday as parade
of closed lows moving through region continues.

As for temperatures, will see lows in the 40s and 50s with daytime
highs in the 60s.


.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1242 PM CDT Thu Mar 23 2017

Residual showers currently located from west central through south
central IL will continue to push east away from all the terminals.
Clouds with bases from 3500-6000 ft will also move east/northeast,
thus VFR flight conditions are expected through the afternoon. VFR
flight conditions will also prevail tonight and are expected to
persist through early afternoon on Friday. A stout south-
southwesterly LLJ will contribute to LLWS beginning this evening
and lasting until near mid-morning on Friday.


VFR flight conditions are expected through the forecast period.
A stout south-southwesterly LLJ will contribute to LLWS beginning
this evening and lasting until near mid-morning on Friday.


Saint Louis     57  78  57  69 /   0  20  90  80
Quincy          53  75  54  66 /   5  50  90  90
Columbia        58  74  53  65 /   0  80  80  80
Jefferson City  58  75  54  65 /   0  80  80  80
Salem           54  74  58  68 /   5  10  90  80
Farmington      58  75  56  67 /   5  30  90  80



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