Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 021212

612 AM CST TUE FEB 2 2016

.SHORT TERM:  (Through Late This Afternoon)
Issued at 235 AM CST Tue Feb 2 2016

Showers and a few thunderstorms were moving north-northeastward
through western MO, just west of our forecast area early this
morning. This activity was in the vicinity of a strong southerly
low level jet and ahead of an upper level low and associated
surface low over southwest KS. The upper level low will move
northeastward into southeast Nebraska and western Iowa by 00z
Wednesday while the surface low moves into northwest MO. Showers
and scattered thunderstorms will sweep eastward through our
forecast area today as depicted by the latest HRRR run. The
models were depicting very strong 850 mb warm air advection,
theta-e advecton, and moisture convergence across much of our area
this morning into the afternoon on the nose of the strong
southerly low level jet as it translates eastward through our
region. Best potential for any severe storms will be across parts
of southeast MO and southwest IL this afternoon where the best
instability will be. The primary threat will be damaging winds.
The precipitation should shut off quickly this afternoon over
central MO as the dry slot moves northeastward into our area with
partial clearing. Strong and gusty surface winds can be expected
this morning into the afternoon, close to wind advisory criteria
due to the relatively tight surface pressure gradient and momentum
transfer to the surface from the strong low level jet. Despite the
cloud cover and precipitation, highs will be well above normal
today and warmer than yesterday.


.LONG TERM:  (Tonight through Monday)
Issued at 235 AM CST Tue Feb 2 2016

The precipitation should shift east of our forecast area this
evening with colder air filtering eastward into our area south and
southwest of the surface and upper level low. Wrap-around type
low level cloudiness will advect southeastward into our area
tonight with light snow or flurries possible, mainly across
northeast MO late tonight. Little if any accumulation is expected.
Much colder temperatures can be expected late tonight and
Wednesday with highs on Wednesday close to seasonal normals for
early February. Low level cloudiness will keep highs down on
Wednesday and there may be a few flurries. Winds will also be
strong and gusty with a tight surface pressure gradient between
the surface low moving northeastward through the Great Lakes
region and the surface ridge building eastward into our area from
the Plains. Tranquil and dry weather can be expected for the later
portion of the work week with temperatures close to seasonal
normals, then a little warmer for the weekend. A deepening upper
level trough over the northern Plains will send a cold front
southeastward through our area Sunday night. Both the GFS and
ECMWF models depict a cold pattern for the early portion of the
next work week with a deep upper level trough extending from the
Great Lakes into our area, along with persistent northwesterly
surface winds, and cold 850 mb temperatures.



.AVIATION:  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 548 AM CST Tue Feb 2 2016

Primary concern this morning is low level wind shear. AMDAR
sounding out of KSTL is confirming guidance forecasts of southeast
flow in excess of 40kts within 2000 ft of the surface this
morning. LLWS conditions should persist through much of the
morning. Second concern is MVFR ceilings spreading north out of
southern Missouri. These low ceilings should overspread the entire
area this morning...eventually falling to IFR as the day
progresses and precipitation increases in areal coverage. Will
also have to deal with scattered thunderstorms and the possibility
of wind gusts in excess of 50kts primarily over eastern Missouri
and Illinois today. A dry slot will punch into the area this
afternoon, switching the wind to the south-southwest and the low
ceilings will quickly erode leaving VFR flight conditions over the
area for the evening. Low clouds will wrap around the storm system
which is causing all of this weather and will overspread the area
from the northwest late tonight.

Specifics for KSTL:

AMDAR sounding from KSTL is confirming wind in excess of 40kts
within 2000 ft of the ground this morning. Have therefore
continued mention of LLWS in the TAF. Really only dropped the LLWS
later this morning when TS is started since TS implies wind shear.
The timing on ceilings below 2000 ft is not certain...think model
guidance is a little fast which is why I held off until 15Z...tho
1500 ft cigs are lurking over KFAM and KVIH. At any rate, ceiling
should drop over the next 2-4 hours and showers with a few
thunderstorms should overspread the terminal. Should see ceilings
improve during the late afternoon as the dry slot moves through.
Expect VFR flight conditions to prevail through the evening and
probably most of the night until low clouds move in early
Wednesday morning.





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