Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 301723

1223 PM CDT TUE JUN 30 2015

Issued at 919 AM CDT Tue Jun 30 2015

With the passage of the shortwave to the east with its isolated
convection have pretty dropped all PoPs from this morning except
over the far eastern CWA. Will monitor the weak cold front sliding
southeast through northern IL for any afternoon development.
Satellite imagery not showing any feature immediately upstream
although the 12z NAM indicates a couple of weak h7 vorticity maxima
that may or may not exist. IL counties within the CWA will have the
best chance for afternoon convection.



.SHORT TERM...  (Through Late This Afternoon)
Issued at 434 AM CDT Tue Jun 30 2015

Scattered showers and storms are expected mainly this afternoon and
mainly across west central and southwest IL, east of the Mississippi
River as northwest flow shortwaves move southeastward through our
area.  The atmosphere will destabilize this afternoon due to daytime
heating, especially across IL near the axis of the upper level
trough centered over the Great Lakes region where mid level
temperatures will be a little colder and hence lapse rates steeper.
High temperatures should be a little warmer today compared to Monday
and close to seasonal normals for the end of June.


.LONG TERM...  (Tonight through Monday)
Issued at 434 AM CDT Tue Jun 30 2015

Showers and thunderstorms can be expected late tonight and Wednesday
as a southwesterly low level jet brings strong low level warm air
advection and moisture convergence to our forecast area, and a
surface low approaches from KS while a front sags slowly southward
through the region.  The models were also depicting strong upper
level divergence over our forecast area ahead of a northwest flow
shortwave.  There will be the potential for heavy rainfall which
could result in more flooding.  High temperatures on Wednesday will
be cooler due to the increased cloud cover along with fairly
widespread precipitation.  As the surface low and front sag slowly
southward the best threat for convection will shift to the southern
portion of the area Wednesday night and Thursday.  A surface ridge
across the Great Lakes region will nose into northeast MO and west
central IL likely ending the chance of precipitation across this
area Thursday and Thursday night.  Another upper level trough
dropping southeastward into the region will keep the threat for
showers/storms going at least across the western and southern
portion of our area Thursday through Friday.  The GFS model is a
little stronger with the surface ridge over the Great Lakes region
and is a little further south with its QPF than the NAM and the
ECMWF models.  Upper level troffing over the region coupled with a
moist low level southerly flow should lead to at least scattered
afternoon and evening convection Saturday and Sunday.



.AVIATION... (For the 18z TAFs through 18z Wednesday)
Issued at 1223 PM CDT Tue Jun 30 2015

Mainly seeing a thick smoke layer aloft at midday, although some
diurnal cumulus was forming east of the Mississippi River. KUIN most
likely to see these lower clouds this afternoon. 17z obs have these
as low as 2000 feet, but heights should increase quickly as the
clouds track through west central Illinois.

Main concern for this TAF set will be with a developing convective
complex to the northwest this evening. 12z model guidance showing
this complex to be taking a southeast turn through Missouri after
06z. Ensemble members keep the general edge of this cluster near the
St. Louis metro, so have hit KCOU harder with TSRA beginning around
08z and the metro TAF`s more as VCSH for now. The frontal boundary
associated with this cluster will stall out near the I-70 corridor
toward midday, increasing the risk of afternoon redevelopment.

Specifics for KSTL:

Northwest winds around 10 knots this afternoon will gradually trend
toward the north by mid evening. Winds to become light and variable
late evening before trending more southerly Wednesday morning. Have
kept TSRA mention west of KSTL for late night where the low level
jet is more favorable, but some showers are likely by 10-11z. As a
frontal boundary become stationary over the metro, a better chance
of thunder will be present by Wednesday afternoon, so have
introduced a VCTS mention beginning around 18Z.




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