Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 050303

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
1003 PM CDT WED MAY 4 2016

Issued at 958 PM CDT Wed May 4 2016

No significant changes were made to the recently issued zones
other than updating for current trends. Clouds across S IL have
been a little slower to dsspt this evng and grids now have sctrd
clouds most of the night in our far ern zones. Otherwise going
fcst appears to be on track tonight. Other than S cntrl IL...skies
should be clear with a light NW breeze which should allow for a
seasonably cool night.



.SHORT TERM...  (Through Late Tonight)
Issued at 324 PM CDT Wed May 4 2016

A highly amplified pattern existed this afternoon of a longwave RIDGE
over the western CONUS and a TROF over the eastern CONUS, leaving N-
NW flow aloft for our region.  A sheared area of vorticity extended
over southern IL and was acting on the diurnal CU cloud field in
place over much of the area to result in isolated-scattered showers
in southern IL.  Temps were in the 60s most locations, with a few
spots around 70F.  Further upstream, a closed LOW was located over
southwest Lower MI with a much stronger disturbance on its near
western flank.

The ongoing showers associated with the sheared vorticity should
fade by sunset with loss of heating and diurnal influences.  The LOW
is expected to drop nearly straight south into eastern KY by dawn
Thursday and will carry the strong disturbance on its western flank
south with it.  The track should be far enough east for this feature
to miss our eastern CWA, but not by much.  As a result, the rain
chances associated with this feature should stay east--in Indiana

Otherwise, clouds will clear out this evening with a light NW
surface wind.  Widespread min temps in the low-mid 40s are
anticipated, with spots of upper 30s in northeast MO and the
eastern Ozarks of southeast MO.

Weak sheared vorticity and weak deep cyclonic flow will linger into
Thursday, but the results should be less than previous days and have
gone dry.  Otherwise, the cooler start in the morning, slightly less
diurnal CU clouds, and a very similar airmass should result in max
temps very close to persistence:  upper 60s to around 70F.


.LONG TERM...  (Thursday through Next Wednesday)
Issued at 324 PM CDT Wed May 4 2016

(Thursday Night - Saturday)

Surface high will remain in control on Thursday night and
early Friday. As a result...a mostly clear sky and one more cool
night should be in store for Thursday night. Expect lows
predominantly in the 40s. Expect coldest locations to be in the
favored locations across the eastern Ozarks where some low 40s
are possible.

Quick warmup looks to be in store on Friday. Combination of rising
mid/upper level heights...moderate-strong 850-hPa temperature
advection...and a westerly component to the sfc wind all suggest a
high diurnal range type day in temperatures and highs roughly 10
degrees warmer than the previous day. High temperatures are
forecast to range from the mid 70s to low 80s across the CWFA.

Dry weather will continue on Friday night as sfc ridging still holds
strong across the lower Mississippi River Valley. Next frontal
boundary will be moving south...but even late Friday night is
expected to be well to the north of the bi-state area. Another clear
or mostly clear night is expected on Friday night with lows much
warmer than Thursday night. This is due to a combination of slightly
increased sfc WSW wind speeds as well as a much warmer start to
the evening compared to Thursday.

Forecast begins to get more complicated by Saturday as
aforementioned cold front slowly moves southward into the northern
sections of the area by afternoon. Will be some capping in place and
with stronger mid/upper level support staying well to the north and
east...coverage of showers/thunderstorms may stay in the isolated-
scattered range. Temperatures will be well above normal once again
ahead/south of the approaching cold front. Highs should range from
the upper 70s across the far north to low/mid 80s along and south
of Interstate 70.


(Saturday Night - Next Wednesday)

       The period starts with a frontal boundary continuing to
slowly move southward Saturday evening. This will lead to a small
increase in winds along and north of the boundary. The frontal
boundary will pass through the metro and stall somewhere in
south-central MO/ southwest IL Saturday night. Pops should be
highest along and north of the frontal boundary at this time. The
frontal boundary should then lift north to along the I-70 corridor
Sunday night and Monday in response to the next system
approaching from the southwest. Pops become more likely starting
from COU west...pushing east during the day monday with the
approaching system. The frontal boundary will likely then be
draped roughly along the I-70 corridor during the day Tuesday
with POPS likely before the system exits the area late Wednesday.



.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 457 PM CDT Wed May 4 2016

A low pressure system was over southern MI, with surface ridging
over the Plains. Nwly surface wind will weaken early this evening
and lose its gustiness. The northwest wind will strengthen again
Thursday morning, although the wind will not be as strong as today
as the surface ridge shifts east-southeastward into MO. Diurnal
high based cumulus clouds will dissipate early this evening due to
lose of daytime heating. There may be scattered diurnal cumulus
clouds again late Thursday morning and afternoon, mainly in the
St Louis metro area.

Specifics for KSTL: Scattered high based diurnal cumulus clouds
will dissipate early this evening. There may be scattered diurnal
cumulus clouds again late Thursday morning and afternoon.  Gusty
northwest surface winds will weaken early this evening, then
increase to around 12 kts late Thursday morning. The surface wind
will become light Thursday evening with the surface high just w-sw
of STL.





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