Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 020424

1124 PM CDT Mon Jun 1 2015

Issued at 920 PM CDT Mon Jun 1 2015

Low cloud field that has dominated our area the past 36 hours or
so is starting to clear out upstream from our region in eastern
IL. RAP cloud level flow at 1km AGL shows predominantly E-NE flow
slowly veering SE thru 18z/Tue with about a mean speed of
10-15mph. Redrew the cloud forecast along these lines, with
partial clearing occurring for much of STL Metro from late evening
on, the UIN area being on the edge of the clouds much of the
night, and COU/JEF areas likely remaining cloudy all night long,
along with much of southeast MO. Adjusted temps downward a bit
more where some clearing is now expected to occur.

Heading into Tuesday, this trend will likely continue and probably
be further complicated by a diurnal factor that will fill in a bit
during the day and recede towards sunset. It still remains to be
seen whether or not parts of southeast MO and central MO ever
clear out before Tuesday night.



.SHORT TERM: (Tonight through Tuesday)
Issued at 315 PM CDT Mon Jun 1 2015

Main issue in the short term is pesky stratus which has blanketed the
region the last few days and has been responsible for well below
average temperatures. The guidance is only showing minor changes
over the next 24 hours that would influence the evolution/erosion.
The upper trof axis has now pushed east of the CWA with the upper
low now in western TN and it will continue moving slowly east.
More important is the expansive and dominate surface/low level
ridge, and it will continue to have a significant influence with only
very slight veering of the lower tropospheric winds. Satellite today
shows a bit more cumuliform appearance to the cloud tops but it remains
quite thick outside of the diurnally driven stratocu on the periphery.
I have been pessimistic and held onto more clouds tonight and into
Tuesday than some of the low level RH fields might suggest. Accordingly
I lowered high temps on Tuesday a bit from the previous forecast.


.LONG TERM:  (Wednesday through Next Monday)
Issued at 315 PM CDT Mon Jun 1 2015

With each successive model cycle there are new small changes with
the mass and moisture fields during the later part of the week
and into the weekend that suggest greater thunderstorm chances and
lesser heat magnitude. In general the upper ridge now centered in
the Rockies appears to never build into the MS Valley and instead
stays centered through the Plains. From Wednesday night into the
later part of the week a series of weak shortwaves are forecast to
top the ridge crest and traverse parts of the region in the NW
flow aloft. The models differ on timing and placement of these as
well as the moisture return and specifics of the WAA regime on the
backside of the retreating low level anticyclone, with the NAM the
most agressive and fastest. Then as we head into the weekend and
early next week, the northern stream will be more active with
greater digging of shortwaves out of south central Canada and
development of a deepening broad long wave trof over the eastern
U.S. centered in the Great Lakes region. Several fropas will occur
as a result with a wavy frontal boundary impacting the area
Friday-Saturday and another on Monday.



.AVIATION:  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1100 PM CDT Mon Jun 1 2015

Dry air advecting in from IL should lead to at least partial
clearing in the St Louis metro area and possibly also COU as has
just occurred in UIN this evening, with resulting VFR conditions
for most of the night. Mainly just scattered low level clouds is
expected on Tuesday as the low level moisture becomes more shallow
or thinner.  The surface wind will be light late tonight, then
mainly e-sely on Tuesday as the surface ridge extending from the
Great Lakes region southwest into MO shifts slowly eastward.

Specifics for KSTL: The cloud ceiling of around 3000-4000 feet
will likely scatter out late tonight, then eventually totally
clear out Tuesday night. A light surface wind late tonight will
become ely Tuesday afternoon, albeit still quite weak.





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