Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 020220

920 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 00z TAFs through 00z Tuesday Evening)
Issued at 558 PM CDT Mon Jun 1 2015

Dry air advecting in from IL should lead to breaks in the low
level cloud ceiling at UIN and in the St Louis metro area as well
as the tendency for improvement to VFR conditions later this
evening and overnight. The COU site will likely remain MVFR
through the night. Improvement is expected on Tuesday as the low
level moisture becomes more shallow or thinner with the cloud
ceiling likely scattering out in UIN Tuesday morning, in COU
Tuesday afternoon, and scattering out in the St Louis metro area
by Tuesday evening. The surface wind will be light 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: Cloud ceilings of around 3000-3500 feet can be
expected tonight, then rising to around 4000 feet Tuesday morning,
and eventually scattering out by Tuesday evening. A weak nely
surface wind tonight will veer around to an ely direction on Tuesday.





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