Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 180903

403 AM CDT Mon Aug 18 2014

.SHORT TERM:  (Today)
Issued at 359 AM CDT Mon Aug 18 2014

Temperatures will begin to moderate today as low clouds and early morning
fog dissipate/lift. Skies will first begin to clear up across central
Missouri with areas east of the Mississippi River seeing more cloud cover
into the early afternoon. Consequently...did lean a bit warmer across
western sections of the CWFA and a bit cooler than guidance for
south-central Illinois.


.LONG TERM:  (Tonight through Sunday)
Issued at 359 AM CDT Mon Aug 18 2014

(Tonight - Tuesday night)

Upper-air pattern will begin a transition period from northwest flow
to a building and amplifying anticyclone aloft by later in the week.
During the transition period...a potentialy active period of time
is possible through Tuesday night. The first chance of showers and
thunderstorms will be overnight tonight as a Pacific cold front approaches
the mid-Mississippi Valley. GFS hints at a subtle shortwave trough
transversing the area interacting with a broad westerly LLJ. There
actually could be two distinct areas of precipitation that may develop:
1) mainly to the north of the area in closer proximity to parent
UL trough axis and where stronger LL convergence will reside and 2) further
to the southwest across the Missouri River Valley on nose of westerly
LLJ. For now...broadbrushed PoPs with highest PoPs across central
and north-central Missouri. Area of showers/storms likely will weaken
late night and into Tuesday as 850-hPa frontal boundary progresses
through most of region.

Believe Tuesday should mostly be a dry day as Pacific cold front pushes
through the area and washes out. Chances of showers and storms should be
confined to southeastern portions of the CWFA ahead of front.

A better chance of more widespread convection will be on Tuesday night
as frontal boundary slowly retreats northward as a warm front and interacts
with 20+ knot zonal LLJ.

(Wednesday - Sunday)

Upper-level heights will begin to rise on Wednesday as high pressure aloft
begins to take hold. Leeside cyclogenesis is forecast to occur over the
western High Plains as a vort max ejects out of the deep trough near
southern California. This sfc low is expected to move northeast into
the northern Plains by Wednesday night and should push the warm front
north of our area by Thursday. Chances for convection will decrease from
south to north mid to late this week as frontal boundary moves north of
area and midlevel temperatures warm aiding in capping the atmosphere.

Dominant feature will continue to be amplified upper ridge across
the mid-Mississippi Valley. This will be in stark contrast to the
prevailing pattern across the CONUS since July 1st. Highs will be in the
90s beginning Thursday through the end of next weekend. Raised highs a
couple of degrees from CR initialization and still likely am not warm
enough. Ambient temperatures may even approach or top the century mark
depending on if afternoon dewpoints mix out for portions of the area late
this week and/or next weekend. To add insult to this juncture
do not see a definitive end to the heat/humidity in prepare for
a prolonged period of potentially dangerous heat. Heat headlines will likely
be needed at some point this week if forecast confidence continues to
increase. A silver least this heat will be occuring in late
August...cooler fall weather is not too terribly long over the horizon.



.AVIATION:  (For the 06z TAFs through 06z Monday Night)
Issued at 1107 PM CDT Sun Aug 17 2014

Against all previous expectations, an expansive IFR/MVFR cloud
deck dissipated within a few hours after sunset despite the highly
moist low layers and the onset of nocturnal cooling. The resulting
conditions (mostly clear skies and light winds) are now highly
favorable for radiation fog, which had already developed at KUIN
prior to the 06z TAF issuance. The latest thinking is that fog
with IFR visibilities and occasional broken ceilings/limited
vertical visibilities will occur at all TAF sites overnight, then
lift during the morning hours with VFR conditions expected by 18z
at all sites. This is a much more optimistic forecast than the
previous set of TAFs due to the lack of an initial stratus deck.
One element that may complicate the forecast is an expanding area
of cirrus associated with ongoing thunderstorm complexes over
KS/NE. This area of cirrus could interfere with radiational fog
processes at times, particularly at KCOU/KUIN. Such interference
would keep visibilities from falling as low as currently forecast.



Saint Louis     86  73  90  73 /  10  30  20  30
Quincy          83  69  87  68 /  10  40  10  30
Columbia        88  70  91  71 /  10  50  20  40
Jefferson City  88  71  91  72 /  10  50  20  40
Salem           83  69  88  70 /  10  20  30  30
Farmington      86  71  91  72 /  10  30  30  30




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