Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 262026

Area Forecast Discussion
National Weather Service Saint Louis MO
326 PM CDT Mon Jun 26 2017

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 325 PM CDT Mon Jun 26 2017

Two areas of precipitation ongoing this afternoon. One area of light
rain across the southern half of the area will slide east/southeast
through the early evening hours and affect mainly portions of
southeast Missouri early this evening. Isolated showers and
thunderstorms have also formed over the past few hours across
eastern Iowa and northern Illinois along a secondary cold front. The
front will push southward and may produce some isolated showers and
storms early this evening across portions of northeast Missouri and
west-central Illinois. Behind this front, an overall decrease in
cloudiness is expected along with lighter winds. This combination
should allow quite chilly temperatures to settle into the bi-state
area with lows generally in the 50s expected. Will also watch for
patchy fog development late tonight, primarily in river valleys.

One more beautiful summer day is on tap for Tuesday with a sunny sky
and light southeast winds by afternoon. High temperatures will be
well below normal even in lieu of plentiful sunshine due to
seasonably cold Canadian airmass in place. Expect highs in the upper
70s to near 80 degrees across the area.


.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 325 PM CDT Mon Jun 26 2017

The weather pattern becomes much more active starting on Wednesday
afternoon and evening. The ridge that provided unseasonably cool
temperatures to the area continues to push east into the Ohio
Valley.  The flow will turn from southerly to southwesterly while
continuing to pull warm moist area into the region. A storm system
in Great Plains will slowly moves toward the area.

The front will likely stretch from southeast Nebraska to
northeast Kansas down to the Southern Plains by Wednesday evening.
A series of short waves will ride along the boundary and bring
chances of showers and thunderstorms to central Missouri and
western Illinois. The boundary pushes into the area on Thursday
and becomes nearly stationary with another round of showers and
thunderstorms moving into the area. A look at forecast soundings
in central Missouri and western Illinois show a short Cofidi
vector with the potential for linear storm motion which will help
promote training of showers and thunderstorms along the surface
boundary on both Thursday and Friday. Additionally, forecast PWAT
values from forecast soundings show up to 2 inches suggesting
heavy rainfall and flooding are possible. Some areas locally along
and north of I-70 in central Missouri and western Illinois could
receive in excess of five inches of rainfall.

The atmosphere on Thursday afternoon will become unstable with CAPE
values in excess of 2500 J/kg and forecast bulk shear values up to
40 knots along with mid level lapse rates up to 7C/km.  Friday
will see CAPE values in excess of 1500J/kg with forecast bulk shear
up to 50 knots and mid level lapse rates up to 7C/km. Some of the
storms on both Thursday afternoon and evening and Friday afternoon
and evening could be strong to severe. The primary threats will be
damaging winds and large hail.

Another round of showers and thunderstorms will be possible on
Saturday as the frontal boundary will likely be somewhere south of
the St. Louis Metro. The front will lift north by Saturday
afternoon/evening, then to the I-70 corridor by Sunday morning. The
boundary lifts to near the Iowa/Missouri state line by Monday
morning with more chances for showers and thunderstorms.
Temperatures in the long term period are right around seasonal norms
for both afternoon highs and morning lows.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1237 PM CDT Mon Jun 26 2017

Area of light rain will impact KCOU early this afternoon, but VFR
visibilities expected. This area of rain should continue to weaken
as it approaches the metro terminals later on this afternoon so
have no mention in TAFs for now. Cannot rule out some very light
rain or sprinkles however. Isolated showers and perhaps a few
thunderstorms should develop across IA/IL this afternoon and sag
southward. Could see these storms approach KUIN very late this
afternoon/early this evening, but coverage too low to mention in
TAF. Wind direction the next several hours will be problematic,
but predominant winds behind the secondary cold front will be
light out of the north/northwest early on tonight. Light/variable
winds are expected late tonight and early Tuesday with surface
high in close proximity to area. Will have to watch for fog
tonight with a clearing sky and calm or near calm winds. With lack
of widespread measurable rain however, believe any fog would be
isolated to river valleys. For that reason, will have to watch
KSUS and possibly KCPS for fog development tonight.


Area of light rain to the northwest should weaken as it
approaches. Cannot rule out very light rain or a sprinkle however.
Secondary cold front should move through dry late this evening
with light northwest winds. Later tonight, light/variable winds
are expected near surface high pressure center. This high will
slide eastward so winds to become light out of the southeast on





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