Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 252336

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
636 PM CDT Wed Apr 25 2018

Issued at 621 PM CDT Wed Apr 25 2018

Updated the forecast earlier to account for scattered showers
which have developed from south of St. Louis into southwest IL.
These are occuring within an area of weak CAPE (100-250 J/KG) and
an axis of weak low-level convergence to the northeast of the
surface low near KPAH. Have seen one lightning strike thus far in
southern St. Clair Co. I would expected the intensity of these
showers to diminish with loss of heating and diminishing CAPE over
the next few hours.



.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 311 PM CDT Wed Apr 25 2018

Upper level LOW currently centered over southeast Kansas continues
to move slowly southeastward early this afternoon and has helped to
overspread a large area of light rain across the western and central
sections of Missouri.  Skies were otherwise cloudy across our region
with a light northerly flow, resulting in temperatures being largely
stagnant this afternoon, with readings in the 65 to 70 range for
areas around Saint Louis and further S and E, and upper 50s and
lower 60s elsewhere.

Models continue to track the center of the upper LOW to the
intersection of MO/AR/OK/KS by early this evening and then pivot
the LOW more to the east overnight tonight to near Memphis by
12z/Thu and further east from there.  This will pivot the light rain
as well, allowing it to overspread into much of central and
southeast MO and far southern IL tonight while leaving areas near
Saint Louis and sections of IL near I-70 near the northern edge or
gradient. Believe the likelihood of pcpn is high for many of these
areas, but realized rainfall will be only a few hundredths for much
of the area, except southeast MO where up to a half inch will be
possible, mainly tonight.  Areas around Quincy and towards central
IL will miss out on this rain opportunity.  Rain is then expected to
exit southeastern Missouri by late Thursday morning with decreasing
clouds during the day on Thursday.

The approach of another shortwave is now expected to be uneventful
with the main strength of this diving well south of our area, and
with limited moisture and a shear axis sliding thru, will be
difficult to produce much in the way of sensible wx.

Min temperatures tonight will largely be in the 40s, with many sites
not getting there until late as clouds clear in the north, with a
preference for slightly above MOS in the south where clouds will
hold and slightly below MOS in the far north where clearing is
expected.  Max temperatures should recover well on Thursday for an
unusual "average" temperature day with afternoon peaks around 70 for
many locales.


.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 311 PM CDT Wed Apr 25 2018

Northwest upper flow will prevail thru Sunday.  One final shortwave
will slide thru at the start of this period on Thursday night, but
as mentioned in the SHORT TERM section, is not expected to result in
any precipitation and has been trending lower on PoPs the past
couple of days.

Friday thru Sunday should otherwise be a dry period with
temperatures within 5 degrees of average for this time of year.

A big pattern shift is then anticipated with passage of the upper
RIDGE axis late Sunday and a deepening of the western CONUS TROF
early next week, setting it up for warmer and active wx to dominate
the middle and latter part of next week.  Dry weather should prevail
until the combo of moisture and lift from shortwave disturbances
ejecting from the main TROF reach here, which looks to begin on
Tuesday afternoon.  Max temps are expected to rise into the lower
80s for parts of the area on Monday thru Wednesday.



.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 621 PM CDT Wed Apr 25 2018

An upper low in the vicinity of far southeast KS is producing
light rain across much of southwest MO into portions of central
and southeast MO. This low is forecast to move to the southeast
into the lower MS Valley tonight. Present indications are that
the coverage of light rain will increase this evening, primarily
south of Interstate 70, however close enough to KCOU and the St.
Louis metro terminals to include TEMPO groups for unrestricted
visibility with light rain. The exception is KCPS where showers
have developed to the south and have actually shown some tendency
to develop back to the northeast from 00-03Z. Other than some
MVFR stratus floating around mid MO and possibly impacting KCOU,
VFR flight conditions are expected to be the norm through the
forecast period. Any precipitation should be south of all the
terminals by 07-08Z.


Present indications are that the coverage of light rain will
increase this evening, primarily south of Interstate 70, however
close enough to include a TEMPO group for unrestricted visibility
with light rain. Precipitation should be well south of the
terminal by 07-08Z. VFR flight conditions are expected to be the
norm through the forecast period.





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