Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 170300

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
1000 PM CDT Fri Jun 16 2017

Issued at 1000 PM CDT Fri Jun 16 2017

Complex of severe thunderstorms now over northwest Missouri will
continue to move southeast tonight. Expect this complex to
gradually lose intensity as the instability and shear is weaker
over eastern Missouri. With this said, there will still be the
possibility of a few severe thunderstorms capable of producing
primarily damaging winds across northeast and central Missouri
through 09Z. This shows up well on recent runs of the CAMS. Line
of showers and thunderstorms will gradually weaken toward morning
as it continues to progress southeast across Illinois and
southeast Missouri.  Otherwise temperature trends still look good
outside of thunderstorms.



.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 342 PM CDT Fri Jun 16 2017

Ongoing convection shud dissipate with sunset. Main focus for
tonight will be an MCS expecting to develop across wrn IA into ern
NEB that is expected to move sewd into central MO late tonight.
This MCS shud weaken thru Sat morning as it moves swd out of the
CWA. Timing is still uncertain, however, latest thoughts are that
the MCS shud enter the nwrn portions of the CWA shortly after
Midnight and primarily impact the wrn third to half of the CWA

This MCS activity generates some questions regarding temps with a
modified airmass, as well as dewpoints as dewpoints will likely
pool along any outflow boundary. Have therefore made only slight
modifications to the prev temps and held off issuing any headlines
due to heat. That said, expect Heat Index values between 100 and
105 degrees Sat afternoon for portions of central MO. This area is
most likely to see convection overnight and therefore wud
expected heating to be at least delayed, but shud also be somewhat
suppressed. However, if clouds clear out quickly enuf, this may
lead to even higher dewpoints.

With these higher dewpoints in place Sat afternoon, mdls suggest
CAPE values in excess of 5000 J/kg across wrn and nrn portions of
the CWA. Appears two areas of storms are possible late Sat
afternoon, one across central MO and another further north along
the cdfnt. Either of these has the potential to produce severe


.LONG TERM...  (Saturday Night through Next Friday)
Issued at 342 PM CDT Fri Jun 16 2017

The cold front and associated trough responsible for the morning
MCS will slowly move eastward into north central and central
Missouri. The front will encounter an environment of forecast CAPE
values in the range of 4500 J/kg, mid level lapse rates of 7C/KM.
The forecast bulk shear in the range initially of up to 50 knots
by mid evening increases to over 70 knots through the late night
hours. This will likely lead to another MCS which will primarily
be a damaging wind threat with some hail also possible.

The cold front will likely clear the area by mid morning on
Sunday with high pressure building in from the great plains. The
entire area will see cool and drier air with temperatures just
below climatological norms. This will be short lived as high
pressure will slowly push east to the Ohio Valley by Wednesday
evening. The flow will turn to the south by early Tuesday
allowing warm moist air to return to the area. A storm system in
the great plains will begin to push east Wednesday afternoon.
This will likely set the stage for another MCS to impact the area
toward the end of next week.



.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1240 PM CDT Fri Jun 16 2017

An MCV over srn MO will be a focus for TSRA this afternoon, tho
can not completely rule out storm further north across ern MO/SW
IL. Otherwise, expect VFR conditions thru this evening with winds
becoming sly to sswly.

Expect another MCS to develop and impact KUIN/KCOU terminals just
after Midnight tonight into Sat morning. Severe wind gusts will be
possible. However, these details will be added with future updates
as confidence in timing/location increase.

SPECIFICS FOR KSTL/KSUS/KCPS: MCS mentioned above shud impact
terminals around sunrise Sat. These storms shud be weaker and do
not anticipate severe gusts. Storms shud diminish thru the
morning hours leaving the rest of Sat dry and VFR.





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