Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 232350

650 PM CDT Thu Apr 23 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 321 PM CDT Thu Apr 23 2015

A large surface high currently centered through eastern MO was
responsible for a dry conditions and pleasant temperatures across
the region today. This high will retreat eastward tonight. The
lightest winds and least clouds will be this evening and this will
also be the period of greatest temperature drop. Overnight
progression of the upstream upper trof and ridge and veering of the
Great Plains LLJ will result in the onset of low-mid level warm
advection as well as the east and northeast transport of moisture.
While the highest quality moisture will remain well to our west
through 12z Friday, the warm advection associated lift, increase in
mid level moisture, and advection of steeper mid level lapse rates
into the area will result in a chance of showers and thunderstorms
into portions of central and eastern MO late tonight into the
predawn hours. At least a few of the CAM are showing scattered
showers after 09z. The new forecast continues with pops in the 20-30
percent range but expands them slightly to the east.


.LONG TERM:  (Friday through Next Thursday)
Issued at 321 PM CDT Thu Apr 23 2015

Still seeing timing and placement issues between the 12z NAM and GFS
especially with warm front that will be over region. No matter what
feel that elevated convection will continue to increase in coverage
and spread east across forecast area on Friday on nose of low level
jet. With the cloud cover and precipitation, highs will only be in
the upper 50s to mid 60s.

Then Friday night, will see system begin to lift and slide east
across Missouri. Best chances of rain will be along and north of
I-70 with possible MCS developing and sliding east. Could see some
strong to severe storms with this wave, but will have better chances
during the day on Saturday as main cold front slides through. CAPE
in excess of 1000 J/kg expected with decent convergence along and
ahead of low, with best chances of severe weather over southeast
Missouri and southern Illinois. As for rainfall amounts, could see
up to an inch of rain mainly along and north of I-70 with higher
amounts possible Friday through Saturday night. Will see wide range
of temps on Saturday with highs in the upper 50s far north to the
mid 70s far south.

System to exit Saturday night with precipitation tapering off from
west to east. Then dry weather to persist through first part of next
week. Extended models are now a bit further south with next system,
so chances of rain a bit less, so just have slight chance pops
Tuesday through Wednesday, before dry and near normal temps return
next Thursday.



.AVIATION:  (For the 00z TAFs through 00z Friday Evening)
Issued at 650 PM CDT Thu Apr 23 2015

VFR conditions and dry wx will prevail at the TAF sites thru
tonight. Showers are expected to develop late tonight and are
still anticipated to move into central MO around 12z/Fri and then
attempt to proceed eastward to the airports near the MS river by
late morning and into early afternoon. The best chances for
thunder will remain to the west, with COU being the most likely
airport out of the TAF sites here, and retained the thunder
mention but converted to VCTS. Otherwise, progressively and slowly
deteriorating prevailing conditions will be the rule for Friday
afternoon and into the night with widespread MVFR and perhaps IFR
CIGs developing eventually. E to SE surface winds will prevail
thru the period, gradually strengthening with time.

Specifics for KSTL: VFR and dry until late Friday morning, with an
episode of rain towards midday and into early afternoon expected.
Thunder should be limited enough with what should be a weakening
broken band of SHRA to preclude mention at this time. VFR
conditions will gradually transition to MVFR Friday night and
perhaps eventually to IFR. E-SE winds will be set by late this
evening and then gradually strengthen thru Friday. Another episode
of at least showers expected Friday night, with better chances for
thunder. Given how this second round is at the very end of the
valid period, will take another look later this evening before
adding thunder.





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