Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 212359

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
659 PM CDT Sat Apr 21 2018

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 316 PM CDT Sat Apr 21 2018

Initial wave of activity has been slowly diminishing as it tracks
across forecast area today, so just seeing some sprinkles. In the
meantime, the main system, a closed upper low over western KS to
slowly track to the east southeast tonight, lifting and deepening
associated surface low, currently over north central TX, as it
does this. Despite dry easterly flow at the surface, low level
moisture will be on the increase which will slowly offset the dry
air. Explicit models showing this as well, so pops to increase
tonight, with likelies as far north as I-70 corridor towards
daybreak. Then as initial shortwave exits, precip chances drop
south a bit, then another shortwave to bring precip chances back
north towards I-70 corridor during the afternoon and early evening
hours on Sunday. Otherwise, near normal lows tonight in the mid
40s to low 50s. Highs on Sunday, just a bit below normal,
especially along and south of I-70 due to cloud cover and
precipitation. The warmest temps will be across portions of
northeast MO and west central IL.


.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 316 PM CDT Sat Apr 21 2018

By Sunday evening, upper low will be centered over northern AR and
will continue its very slow track to the east northeast through
Monday night. So precipitation to persist across area then come to
an end by early Tuesday morning. Models are hinting at an even
slower pace for this system, so may need to keep precip chances
going on Tuesday, so will pass this onto mid crew.

Beyond that, dry wx to not persist for long as next system slides
southeast into area on busy northwest flow aloft. This system will
be more progressive, so rain to taper off by Wednesday afternoon.
Slightly cooler air to filter in for mid week. Then dry wx once
again, before a cold front tracks through beginning Thursday
afternoon through Friday morning with another round of light rain
before tapering off Friday afternoon.

Otherwise, temps to remain near or just below normal through the
week with daytime highs in the 60s and lows in the 40s.



.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 633 PM CDT Sat Apr 21 2018

Low pressure system over TX will continue east overnight and
develop further northward on Sun. As it does, light rain showers
are expected to spread east and northward overnight and into Sun.
KUIN will remain VFR and dry thru the period with ely winds. Main
question will be how far north the precip will spread. Believe
that showers will move north to impact KCOU/KSUS/KCPS overnight
and toward sunrise Sun. The precip shield shud sink back south
thru the morning hours, with a second round possible during the
afternoon hours. That said, can not rule out showers moving into
and impacting the terminals off and on throughout much of the day.
A secondary question will be how far north MVFR cigs will
develop. Latest guidance suggests MVFR cigs shud remain south of
the terminals, albeit not far south. Best chances for lower cigs
are during the Sun afternoon hours and will continue to monitor as
new data becomes available.

SPECIFICS FOR KSTL: Have added the first round of expected showers
to the overnight hours. A second round is possible during the
afternoon, but with questions regarding how far north precip will
spread, have kept out for now. Similar situation with MVFR cigs.
Latest guidance keeps MVFR cigs south of the terminal, but this
may move north with updates.



Saint Louis     50  64  50  63 /  60  60  50  40
Quincy          46  64  46  64 /  10  10  10  10
Columbia        50  64  48  62 /  60  60  30  20
Jefferson City  51  62  49  63 /  70  80  50  30
Salem           49  64  51  62 /  60  60  50  50
Farmington      50  57  49  60 /  80  90  90  50




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