Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251149
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
649 AM CDT Fri May 25 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 356 AM CDT Fri May 25 2018

Isolated activity continues to fire up over western portions of
forecast area early this morning on western periphery of upper
ridge. In the meantime, system that was over western MO Thursday
evening, initially diminished but has fired up once again on nose of
low level jet and various convective boundaries. This cluster of
storms is slowly tracking to the east and the latest HRRR run has
this complex expanding as energy from another MCS that is over
central KS, slides east southeastward into west central and
southwestern MO. This new complex to track mainly east southeast
through southern half of forecast area through mid morning before
diminishing.

Beyond that, still some uncertainty on redevelopment this afternoon
as it will depend on how much the atmosphere recovers from morning
activity. For now kept chance pops going. By this evening, afternoon
activity that does fire up will slowly diminish with loss of daytime
heating.

As for highs, still depends on many factors, so have mid to upper
80s. Lows tonight to remain rather mild, in the mid to upper 60s.

Byrd

.LONG TERM...  (Saturday through Thursday)
Issued at 356 AM CDT Fri May 25 2018

The synoptic pattern at the start of the long term period will
feature a developing Rex Block over the region due to a trough in
the Southeast and an amplified ridge building northeast into the
central Plains and Midwest. This pattern will only slowly change
through the period, as ridging slowly becomes established over much
of the country by the end of next week as the block breaks down.

All in all, an unusually quiet pattern is expected to continue for
late May/early June. The upper-level trough axis shifting through
the area today will have pushed east by Saturday. With its passing,
PWATs will be reduced to around 1.25" (from 1.8" today). However,
there will still be a weak boundary in the region which could focus
enough surface convergence to pop a few isolated storms Saturday
afternoon, but all-in-all think most locations will remain dry.

On Sunday the upper-level ridging will become more established over
the region as the trough shifts off to the southeast. Given no
appreciable forcing mechanisms for convection and a small cap
building in, expect Sunday to largely be dry. With mostly sunny
conditions expected and 850mb temps climbing to near 20C, Sunday is
looking hot. Expect high temperatures in the low to mid 90s, and
even these may not be high enough if the latest trends hold. With
dewpoints in the mid/upper 60s, it will be fairly unpleasant to be
outside. Monday will feature similar conditions, with dry weather
expected and highs once again in the low 90s.

Some sort of tropical system looks to make landfall somewhere on the
northern Gulf Coast early next week. Its approach will allow the
upper-level ridge to weaken. There are still substantial differences
in guidance as to where the tropical moisture with this system will
track, but do think most of it will stay southeast of the region.
That being said, with the upper-level ridge weakening overhead, the
area will become more susceptible to diurnally forced convection
Tuesday through the end of next week. Given perhaps a few more
clouds around, temperatures will be slightly cooler with highs in
the upper 80s/low 90s expected, which is still about 10 degrees
warmer than normal for this time of year!

Deitsch
&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 644 AM CDT Fri May 25 2018

VFR conditions expected through forecast period. Timing and
placement of storms hard to pin down, so kept vicinity storms with
best chances over KCOU and KUIN. Metro area could see storms
between 17z and 00z Saturday. As for winds, light and from the
south to southwest through forecast period.

SPECIFICS FOR KSTL:
VFR conditions expected through forecast period. Timing and
placement of storms hard to pin down, so kept vicinity storms in metro
area could see storms between 17z and 00z Saturday. As for winds,
light and from the south to southwest through forecast period.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$
WFO LSX



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