Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 201801
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
101 PM CDT Sat May 20 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 343 AM CDT Sat May 20 2017

As individual storms move northward this morning MCS continues to
track east, exiting forecast area by midday. Then will see
redevelopment as surface low lifts northward through Iowa, dragging
cold front through forecast area late this afternoon/evening. Storms
to finally taper off after midnight tonight.

As for temperatures today, since we are starting out cooler than
originally forecast, in the upper 40s to mid 60s, went close to
guidance or even a degree or two lower for highs due to cloud cover
and precipitation. Only fly in ointment is as surface low lifts
northward today, it will lift stalled warm front back north through
region, so if clouds thin out, even a little, temps could be warmer
than we are forecasting. For now have highs in the 70 to 80 degree
range. Lows tonight will be in the upper 40s to upper 50s.

Byrd

.LONG TERM...  (Sunday through Friday)
Issued at 343 AM CDT Sat May 20 2017

(Sunday through Monday)

Period begins with the cdfnt well east of the CWA with the sfc low
in central WI and the sfc ridge building into the region.

Behind the fnt, a much cooler sfc ridge will build into the region
for Sun. This ridge will keep the area dry with temps struggling to
reach the 70s. While deeper mixing is still expected, have trended
slightly cooler on Sun due to expected cool 850 mb temps. Mon shud be
slightly warmer with 850mb trof moving ewd allowing slightly warmer
temps into the region. However, did not go too warm with clouds
expected to spread into the area and a leading s/w bringing precip
to the area.

(Tuesday through Friday)

Mdls begin the period in fairly good agreement. By the middle of
next week, differences appear, tho mainly timing issues. After the
leading s/w mentioned above pulls ewd out of the region, a fast
moving clipper system is expected to move into the area.

With the region under persistent NW flow and a strong sfc ridge
likely settling south of the region, expect temps to be well below
seasonal avg for much of next week.

Tilly

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1247 PM CDT Sat May 20 2017

Morning IFR and MVFR ceilings are lifting from south to north at
this time...with another MVFR deck moving east from central
Missouri. Expect the lifting trend to continue this
afternoon...and daytime heating should also allow the central MO
MVFR deck to lift to VFR by the time it reaches east central
Missouri later this afternoon. Model guidance is pretty insistent
that another round of showers and thunderstorms will develop along
the cold front during the late afternoon/early evening hours as
it pushes through central into eastern Missouri. Think coverage
will be scattered...30-50%...so did not go with TEMPOs at this
time. Think the last few showers should exit the eastern portions
of the area (vicinity of KSLO) by 07-08Z. VFR flight conditions
are expected to prevail outside of showers and storms.

SPECIFICS FOR KSTL:

Last shreds of morning stratus should move out of the vicinity of
the terminal any minute and VFR conditions are expected to prevail
for the remainder of the afternoon. There is a stratocumulus deck
moving east toward the terminal from central Missouri, but I
expect the bases of this ceiling will lift to VFR by the time it
reaches Lambert. Model guidance is pretty insistent that another
round of showers and thunderstorms will develop along the cold
front during the early evening hours as it moves toward the
terminal. Think coverage will be scattered...30-50%...so did not
go with TEMPO at this time. Expect VFR conditions to prevail
outside of any shower or storm that hits the terminal.

Carney

&&

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

$$

WFO LSX



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