Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 162331
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
631 PM CDT Thu Apr 16 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 307 PM CDT Thu Apr 16 2015

A weak upper level RIDGE is currently overhead with a very weak
pressure pattern in place at the surface yielding light and variable
winds across our region.  While the regional radar mosaic is
rain-free, the visible satellite imagery shows lots of diurnal
cumulus that has developed with the heating of the day--indicative
of the same moisture that also played a role in the morning stratus
and fog last night.  Temperatures have risen into the 70s at most
locations, with some 60s still lingering in areas where they
retained the morning clouds the best--across southeast MO and far
southern IL.

The weak upper ridge and very weak surface pressure pattern will
persist thru tonight and with little anticipated change in the
airmass composition in the boundary layer from minimal mixing, am
heavily favoring a persistence forecast with temps expected to drop
into the 50s once again tonight with fog formation likely,
especially in areas south and east of STL metro.  May ultimately
need a fog advisory for some of these areas but prefer to let
evening shift monitor to see how it develops.

TES

.LONG TERM:  (Friday through Next Thursday)
Issued at 307 PM CDT Thu Apr 16 2015

Upper ridge will remain over region on Friday, so kept dry
conditions going with highs in the upper 70s. Then as upper ridge
begins to move east, surface warm front develops south of forecast
area. So will see showers and thunderstorms develop over western MO
and increase in coverage across central MO Friday night and across
rest of forecast area Saturday and Saturday night as warm front
lifts north through region.

Then main upper level shortwave to begin to lift out Sunday with
cold front sliding through region. Decent instability with capes
between 500 and 1500 J/kg as well as decent shear, so SPC still has
15 percent probability of severe weather on Day 4. Precipitation to
taper off Sunday night as front exits region.

Beyond that, weak surface ridge builds with dry and colder weather
expected for the first part of the work week with highs in the 60s.
Then extended models have differing timing and solutions for next
weather system. For now kept slight chance/chance pops for Wednesday
through Thursday.

Byrd

&&

.AVIATION:  (For the 00z TAFs through 00z Friday Evening)
Issued at 621 PM CDT Thu Apr 16 2015

Scattered to broken diurnal cu should dissipate by 02-03z with VFR
flight conditions persisting through the evening. During the
overnight hours it appears that fog should develop, especially
from the St. Louis area southeastward into southern IL.
Visibilities should lower to MVFR with IFR flight conditions
anticipated from around 10-14z, perhaps a bit quicker at KSUS and
KCPS. By mid-morning the fog should dissipate and VFR flight
conditions with scattered diurnal cu is expected.

Specifics for KSTL:

Scattered to broken diurnal cu should dissipate by 02z with VFR
flight conditions persisting through the evening. During the
overnight hours it appears that fog should develop. Visibilities
should lower to MVFR with IFR flight conditions anticipated from
around 10-14z. By mid-morning the fog should dissipate and VFR
flight conditions with scattered diurnal cu is expected.

Glass

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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