Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KLSX 170456
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1156 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 06z TAFs through 06z Friday Night)
Issued at 1147 PM CDT Thu Apr 16 2015

The main forecast issue continues to focus on fog development
overnight. The lingering patches of clouds from 5000-6000 ft and
high clouds spreading across the region lower confidence some, but
not enough to remove the mention from the terminals. Anticipating
that during the overnight hours, areas of fog should develop,
especially from the St. Louis area southeastward into southern IL.
I have delayed the onset from the previous forecast by a few
hours, thinking that it will be after 08-09z before visibilities
lower with potential for IFR flight conditions from around 10-14z.
By mid-morning the fog should dissipate and VFR flight conditions
will dominate with scattered diurnal cu and some high cloudiness.


Specifics for KSTL:

The main forecast issue continues to focus on fog development
overnight. The lingering patches of clouds from 5000-6000 ft and
high clouds spreading across the region lower confidence some, but
not enough to remove the mention from the terminal. Anticipating
that it will be after 09z before visibilities lower with potential
for IFR flight conditions from around 10-14z. By mid-morning the
fog should dissipate and VFR flight conditions will dominate with
scattered diurnal cu and some high cloudiness.

Glass

&&

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

$$

WFO LSX






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.