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000
FXUS63 KLSX 011204
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
704 AM CDT Fri Aug 1 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 320 AM CDT Fri Aug 1 2014

Primary forecast issue for today is PoPs.  Dirty surface ridge
remains in control of the weather today.  A shortwave will pass over
the area on northwest flow aloft.  Looks like a combination of broad
mid-level lift ahead of the shortwave and weak low level moisture
convergence east of the surface-850mb reflection of the shortwave
which is causing the precip currently over northwest Missouri.
Expect these features to continue to migrate southeastward through
the day, and short-range guidance has the shortwave sharpening up as
it approaches the base of the longwave trof east of the
Mississippi.  All short-range guidance has precip over the area to a
greater or lesser extent today, so have increasing PoPs through the
day from slight chance to chance category as diurnal heating becomes
a greater factor.  However, with the lack of a true surface trigger
have kept PoPs at 30% or less.  This may ultimately need to be
increased if afternoon thunderstorms can get organized into
clusters.  This is certainly possible if forecast SBCAPE 1000-2000
J/kg is realized.  Highs today will be highly dependent on cloud
cover and afternoon precip.  Used a combination of persistence and
MOS which yielded temperatures a degree or two cooler than yesterday
in the low to mid 80s.  Still relatively mild for August 1st.

Carney

.LONG TERM:  (Tonight through Thursday)
Issued at 320 AM CDT Fri Aug 1 2014

A longwave upper TROF will persist over eastern North America thru
Tuesday, although it will slowly de-amplify heading into early next
week.  Some upper level disturbances from this resultant NW flow can
be expected early, with one this evening--a leftover from today--and
another possibly rolling down for Saturday.  What does develop today
should carryover a bit into this evening and maintained a
mentionable slight chance PoP until about 9pm with the loss of
heating and upper level support moving downstream then should shut
things down.  Another upper level disturbance may slide down on
Saturday as well, although the signals for this are considerably
less clear and moisture should be a bit more limited than with the
first disturbance today with the latter taking some of the moisture
with it as they are oft to do in the wake of passage of an upper
TROF axis.  Kept some low PoPs around for Saturday, maintaining the
timing of late morning and afternoon, but trimmed its expanse and
confined more to the eastern Ozarks and southwest IL.

Otherwise, lack of upper level support and surface fronts with
marginal levels of moisture for August will result in PoPs largely
being a wash and favor values below climo--climo being around 20%.

By mid-late next week, a storm over the upper Midwest appears to get
caught in the upper level "undertow" and stalls as the overall
regime becomes more zonal and split, and so not as progressive as
one might initially think.  A warm frontal boundary appears to
extend into the area late Wednesday with approach of a cold front on
Thursday representing the best widespread chance for rain over the
next seven days--with PoPs to show for it--about 40%.

Max temps on Thursday were already within 2-3 degrees of normal and
should effectively be at normal values by the latter half of the
weekend and will even edge above normal for a period next week
before another return of some cooler air for late week.

TES

&&

.AVIATION:  (For the 12z TAFs through 12z Saturday Morning)
Issued at 644 AM CDT Fri Aug 1 2014

Primary concern this morning is areas of fog and low ceilings
across the eastern Ozarks extending northeast into southwest
Illinois. Fog is trying to trickle into the southern portions of
the St. Louis Metro area. Within these areas, widespread IFR with
visibilities at or below 2SM and ceilings as low as 200FT prevail.
Expect flight conditions to improve between 12Z-14Z. After that,
VFR flight conditions are expected to prevail with light and
variable wind. An upper level disturbance will produce widely scattered
showers and thunderstorms later today. A few of the storms will
likely be strong enough to produce isolated MVFR or even IFR
conditions in moderate to heavy rain. Expect showers and storms to
dissipate quickly after sunset. Fog will be possible again late tonight.

Specifics for KSTL:

Expect VFR flight conditions to prevail at Lambert today. Fog/low
ceilings are expected to stay south of the terminal. Attention
turns to this afternoon when an upper level disturbance is
expected to produce widely scattered showers and thunderstorms.
Think it will be hit and miss in the STL Metro area, but if a
storm does drift over the terminal visibility could briefly.drop
below VFR. Expect VFR to prevail tonight. If the terminal does
receive rain, there could be some light fog late.

Carney

&&

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

$$

WFO LSX