Area Forecast Discussion
Issued by NWS St. Louis, MO

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231
FXUS63 KLSX 280234
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
934 PM CDT SAT AUG 27 2016

.UPDATE...
Issued at 912 PM CDT Sat Aug 27 2016

Still getting a southwest to northeast corridor of scattered
showers and storms from near Owensville MO through Foristell MO to
Brussels IL this evening. Although these storms were not severe
they were producing brief periods of very heavy rainfall. This
band of storms will continue to shift slowly northward with time,
with most of the storms likely dissipating by midnight or shortly
after. As the clouds thin out could not rule out some patchy fog
late tonight/early Sunday morning due to the light surface winds
and high surface dew points, especially in areas which received
rainfall this evening.

GKS

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 248 PM CDT Sat Aug 27 2016

Despite decent low level moisture and instability over forecast
area, there are no distinct focusing mechanisms. So no definite
location for where storms will pop up through the early evening
hours since they will be diurnally driven. Will keep isolated/
scattered wording through the evening, then kept slight chance pops
for areas along and north of I-70 after 06z Sunday as this area is
closer to boundary that is north of forecast area. Otherwise, lows
will be mild, in the upper 60s to low 70s, just a bit above normal
for this time of year.

Byrd

.LONG TERM...  (Sunday through Next Saturday)
Issued at 248 PM CDT Sat Aug 27 2016

The synoptic pattern at the start of the long term period Sunday
morning will feature slowly rising heights aloft as an upper-level
ridge builds into the Central CONUS.  This ridge will amplify
through the beginning of next week, before a trough diving into the
Northwest begins to break down the ridge by the middle of next week.

Not really much synoptically to hang our hats on through early next
week.  Despite the weak height rises, it doesn`t appear the warming
temps aloft will be quite strong enough to completely limit diurnally
driven thunderstorms.  Therefore, will continue with the forecast of
isolated to scattered thunderstorms Sunday into Monday.  Best
chances will reside on the fringe of the ridge across north-central
MO, with smaller chances closer to the ridge over southeast MO/west-
central IL.  Have bumped up temperatures a bit from the previous
forecast across the southeastern FA due to less expected convection
leading to higher prospects for prolonged solar insolation.

The latest guidance continues to suggest a weak front will drop
south near the region by midweek.  Timing differences remain, but
the GFS/ECMWF and GEFS solutions all show fropa through the bulk of
the area by early Thursday (slower than previously advertised).
Precipitation chances will be a bit higher Tuesday into Wednesday
ahead of the front, but will go ahead and trend the forecast drier
for Thursday into Friday in the wake of the front. Fronts this time
of year can often struggle to get as far south as guidance suggests,
so that is a trend we will continue to monitor in the coming
forecasts. Temperatures will remain warm and humid ahead of the
front with temps in the upper 80s/low 90s and heat indices in the
mid/upper 90s Sunday into Monday, but cooler conditions will arrive
by Thursday with temps back in the low/mid 80s.

KD

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 458 PM CDT Sat Aug 27 2016

Scattered diurnal showers/storms have developed in the St Louis
metro area early this evening. Will need to include at least VCTS
in the St Louis area tafs until at least 01Z this evening. This
activity along with the cumulus cloud field should dissipate later
this evening with the loss of daytime heating/instability. May be
patchy fog late tonight/early Sunday morning with potentially
only high level clouds, a light southeast surface wind, and high
surface dew points. A south-southeast wind can be expected on
Sunday with surface ridging extending from the Great Lakes region
southwest into MO. There will be scattered diurnal cumulus clouds
again late Sunday morning and afternoon along with isolated to
scattered showers/storms.

SPECIFICS FOR KSTL: Scattered diurnal showers/storms have developed
in the St Louis metro area early this evening. Will need to
include at least VCTS in the STL taf until at least 01Z this
evening. This activity along with the cumulus cloud field should
dissipate later this evening with the loss of daytime
heating/instability. May be patchy fog late tonight/early Sunday
morning with potentially only high level clouds, a light southeast
surface wind, and high surface dew points. A south-southeast wind
can be expected on Sunday with surface ridging extending from the
Great Lakes region southwest into MO. There will be scattered
diurnal cumulus clouds again late Sunday morning and afternoon
along with isolated to scattered showers/storms.

GKS

&&

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

$$

WFO LSX



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