Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 012253
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
553 PM CDT SAT OCT 1 2016

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 253 PM CDT Sat Oct 1 2016

Upper low finally lifting out to the north northeast, in northern
Indiana as of 19z. In the meantime, isolated/scattered showers to
persist through sunset before diminishing. Clouds to remain over
region with lows in the 50s.

By Sunday, system to lift into southeastern Ontario. However, models
showing a weak trof/cold front to slide through forecast area on
backside of system. So with lingering cyclonic flow and low level
moisture as well as decent lift with boundary, isolated/scattered
showers not out of question once again, as well as mostly cloudy
skies. So added slight chance pops between 18z Sunday and 00z
Monday. Highs will be in the upper 60s to low 70s once again.

Byrd

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 253 PM CDT Sat Oct 1 2016

The upper pattern will be in transition exiting the weekend and
heading into early next week. The pesky upper low will continue to
depart the lower Great Lakes and into the northeastern U.S. as
ridging aloft builds into the MS Valley ahead of the deepening
progressive western longwave trof. In the low levels the response
will be for the gradual retreat of the low level ridge/anticyclone.

For Sunday Night into early Monday we will still be under the
influence of weakening cyclonic flow aloft and surface high
pressure. As a result I think we will see alot of the cloudiness
during the day on Sunday persist. If areas do infact clear or
break out, the high PBL RH and light winds suggest that those
locations will see radiational fog/stratus development Sunday
night. Finally, as the day progresses on Monday, the flow aloft
will become more southwesterly as the ridge aloft shifts through
the MS Valley. This in tandem with increasing south/southeasterly
low level flow will allow for eastward clearing/erosion of the
lower clouds and the resultant moderation of temperatures.
Temperatures will continue to warm on Tuesday in response to
continued progression of the western upper trof and evolution of
the low level WAA regime.

There remains a fair amount of uncertainty in the forecast
details in the late Wednesday-Friday time frame. The longwave trof
will continue to progress eastward Wed-Thurs with the accompanying
upper low and strongest height falls shifting northeast across the
northern Plains/upper MS Valley and south central Canada. The
trailing upper trof in the Thursday-Friday period is the problematic
aspect and we continue to see model differences. The ECWMF has at
least come into line with the GFS that the cold front will initially
slow its eastward progress on Wednesday as the initial trof lifts
to the northeast, but ultimately remains faster with the trailing
upper trof and attendant cold frontal passage. In terms of sensible
weather this should lead to another warm day on Wednesday featuring
above normal temps, and then a prolonged period from Wed-Friday
with a chance of showers and thunderstorms, but not continuously
wet.

Glass

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 534 PM CDT Sat Oct 1 2016

Upper level low and surface low over northern IN and southwest MI
will move slowly northeastward. Scattered showers mainly east of
the taf sites should dissipate or shift further east of the taf
sites this evening. Low level cloudiness should continue across
the area tonight with a gradual lowering of the ceiling to MVFR
conditions. There may also be some light fog late tonight and
early Sunday morning as well. The cloud ceiling will rise back
into the VFR catagory Sunday afternoon due to deepening boundary
layer with daytime heating and mixing. West-northwest surface wind
will become light this evening and remain light on Sunday with
weak surface ridging across the area.

SPECIFICS FOR KSTL: Upper level low and surface low over northern
IN and southwest MI will move slowly northeastward. Scattered
showers mainly east of the STL area should dissipate or shift
further east of the STL area this evening. Low level cloudiness
should continue across the area tonight with a gradual lowering of
the ceiling to MVFR conditions. There may also be some light fog
late tonight and early Sunday morning as well. The cloud ceiling
will rise back into the VFR catagory Sunday afternoon due to
deepening boundary layer with daytime heating and mixing. West-
northwest surface wind will become light this evening and remain
light on Sunday with weak surface ridging across the area.

GKS

&&

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

$$

WFO LSX


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