Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 160516
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1216 AM CDT Fri Jun 16 2017

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 300 PM CDT Thu Jun 15 2017

The synoptic pattern early this afternoon features westerly flow
persisting across the region. This regime will persist through the
period, allowing for another weak shortwave to slide through the
area late tonight into Friday.

Main focus will be on convection out west tonight. Latest
satellite and radar imagery shows intense convection blossoming
across portions of west-central Kansas. This is located along the
intersection of a remnant outflow boundary from the convection
last night and a weak cold front. This convection should continue
to grow upscale, and track east/southeast. Additional convection
may fire further north along the cold front which extends to the
northeast across northern KS, southeast NE, and IA. Last night`s
MCS did not affect this area, thus a rather unstable airmass
resides ahead of this weak front. Therefore, additional convection
could develop to the north of the current activity across KS and
spread quickly into western MO. As this activity progresses
eastward tonight, it will encounter a more stable airmass over
central MO. Thus, activity should weaken once it moves into
central MO. Can`t completely rule out a strong storm getting into
central MO before weakening, but I think the severe threat it
fairly low tonight.

The forecast for tomorrow hinges on tonight`s expected decaying
MCS. Latest indications are that clouds/light showers may linger
into the mid morning hours over central and northeast MO. Most of
the region will likely go dry through the late morning/early
afternoon before additional showers/storms flare up along the
remnant outflow/differential heating boundary Friday afternoon.
This renewed convection appears most favored along and east of the
MS River. Coverage likely won`t be great given an overall lack of
upper-level support, but MLCAPEs of 2500+ J/kg coupled with about
30 knots of deep-layer shear could lead to a few strong/isolated
severe storms capable of locally damaging winds and large hail.

KD

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 300 PM CDT Thu Jun 15 2017

An active and unsettled weather pattern continues over the area
for the first part of the weekend. A quasi-stationary cold front
will extend from extreme northwest Missouri into the southern
plains. A shortwave will ride up the boundary Friday afternoon.
The wave will initially kick off a line of storms that will push
eastward toward central Missouri. The line will likely congeal
into an MCS before entering central Missouri. The MCS will likely
encounter forecast CAPE values of 1500 to 2000J/kg with mid level
lapse rates between 7 to 8C/KM. The best shear will remain north
and west of the area. The main threat with the MCS will be
damaging winds and large hail.

Attention turns to Saturday night into Sunday morning for another
potential round of severe weather. The cold front pushes eastward
into central and northeast Missouri. The boundary will be roughly
oriented from north of a Columbia to Quincy line by mid morning.
The environment ahead of the boundary will likely again see
forecast CAPE values 1500 to 2500J/kg with forecast mid level
lapse rates 7 to 7.5 C/KM. The forecast shear along the front will
likely be up to 40 knots. This will be conducive for a line of
multicellular storms with some embedded supercellular structures.
The primary hazard will be damaging winds and large hail. The time
frame for storms would be in the late afternoon hours into the
late evening hours. The front will clear the area by the middle of
Sunday morning.

A period of quiet weather will begin Sunday afternoon as high
pressure builds in from the central plains. This will bring cool
and drier air along with temperatures just below climatological
norms. The quiet weather is expect to continue through Tuesday.

A low pressure system forms somewhere in the west central plains
Tuesday night. There is the normal expected spread on orientation
of the warm front on Wednesday along with timing difference on
cold front passage late next week. Temperatures return to above
seasonal values for the remainder of the period.

Kelly

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1159 PM CDT Thu Jun 15 2017

Primary concern is the complex of thunderstorms moving through
central and northeast Missouri. Current indications are that this
line of storms will continue moving east-northeast at around
30kts. Looks like the storms will be capable of producing a brief
period of heavy rain and 30-40kt wind gusts as they move through.
Expect VFR conditions and light southerly wind to prevail outside
of these storms for the rest of the night.

There will be another chance of thunderstorms on Friday
afternoon...mainly along and east of the Mississippi river.

SPECIFICS FOR KSTL:

VFR flight conditions are expected to prevail at Lambert for the
rest of the night. The thunderstorms over central and northeast
Missouri are not expected to reach Lambert before they dissipate.
However, the storms will likely lay down a boundary and/or produce
a lingering upper level disturbance which could provide a focus
for thunderstorms on Friday afternoon. Current indications are
that scattered storms will develop in the STL Metro area between
20-22Z.

Carney

&&

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

$$

WFO LSX



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