Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 192048
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
348 PM CDT Wed Apr 19 2017

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 347 PM CDT Wed Apr 19 2017

Unseasonably warm weather this afternoon with gusty southerly winds
and a diurnal cumulus field, more typical of an early summertime
pattern. We are getting isolated showers across parts of east
central and southeast MO and southwest IL.  The diurnal cumulus
clouds along with any isolated showers will dissipate by early this
evening as the sun goes down.  More significant showers and storms
will move into parts of northeast and central MO and west central IL
late tonight and early Thursday morning as an upper level trough
moves eastward through the northern Plains and sends a cold front
southeastward into our forecast area.  May have some severe storms
across northwest MO tonight, but these will likely weaken in
intensity as they get into our forecast area late tonight.
Unseasonably warm temperatures will continue tonight with a
southwesterly low level jet translating eastward into our region
along with southerly surface winds.  The convection will redevelop
late Thursday morning and afternoon across southeast MO and
southwest IL as the cold front continues moving southeastward
through our forecast area. Temperatures may be nearly steady or fall
slightly Thursday afternoon across parts of our area due to low
level cold air advection behind the cold front along with low level
cloud cover and precipitation.

GKS

.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 347 PM CDT Wed Apr 19 2017

A potentially active west-southwest flow aloft will continue for
much of this period thru the middle of next week.

The main wx-maker will initially be a surface cold front that will
be ongoing thru areas south and east of STL metro on Thursday
evening and should exit just to the south of the CWA later that
night.  However, the baroclinic zone aloft will be maintained thru
southern MO and far southern IL thru the night and into Friday
morning to justify some mentionable PoP in those areas.

The main wx-maker of this period will be in the form of an upper LO
that will slowly traverse thru our region Friday night thru Saturday
night.  It will overspread rain by late Friday night, continuing
thru Saturday morning before beginning a measured retreat during the
afternoon from northwest to southeast, finally exiting Saturday
night.  The situation is such that with a surface LO track expected
to the south of our region thru northern AR, a stout NE flow at the
surface, extensive thick cloudiness and high probs for rain, diurnal
temp swings will be minimal.  In fact, temps do not look to exit the
40s for many areas on Saturday during the daytime.

The storm system should be sufficiently far away on Sunday to result
in a dry day, although some model guidance is suggesting a slower
exit and could see another cool day if occurs with low cloud likely
lingering as well.  Either way, it will not be as cool, with temps
likely to make a recovery back into the 60s.

A surface RIDGE will dominate Monday with a frontal boundary
slipping southward into our area on Tuesday, but general model
consensus is on a very limited moisture return and have kept this
period dry with this package.  Max temps will continue to recover
back into the 70s by early next week, especially with flow from the
south.

The next system looks slated for late Wednesday and by this time
moisture looks sufficient to justify at least a climo PoP for many
areas, and something more further to the west.

TES

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1139 AM CDT Wed Apr 19 2017

Just scattered diurnal cumulus clouds along with high level
clouds this afternoon. A cold front will drop southeastward
through the taf sites late tonight and Thursday. Showers and
thunderstorms may move into UIN and COU late tonight or early
Thursday morning, then into the St Louis metro area by late
morning. Prevailing cloud ceiling may drop into the MVFR catagory
by 12Z Thursday in UIN and COU and by 15Z Thursday in the St
Louis metro area. South-southwesterly surface wind will veer
around to a northwesterly direction after fropa in UIN and COU
Thursday morning and in the St Louis metro area Thursday
afternoon.

SPECIFICS FOR KSTL: Just scattered to broken diurnal cumulus
clouds along with high level clouds this afternoon. A cold front
will drop southeastward through the STL area by late Thursday
morning. Showers and thunderstorms may move into the STL area
by late morning as well. Prevailing cloud ceiling may drop into
the MVFR catagory by 15Z Thursday. South-southwesterly surface
wind will veer around to a northwesterly direction after fropa
Thursday afternoon.

GKS

&&

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

$$

WFO LSX



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