Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

FXUS63 KLSX 301747

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1247 PM CDT SAT JUL 30 2016

.SHORT TERM... (Today and Tonight)
Issued at 320 AM CDT Sat Jul 30 2016

A weak surface boundary presently stretching from the OH Valley
across southern IL and southern MO will settle southward this
morning stalling to the south of the CWA this afternoon. Meanwhile
another weak surface wind shift boundary will move into northern
MO and west central IL late morning/early this afternoon. Any
threat of precipitation today should occur in the vicinity of
these two weak surface features, with generally limited coverage.
Otherwise we should see another day with temperatures just below
average and lower than normal humidity.


.LONG TERM... (Saturday through Friday)
Issued at 320 AM CDT Sat Jul 30 2016

Predominately dry tranquil weather is expected tonight with weak
surface high pressure dominating. The main focus for showers and
thunderstorms should be across the central Plains where the
western portion of the stalled front will begin a slow northward
retreat and a veering south/southwesterly LLJ will provide
forcing. The threat of showers and thunderstorms should begin
ramping-up Sunday, and especially Sunday night into Monday as the
front continues a slowly north/northeastward retreat thru the CWA,
a focusing southwesterly LLJ evolves and provides lift, and a
series of weak disturbances track across the region. The location
of the later disturbances and model QPF varies considerably with
the NAM most robust. This forecast is weighted most heavily towards
the ECMWF which has been rather consistent in its depictions.

Present indications are that by late Tuesday the front should
finally shift to the northeast of the area, and heights aloft
will be rising as an upper ridge shifts/builds from the Plains
into the MS Valley and Great Lakes region. This will set the stage
for a return to potentially dangerous heat and humidity in the
Tuesday-Thursday time frame and especially the later 2 of these
days. The current high temp forecast is conservatively in the
lower-mid 90s this period and this still yields heat index values
in the 100-105 range. Progressive flow aloft across southern
Canada and the northern tier of the U.S. and interaction with a
vortex in eastern Canada ultimately leads to development of a
broad mean trof from the Upper MS Valley through the Great Lakes
and into the northeast CONUS by next Saturday. Associated with the
eventual pattern change would be a cold frontal passage in the
Friday/Saturday time frame.



.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1239 PM CDT Sat Jul 30 2016

A weak trof of low pressure over the area is producing scattered
to broken clouds with primarily VFR bases across the area. There
are still some pockets of MVFR across parts of northern MO/west
central IL...but those clouds should continue to rise. There may
be some isolated showers or thunderstorms this afternoon across
parts of the area...most likely along and south of I-70. Any
storms that do form should dissipate quickly after 00-01Z. VFR
conditions should prevail otherwise. There continues to be some
concern for fog and low stratus tonight. The best chances look to
be over west central and parts of central Illinois.


Cumulus with VFR bases are expected to prevail this afternoon.
There`s a chance there could be some isolated showers or
thunderstorms in the vicinity of the terminal through about
00Z...but chance is only about 15-20% so I did not mention it the
TAF. VFR conditions are expected tonight.





WFO LSX is the U.S. government's official web portal to all federal, state and local government web resources and services.