Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 182126

Area Forecast Discussion
National Weather Service Saint Louis MO
326 PM CST Wed Jan 18 2017

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 325 PM CST Wed Jan 18 2017

Forecast is still on track that showers and a few thunderstorms will
move into the area late tonight and tomorrow.

Low clouds broke up across the area today only to be replaced by mid
and high clouds that are streaming northward ahead of a dual upper
low currently over western Kansas and New Mexico.  This moisture
stream will continue to cause clouds to lower and thicken across the
area through the evening hours.  The chance for showers will
increase by late this evening over southeast Missouri as moisture
convergence increases on the nose of a low level jet underneath
increasing mid level ascent ahead of the upper low.  The chance of
for showers will will spread northward and increase across the area
overnight into Thursday morning as the upper low moves eastward. The
greatest chance for showers and highest rainfall totals will be
across southeast Missouri into southern Illinois where the strongest
low level forcing and precipitable moisture will be.  There will
still some potential for thunderstorms tomorrow as lapse rates
steepen with the upper low.  The chance of rain will begin to taper
off from west to east late in the day as the forcing lifts eastward.

Temperatures will show little diurnal swing the next 24 hours
because of the clouds and the rain.  They are a combination of
compromise MOS values and SREF 2 meter temperatures.


.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 325 PM CST Wed Jan 18 2017

Amplified weather pattern will remain over the CONUS from Thursday
night through the end of the forecast period on Wednesday. The main
feature of this pattern will be the longwave trof now off the west
coast of North America.  This trof will dig across the western
states remaining in place through early next week.  Persistent south
to southwest flow over the region will keep temperatures well above
normal.  In fact, the warmest day in the upcoming stretch looks to
be Saturday with highs in the low to mid 60s which is pushing 30
degrees above normal for mid to late January.

Several shortwaves will rotate around the base of the persistent
western trof and eject northeast across the Plains.  These waves
combined with moisture convergence on the low level jet will keep a
persistent chance of showers to the area at least through Sunday
night and into Monday morning.  The pattern begins to shift Monday
night and Tuesday as the longwave trof finally moves east into the
Great Plains.  Current indications are that Tuesday will be dry but
the chance of showers will return Tuesday night as ridging ahead of
the longwave shifts east and southwest flow returns.



.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1138 AM CST Wed Jan 18 2017

Large area of clearing has developed around the St. Louis area
terminals with VFR conditions now expected through afternoon hours
into the evening. The clearing line is now close to KCOU, and VFR
conditions will likely develop there early in the afternoon. KUIN
will likely take longer to go VFR as the clearing line is slightly
farther away. MVFR ceilings that are currently over southern
Missouri will likely move back into the area this evening as
moisture streams back into the area ahead of the storm system.
Showers will develop over the area late tonight and tomorrow as
this system moves through Missouri and Illinois.

SPECIFICS FOR KSTL: VFR conditions are expected through early
evening before MVFR ceilings redevelop. Moisture will stream back
into the area causing MVFR ceilings and visibilities to develop
tonight as well as showers as a storm system approaches the area.
Showers and IFR conditions are expected on Thursday as this system
moves across the area.



Saint Louis     40  50  44  58 /  40  70  50  20
Quincy          35  44  39  52 /  10  60  60  20
Columbia        39  48  42  57 /  40  40  30  20
Jefferson City  41  49  42  58 /  40  40  30  20
Salem           39  51  46  57 /  30  70  70  20
Farmington      41  51  44  58 /  60  70  40  20




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