Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 162134

Area Forecast Discussion
National Weather Service Saint Louis MO
334 PM CST Sat Dec 16 2017

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 241 PM CST Sat Dec 16 2017

A vigorous shortwave is ejecting northeast through west Texas and
New Mexico this afternoon. Water vapor imagery is showing a good
moisture plume ahead of the wave moving out of the western Gulf of
Mexico and and tropical Pacific south of Mexico. Rain associated
with this moisture plume is already spreading northeast across
Texas. The northern edge of the clouds associated with the plume
are also spreading out ahead of the precip into Arkansas and
southern Missouri. Expect clouds to lower and thicken tonight over
our area as moisture deepens. Southerly flow and cloud cover will
produce a relatively mild night with lows bottoming out during
the late evening or just after midnight then remaining steady in
the upper 30s to mid 40s through daybreak.

Guidance has been very consistent over the past few days and
remains consistent in bringing precipitation up through the Ozarks
late tonight...reaching our forecast area by 09-11Z, continuing
to spread northeast to near the I-70 corridor by 14-16Z, and up
into northeast Missouri and west central Illinois by around 18Z.
Rain should end from southwest to northeast during the late
morning and early afternoon. QPF continues to be very light in
all guidance with highest amounts totaling up to 1/4 inch or
less. Clouds and precipitation will suppress temperatures
tomorrow so only expect highs to reach the mid and upper 40s.


.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 241 PM CST Sat Dec 16 2017

After the PV anomaly responsible for Sunday`s precipitation has
moved out of the area, there appears to be little opportunity for
additional widespread precipitation through at least the middle
of the upcoming week. The pattern aloft will remain weakly
northwesterly to nearly quasizonal over most of MO/IL while a
strong PV anomaly near Baja California becomes cut off from the
prevailing flow. This feature will gradually weaken and shift
eastward, bringing a chance of rain to the southern CWA on Tue
night and Wed when it passes through AR. Model solutions then
diverge significantly by the end of the week/early next weekend,
leading to low confidence in any given model`s depiction of the
state of the atmosphere heading into the busy travel period ahead
of next weekend. There is general agreement that a positively-
tilted trough will reach the PacNW coast on Wed and move over the
Four Corners region on Thu, but there is no consensus on how the
upper air pattern evolves thereafter.

Temperatures will be as much as 10-20 degrees above average for
most of next week. A weak cold front will move through the area on
Tuesday night, but overnight lows on Tue night and daytime highs
on Wed will still be around 10 degrees above average even within
the cooler post-frontal air mass. The current forecast shows
cooler highs for next Fri/Sat after another cold front moves
across the area, but there is considerable uncertainty due to the
poor model agreement discussed above.



.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1135 AM CST Sat Dec 16 2017

VFR flight conditions will prevail across the area into early
Sunday morning. Light rain and low MVFR ceilings will overspread
much of the area from around 12Z through 18Z Sunday. Current gusty
southwest flow will diminish by mid to late this afternoon and
back to a more southerly direction tonight ahead of the rain.


VFR flight conditions are expected at Lambert until Sunday
morning. Expecting light rain and MVFR ceilings to move into the
STL area between 14Z and 16Z Sunday morning. Rain should end by
early afternoon. There are some indications that ceilings will
rise above 1900ft during the afternoon, but this may not happen
until very late or even after 00Z Monday so left low MVFR in the
TAF through the end of the period.





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