Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 281818

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
118 PM CDT SUN AUG 28 2016

.SHORT TERM...  (Through Late This Afternoon)
Issued at 345 AM CDT Sun Aug 28 2016

500mb zonal flow has dvlpd as anticipated with several perturbations
running along the US/Canadian border. The Bermuda high is nosing
into the Mid-Atlantic with a low amplitude ridge extending into the
NE and ern Canada. A weak upper lvl disturbance is meandering around
the four corners region of the desert SW. The humid unstable airmass
that has been around for the past several days remains in place so
expect aoa normal temps with diurnal convection. The lack of focus
for convective dvlpmnt means a broad brush of slight chance/chance
PoPs drng the aftn/evng.

Guidance has been on the cool side by a couple degrees the past
couple days due to fcstng too much cloud cover so bumped highs up a
degree or two. Models have backed off the clouds a bit for today
which appears to be trending in the right direction given existing
cloud cover on current IR sat image. Highs should once again be
similar to the past several days though with highs in the mid 80s to
lower 90s.


.LONG TERM...  (Tonight through Saturday)
Issued at 345 AM CDT Sun Aug 28 2016

Tonight thru Tuesday

Zonal flow continues with 594dm ridge bcmng centered over the FA by
Mon. The stagnant pattern means the broken record fcst continues
with more of the same. High temps are not expected to vary much from
day to day with highs in the mid 80s to lower 90s. Despite rising
heights...thermal profiles (700mb temps in the upper single digits
and 850 temps in the upper teens) still favor daily diurnal
convection. SFC ridge across the Grt Lks will cause winds to become
E/SE. Tue PM may have better coverage of SHRAs/TSTMs due to an
approaching cold front...esp across NE MO and W cntrl IL.

Tuesday night thru Thursday

The upper lvl pattern finally begins to change this prd. Significant
energy will approach the Pacific NW Coast which will cause the zonal
flow to buckle across the N. American Prairies. Meanwhile...another
short wave traversing cntrl Canada will dig out a trough across ern
Canada and New England. This will put the FA on the SWrn fringes of
NW flow. A weak cold front attached to a SFC low assoc with the Ern
trough will move thru the region drng the middle of the week
bringing a decent shot at organized precip from late Tue into early
Wed. This bndry will finally end the recent muggy conditions but the
relief will arrive in stages. The wind shift and assoc pressure
trough is fcst to move thru Tue night which will bring slightly
cooler temps on Wed...but the Dp gradient lags substantially behind
the FROPA. The GFS/ECMWF don`t have lower DPs arriving til Wed night
across NE MO and W cntrl IL and Thu for the rest of the CWA as a
1025+mb SFC ridge builds into the region.

Behind the front...temps on Wed should be about 5 degrees cooler
than earlier in the week. 850 temps are fcst to drop from the upper
teens Wed to the lower/middle teens by Thu which corresponds to
highs in the upper 70s to middle 80s on Thu.

Thursday night thru Saturday

Overall synoptic pattern doesn`t change much from earlier in the
week with troughs along the Coasts and a cntrl CONUS ridge. The
amplitude of the ridge decreases as the W Coast trough begins to
move E...ever so slowly. At the of the seasonally
strong SFC ridge moves from the Grt Lks to off the coast of New
England. The high will introduce a pleasant airmass to the region.
with highs in the upper 70s to middle 80s...but more noticeably...
lower humidity levels. Details on when the ridge axis moves thru
determines when return flow and the warm-up begins in earnest. The
GFS is faster and has the potential for WAA precip in advance of
the next cold front as early as Fri night/Sat mrng while the
ECMWF is a full 24hrs slower. Either solution reflects a warming
trend for next wknd with increasing rain chances.


.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 113 PM CDT Sun Aug 28 2016

Once again with isolated/scattered storms firing up over region.
As of 18z, most of activity closer to KUIN, so added tempo group
from 18z to 19z. Otherwise, kept VCTS mention at all other sites
through the afternoon hours, diminishing after 01z Monday. Light
southeast to south winds to become light and variable tonight,
then pick back up a bit from the east to southeast Monday morning.

Once again with isolated/scattered storms firing up over region.
As of 18z, activity well northwest of KSTL, so kept VCTS mention
from 21z Sunday to 01z Monday. Light southeast winds to become
light and variable tonight, then pick back up a bit from the east
by 15z Monday.



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