Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 160356
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1056 PM CDT Wed Apr 15 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 332 PM CDT Wed Apr 15 2015

The main forecast issue tonight is the chance of precipitation. Northward
moving scattered showers continue to come and go across parts of western
and central MO in advance of a lifting and weakening short wave trof
currently stretching across far eastern KS. Guidance continues to
eject this short wave trof northeast across the area tonight as the
western U.S. upper low meanders southward, with the ejecting short
wave just east of the MS River at 12z Thurs. Lift associated with
the short wave is rather meager and the moisture stratification
across eastern MO and western IL while improving is not overly
abundant. A 1940z AMDAR sounding from KSTL shows the moisture is
primarily above 5000 ft. These factors cumulatively suggest that
precipitation tonight will be spotty-scattered in nature. Clouds
should remain abundant with lows in the 50s.

Glass

.LONG TERM:  (Thursday through Next Wednesday)
Issued at 332 PM CDT Wed Apr 15 2015

There is a slight chance of lingering showers across southwest IL
on Thursday morning ahead of the lifting and weakening short wave
trof with large scale subsidence overspreading the entire region
in its wake. The big unknown on Thursday is the extent of cloud
cover and impact on temperatures. My present thinking is there
will be extensive clouds at the start of the day given the weak
overall flow aloft and rather moist 925 mb RH progs. I think
clouds will gradually clear/thin west to east during the day, in
part due to the shallow nature of the moisture and high sun angle
and this should allow temps to rise into the 70s.

Thereafter weak surface high pressure slowly retreating into the
OH Valley will produce easterly surface winds and delay southerly
low level return flow. This should allow for a dry period into
Friday morning and potentially longer. The overall trend in the
new forecast is to slow down the eastward spread of pops/precipitation
from the previous one. Present indications are that ridging aloft
will delay the eastward moisture transport and hence the arrival
of precipitation until sometime Saturday. The threat of precipitation
should ramp up on Saturday and into Saturday night as the western
U.S. upper low/trof advances into the Plains bringing south/southwest
flow aloft, embedded disturbances aloft, and deeper moisture
transport into the region. Sunday and Sunday evening look wet as
well with the migration of the main upper trof and associated cold
front.

In the wake of the cold front, a cooler than normal pattern will
persist through the first half of next week thanks to a rather
strong upper low centered north of the Great Lakes and accompanying
broad trof. Several disturbances within the cyclonic west-northwest
flow could bring additional showers from late Tuesday night into
Thursday.

Glass
&&

.AVIATION:  (For the 06z TAFs through 06z Thursday Night)
Issued at 1055 PM CDT Wed Apr 15 2015

Shortwave exiting region, so chances of precipitation have moved
out. VFR clouds will linger across the region for most of the
forecast period. SREF and NARRE model probabilities shows some low
level moisture advecting north towards taf sites, though best
chances of MVFR cigs/vsbys will be just east of metro area. For now
kept tempo MVFR cigs from 09z to 13z Thursday for these tafs.
East winds to become light and variable for remainder of forecast
period.

Specifics for KSTL:
Shortwave exiting region, so chances of precipitation have moved
out. VFR clouds will linger for most of the forecast period. SREF
and NARRE model probabilities shows some low level moisture
advecting north towards region, though best chances of MVFR
cigs/vsbys will be just east of metro area. For now kept tempo MVFR
cigs from 09z to 13z Thursday for STL. East winds to become light
and variable for remainder of forecast period.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$
WFO LSX





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