Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 48 49 50
FXUS63 KLSX 170847

347 AM CDT Sun Aug 17 2014

.SHORT TERM:  (Today)
Issued at 343 AM CDT Sun Aug 17 2014

Vorticity maxima/MCV will slowly move to the southeast to around KSLO by
mid morning. Precipitation shield overnight as largely been tied to
forcing via aforementioned vort max as well as WSW LLJ. Convection
on nose of LLJ has already moved off to the south and east of forecast
area so primary focus will be on track of closed low/MCV. Since it will
be exiting the CWA around late morning...believe highest PoPs this morning
will be across portions of southwest Illinois or far eastern sections of
the CWFA. With subsidence setting in behind this feature...believe
measurable showers/storms will be tough to come by. Weak convergence along
trailing sfc inverted trough may yield areas of drizzle beneath low
ceilings however. Similar to previous forecaster...leaned cool for high
temperatures today yielding upper 70s to low 80s or 5-10 degrees below
average. This is due to weak cold advection and low clouds hanging around
through the daylight hours.


.LONG TERM:  (Tonight through Saturday)
Issued at 343 AM CDT Sun Aug 17 2014

(Tonight - Wednesday night)

Slowly decreasing clouds should be the rule tonight with mild temperatures.
Lows should be near or slightly above average in the mid 60s to low 70s.
A potential issue tonight could be boundary layer will remain
very moist. Due to uncertainty in cloud cover overnight tonight...elected
not add fog to forecast for now.

Monday should also be dry with warmer conditions returning. By Monday
night...a shortwave trough transverses northern sections of the area
with a trailing cold front swinging in from the northwest. Raised PoPs into
the high chance category over portions of central and northeastern Missouri
where combination of strongest moist/warm advection and upper-air
dynamics interact.

Weak Pacific "cold" front will wash out and stall across southern sections
of the area on Tuesday as upper-level heights begin to climb. Raised
highs across portions of the region on Tuesday due to favorable WSW
downslope sfc flow and partly cloudy skies expected. Chances of showers
and thunderstorms will continue and move northward through the region
Tuesday night through Wednesday night invof retreating warm frontal
boundary as upper-level heights climb.

(Thursday - Saturday)

Warm front is expected to move northward of the CWA by Thursday as
upper ridge continues to build into mid-Mississippi Valley. Some concern
that antecedent convection may prevent or retard northward progression of
warm front or effective baroclinic zone. Also some uncertainty as to
how far north upper ridge will build models tonight have
backed off the strength of 500-hPa anticyclone. This could result
in increased cloudiness/PoPs and consequently lower temperatures
for Thursday and maybe Friday as parts of the forecast area...
especially far northern sections...may be on northern edge of
upper ridge or in the so-called "ring of fire". Current forecast
package still reflects the scenario where upper ridge does indeed
build in late in the work week brining potentially our hottest
stretch of weather all summer...but again due to the possibilities
above...that is not a given at this juncture.



.AVIATION:  (For the 06z TAFs through 06z Sunday Night)
Issued at 1114 PM CDT Sat Aug 16 2014

A slow-moving low pressure system will continue to bring scattered
SH/TS to the terminals over the next few hours. Coverage will
probably be greater at St. Louis metro area TAF sites due to their
proximity to the low. Once the precipitation moves out, ceilings
should drop to IFR and remain there for the rest of the night and
into tomorrow. There will probably also be transient MVFR to IFR
visibilities in fog overnight because of the highly saturated air
mass, but models are forecasting winds to stay high enough
overnight that it looks more like a low stratus situation rather
than widespread dense fog. Ceilings should slowly improve during
the afternoon as the low pressure system moves away from the area.
Prevailing winds will eventually turn around to the north behind a
cold front and on the back side of the departing surface low.



Saint Louis     80  70  89  74 /  20  20  10  30
Quincy          78  66  83  68 /  10  10  10  40
Columbia        81  67  90  70 /  10  10  10  40
Jefferson City  82  67  89  71 /  10  10  10  30
Salem           79  68  86  69 /  70  30  10  20
Farmington      82  68  90  70 /  10  20  10  20




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