Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 292301

601 PM CDT Fri May 29 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 340 PM CDT Fri May 29 2015

Complex of showers and thunderstorms ahead of an MCV over E OK will
slowly translate north and eastward overnight. Main threat with this
feature looks to be the potential for localized heavy rainfall due to
long/narrow CAPE profiles with high PWAT values and slow
translational speed of convection. Best bet right now of where
heaviest axis of rainfall would be across south-central Missouri
extending toward the Missouri River between KCOU and KSUS where
1.00-1.50"+ of rain is likely. Threat of widespread severe weather
continues to look low as low-level atmosphere nocturnally stabilizes
through the evening hours along with weak deep-layer shear.
However...cannot rule out an isolated strong wind gust or two in any
heavy precipitation core.

Another seasonably mild night should be in store ahead of synoptic cold
front which will move into northwestern sections of the are very late
tonight. Lows are expected to be in the 60s.


.LONG TERM:  (Saturday through Next Friday)
Issued at 340 PM CDT Fri May 29 2015

(Saturday-Saturday Night)

Front will slowly progress south and east on Saturday clearing the
CWFA by late afternoon per latest model guidance. Showers and
thunderstorms along and ahead of the front along with post-frontal
showers as UL jet streak backbuilds. A few storms across southeast
Missouri and southwest Illinois may be strong to severe with CAPE
values of 1000-1500 J/kg and 0-6km shear on the order of 20 knots or
so. Isolated severe wind gusts along with small hail look to be the
primary threats. A cooler day compared to this afternoon is also
expected due to copious amounts of cloud cover...precipiation...and
cold advection commencing to the northwest of the low-level
baroclinic zone. Coolest conditions will be across portions of
northeast Missouri with highs only in the mid 60s with warmest highs
near 80 degrees toward KFAM and KSLO.

Cold/dry advection begins to really amplify and take hold late
Saturday night as low-level anticyclone slides southeast toward the
Great Lakes. Chances of showers should wane overnight from north to
south as the drier/more stable air filters in from the north and
east. A cool night for very late May should be in store just from
the strength of the cold advection as clouds look to linger across
the area. Look for lows to range from the upper 40s to mid 50s from
north to south across the bi-state area.


The Sunday through Friday timeframe will be marked by mostly dry
weather along with moderating temperatures. Cool day still appears
to be in store on Sunday with highs likely failing to hit 70 degrees
across the area. Upper-level low as previous forecaster mentioned
looks to get stuck beneath/to the south of building ridge axis
across lower Mississippi Valley. This should yield fairly
tranquil/dry weather through much of next week with highs warming
back above normal by Wednesday. Next chance of showers/storms still
appears to be on Thursday though large model disagreements do exist
between the GFS/ECMWF with the European solution continuing the dry
trend while the GFS brings the area some showers/storms.



.AVIATION:  (For the 00z TAFs through 00z Saturday Evening)
Issued at 505 PM CDT Fri May 29 2015

Most of the showers/storms across southeast MO and southwest IL
should remain southeast of the St Louis metro area this evening.
Large area of showers and thunderstorms across west central and
southwest MO ahead or northeast of an upper level disturbance and
associated surface low will shift northeast through the taf sites
tonight. A strong southerly low level jet will also lead to
redevelopment of convection across our area late tonight. The MOS
cloud guidance is consistent in dropping the cloud ceilings late
tonight and Saturday morning down to around 1000-1500 feet.
Prevailing surface winds will be mainly sly for most of tonight,
then shift to a nwly direction Saturday morning as the surface low
moves northeastward through southeastern MO and as a cold front now
across the northern Plains drops southeastward through our area.
The showers and thunderstorms will taper off from northwest to
southeast on Saturday.

Specifics for KSTL: Most of the showers/storms across southeast MO
and southwest IL should remain southeast of STL this evening, but
larger area of showers and storms across southwest MO will move
northeastward into STL by late evening, then continue for much of
the rest of the night into at least Saturday morning. The cloud
ceiling will drop later tonight and Saturday morning down to around
1000-1500 feet. Prevailing surface winds will be s-sely tonight,
although there will be some variability near thunderstorms. The
surface wind will become nwly Saturday morning. The showers and
storms should taper off Saturday afternoon and evening after
passage of the surface low and cold front, but cloud ceilings will
remain low.



Saint Louis     68  76  54  66 /  90  80  30   5
Quincy          64  67  47  65 /  80  60  10   0
Columbia        64  69  51  66 /  90  30  20   5
Jefferson City  64  71  49  66 /  90  40  20   5
Salem           70  77  54  67 /  60  70  40  10
Farmington      67  76  54  65 /  70  70  30  10




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