Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 242044
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
344 PM CDT Thu Jul 24 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 342 PM CDT Thu Jul 24 2014

A gorgeous late July day is ongoing across the forecast area, with
temps in the upper 70s and low 80s, dewpoints in the low 50s, and
plenty of sunshine.

NW upper level flow prevailed this afternoon with a few upper level
disturbances keying off complexes of TSRA over the Mid-MO river
valley.  These complexes are trying to push southeast into our
region, but we are much too dry and stable for this rain to have
much success.  Instead we are just seeing the convective blowoff
slide into our area.

It appears the convection will continue to weaken and dissipate as
it pushes southeast late this afternoon and evening from IA with
continued thin high Cirrus clouds moving thru as the diurnal Cumulus
dissipates with the setting sun.  A new round of TSRA is expected to
form around midnight in central IA and this is anticipated to have
more success in propagating southeast with our region not as dry and
stable as before but should still be slow in moving towards us and
probably in a weakening phase as it does so.  Have not changed the
PoPs for the northern CWA as a result, with low mentionable values
in place for late...after 09z.

Clear skies for most areas and light winds from a slowly departing
surface ridge will promote good cooling, however, with temps
expected to drop into the upper 50s and low 60s outside of urban
heat islands.  Clouds are not expected to have much influence until
thicker clouds arrive after midnight.

TES

.LONG TERM:  (Friday through Next Thursday)
Issued at 342 PM CDT Thu Jul 24 2014

Shortwave rounding the top of the ridge over the Dakotas should be
near the Missouri/Iowa/Illinois border by 12Z Friday.  Models are
forecasting a modest amount of elevated CAPE between 500-1000 j/kg
ahead of the shortwave as it passes southeast across our Central
Illinois counties.  Expect there to be some convection stretching
into our CWFA due to these factors and a 30-40kt LLJ nosing into
southeast Iowa, however am not very confident on areal
coverage/timing of precip.  Am therefore keeping only chance
PoPs...especially since surface based convection looks unlikely due
to 200+ j/kg CINH.  Looks like there will be another round of
nighttime convection on Friday night as the upper level ridge
flattens and the low level jet pushes into Illinois.  Looks like the
majority of the forcing will be east of the area in central/south
central Illinois, however can`t rule out far eastern sections of the
CWFA could see some isolated/widely scattered showers and storms
overnight.  Temperatures will be warming through Friday with highs
reaching up to near seasonal normals as the cool surface high moves
east and away from the region.

Saturday still looks like the hottest day of the next 7 days.  850mb
thermal ridge builds directly across the I-70 corridor with
temperatures ranging from 24-26C.  This would mix dry adiabatically
down to around 100 F.  Don`t quite have the guts to go that warm
just yet, especially with the possibility of some afternoon
thunderstorms.  That being said, guidance does look a little cool
along and south of the I-70 corridor, so I did bump it up a bit.
Soundings look pretty capped, but with falling heights aloft and
with the potential for a front in the area I can`t rule out the
aforementioned afternoon thunderstorms.

Saturday night looks like the best chance for precip as the next
strong shortwave dips down across the Upper Midwest and finally
pushes a strong cold front into our area.  Have mid-high chance PoPs
for this period.  Can`t quite talk myself into likely yet due to the
climatologically unfavorable time of day and relatively warm
temperatures aloft.

Medium range models continue to show the shortwave phasing up with
the longwave pattern over eastern North America.  The highly
amplified trof allows a cool dry Canadian airmass to move south into
the CONUS.  Temperatures  Below normal temperatures in the upper 70s
and low 80s will prevail through the first 1/2 of the week with lows
in the low 60s.  Temperatures will slowly moderate Wednesday into
Thursday but still look below normal.

Carney

&&

.AVIATION:  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1235 PM CDT Thu Jul 24 2014

VFR conditions will prevail at the TAF sites thru the valid
period. A minor question of steam fog potential at SUS and perhaps
CPS due to unusual cool temps versus relatively warm river temps,
but airmass itself is quite dry and should inhibit this to some
degree and for now have not placed in the TAFs although if I did,
it would be more as VCFG than any direct impact. Otherwise look
for variable winds due to proximity of surface ridge to become SE
and S heading into Friday.

Specifics for KSTL: VFR thru the period with veering surface winds
to S by Friday.

TES

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     63  85  74  94 /   0   5  10  30
Quincy          60  83  71  91 /  20  30  20  30
Columbia        62  90  73  95 /  10   5  10  20
Jefferson City  61  91  74  96 /  10   5  10  20
Salem           58  81  70  91 /   0   5  20  30
Farmington      58  86  68  92 /   0   5  10  20

&&

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

$$

WFO LSX






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