Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Graphics & Text | 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
000
FXUS63 KLSX 242339
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
639 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 00z TAFs through 00z Friday Evening)
Issued at 556 PM CDT Thu Jul 24 2014

VFR fcst with sfc high sliding thru the OH vly and near the east
coast by the end of the prd. Main fcst concern will be precip
potential assoc with a couple upper lvl disturbances embedded in
the NW flow. The first of the two is currently dropping SE out of
IA. It is weakening and expect that trend to continue thru the
evng as the precip moves into a drier more stable airmass. It is
possible for the KUIN terminal to see a few sprinkles this evng
though. The next disturbance should ignite another round of
convection across ERN SD...SW MN and NW IA overnight. This
activity is also expected to drop SE and may affect the KUIN
terminal Friday morning. By then...a substantial increase in
moisture is expected allowing the precip to hold together farther
to the east. Still not confident that it will impact the terminal
or slide just to the east...so left the VCSH group alone. It is
not out of the question to have precip in or near the STL metro
area on Friday...but not confident enough in this scenario to
include mention attm. Regardless whether it rains at any of the
terminals or not tomorrow...there will be an abundance of mid/high
lvl convective debris clouds. Winds should become srly by tomorrow
allowing for return flow and aiding in the increase in moisture.

Specifics for KSTL:

VFR fcst thru the prd. Two upper lvl disturbances will impact the
region over the next 24-30 hrs. A batch of precip assoc with the
first disturbance is dropping SE out of IA this evng. It is
weakening and is expected to continue to do so as it moves away
from the better moisture and instability. The next disturbance
should spark another round of TSTMs to across the mid-MO vly
overnight. This activity may graze the terminal from late mrng
thru early aftn on Friday...but not confident enough in this
scenario to include mention attm.

2%

&&

.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



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