Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 klsx 251642 
afdlsx

Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
1142 am CDT Thu may 25 2017

Short term... (through late tonight)
issued at 333 am CDT Thu may 25 2017

Low system, currently centered over in/Ohio region at the sfc, will
continue to move ewd today. Expect cloud cover over the ern half of
the County Warning Area to gradually clear out of the area today before mid clouds
move into the wrn portions of the County Warning Area.

With ample insolation expected today, have trended twd the warmer
guidance despite weak advection. Have also trended twd warmer
guidance for tonight as clouds move into the region and winds
becoming sly across the region.

Expect today to remain dry as well as much of tonight. However, have
kept low pops late tonight across wrn and nrn portions of the County Warning Area as
the wrmfnt lifts thru the area. There are some mdls that suggest
thunderstorms and rain moving further south impacting srn portions of the County Warning Area.
However, given the strong and deep warm air advection across this area, it wud seem
this area would be capped with convection remaining further north.
Mdls disagree on timing, but with a weak trof moving thru Iowa late
tonight into Fri morning, have focused further north late tonight.

Tilly

Long term... (friday through wednesday)
issued at 333 am CDT Thu may 25 2017

Surface ridge to continue weakening and shift off to the east on
Friday as next system moves in. Frontal boundary associated with
system to sink south across forecast area and stall out along I-70
corridor. Low level moisture will be on the increase with moderate
instability. However, decent cap so activity will be slow to
develop, if at all. If anything does fire up by late afternoon/
early evening, it could be strong to severe.

The threat for storms will persist Saturday through Saturday night,
with models continuing to indicate very high convective available potential energy and strong 0-1km
shear. As frontal boundary lifts north as a warm front, will see
elevated hailers during the morning hours, then transition to more
of a supercell environment for the afternoon and evening hours. Storm Prediction Center
has placed areas along and south of I-70 in an enhanced risk for
Saturday/Saturday night.

As system exits, will see showers taper off on Sunday. Quieter
weather for Monday and Tuesday, though could see isolated/scattered
showers and storms as shortwaves rotate around upper low anchored
over Great Lakes region each day. Weak surface ridge builds in by
Wednesday.

As for temperatures through the period, will be near normal or just
a bit above normal.

Byrd

&&

Aviation... (for the 18z tafs through 18z Friday afternoon)
issued at 1101 am CDT Thu may 25 2017

Surface ridge axis will move eastward through the taf sites this
afternoon causing the northwest surface winds in uin and the St
Louis Metro area to weaken. Only few to scattered diurnal cumulus
clouds are expected. Could not rule out a few showers/storms late
tonight and Friday morning in the uin and cou areas due to weak
upper level disturbances and as a southwest low level jet over
southwestern MO brings increasing low level moisture into this
area, but the probability or possible coverage is too low to
warrant including in the tafs. Should see increasing mid-high
level cloudiness late tonight, with low level cloudiness Friday
morning though still likely VFR. The wind will gradually
stengthen from a southeast direction tonight, then southerly
Friday morning as the surface ridge shifts east of the region.

Specifics for kstl: surface ridge axis will move eastward through
the stl area this afternoon causing the northwest surface wind to
weaken. Only scattered diurnal cumulus clouds are expected. Could
not rule out a few showers/storms Friday afternoon due to weak
upper level disturbances and as a cold front approaches, but the
probability or possible coverage looks too low to warrant
including in the stl taf for now. Should see increasing mid-high
level cloudiness late tonight, with low level cloudiness Friday
though still likely VFR. The wind will gradually stengthen from a
southeast direction tonight, then veer around to a southwest
direction Friday afternoon as the surface ridge shifts east of the
region.

Gks

&&

Lsx watches/warnings/advisories...
MO...none.
Illinois...none.
&&

National Weather Service Glossary of Abbreviations