Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 klsx 290343 
afdlsx

Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
1043 PM CDT Tue Mar 28 2017

Update...
issued at 913 PM CDT Tue Mar 28 2017

Latest NAM and hrrr model guidance is a little slower bringing
showers into our forecast area late tonight/early Wednesday
morning. It appears that showers will move into central MO around
12z Wednesday morning, then move into northeast MO and west
central Illinois later in the morning, mainly north and west of stl as a
southerly low level jet brings increasing temperature and
moisture advection into this area. Lows tonight will be slightly
above normal for late March with a low level cloud cover along
with gradually increasing east-northeasterly surface winds as the
surface pressure gradient tightens.

Gks

&&

Short term... (through late Wednesday afternoon)
issued at 327 PM CDT Tue Mar 28 2017

Clouds have stayed locked in over the area as the clearing over east
central Illinois that was working into the eastern County Warning Area filled back
in with stratocumulus this afternoon. Forecast soundings do show
that the low levels will stay saturated through the night, with an
increase in mid-high clouds as upper low currently over New Mexico
moves northeast into the plains. Showers and isolated thunderstorms
will move into the area late tonight per the GFS and NAM as the
upper ridge moves east and a band of strong moisture convergence
sets up on the nose of a 40kt low level jet. This low level forcing
combined with increased mid-upper ascent from approaching low will
be enough to set up one round of showers and scattered thunderstorms
late tonight and tomorrow morning. Then there may be a break during
the late morning and early afternoon before both models show another
round of showers and thunderstorms moving into central Missouri by
late afternoon.

Went closer to the GFS MOS temperatures over the next 24 hours.

Britt

Long term... (wednesday night through next tuesday)
issued at 327 PM CDT Tue Mar 28 2017

Primary concern heading into Wednesday night is the potential for
severe weather. Guidance is in good agreement that there will be
thunderstorms over western Missouri at 00z moving toward our area.
Forecast instability falls of pretty quickly in the evening with
MUCAPE values not exceeding 500 j/kg on the GFS until after 09z.
NAM has more energy in the evening pushing 1000 j/kg, but it tends
to be a bit too high, and even with that high bias MUCAPE values
fall off overnight. Regardless...with 50-60kts of deep layer
shear, can't say there won't be severe storms; but the threat
should stay over our eastern Ozark counties where instability will
be greatest. Should be a better chance for severe storms on
Thursday ahead of the low. SBCAPE increases to around 2000 j/kg
during the afternoon. Deep layer shear isn't as impressive
initially at 18z but increases to 40+ kts along and southeast of
I-44 and south of I-70. 0-1km helicity is less than 100 m2/s2 for
the afternoon hours on Thursday so think the primary threats will
be hail and damaging wind rather than tornadoes.

Thunderstorm threat will be coming to an end Thursday night although
rain will likely continue on the west side of the low as it passes
for a good portion of the night. Cooler and drier air will move
into the area on Friday and Saturday. Overnight lows will dip into
the upper 30s and 40s with daytime highs mainly in the upper 50s to
mid 60s. There is a chance there could be some rain on Sunday ahead
of the next system as the upper level shortwave digs into the
Southern Plains. However the GFS and European model (ecmwf) disagree on how much
quantitative precipitation forecast to print out so have reduced pops for Sunday until we see a
little better agreement. The system lifts out of the Southern
Plains into the Mississippi Valley on Monday so rain chances for
early in the week look good. The GFS and European model (ecmwf) can't agree on a
track for the surface system just yet with the GFS being further
north and therefore warmer than the ec. Think the current hedge
between the two with highs mainly in the 60s and lows in the mid
40s to low 50s looks good.

Carney

&&

Aviation... (for the 06z tafs through 06z Wednesday night)
issued at 1027 PM CDT Tue Mar 28 2017

Cloud ceiling around 3000 feet should gradually lower late
tonight and early Wednesday morning, eventually down to IFR
by late Wednesday morning. It appears that showers will move into
the cou area around 12z Wednesday, and into uin and possibly also
the St Louis Metro area as well later in the morning as a
southerly low level jet brings increasing low level moisture into
the area ahead of an approaching low pressure system over the
Southern Plains. East-northeast surface winds will strengthen
late tonight and Wednesday morning as the surface pressure
gradient tightens. There will likely be a break in the convection
Wednesday afternoon, then another round of showers and storms will
move through the taf sites Wednesday night as a warm front
approaches from the south.

Specifics for kstl: cloud ceiling around 3000 feet should gradually
lower late tonight and early Wednesday morning, eventually down
to IFR by late Wednesday morning. It appears that scattered showers
will move into the St Louis Metro area in the morning as a
southerly low level jet brings increasing low level moisture into
the area ahead of an approaching low pressure system over the
Southern Plains. Northeast surface winds will strengthen late
tonight and Wednesday as the surface pressure gradient tightens.
There will likely be a break in the convection Wednesday
afternoon, then another round of showers and storms will move
into the stl area by late Wednesday night as a warm front
approaches from the south.

Gks

&&

Preliminary point temps/pops...
Saint Louis 47 63 56 71 / 5 60 90 80
Quincy 42 55 50 61 / 5 70 90 80
Columbia 47 60 54 67 / 40 70 90 70
Jefferson City 49 62 55 68 / 30 60 90 70
Salem 48 64 56 72 / 0 30 70 90
Farmington 50 64 58 71 / 5 50 90 80

&&

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

National Weather Service Glossary of Abbreviations