Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Text Only | 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
FXUS63 KLSX 282029

Area Forecast Discussion
National Weather Service Saint Louis MO
329 PM CDT Tue Mar 28 2017

.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 CWA 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.


.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 ECMWF disagree on how much
QPF 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 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.



.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1240 PM CDT Tue Mar 28 2017

Kept with mostly MVFR or low VFR ceilings throughout the period.
Showers and scattered thunderstorms are expected to move into the
area late tonight and Wednesday morning bringing a period of
showers to each of the terminals. Some IFR ceilings will be
possible behind the rain at KCOU and KSTL.

SPECIFICS FOR KSTL: Have mostly MVFR or low VFR ceilings going
throughout the period at the terminal. Showers and isolated
thunderstorms will be possible between 12-18Z tomorrow morning
with IFR ceilings during the afternoon.



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




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