Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 260215
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
915 PM CDT MON APR 25 2016
Issued at 914 PM CDT Mon Apr 25 2016
Have made some adjustments to PoP trends. Thunderstorms have had a
hard time developing over the CWA so far this evening as the 00Z
SGF sounding was showing a large inversion around 750mb. The RAP
is showing an increase in low level moisture convergence along
I-70 across western and central MO after midnight on the nose of a
40kt low level jet. This will be occuring at the same time a weak
shortwave will be approaching the area from the Central Plains.
Have shown an increase in scattered thunderstorms after midnight
over central Missouri that spreads into eastern Missouri towards
morning. There will be some risk for large hail with these storms
over central Missouri per the latest SPC outlook with MUCAPES of
1000-1500 J/kg and effective shear 30-35kts.
Going low temperatures still look good.
.SHORT TERM... (Through Tuesday)
Issued at 242 PM CDT Mon Apr 25 2016
Main focus will continue to be on convective trends. Cold front will
come into northern CWA late this evening and stall out across CWA.
Frontal boundary will remain quasi-stationary through Tuesday.
Highest PoPs for tonight in theory should be closely tied to where
low-level warm/moist advection maximizes on nose of anticyclonically
curved portion of LLJ intersects with sfc boundary. Current
expectation is for isolated-scattered activity developing this
evening and lasting through the night tonight. May need higher PoPs
tonight...but uncertainty exists with coverage but also placement of
Marginally severe hail will also be possible this evening with any
thunderstorms as well as for portions of central Missouri late
tonight as instability aloft increases.
Temperatures will remain very mild tonight as clouds increase with a
very warm start given today`s highs. Lows for a vast majority of the
area will be in the 60s.
Believe scattered showers/storms will be ongoing on Tuesday morning
with the best chances across the southern 2/3 of the CWA. Should be
a lull in the activity late Tuesday morning into early Tuesday
afternoon...though still carried slights due to frontal boundary
remaining across the area. Uncertainty increases for Tuesday
afternoon. Best chance of thunderstorms developing will be
along/near the quasi-stationary front but coverage (if any) is
highly unknown. Mid/upper level ridge builds across area so not
exactly a favorable environment aloft for convective initiation.
However...atmosphere should be very unstable on Tuesday afternoon
with 3000+ J/kg of SBCAPE possible depending on how the morning
activity evolves. So...any storms that do develop would likely go
severe and potentially quickly as well. Deep layer shear is not
impressive (20-25 knots)...though this may be overcome by
instability. Large hail looks to be the primary threat with any
thunderstorms on Tuesday afternoon...with very large hail possible
if any storms can sustain a rotating updraft.
Temperatures on Tuesday will be fairly similar to that of today.
Expectation is for most locations to top off in the low to mid 80s.
.LONG TERM... (Tuesday Night through Next Monday)
Issued at 242 PM CDT Mon Apr 25 2016
Stalled frontal boundary along I-70 corridor to remain the focus for
another round of storms Tuesday night. Models still indicating
possible MCS development as elevated convection fires up and congeals
into a complex, sliding east along boundary. Main severe threat will
be large hail.
Depending on when/if MCS develops will affect what happens on
Wednesday with another round of storms as warm front lifts north and
if there is time for atmosphere to recover. Either way, shear will
increase substantially as the storm system approaches and
instability may not need to be as high as what it was Tuesday anyway
to justify a continuation of a severe risk. For now will see best
chances of storms over northeast MO/west central-southwest IL
Models are slower with system as far as moving the surface low and
attendant cold front through region, not exiting til Thursday
morning. Precipitation to slowly taper off on Thursday.
Still looks to be a wet weekend as another system moves in from the
west. This system will be a bit further south than current storm, so
we will be on the cool side with mostly showers and a few
As for temperatures this week, will remain above average through
Thursday, then dip down to near normal levels through the weekend
and into early next week.
.AVIATION... (For the 00z TAFs through 00z Tuesday Evening)
Issued at 619 PM CDT Mon Apr 25 2016
There is still some potential for scattered thunderstorms to
develop over the area this evening that could affect any of the
the terminals. This chance is too low however to include in any of
the TAFs at this point. Models are hinting that a complex of
storms could develop over western MO later tonight and move east
which would affect KCOU and possibly the St. Louis area terminals.
Have gone ahead and added VCTS at KCOU for a short period to
include this possibility. Cold front that currently extends from
southern Iowa into northern Missouri will move south into the area
by tomorrow afternoon. Additional scattered thunderstorms could
develop along it which could affect KCOU and the St. Louis area
terminals. Any thunderstorms that move over an airport could
produce MVFR or brief IFR ceilings and visibilities. There is
also the possibility that a few storms could produce hail and wind
gusts over 50 kts.
Specifics for KSTL: Have gone with a dry and VFR TAF for now,
however there will a 20-30 percent chance of thunderstorms through
the period. A cold front will move south to near the terminal
during the day tomorrow causing winds to shift to the southeast.