Area Forecast Discussion
Issued by NWS St. Louis, MO

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844
FXUS63 KLSX 251946
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
246 PM CDT MON APR 25 2016

.SHORT TERM... (Through Tuesday)
Issued at 242 PM CDT Mon Apr 25 2016

(Tonight)

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
boundary.

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.

(Tuesday)

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.

Gosselin

.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
Wednesday/Wednesday night.

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
thunderstorms.

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.

Byrd
&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1245 PM CDT Mon Apr 25 2016

Main concern through Tuesday afternoon will be on chances of
showers and thunderstorms. Cold front will move into the northern
sections of the forecast area late this evening and eventually
become stationary overnight tonight. Chances of showers/storms
hard to pin down tonight and especially on Tuesday but believe
scattered activity will develop by mid evening and to persist
through the night. Given the uncertainty in timing/placement of
this expected activity...just have VCTS groups in for now.

Consensus of guidance also suggests ceilings lowering into MVFR
overnight tonight and lasting into early Tuesday morning before
lifting.

Complicated scenario for tomorrow. Not sure how much convective activity
will be still ongoing at daybreak but frontal boundary will remain
draped across the CWA on Tuesday. Believe there likely will be a
lull however in activity from late morning to early afternoon.
Additional activity may develop by mid afternoon with the best
chances right along the frontal boundary.

Specifics for KSTL:

Cold front will stall near the terminal late tonight and bring a
chance of showers/storms. Latest HRRR also suggests some scattered
activity a bit earlier along a prefrontal trough though not sure
if this actually will develop. Guidance suggests MVFR ceilings
also coming in around daybreak and lasting into late Tuesday
morning. Convective trends looking into Tuesday are highly
uncertain but with frontal boundary remaining near the
terminal...storms could develop at any time.

Gosselin
&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     68  84  64  78 /  40  40  60  70
Quincy          61  80  59  70 /  20  20  90  80
Columbia        65  81  63  76 /  50  50  80  70
Jefferson City  65  82  63  78 /  40  40  80  70
Salem           64  80  63  74 /  30  30  60  80
Farmington      61  79  62  75 /  20  30  60  70

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$
WFO LSX



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