SPC Forecast Products

SPC - No watches are valid as of Mon Apr 12 12:45:02 UTC 2021

No watches are valid as of Mon Apr 12 12:45:02 UTC 2021.

SPC - No MDs are in effect as of Mon Apr 12 12:45:02 UTC 2021

No Mesoscale Discussions are in effect as of Mon Apr 12 12:45:02 UTC 2021.

SPC Apr 12, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook
      
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0740 AM CDT Mon Apr 12 2021

Valid 121300Z - 131200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN PARTS OF
SOUTHWEST...CENTRAL AND NORTH TEXAS...

...SUMMARY...
At least a few afternoon and evening thunderstorms will produce
large hail -- including destructive hailstones 2+ inches across --
as well as locally damaging winds, in parts of southwest, central
and north Texas.

...Synopsis...
While a mid/upper cyclone meanders eastward over the Upper Midwest,
a strong shortwave trough will dig southward and intensify from
southeastern BC across the Pacific Northwest.  Largely zonal to
southwesterly flow will be maintained to their south across the
Southwest and southern Plains, while a separate northern-stream low
now over OH accelerates southeastward past Chesapeake Bay.  In the
southern stream, a perturbation is apparent in moisture-channel
imagery over northwestern MX, which will move northeastward over
much of the main body of TX through this evening.  

At the surface, 11Z analysis showed a primary low over northwestern
WI, with cold front southward/southwestward over southern WI,
western IL, the MO Ozarks, southeastern OK, to a low near ABI, then
westward to near CNM.  The northern low will continue to become more
deeply occluded and meander around the western Lake Superior/
northern MN region through the period.  The cold front should reach
northeastern AR, southeastern OK, north-central TX, the Edwards
Plateau, and the lowest segment of the Pecos Valley by 00Z.  By 12Z,
the front should extend from central/southern AR across portions of
south-central/southwest TX.  As moisture returns to its east, a
dryline should sharpen today from northern Coahuila to its afternoon
frontal intersection -- roughly between SJT-MAF.

...Southwest TX to southeastern OK...
Isolated to widely scattered thunderstorms are expected to form
mid/late afternoon along the front, dryline and/or Serranias del
Burro in MX.  The latter activity may remain southwest of the Rio
Grande or barely cross, except for left-moving storms, which
forecast hodographs favor across much of the outlook area.  A few
supercells are possible, offering severe to very large hail (some
significant, over 2 inches in diameter), and localized damaging
wind. 

Morning RAOBs and near-term model soundings across the region depict
a substantial EML, which will require combined lift from sustained
diurnal heating (through some cloud cover preceding the southern-
stream perturbation) and the boundaries/mountains to overcome. 
Large-scale ascent -- increasing ahead of the ejecting shortwave
trough -- also will help to maintain a favorable environment aloft. 
Development will be somewhat high-based, atop increasing low-level
moisture and a well-mixed subcloud layer, and amidst steep (7.5-8.5
deg C/km) midlevel lapse rates.  This will contribute to peak
preconvective MLCAPE ranging from 2000-3000 J/kg, weakening
northeastward past the DFW Metroplex and into southeastern OK where
moisture recovery will be less mature.  Though low-level wind speeds
will be modest, favorable directional shear and favorable winds
aloft (45-70 kt in the 500-250-mb layer) will contribute to
supercell-favoring effective-shear magnitudes in the 45-55-kt range
over the 15%/"Slight" area.  Remaining convection should weaken late
this evening as nocturnal diabatic stabilization proceeds. 

...South FL and Keys...
An extensive cold pool from yesterday's severe MCS covers South FL
and surrounding waters across the Straits, to parts of the Bahamas
and coastal northern Cuba.  This is being reinforced by another 
complex of thunderstorms now moving southeastward across the eastern
Gulf and western Straits, west through south of the Dry Tortugas and
lower Keys.  Still, elevated instability atop the cold pool will
continue to support the development of widely scattered
thunderstorms through the remainder of the morning, before
supportive ascent weakens.  MUCAPE in the 500-1000 J/kg range,
coupled with 50-60-kt effective-shear magnitudes, suggest isolated
hail near severe limits cannot be ruled out.  However, the threat
appears too isolated and uncertain to introduce an unconditional
severe risk.

..Edwards/Broyles.. 04/12/2021


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SPC Apr 12, 2021 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook
      
Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0343 AM CDT Mon Apr 12 2021

Valid 151200Z - 201200Z

...DISCUSSION...
Severe potential appears limited during the Day 4-8 period. A series
of surface cold fronts is forecast to push southeast into the Gulf
of Mexico as the western upper low/trough weakens and ejects
eastward across the Plains and Midwest through the end of the week.
This will keep Gulf moisture limited to south Texas and the FL
Peninsula, with only weak elevated instability forecast across
portions of the southern Plains into the southeastern states.
Southwesterly low level flow will maintain warm advection across
parts of the southern Plains and central Gulf Coast vicinity, but
limited instability, along with stronger upper forcing remaining
well north of the region, should preclude any substantial severe
threat through Days 5-6/Fri-Sat. Surface high pressure will build
behind the cold front during the weekend/early next week, leaving a
dearth of moisture across the U.S. east of the Rockies and severe
potential will be low.


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