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SPC Activity Chart
Hazard Thu (07/07) Fri (07/08) Sat (07/09) Sun (07/10) Mon (07/11) Tue (07/12) Wed (07/13) Thu (07/14)
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Forecast Discussion - Convective Outlook

   SPC AC 071255

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0755 AM CDT Thu Jul 07 2022

   Valid 071300Z - 081200Z


   Scattered thunderstorms, some severe, will be possible today mainly
   across parts of Montana, and from the lower Missouri Valley into the
   Carolinas. Damaging winds are possible over all areas, with large
   hail also expected over Montana.

   The large-scale pattern in mid/upper levels will continue to feature
   troughing off the West Coast, mean ridging across the south-central
   CONUS and Rockies, and west-northwest to northwest flow across much
   of the Upper Midwest, Great Lakes and Appalachians.  The Rockies
   ridging is expected to amplify through the period, leading to a net
   westward displacement of the main/anchoring 500-mb high across the
   southern Plains and toward NM.  An embedded shortwave trough -- now
   evident in moisture-channel imagery over eastern portions of CO/WY
   and central NM -- should pivot eastward over the central Plains,
   closely following a smaller, MCV-reinforced shortwave trough now
   over north-central/west-central KS.  Downstream, a series of mostly
   low-amplitude/mesoscale perturbations will cross the Ohio Valley and

   At the surface 11Z analysis showed a wavy/quasistationary front from
   a low over the Delmarva Peninsula, across west-central VA, WV,
   southern IN, and northern MO, with a diffuse segment northwestward
   to a low over central SD.  A cold front was drawn from a low over
   west-central KS across the TX Panhandle and northeastern NM.  The
   main foci for convection this period should be boundaries south of
   the front over the eastern outlook area, and north of the front
   across the northern Rockies/northern High Plains regions.

   ...MT and vicinity...
   Isolated to scattered thunderstorms are expected to develop this
   afternoon -- mainly over higher terrain of southern/western MT --
   and move northeastward while offering the potential for sporadic
   severe gusts and large hail.  Any supercells that survive into the
   more-suitable moisture profiles of central/northern MT will be
   capable of significant hail, and depending on storm-scale processes
   and boundary interactions, a marginal/conditional tornado threat.

   Large-scale support will be more nebulous today compared to previous
   days, with net height rises forecast across the region.  Convection
   will be focused largely by heating of elevated terrain,
   preferentially weakening MLCINH sooner compared to lower elevations
   in the northern/eastern areas, and secondarily along boundaries left
   from prior activity.  A drier and more deeply mixed boundary layer
   is expected with southwestward extent (and increasing elevation)
   across MT, away from a low-level moist/theta-e axis extending from
   central SD to north-central/northeastern MT.  This should contribute
   to MLCAPE ranging from around 2000-2500 J/kg near that axis to 1000
   J/kg over southern/western MT near the main, orographically aided
   convective initiation zones.  Forecast soundings also suggest strong
   veering of winds with height, though modest low-level wind speeds
   will keep hodographs and SRH marginal in magnitude.  Some of the
   diurnal activity may aggregate upscale into an evening cluster
   across eastern MT into the western Dakotas, nearer to the moist
   axis, with severe gusts being the main concern until convection
   encounters progressively more-stable boundary layer and stronger
   MLCINH tonight in the Dakotas.

   ...KY/TN to Carolinas...
   Again today, a large swath of the area from the Ohio Valley to
   Southeast will have thunderstorm potential, with the greatest
   concentration likely in and near the "slight"/15%-wind outlook area.
   Multicell clusters and pulse storms will be common and locally
   numerous, offering the threat of damaging gusts, with a few
   severe/50+ kt gusts possible.

   Development should be focused mainly along higher terrain, a surface
   trough east of the mountains, and especially any number of outflow
   boundaries south of the synoptic front -- both from prior convection
   and generated throughout today's event.  Strong surface heating in a
   richly moist air mass (dewpoints commonly in the upper 60s to mid
   70s F), along with a deep troposphere, will offset modest midlevel
   lapse rates enough to yield MLCAPE in the 1500-2500 J/kg (locally
   higher) over much of the outlook area.  Deep-tropospheric flow and
   vertical shear each will be weak, but oriented such that
   southeastward-propagating clusters will be favored.  Potential
   should wane after dark as the boundary layer stabilizes from a
   combination of outflows and nocturnal/diabatic cooling.

   ...Central Plains to mid Mississippi Valley...
   Scattered thunderstorms are possible today over parts of IL as an
   eastward extension of ongoing activity in northeastern MO, as well
   as near a diurnally heated/modified version of the trailing outflow
   boundary across parts of northern MO to eastern KS.  Damaging gusts
   and isolated large hail will be the main concerns, and at least a
   marginal tornado threat may develop with any supercell that can take
   advantage of favorable low-level vorticity/SRH along the boundary.

   In addition to the northern KS MCV, others are evident in
   west-central to central NE and over northeastern KS/southeastern NE.
   Mesoscale enhancements to both large-scale lift aloft, and vertical
   shear, are possible east and south of these features as they move
   eastward today, while the outflow boundary moves/diffuses somewhat
   northward.  Relatively undisturbed, richly moist boundary-layer air
   over the mid Mississippi Valley, central/southern MO and eastern KS
   will be available as inflow to convection developing today, and over
   IL for convection moving in from MO.  By midafternoon, 2500-3500
   J/kg MLCAPE and negligible CINH are expected.  Weak mid/upper flow
   over most areas suggests modes could become clustered and messy, but
   favorable low-level shear may persist along or north of the outflow
   boundary for support of at least transient supercellular
   characteristics.  Overall coverage/intensity should diminish from
   late evening into tonight.

   ..Edwards/Goss.. 07/07/2022



   SPC AC 070559

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Thu Jul 07 2022

   Valid 081200Z - 091200Z


   Isolated to scattered severe thunderstorms may occur Friday across
   parts of the northern Rockies/Plains. Large hail and severe/damaging
   wind gusts should be the main threats.

   ...Northern Rockies/Plains...
   An upper ridge will remain prominent across much of the Southwest,
   Rockies, Plains and central Canada on Friday. Around 35-45 kt of
   mid-level southwesterly flow preceding an upper trough over the West
   Coast is forecast to overspread parts of the northern Rockies and
   adjacent northern Plains of MT through the period. A moist low-level
   airmass will likely be present along/east of a surface trough
   extending across the northern High Plains. At least moderate
   instability should once again develop across much of MT and vicinity
   as daytime heating occurs. Steep mid-level lapse rates should also
   be present over the warm sector.

   Initially high-based convection that forms over the northern Rockies
   Friday afternoon will spread generally east-northeastward across MT
   through Friday night. Deep-layer shear should be strong enough for
   some supercell structures. Both large hail and severe wind gusts may
   occur with this convection. Some upscale growth into one or more
   bowing clusters may also occur Friday evening/night with eastward
   extent into MT as a low-level jet modestly strengthens. Overall
   coverage of thunderstorms becomes more uncertain with eastward
   extent into ND. But, an isolated severe threat should exist owing to
   a favorable thermodynamic and kinematic environment.

   ...Mid Mississippi Valley into the Midwest, Ohio Valley,
   Central/Southern Appalachians, and Southeast...
   Modest enhancement to the mid-level west-northwesterly flow should
   be present Friday from parts of the mid MS Valley/Midwest into the
   OH Valley, central Appalachians, and Carolinas. A moist low-level
   airmass, with dewpoints generally in the low to mid 70s, will likely
   be present across these regions along/south of a weak front. Diurnal
   heating of this airmass should aid the development of moderate to
   locally strong instability by Friday afternoon. The fairly modest
   deep-layer shear should limit updraft organization to some extent.
   Still, some clustering of convection should occur, and multicells
   capable of producing mainly isolated damaging winds should spread
   east-southeastward across these regions through Friday evening.

   Some guidance suggests that an MCV and remnant convection will be
   present across parts of the mid MS Valley at the start of the period
   Friday morning. If it holds together, this activity may pose an
   isolated severe threat through the morning hours as it spreads
   eastward into the Midwest and lower OH Valley. High-resolution
   guidance suggests varying solutions regarding the track/evolution of
   this MCV and related potential for the redevelopment of strong to
   severe thunderstorms across these areas Friday afternoon. Have
   expanded the Marginal Risk to account for this uncertainty, and
   greater severe wind probabilities may be needed if a more focused
   corridor of MCS damaging wind potential becomes apparent.

   ...Central High Plains...
   High-based convection that forms Friday afternoon over parts of the
   central Rockies should spread into the adjacent High Plains by early
   Friday evening. Modest low-level upslope flow should also occur
   through the day. Even with mid-level winds and related deep-layer
   shear remaining modest, weak to moderate instability and steepened
   low-level lapse rates should aid in robust updrafts being maintained
   as convection spreads generally east-southeastward. Isolated severe
   wind gusts and hail may occur with the strongest updrafts.

   Strong mid-level westerly flow associated with an upper trough over
   eastern Canada will be present across ME on Friday. Although
   low-level moisture is forecast to remain fairly limited, modest
   heating and weak instability may develop in a narrow corridor by
   Friday afternoon. A couple of strong to marginally severe
   thunderstorms capable of producing occasional hail/wind may develop
   in this regime.

   ..Gleason.. 07/07/2022



   SPC AC 070729

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0229 AM CDT Thu Jul 07 2022

   Valid 091200Z - 101200Z


   Isolated to scattered severe thunderstorms may occur Saturday into
   Saturday night across parts of the northern Plains.

   ...Northern Plains...
   An upper trough over the Pacific Northwest is forecast to move
   eastward across the northern Rockies/Plains and western Canada on
   Saturday. This trough will act to suppress large-scale upper ridging
   over the northern Plains. Warm low/mid-level temperatures associated
   with a strong cap should tend to suppress convection through much of
   the day. However, some guidance does show robust thunderstorms
   developing across the open warm sector in ND during the day. If this
   convection forms, it would be on the northeastern extent of the cap
   and EML plume emanating from the higher terrain of the
   northern/central Rockies. Additional thunderstorms are expected to
   form Saturday evening/night across MT into ND as ascent associated
   with the upper trough overspreads this region, and as a cold front
   sweeps eastward. Even though details in convective evolution remain
   somewhat unclear, the strong forecast instability and deep-layer
   shear will be more than sufficient for severe thunderstorms posing a
   threat for all hazards through Saturday night.

   Modest west-northwesterly mid-level flow will overspread much of the
   Southeast on Saturday. A weak front is also forecast to sag slowly
   southward across this region through the period. A very moist
   low-level airmass should be in place across the warm sector. Diurnal
   heating will contribute to moderate/strong instability and steepened
   low-level lapse rates by Saturday afternoon. Even though deep-layer
   shear should remain modest, multiple loosely organized clusters
   capable of producing mainly wind damage should spread
   south-southeastward across much of the Southeast through Saturday
   afternoon. A broad Marginal Risk has been included to account for
   the damaging-wind potential, and greater severe probabilities may
   eventually be needed if corridors of greater mesoscale severe
   potential become evident.

   ..Gleason.. 07/07/2022