SPC AC 131958

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0258 PM CDT Sun Jun 13 2021

   Valid 132000Z - 141200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MID-ATLANTIC...CENTRAL GULF COAST...AND CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Scattered damaging winds will remain possible through about dusk
   across the central Appalachians and the Deep South to central Gulf
   Coast region. Scattered severe wind and hail are possible across the
   central High Plains, mainly this evening.

   ...20Z Update...
   The Slight Risk across parts of the lower MS Valley/Southeast has
   been expanded into more of MS and western AL to account for a
   loosely organized cluster of storms ongoing along the MS/AL border.
   The very moist and strongly unstable airmass exists across this
   region, and severe/damaging winds will likely remain the primary
   threat this afternoon. See Mesoscale Discussion 950 and Severe
   Thunderstorm Watch 265 for more information on the near-term severe
   threat across this region.

   Scattered storms have developed this afternoon across the OH Valley
   and WV to the east of a weak cold front. Moderate instability and
   marginal deep-layer shear should continue to support mainly
   multicells capable of damaging wind gusts and marginally severe
   hail. The Slight Risk has been trimmed from parts of western MD, the
   eastern WV Panhandle, and south-central PA where stabilization from
   prior convection has occurred. See Mesoscale Discussions 951/953 and
   Severe Thunderstorm Watches 264/266 for more information.

   It still appears that robust convective development along the
   Laramie Range in WY and Black Hills in western SD may occur within
   the next few hours. Although deep-layer shear is modest owing to the
   influence of an upper ridge, moderate to strong instability and
   steep mid-level lapse rates should support an isolated hail threat
   with any storms that can form. See Mesoscale Discussion 952 for
   additional meteorological details.

   Considerable uncertainty remains regarding convective evolution and
   coverage across OK and northwest TX this afternoon and evening in
   association with a pronounced MCV evident on visible satellite
   imagery. Any storms that form and can persist will be capable of
   producing isolated large hail and strong/gusty winds. Minor
   adjustments to the Marginal Risk have been made based on the current
   placement of the MCV and observational trends.

   No changes have be made to the Marginal Risk areas across parts of
   the Upper Midwest and Pacific Northwest.

   ..Gleason.. 06/13/2021

   .PREV DISCUSSION... /ISSUED 1112 AM CDT Sun Jun 13 2021/

   ...Central Appalachians...
   Convection associated with a leading mid-level impulse is ongoing
   near the MD/WV/VA border region along the periphery of weak
   buoyancy. Additional scattered convection should develop in its wake
   shortly along a weak surface front from the lee of Lake Erie
   southwest to southern OH. Despite weak mid-level lapse rates, robust
   boundary-layer heating amid upper 60s to low 70s dew points will
   support moderate buoyancy with MLCAPE of 1500-2500 J/kg across the
   OH Valley. Within a belt of 25-35 kt mid-level northwesterlies, a
   few organized multicell clusters and low-end supercells will pose a
   primary threat of damaging wind, along with isolated marginally
   severe hail through about dusk.

   ...Central High Plains...
   Low-level moisture characterized by a plume of low 60s surface dew
   points is spreading north on the western periphery of a surface
   high. Intense boundary-layer heating beneath steep mid-level lapse
   rates will result in MLCAPE of 2000-3000 J/kg by late afternoon as
   thermodynamic profiles become deeply mixed. Thunderstorm initiation
   is most likely near the higher terrain in southeast WY and the NE
   Panhandle along a quasi-stationary front despite small mid-level
   height rises associated with the high centered over western NM.
   Storms will probably coalesce through outflow interactions, with the
   potential for a cluster to form and develop south-southeastward into
   the low-level inflow and moisture/buoyancy corridor through at least
   midnight. Vertical shear will be on the lower margins for supercells
   initially, with some potential for splitting cells producing large
   hail. Thereafter, severe winds will become the main threat given the
   expected cluster storm mode in an environment with strong downdraft
   potential. 

   ...TN Valley to central Gulf Coast...
   12Z area soundings sampled a plume of probable large MLCAPE in
   excess of 3000 J/kg should develop as further boundary-layer heating
   occurs amid very rich low-level moisture characterized by 70s dew
   points. Scattered thunderstorms are expected from the TN Valley
   south-southwest towards the central Gulf Coast. Within a belt of
   confluent 20-25 kt mid-level northerlies, multiple loosely-organized
   multicells clusters are expected with occasional wet microbursts
   producing scattered wind damage. See MCD 0943 for additional
   short-term forecast information.

   ...WI...
   A shortwave trough over northwest ON this morning will dig southeast
   and amplify through tonight across the Great Lakes, in response to
   upstream height rises over the northern High Plains.  The trough
   will be accompanied by a strong northwesterly mid-level jet which
   will yield a highly elongated hodograph as 0-6 km bulk shear
   increases to 60-70 kt this evening. The primary concern is the lack
   of low-level moisture return after a prior frontal intrusion. With
   only meager buoyancy, an inverted-v thermodynamic profile should
   support a few high-based/lower-topped cells capable of isolated
   damaging winds and marginally severe hail from late afternoon
   through about dusk.

   ...Interior OR/WA...
   Embedded speed maxima will eject north-northeast over western OR/WA
   on the eastern periphery of a midlevel trough offshore. On the east
   edge of the more persistent rain/clouds along a baroclinic zone,
   meager buoyancy from parcels rooted near 700 mb is expected along
   and east of the crest of the Cascades amid modest mid-level lapse
   rates. Strong speed shear from the boundary-layer to mid-levels will
   support a few fast-moving cells with isolated severe gusts and small
   to marginally severe hail as the main hazards.

   ...Southwest OK and northwest TX...
   An MCV drifting across southwest OK may be the focus for
   intensifying thunderstorm development this afternoon. Guidance
   differs greatly with the degree of development, but the westward
   advection of rich boundary-layer moisture from the I-35 corridor
   should be adequate to overcome MLCIN by late afternoon. A couple of
   multicell clusters could develop into this evening with a risk for
   at least isolated severe wind and hail.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z