Jun 22, 2017 1300 UTC Day 1 Convective Outlook
Updated: Thu Jun 22 12:59:12 UTC 2017 (20170622 1300Z Day 1 shapefile | 20170622 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170622 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 301,389 31,582,935 Chicago, IL...Milwaukee, WI...Denver, CO...New Orleans, LA...Aurora, CO...
MARGINAL 446,348 41,036,693 Detroit, MI...Memphis, TN...Nashville, TN...Kansas City, MO...Cleveland, OH...
Probabilistic Tornado Graphic
20170622 1300 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 118,204 9,671,758 New Orleans, LA...Birmingham, AL...Baton Rouge, LA...Montgomery, AL...Mobile, AL...
2 % 115,073 11,314,961 Memphis, TN...Nashville, TN...Huntsville, AL...Chattanooga, TN...Clarksville, TN...
Probabilistic Damaging Wind Graphic
20170622 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 183,157 21,721,729 Chicago, IL...Milwaukee, WI...Denver, CO...Aurora, CO...Madison, WI...
5 % 528,851 49,191,125 Detroit, MI...Memphis, TN...Nashville, TN...Kansas City, MO...New Orleans, LA...
Probabilistic Large Hail Graphic
20170622 1300 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 176,383 21,027,630 Chicago, IL...Milwaukee, WI...Denver, CO...Aurora, CO...Madison, WI...
5 % 305,540 26,441,680 Detroit, MI...Cleveland, OH...Omaha, NE...Toledo, OH...Buffalo, NY...
   SPC AC 221259

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0759 AM CDT Thu Jun 22 2017

   Valid 221300Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
   MISSISSIPPI DELTA...TENNESSEE VALLEY AND CENTRAL GULF COAST
   REGIONS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
   CENTRAL AND SOUTHERN HIGH PLAINS AND COLORADO FRONT RANGE...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA
   TO PARTS OF LOWER MICHIGAN...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK IN THE SOUTH...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING AND
   CONNECTING THE OTHER TWO SLIGHT RISKS...

   ...SUMMARY...
   A few tornadoes and isolated damaging gusts are possible over a
   broad area east and northeast of the center of inland Tropical Storm
   Cindy.  Elsewhere, severe thunderstorms with damaging winds and
   large hail are possible from the south-central High Plains to
   portions of the Great Lakes.

   ...Synopsis...
   The mid/upper-level pattern will remain dominated by three primary
   synoptic to mesoalpha-scale features:
   1.  TC Cindy and its accompanying upper-air perturbation;
   2.  An intense ridge that will remain entrenched over the
   southwestern U.S.;
   3.  A belt of relatively fast northern-stream flow from the Pacific
   Northwest across the Northern Plains and Great Lakes, to New
   England.  The northern Plains and Upper Midwest segment of this
   pattern will become more cyclonic with time, as a cyclone now over
   MB and trailing positively-tilted trough move southeastward.  By
   00Z, the trough should extend from the southern section of MB/ON
   border across ND to southwestern MT.  By 12Z the mid/upper trough
   should reach the MN Arrowhead and extend to southwestern MN then
   westward over SD.

   At the surface, the 11Z analysis showed a weak frontal-wave low over
   north-central NE, with a cold front southwestward across
   southwestern NE and south-central CO.  The frontal zone extended
   from the low across southern NM -- north of an area of convective
   outflow with a southern boundary arching across northeastern IA. 
   The front then was analyzed over central lower MI and Lake Erie. 
   That boundary will sag southward as a cold front today across WI, IA
   and eastern NE, as well as the south-central High Plains, as the
   northern-stream trough moves southeastward.  By 00Z the front should
   extend from northern lower MI to central IA,
   northwestern/west-central KS and northeastern NM.  By the end of the
   period, the front should extend from southern lower MI across
   southwestern MO, southwestern OK and east-central NM.

   ...Southern States:  Tropical Storm Cindy...
   T.S. Cindy is forecast to progress farther inland/northeastward
   through the period toward an eventual merger with the aforementioned
   frontal zone day-2, experiencing a general weakening of surface
   winds and filling of central pressure, as forecast by NHC.  However,
   as often is the case with inland-penetrating tropical and
   subtropical systems, low-level flow above the surface will be slower
   to weaken.  This will lead to maintenance (and perhaps areas of
   mesobeta-scale strengthening) of low-level shear/hodographs in the
   favorable northeastern and eastern sector through the day.  In
   addition, this system's dramatically asymmetric structure will
   continue to spread a rather large area of at least marginally
   favorable shear across the South.

   Last night's 00Z 500-mb analysis showed several pockets of
   distinctive, relatively warm and cold (and dry and moist) air
   wrapping into this system, revealing complex internal baroclinic
   influences revolving around the circulation that will contribute to
   moving swaths of relative clearing today.  With low/middle-level
   lapse rates nearly moist adiabatic, only a few deg F of surface
   heating will be needed to boost the magnitude and depth of buoyancy
   such that MLCAPE 200-500 J/kg should be fairly common, with patches
   of 500-1000 J/kg values this afternoon, amidst effective SRH 200-600
   J/kg.  Any sustained discrete or semi-discrete cells moving through
   such a favorable environment will pose a tornado risk, though
   coverage of those may be isolated overall.  Also, differential-
   heating boundaries and convergence bands will be corridors to
   monitor for more localized augmentation of tornado potential within
   this broad-brushed outlook area.  The tornado potential should peak
   mid-late afternoon and generally ramp down overnight (but not go
   away altogether), amidst weaker boundary-layer instability, lower
   convective coverage, and more nebulous foci.

   Isolated damaging/nontornadic wind gusts also are possible from the
   deeper cells even well away from center, especially where areas of
   diabatic heating create shallow but well-mixed subcloud layers that
   augment downward momentum transfer out of the layer of faster winds
   just above surface.  For near-term coverage of tornado potential,
   see SPC watch 363 and related mesoscale discussions.  For forecast
   of Cindy's path/intensity and tropical-related watches/warnings,
   refer to NHC advisories.

   ...Central/southern High Plains, CO Front Range...
   Widely scattered thunderstorms are expected to develop near the
   front this afternoon, in an environment characterized by a hot and
   well-mixed warm-sector boundary layer supporting potential for large
   hail and damaging gusts generated aloft to reach the surface. 
   Concerns exist over storm coverage, and some areas of this outlook
   may not experience any.  The threat itself is probably more locally
   clustered than the outlook area indicates; however it is too soon to
   narrow that down until mesoscale destabilization/lift trends near
   the frontal zone become more readily apparent.  Though low-level
   winds will be weak, strong directional shear will contribute to
   30-40 kt effective-shear magnitudes amidst MLCAPE 1000-1500 J/kg,
   supporting a few clusters of organized and probably outflow-dominant
   convection.

   Post-frontal flow is expected to veer to a substantially easterly
   component by this afternoon, setting up an upslope regime into the
   Front Range region, beneath difluent northwest flow aloft.  This
   will contribute to moist advection, increasing deep speed/bulk
   shear, and favorable storm-relative low-level wind vectors for
   supercells moving either leftward or rightward off a long, nearly
   straight hodograph.  Large hail and isolated damaging gusts each
   will be possible, given the deep/well-mixed subcloud layers likely
   with 40s F surface dew points.  A conditional threat for isolated
   significant/2+ inch hail may develop in the I-25/I-76/I-70 areas
   near and downshear from the DEN/FCL corridor, though uncertainties
   remain related to both optimal cloud-water content and maintenance
   of discrete storm modes most suitable for it.  Mesoscale trends will
   be monitored for enough coverage of this threat to introduce an
   unconditional significant-hail area in a later outlook.  Convection
   will offer some wind/hail threat eastward across the High Plains of
   eastern CO before diminishing.

   ...Portions of the Corn Belt to Great Lakes...
   Multiple episodes of scattered thunderstorms are possible through
   the period, with the greatest cumulative concentration expected
   across the 15% wind/hail corridor representing the categorical
   slight risk.  This includes ongoing convection that will move
   eastward from northern IA across at least parts of southern WI and
   perhaps northern IL, offering a threat for sporadic large hail. 
   Additional thunderstorms currently north of the surface low and
   frontal zone across central/eastern SD, as well as in southern MN
   near the front and north of the outflow boundary, will pose a
   marginal risk of isolated large hail as well as damaging gusts in
   the next few hours,  The SD/MN activity, based on modifications to
   the OAX sounding and RAP forecast soundings, resides in an
   environment of steep midlevel lapse rates and elevated moistening,
   atop a dry layer between 750-900 mb that may support evaporative
   downdraft-parcel accelerations through the near-surface stable
   layer.

   Additionally, surface-based thunderstorms are expected to develop
   this afternoon along the front and outflow boundary, as well as in a
   low-level warm advection/convergence zone farther east across parts
   of Lake Michigan and Lower MI.  This activity should occur mainly
   south of the southern rim of optimally favorable mid/upper level
   flow.  Still, sufficient deep shear will exist for organized
   multicellular convection or transient/marginal supercells, with hail
   and damaging gusts possible.  Diabatic surface heating and dew
   points 60s F should contribute to MLCAPE 1500-2500 J/kg amidst 30-40
   kt effective-shear magnitudes.

   ..Edwards/Picca.. 06/22/2017

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