SPC AC 271630

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1130 AM CDT Sat Jun 27 2020

   Valid 271630Z - 281200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   FROM PARTS OF THE UPPER OH VALLEY TO THE NORTHERN MID-ATLANTIC
   COAST...AND THIS AFTERNOON INTO EARLY TONIGHT FROM EASTERN CO INTO
   NORTHWESTERN KS...

   ...SUMMARY...
   Scattered damaging winds and a brief tornado are possible across
   parts of the Northeast this afternoon into early evening. Scattered
   large hail and isolated severe winds are possible across a portion
   of southwest to central Montana during the late afternoon and early
   evening. A few severe wind gusts will also be possible this
   afternoon into early tonight from eastern Colorado into northwestern
   Kansas.

   ...Eastern PA to NJ/NYC area early this afternoon...
   A midlevel shortwave trough/remnant MCV will move eastward along the
   NY/PA border to southern New England this afternoon.  At the
   surface, a warm front will move northeastward across eastern PA/NJ
   to southeastern NY and CT.  Low-level moistening and warming will
   occur with warm front passage, resulting in modest destabilization
   from west-to-east from late morning through early afternoon.  There
   will be a short window of opportunity for renewed thunderstorm
   development by about midday from eastern PA into NJ, and storms will
   spread eastward and move offshore later this afternoon.  Though
   buoyancy and midlevel lapse rates will remain rather modest,
   steepening low-level lapse rates and 50-60 kt midlevel flow sampled
   by the VWPs at Binghamton and State College suggest that the
   stronger storms will be capable of producing damaging winds.  An
   isolated tornado will be possible in the zone of warm
   advection/enhanced hodograph curvature shifting eastward from PA
   toward NJ.  Please see MD 1023 for additional information.

   ...OH Valley this afternoon...
   A thunderstorm cluster with a diffuse/embedded MCV, now moving over
   western OH, has weakened some since earlier this morning.  Moisture
   advection from the southwest in advance of the storm cluster, as
   well as some surface heating in cloud breaks, will contribute to
   MLCAPE near 1500 J/kg in advance of the remnant cluster.  Though
   thermodynamic profiles are not particularly favorable for strong
   downdrafts, lingering midlevel flow around 30 kt will result in
   sufficient vertical shear for semi-organized multicell clusters. 
   There are questions regarding re-invigoration of the storms this
   afternoon, but new development will pose a threat for isolated
   damaging gusts across southeastern OH/southwestern PA/northern WV.

   ...MT area this afternoon/evening...
   A midlevel trough is in the process of amplifying over the Pacific
   Northwest, which will lead to backing and strengthening flow aloft
   over the northern Rockies.  Though low-level moisture is rather
   limited, surface heating across southern/central MT will result in
   MLCAPE of 500-1000 J/kg along the baroclinic zone across central MT
   this afternoon.  Scattered thunderstorm development is expected by
   mid-late afternoon over the higher terrain of southwest MT, and
   storms will then spread northeastward into central MT.  Though
   buoyancy will be modest at best, relatively steep low-midlevel lapse
   rate and effective bulk shear near 50 kt will favor a threat for
   high-based supercells capable of producing large hail and damaging
   winds. 

   ...Eastern CO into KS/NE this afternoon into tonight...
   A few thunderstorms are expected this afternoon across eastern CO,
   along a weak lee trough and downstream from a diffuse midlevel
   trough now over northwest CO.  More isolated storms may also form
   this afternoon/evening along a diffuse warm front across north
   central NE and vicinity.  Convection that forms in CO will spread
   eastward toward KS and continue along the diffuse front shifting
   slowly northward from southern KS.  A few severe gusts will be
   possible with this convection in the steep low-midlevel lapse rate
   environment, with sufficient deep-layer shear to maintain some
   organized clusters, and added ascent tonight with a developing
   low-level jet.  Isolated large hail may also occur with the
   strongest storms.

   ...Mid MS Valley this afternoon into tonight...
   An overnight MCS is dissipating over MO as of 16z, with a diffuse
   outflow-reinforced front extending westward across southern KS. 
   Downstream from the MCS remnants and an MCV over northern MO,
   scattered thunderstorms will likely continue through the afternoon
   across IL and IN.  These storms will likely remain somewhat
   disorganized multicell clusters, with an attendant threat for
   isolated strong/damaging gusts and marginally severe hail.

   ...LA/MS/AL area this afternoon...
   Regional 12z soundings showed poor lapse rates near 500 mb within
   the mid-high cloud plume, but a shallow layer of steeper lapse rates
   below.  There will be some cloud breaks developing through the
   afternoon as a diffuse midlevel trough drifts eastward over the MS
   Valley.  Within the cloud breaks, widely scattered thunderstorm
   development is possible as the maritime tropical air mass spreads
   north-northeastward from the Gulf coast.  MLCAPE near 3000 J/kg and
   DCAPE in excess of 1000 J/kg will support a threat for isolated wet
   microbursts.

   ..Thompson/Nauslar.. 06/27/2020

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z