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Jul 19, 2017 1730 UTC Day 2 Convective Outlook
Updated: Wed Jul 19 17:30:16 UTC 2017 (Print Version | 20170719 1730Z Day 2 shapefile | 20170719 1730Z Day 2 KML)
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 Forecast Discussion

   SPC AC 191730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Wed Jul 19 2017

   Valid 201200Z - 211200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
   GREAT LAKES INTO PARTS OF PENNSYLVANIA AND NEW YORK...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
   AND CENTRAL HIGH PLAINS INTO THE MIDDLE MISSOURI VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE HIGH
   PLAINS ACROSS THE MIDDLE MISSISSIPPI VALLEY INTO PARTS OF THE
   NORTHEAST STATES...

   ...SUMMARY...
   There is potential for severe storms to spread across the lower
   Great Lakes region and the Northeast on Thursday.  Other severe
   storms are expected to develop in the afternoon over the northern
   High Plains area and spread toward the middle Missouri Valley during
   the night.

   ...Synopsis...
   The stronger westerly flow aloft is forecast to persist across the
   northern states as an upper ridge over the south-central US
   gradually weakens.  Several short wave troughs within the westerlies
   are expected to impact the primary convective potential tomorrow. 
   One trough will be enhanced by Day 1 MCS development over the
   northern Plains and upper Mississippi Valley region, and is expected
   to progress east-southeastward across the lower Great Lakes and
   northeast states during the period.  Farther west, a series of weak
   perturbations are forecast to rotate around the northwest periphery
   of the aforementioned upper ridge and move across the northern
   Plains.  

   At the surface, a cold front will move southeastward across the
   northeastern states and lower Great Lakes region.  This boundary
   will extend westward over parts of Iowa into the central High Plains
   and into eastern Montana.

   ...Lower Great Lakes into parts of Pennsylvania and New York...
   Strong-to-severe storms may be ongoing at the start of the period
   over parts of Lower Michigan and/or northern Indiana in association
   with a long-lived nocturnal MCS.  There is potential for this system
   to progress eastward/east-southeastward across parts of the lower
   Great Lakes during the day, as a very moist and moderately unstable
   air mass will be in place as far east as Ohio.  Over the eastern
   part of the risk in New York and Pennsylvania, the threat area has
   been adjusted southward to align better with projected MCS movement
   and the axis of modest instability.

   The details of the convective evolution are somewhat unclear at this
   time, as new development may occur in advance of the initial MCS. 
   Further, there may be potential for the initial storms to generate
   an outflow boundary along its southern periphery with subsequent
   later development along the boundary and/or cold front during the
   afternoon.  Despite these uncertainties, the overall pattern is
   favorable with a southwesterly low-level jet forecast to shift
   eastward across the lower Great Lakes in tandem with a zone of
   mid-level height falls and coincident 45-55 kt northwest winds,
   resulting in strong low-level convergence and deep-layer shear to
   promote severe weather potential.  The primary threat is expected to
   be damaging wind gusts.

   ...Northern and Central High Plains into the middle Missouri
   Valley...
   A southerly component to the low-level winds over the central and
   northern High Plains will transport moisture northward, with surface
   dew points in the 55-60 F range extending into eastern Montana. 
   Steep lapse rates and strong diabatic heating during the afternoon
   will contribute to destabilization with MLCAPE increasing to
   1000-1500 J/kg.  Widely scattered storms are expected to develop by
   mid-late afternoon over the High Plains as heating and weak ascent
   in advance of mid-level perturbations weaken the cap sufficiently
   for convective initiation.  Veering winds with height and resultant
   30-40 kt deep layer shear will enhance storm organization and
   intensity with isolated supercells possible.  Large hail and
   damaging wind gusts are the most likely hazards.  There is potential
   for activity to grow upscale during the evening with one or more
   MCSs developing in response to a strengthening southerly low-level
   jet over the Plains.  These systems are expected to spread eastward
   during the night with a continuing threat for strong wind gusts and
   possible hail.

   ..Weiss.. 07/19/2017

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z

        
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