SPC AC 280545

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1245 AM CDT Thu May 28 2020

   Valid 291200Z - 301200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
   MID-ATLANTIC INTO THE NORTHEAST STATES...

   ...SUMMARY...
   Severe thunderstorms are possible across portions of the northern
   Mid-Atlantic and Northeast States Friday afternoon through Friday
   evening.

   ...OH Valley into the Northern Mid-Atlantic and Northeast...
   A shortwave trough and attendant vorticity maximum are forecast to
   move from the middle OH Valley northeastward into western portions
   of the Northeast states on Friday. Another shortwave will move
   through the Upper Great Lakes, in close proximity to the lead wave.
   By early Saturday morning, these two shortwaves will have merged
   into one coherent shortwave extending from southern Quebec southward
   into the northern Mid-Atlantic.

   Dewpoints in the upper 60s (possibly low 70s) are anticipated from
   the Mid-Atlantic northward into upstate NY, with slightly lower
   values expected across the middle and upper OH Valley. Given this
   low-level moisture, the air mass will destabilize under modest
   heating ahead of the approaching shortwave troughs and associated
   cold front. Lead shortwave trough is expected to induce convective
   initiation throughout the warm sector over the Northeast and
   northern Mid-Atlantic, while the second shortwave trough and
   attendant cold front aid in convective development over the middle
   and upper OH Valley. 

   A predominately multicell mode with numerous line segments is
   anticipated. Vertical shear is strong enough to support storm
   organization, resulting in the potential for damaging wind gusts
   with the more robust line segments. Some isolated hail is also
   possible, particularly with any more discrete storms. The tornado
   threat will depend largely on direction of the surface winds and
   strength of the low-level flow. A more southerly surface-wind
   direction combined with stronger low-level flow will contribute to
   greater low-level shear and higher tornado potential. Highest
   likelihood for these conditions currently exists from central VA
   northward into upstate NY. However, confidence is occurrence is
   currently low, since most of the guidance either lacks southerly
   surface winds or enhanced low-level flow. Consequently, only
   marginal tornado probabilities will be included with this outlook.  

   ...Pacific Northwest...
   A compact upper cyclone is forecast to move northeasterly toward the
   central CA coast from Friday evening/overnight into Saturday
   morning. The progression of this system will result in mid-level 
   moisture advection into the Pacific Northwest, beginning on Friday
   morning. By Friday afternoon, the combination of this mid-level
   moisture and deep boundary-layer mixing could support moderate
   instability across portions of OR. Large-scale forcing for ascent
   will be weak, but convergence and orographic effects on the western
   edge of a deepening surface low could result in isolated
   thunderstorms. Recent guidance has trended towards later storm
   initiation with coverage now expected to be too low to merit any
   severe probabilities.

   ..Mosier.. 05/28/2020

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   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z