SPC AC 042044

   Day 1 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   0344 PM CDT Fri May 04 2018

   Valid 042000Z - 051200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM WESTERN NY
   INTO THE ADIRONDACKS...

   CORRECTED FOR ERRORS IN CATEGORICAL GRAPHIC

   ...SUMMARY...
   Severe thunderstorms are expected today east of the lower Great
   Lakes into the upper Ohio Valley and western portions of New
   England.  This includes a threat for widespread damaging winds, as
   well as tornadoes across parts of New York and Vermont.

   ...NY/PA into New England...
   Progressive, compact shortwave trough continues to move quickly
   towards the Lower Great Lakes. Strong forcing for ascent along the
   leading edge of this system has resulted in banded thunderstorm
   development across Lower MI and adjacent portions of the Upper OH
   Valley. Numerous severe gusts (i.e. greater than 50 kt) were
   measured around the DTX as this line moved through. This convection
   has weakened somewhat as it moves across the cool water of Lake Erie
   but it is expected to re-intensify quickly once it moves into the
   steep low-level lapse rate environment over western NY and the
   Finger Lakes region. Additionally, storm coverage has increased
   south of Lake Erie across northern OH, with this activity expected
   to pose a downstream wind damage threat. 

   Given current storm and environmental trends, a swath of significant
   wind gusts looks probable from BUF to BTV where very strong winds
   (60 to 70 kt) will exist just above the surface (i.e. 500m to 1 km
   AGL) over the next few hours. Recent BUF VAD sampled the leading
   edge of this stronger flow, measuring 50 kt around 750m. Expectation
   is for these winds to mix down as the convective line moves through.
   As a result, 45% wind probabilities were delineated across the
   region where the best overlap of convective coverage, steep
   low-level lapse rates, and instability exists. This result in an
   upgrade to Moderate Risk from western NY northeastward into the
   Adirondacks.

   As discussed in the previous outlook (appended below),
   isolated/discrete cells are still possible over northeast NY as
   favorable kinematics align with sufficient instability. Tornado
   Watch 76 was recent issued to cover this threat. More short-term
   details can be found in MCD 350.

   ...South TX...
   Northeastern extent of the 5% wind probabilities across the region
   was trimmed based on ongoing precipitation.  Very moist and
   moderately unstable environment over the remainder of the region
   still supports the potential for a few damaging wind gusts.

   ..Mosier.. 05/04/2018

   .PREV DISCUSSION... /ISSUED 1112 AM CDT Fri May 04 2018/

   ...NY/PA into New England...
   Morning water vapor loop shows a very strong, compact, and
   progressive shortwave trough moving eastward across MI.  This
   feature will track rapidly eastward across NY/PA this afternoon. 
   Impressive mid-level height falls will occur across this region this
   afternoon and evening, promoting thunderstorm development along and
   ahead of the approaching cold front.  Wind fields will rapidly
   strengthen through the day, indicating the potential for a rather
   widespread damaging wind event, including a few tornadoes across the
   ENH risk area.  This threat appears to be in two distinct waves.

   The first area of risk today will be as isolated/discrete cells form
   this afternoon in vicinity of the surface warm front over northeast
   NY near the US/Canadian border, and with less confidence farther
   south across eastern NY/ and much of VT/NH.  Forecast soundings show
   only marginally favorable thermodynamic parameters.  However,
   low-level winds will be very strong with large, looping hodographs. 
   If convection can remain discrete for awhile, an enhanced tornado
   threat will develop in this area.  These storms will track eastward
   into western ME before weakening this evening.

   Farther west, 12z model solutions are consistent in the development
   of a fast moving squall line along the front that will race across
   the ENH area this afternoon and evening.  Given the intense wind
   fields (50-60 knots just above the surface), widespread damaging
   winds are possible including significant wind damage.  If the squall
   line can attain sufficient mesoscale organization, the environment
   also supports QLCS tornadoes.  These storms will affect much of NY
   and parts of northern PA before sweeping into VT/NH and parts of
   western ME/MA this evening.  Marginal thermodynamic parameters are
   the primary mitigating factor for a categorical upgrade.

   ...TX...
   A long-lived thunderstorm complex over central TX will likely
   persist through the afternoon, sagging southeastward.  Strong
   heating ahead of the leading edge of storms will promote isolated
   strong cells capable of gusty winds.  At this time, it appears
   unlikely that a more organized severe risk will develop.  Therefore
   will maintain only MRGL risk.

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