The SPC is forecasting ...Severe thunderstorms expected over parts of the northeast US this afternoon....   Please read the latest public statement about this event.  View What is a Watch? clip.

   SPC AC 151959

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0259 PM CDT Tue May 15 2018

   Valid 152000Z - 161200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR NORTHEAST
   PA...NORTHERN NJ...SOUTHEASTERN NY...WESTERN/CENTRAL CT...AND
   SOUTHWESTERN MA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN PLAINS...

   ...SUMMARY...
   Widespread damaging winds, a couple tornadoes, and isolated large
   hail are expected to continue across parts of the Northeast States
   this afternoon into early evening.

   ...Northeast...
   Only significant change to the categorical outlook is the removal of
   areas behind the maturing convective system. 10% tornado
   probabilities have been removed with this update as well. While some
   potential remains in locally backed flow across southeast NY and
   CT/MA, convective mode appears to be trending towards linear
   segments both ahead of and within the main line. Furthermore, with
   any initially discrete development, thermodynamic profiles have
   supported intense, high-precipitation cores, characterized by
   considerable hail and strong outflow. Without a concurrent increase
   in low-level flow strength / helicity, persistent focusing of
   low-level vorticity will be difficult to achieve. Nonetheless, a
   couple embedded tornadoes remain possible. Additionally, while some
   sig-hail potential remains, have opted not to include a sig area (as
   well as remove 30% hail probabilities) due to the aforementioned
   mode evolution. Regardless, swaths of damaging winds will progress
   eastward into the evening hours, and the moderate risk is maintained
   with this update.

   ...Southern/Central Plains...
   Expanded the slight risk eastward in north Texas to account for a
   southward-progressing outflow boundary currently near the Red River.
   As it encounters a moderate/strongly unstable and uncapped
   environment, localized upscale growth into a southward-propagating
   cluster will potentially yield a damaging wind threat. Farther
   northeast, a robust, forward-propagating cluster has maintained
   severe intensity this afternoon over southern Oklahoma and severe
   winds/hail are still possible as it approaches the Red River.
   However, it should eventually weaken as it enters a more stable
   environment over northeast Texas.

   ..Picca.. 05/15/2018

   .PREV DISCUSSION... /ISSUED 1113 AM CDT Tue May 15 2018/

   ...Northeast States...
   Convective evolution will be tied to an MCV and small convective
   cluster currently ongoing near the OH/PA border. Robust diabatic
   heating is underway ahead of this feature with trailing outflow from
   a lead convective cluster currently crossing the Hudson Valley. 12Z
   Pittsburgh sounding sampled a favorable environment for
   destabilization with an EML yielding steep mid-level lapse rates.
   Warm-sector buoyancy of 1000-2000 J/kg will become common by peak
   heating. This sounding also sampled the southern periphery of strong
   700-500 mb winds. As the OH/PA cluster evolves east and becomes
   surface-based, convection will organize into a fast-moving QLCS with
   embedded bowing structures given the strong mid-level westerlies
   nearly orthogonal to the line. Widespread strong to scattered severe
   wind gusts appear likely which may yield a derecho, and thus
   damaging wind coverage probabilities have been increased this
   outlook. A few cells should form ahead of the developing QLCS, most
   likely across parts of southern NY/Hudson Valley vicinity into
   western New England. Supercell wind profiles will support a tornado
   and large hail risk maximized across this region, with this activity
   becoming absorbed within the broader QLCS. The severe threat will
   quickly wane near the Atlantic Coast once the QLCS impinges on the
   stable marine layer.

   ...Southern High Plains...
   Have introduced a SLGT risk for severe hail and wind across the
   region. Two areas of focus for convective development are
   anticipated. One near the dryline/remnant outflow intersection over
   the TX South Plains and the other in the low-level upslope flow
   regime over the Raton Mesa. A belt of enhanced mid-level westerlies
   will yield 30-40 kt effective shear for late afternoon to early
   evening supercells with large hail and isolated downburst winds the
   primary initial threat. Most CAMs suggest an MCS will emanate out of
   the Raton Mesa activity this evening and spread east-southeast
   across the Panhandles into western OK tonight, supported by a
   moderate LLJ over west TX. Abundant convective overturning over the
   lower plains yesterday into this morning should mitigate the overall
   threat with eastern extent overnight.

   ...Midwest...
   A couple multicell clusters may develop east of an MCV over IL with
   decent diabatic heating expected across parts of IN/OH. The
   combination of deep-layer shear and MLCAPE appears modest, so will
   maintain MRGL risk probabilities for wind and hail.

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