SPC AC 151947

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0247 PM CDT Fri May 15 2020

   Valid 152000Z - 161200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM NEW YORK
   INTO NEW ENGLAND...AND ACROSS MUCH OF CENTRAL AND NORTHWEST
   TEXAS...AND FAR SOUTHWEST OKLAHOMA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE SOUTHERN
   PLAINS...CENTRAL PLAINS...AND NORTHEAST...

   ...SUMMARY...
   Scattered damaging winds, severe hail, and a couple tornadoes are
   probable across parts of New York into western New England this
   afternoon through early evening. Scattered to numerous severe wind
   gusts, along with scattered large hail, are possible across southern
   Oklahoma into western and central parts of Texas.

   ...Southern Plains...
   A complex situation continues to evolve across OK and TX, mainly in
   a weak-shear environment characterized by large CAPE. The primary
   storm mode across the entire region will continue to be linear, with
   one or more MCSs producing mainly damaging wind. One such MCS over
   OK continues to backbuild westward into greater instability, and a
   gradual uptick in intensity is likely. Other storms will rapidly
   form over west/northwest TX along dryline. A few storms may produce
   large hail, perhaps approaching 2.00" in this area prior to becoming
   linear mode. For more information, see mesoscale discussions 598 and
   600.

   Elsewhere, isolated hail or wind is possible over the TX Panhandle
   where strong heating continues. The air mass north of I-40, within
   the surface easterlies, remains moist and shear is marginally
   favorable for an isolated severe storm, either forming on retreating
   outflow out of OK, or with storms moving southeast out of northeast
   NM later today.

   ...Northeast...
   No change to the outlook in this region. Storms are rapidly
   increasingly along the cold front this afternoon from western NY
   into northwest PA, where destabilization continues. Backing 850 mb
   winds will further enhance low-level shear, with damaging wind,
   hail, and a couple tornadoes possible. See mesoscale discussion 599
   for detailed information.

   ..Jewell.. 05/15/2020

   .PREV DISCUSSION... /ISSUED 1129 AM CDT Fri May 15 2020/

   ...Northeast States through Ohio Valley...

   As of mid day a warm front was situated from southern New England
   northwestward through northeastern NY. A cold front extends from a
   weak surface low over the Great Lakes, southwest through IL. A
   progressive MCV was indicated over IN with another such feature
   located across southeastern lower MI. A more substantial shortwave
   though moving through the Great Lakes will approach the northeast
   states late this afternoon and early evening. The warm sector
   continues to slowly destabilize from the OH Valley into the
   northeast U.S. with dewpoints in the upper 50s to around 60 F and
   diabatic warming of the surface layer likely to result in 500-1000
   J/kg MLCAPE by mid afternoon. Storms are expected to develop and
   intensify in pre-frontal warm sector by mid afternoon from NY and
   southern New England and southwest into the OH Valley. Vertical
   shear profiles will increase, especially over the northeast U.S.
   with the approach of the northern-stream shortwave trough, becoming
   supportive of a few supercells capable of damaging wind, large hail
   and a couple of tornadoes. Farther southwest across the OH Valley,
   the primary threat is expected to be damaging wind as storms congeal
   into lines as they advance east.

   ...Southern Plains...

   A couple of strong to severe storms persist along convective outflow
   across eastern OK. A deep frontal surge is in the process of merging
   with this boundary and might support continued development of storms
   into southeast OK next couple hours with isolated damaging wind the
   main threat. South of a cold front currently situated from northern
   OK southwestward into the TX Panhandle, a strongly to extremely
   unstable air mass is evolving with MLCAPE from 3000-4500 J/kg amid
   very steep 700-500 mb lapse rates of 8-9 C/km. MLCIN will become
   negligible along the dryline in west TX and scattered thunderstorms
   will develop during the late afternoon along it to the intersection
   with the composite front, aided by a difluent upper-level pattern
   with approach of a weak southern-stream shortwave trough. Compared
   to a typical mid-May severe setup, deep-layer shear will be marginal
   outside of the dryline/front intersection and along the Rio Grande
   Valley. As such, outflow-dominated convection is expected with
   several consolidating cold pools this evening. Consensus of CAMs
   suggest convection on the front should sag south, merging with cold
   pools emanating east from the dryline and higher terrain of
   Coahuila. This should yield widespread convective overturning this
   evening through tonight with multiple large MCSs possible as a
   moderate southerly low-level jet develops across south TX. While
   deep-layer shear will be modest, potential exists for several swaths
   of severe wind gusts into central TX given the supportive
   thermodynamic setup for robust cold pools. 

   ...Central High Plains...

   A zone of low-level convergence is expected to remain oriented
   north-south across eastern CO into the NE Panhandle. While low-level
   moisture is not particularly high across the central High Plains,
   adequate PW should be in place for robust convection along this
   boundary ahead of a shortwave trough over the northern Rockies.
   Around 40-kt effective shear suggests a few supercells should form
   before convection evolves into an eastward-moving cluster that
   outruns the instability axis this evening.

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