Day 2 Severe Weather Outlook

USA Weather — Severe Weather Division

This outlook is expired and is no longer valid.

Issued
14:04Z Wed, Jul 20
Valid
12Z Thu, Jul 21 - 12Z Fri, Jul 22
Forecaster
Wyatt Huber

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR MUCH OF VERMONT...NEW HAMPSHIRE...AND MAINE...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN VIRGINIA...THROUGH THE CAROLINAS...ACROSS THE DEEP SOUTH...AND INTO NORTHEASTERN TEXAS...

...SUMMARY...

NUMEROUS DAMAGING WIND GUSTS ARE EXPECTED FROM A PRE-FRONTAL SQUALL LINE ACROSS THE NORTHEASTERN US. A COUPLE OF TORNADOES WILL ALSO BE POSSIBLE IN THIS REGION AS WELL. ACROSS THE SOUTHEAST...NUMEROUS MULTICELL CLUSTERS AND A FEW MCS STRUCTURES WILL PRODUCE SWATHS OF DAMAGING WINDS. A BRIEF TORNADO IS ALSO POSSIBLE IN THIS REGION.

...SYNOPSIS...

A STRONG MID/UPPER TROUGH LOCATED OVER THE GREAT LAKES AT THE START OF THE D2 PERIOD WILL PIVOT NORTHEASTWARD THROUGH THE PERIOD. L/W TROUGHING EXTENDS WELL SOUTH OF THE LOW INTO THE DEEP SOUTH. ADDITIONAL SHORTWAVE TROUGHING PIVIOTS NORTHEWASTWARD THROUGH THE PERIOD. THE L/W TROUGH WEAKENS ON THE SOUTHERN END DURING THE LATTER PORTIONS OF THE PERIOD.

AT THE SURFACE, A STRONG CYCLONE LOCATED SOUTH OF JAMES BAY WILL MOVE NORTHEASTWARD WITH TIME. A COLD FRONT SWEEPS EASTWARD ACROSS THE NORTHEAST, AND STALLS OVER THE DEEP SOUTH AS A SECOND SYSTEM APPROACHES FROM THE WEST.

...NORTHEAST...

ONGOING CONVECTION WILL EXIT NORTHERN MAIN EARLY ON IN THE PERIOD. LARGE CLOUD BREAKS WILL ALLOW FOR STRONG SURFACE HEATING AND DESTABALIZATION OF SBCAPE VALUES TO 2000 J/kg OR HIGHER. AS THE CAPPING INVERSION BREAKS, THUNDERSTORM INITIATION ALONG THE COLD FRONT SHOULD TAKE PLACE BY LATE MORNING. QUICK UPSCALE GROWTH IS ANTICIPATED, AND A WELL-DEVELOPED QLCS SHOULD DEVELOP ALONG THE COLD FRONT.

BULK SHEAR OF 45-50 KNOTS AND A LLJ OF 35-45 KNOTS WILL BE LOCATED OVER THIS AREA. WITH SHEAR OF THIS MAGNITUDE AND THE POTENTIAL FOR A REAR INFLOW JET, AT LEAST A FEW BOWING SEGMENTS EMBEDDED WITHIN THE QLCS IS LIKELY, AND THESE SEGMENTS WILL POSE AN ENHANCED THREAT FOR NUMEROUS DAMAGING WIND GUSTS, AND PERHAPS A SIGNIFICANT GUST OR TWO (75MPH+). WITH THIS IN MIND, AN ENHANCED RISK IS INTRODUCED FOR THE REGION WHERE THE HIGHEST WIND THREAT EXISTS. 

IN ADDITION TO THE WIND THREAT, A FEW EMBEDDED CIRCULATIONS CAPABLE OF QLCS TORNADOES ARE LIKELY. SOUNDINGS REVEAL LOW-LEVEL CURVING OF HODOGRAPHS RENDERING 1KM SRH OF 115-150 m2/s-2 AND LOCALLY HIGHER. THIS SUPPORTS A MARGINAL TORNADO THREAT AT THIS TIME.

...SOUTHEAST...

A STALLING COLD FRONT FROM THE CAROLINAS INTO THE DEEP SOUTH AND INTO NORTHEASTERN TEXAS. AHEAD OF THE FRONT, INTENSE SURFACE HEATING WITH TEMPERATURES IN THE MID 90S TO NEAR 110 IS EXPECTED. SBCAPE OF 3000-5000 J/kg AND MODEST SHEAR OF 25-35 KNOTS IS EXPECTED. SOUTHWARD-MOVING MULTICELL CLUSTERS WILL POTENTIALLY EVOLVE INTO SEVERAL SMALLER MCS STRUCTURES OR ONE LARGE QLCS STRUCTURE. THIS WILL POSE A THREAT FOR SWATHS OF DAMAGING OUTFLOW/DOWNBURST WINDS.

AT THIS TIME, HRRR MODEL INDICATES THAT MULTCELL CLUSTERS AND A FEW SMALL MCS STRUCTURES WILL OCURR, AND THIS WOULD ALLOW FOR A MORE SCATTERED THREAT FOR DAMAGING WINDS. HOWEVER, NAM-NEST MODEL INDICATED THAT THERE COULD BE SOME POTENTIAL FOR A LARGER QLCS STRUCTURE TO DEVELOP. GIVEN THE UNDERTAINTY, A SLIGHT RISK IS MAINTAINED AT THIS TIME. HOWEVER, AN ENHANCED WIND RISK MAY BE REQUIRED IF UPTRENDS OCURR. 

IN ADDITION TO WIND RISK, A SMALL EMBEDDED TORNADO THREAT CANNOT BE RULED OUT WHERE FAVORABLE BOUNDARY INTERACTIONS MAY ENHANCE LOW-LEVEL SRH TO 150 m2/s-2