Day 1 Severe Weather Outlook

Valid 041300Z – 051200Z


Scattered damaging winds and a couple tornadoes are possible through
about 8 PM EDT across parts of the Mid-Atlantic States and New
England. A few tornadoes may occur along the coast of South
Carolina, mainly tonight through early morning Thursday.

…Mid-Atlantic States and New England…
A shortwave trough from southwest QC to the Lower Great Lakes will
progress east with trailing portion shifting across New England this
evening. Attendant surface cold front will reach the Champlain and
Hudson Valleys by afternoon with trailing portion arcing southwest
across the central Appalachians. Ongoing convection within the warm
conveyor just ahead of the front should persist east, with
additional development expected in its immediate wake along the
front by midday.

Mid 60s to low 70s surface dew points are prevalent from CT/RI
southwest into the Mid-Atlantic States. As a plume of steeper
mid-level lapse rates sampled by the 12Z Pittsburgh sounding spreads
east, MLCAPE of 750-1500 J/kg should develop amid pockets of greater
insolation in the lee of the Appalachians. Strong 700-500 mb
southwesterlies will prevail from PA/NJ northeastward, with more
modest flow to the southwest.

This setup should favor multiple clusters/line segments with
embedded supercell structures, most likely from eastern PA/NJ into
southwest ME. Damaging winds will probably be the main threat given
the strength of the low/mid-level flow, but isolated marginally
severe hail could also occur. A couple tornadoes are possible,
centered on the corridor with the greatest combination of moderate
low-level SRH and buoyancy from southeast NY to NH.

…SC Coast and vicinity…
Hurricane Dorian is expected to continue slowly north off the FL/GA
coast and approach coastal SC by 12Z Thursday. The overall tornado
threat is expected to remain limited through this afternoon along
the GA/SC coast. Greater potential for a few tornadoes should
develop this evening into the overnight across coastal SC as
low-level northeasterlies substantially strengthen and hodographs
enlarge within the favored northeast quadrant. This may yield a few
low-topped supercells within one or more outer bands that approach
the immediate coast of SC into far southern NC.

…Deep South TX…
TC Fernand will continue west across far northeast Mexico. Moderate
low-level easterly flow will support adequate SRH for perhaps a
brief tornado and/or isolated thunderstorm wind damage with
scattered convection that persists from the northwest Gulf across
Deep South TX. This flow should subside during the evening, limiting
the severe storm risk tonight.

…Red River Valley of the North..
A low-amplitude shortwave trough near the BC/AB/MT border will move
east along the international border towards the Lake of the Woods
region by 12Z Thursday. 700-mb warm advection will strengthen across
northeast ND into northwest MN tonight. A cluster of elevated storms
may evolve southeast from southeast SK/southwest MB overnight. Thin
buoyancy will be a limiting factor, but robust speed shear within
the cloud-bearing layer could support a few instances of marginally
severe hail.

..Grams/Smith.. 09/04/2019


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