SPC AC 221244

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0744 AM CDT Sun May 22 2022

   Valid 221300Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
   NORTHERN MID-ATLANTIC AND NEW ENGLAND...

   ...SUMMARY...
   Scattered thunderstorms, some with damaging to severe gusts and
   large hail, are expected today over parts of the northern
   Mid-Atlantic and New England.

   ...Synopsis...
   In mid/upper levels, mean troughing and related large-scale cyclonic
   flow will persist from northeastern/Arctic Canada across the
   northern Plains, with some eastward shift over the Great Basin to
   central Rockies, and across northwestern MX.  Numerous embedded
   shortwaves will perturb that broader cyclonic-flow pattern on the
   mesoscale.

   The most convectively important of those shortwave troughs is
   apparent initially in moisture-channel imagery from northeastern MN
   across IA.  This feature is expected to stretch northeast/southwest
   through the day as the northern portion ejects more rapidly,
   reaching southwestern/central QC by 00Z.  As that occurs, height
   falls, tightening mid/upper height gradient, and accordingly,
   stronger 500-250-mb southwesterlies will overspread much of the
   Northeast today on both sides of the front described below. 
   Otherwise, a series of convectively induced/enhanced vorticity
   maxima will occupy a belt of weaker westerlies and southwesterlies
   aloft, from south TX to VA.

   At the surface, 11Z analysis showed a cold front from southern ON
   across western OH, western KY, southern AR, through a weak frontal-
   wave low near SHV, to south-central TX and northern Coahuila.  As
   the northern-stream shortwave trough approaches, the front will
   accelerate eastward, reaching northern/western New England and near
   the I-95 corridor between NYC and northern VA around 00Z.  From
   there the front should be positioned across western NC, northern AL,
   central MS, southwestern LA, and deep south TX.  By 12Z, the front
   will move offshore from the Northeast, and extend across central NC,
   becoming slow-moving to stationary through a weak frontal wave over
   northern AL, southwestward over southern LA and deep south TX.

   ...Northeastern CONUS...
   Scattered thunderstorms are likely in one or more bands, along/ahead
   of and largely parallel to the surface front.  Activity may develop
   by midday to early afternoon across portions of PA, northern WV and
   western NY.  Mainly multicell bands/clusters, with isolated discrete
   or embedded supercells over New England, are possible.  This
   activity should move eastward to northeastward into a diurnally
   destabilizing, favorably moist air mass and intensify while also
   growing in coverage.  Damaging to severe gusts and sporadic hail are
   possible, and a tornado or two may occur over northeastern portions
   of the area.

   Low-level and deep shear each should increase with northward extent
   under the greater height falls aloft, while moist advection and
   pockets of sustained diurnal heating contribute to favorable
   destabilization, particularly over the "slight" area.  A corridor of
   1000-2000 J/kg MLCAPE may develop ahead of the front across ME and
   adjoining parts of northern/central New England, with peak surface
   dew points in the 60s F and surface temps into the mid/upper 80s and
   90s (elevation-dependent).  Meanwhile, effective-shear magnitudes
   around 40-50 kt are possible over northern/western ME, decreasing to
   less than 35 kt over southern NY and eastern PA.  While bands or
   clusters of thunderstorms may develop farther south, overall
   organization and coverage should be less.  Activity should diminish
   this evening as it moves into areas from Downeast Maine to southern
   New England where the cold/stable marine-layer influence will be
   greater.

   ...Gulf Coast to southern Mid-Atlantic...
   Isolated to scattered thunderstorms, sometimes in loosely organized
   multicellular clusters, should occur today in a broad, favorably
   moist swath from the southern Mid-Atlantic across the Southeast,
   ahead of the surface front and along/ahead of an aggregate of
   outflow/differential-heating boundaries left by prior convection and
   its lingering cloud cover. Additional convection may form along
   sea-breeze fronts and serial outflows from successive daytime
   activity.  Being well-displaced from substantial midlevel flow and
   deep shear, this activity should present a marginal, isolated severe
   concern, mainly for damaging gusts.

   A convectively active/reinforced midlevel perturbation over the
   northern Gulf and southeastern LA may contribute some enhancement to
   low/middle-level flow and shear (e.g., via strengthened 850-500-mb
   speeds, and some backing of surface winds as well).  This suggests
   transient storm-scale rotation may occur with associated cells near
   the coast and offshore, particularly this evening into tonight.  As
   such, marginal tornado probabilities are maintained across parts of
   that region.

   ..Edwards/Kerr.. 05/22/2022

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