SPC AC 081719

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1219 PM CDT Mon Aug 08 2022

   Valid 091200Z - 101200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TUESDAY
   AFTERNOON ACROSS PARTS OF CENTRAL OREGON AND PARTS OF THE NORTHERN
   MID ATLANTIC INTO SOUTHERN NEW ENGLAND...

   ...SUMMARY...
   Isolated to widely scattered strong thunderstorms may impact parts
   of central Oregon, as well as portions of the Mid Atlantic and
   southern New England, Tuesday afternoon, and pose at least some risk
   for severe weather.

   ...Synopsis...
   In the southern mid- and subtropical latitudes, models indicate that
   weak lower/mid tropospheric ridging will prevail across the western
   Atlantic into much of the Southeast through this period.  At the
   same time, to the west, a mid-level high is forecast to become
   increasingly prominent near/east of the Rockies into much of the
   Great Plains, downstream of amplified mid-level troughing
   near/offshore of the U.S. Pacific coast.  While there will likely be
   little, if any, eastward progression of this larger-scale troughing,
   a fairly deep embedded mid-level low may migrate slowly
   north-northeastward offshore of the northern California/southern
   Oregon coast.

   Flow in the higher latitudes likely will remain more zonal and
   progressive.  This is forecast to include one significant mid-level
   trough, with a couple of vigorous embedded smaller-scale
   perturbations, shifting east of the Canadian Prairies through the
   northern Ontario/Hudson Bay/western Quebec vicinity by 12Z
   Wednesday.  A much more modest preceding perturbation is forecast to
   accelerate across and east of the Canadian Maritimes and New England
   into the northern Atlantic.  This will be accompanied by the
   southward advancement of one surface cold front across the St.
   Lawrence Valley, and to the lee of the lower Great Lakes, offshore
   of New England into northern Mid Atlantic coast by late Tuesday
   night.  The western flank of this front likely will stall across the
   lower Ohio into middle Mississippi Valleys, while a reinforcing
   front advances into the Upper Midwest and northern Great Plains.

   Moisture content will remain seasonably high along and to the south
   of the lead front, to the east of the Rockies, while monsoonal
   moisture will gradually advect around the southwestern periphery of
   the strengthening high, from the Southwest into the northern
   intermountain region, to the east of the developing low offshore of
   the Pacific coast.

   ...Northeast...
   Large-scale forcing for ascent along and ahead of the southward
   advancing front appears likely to remain generally modest to weak. 
   However, strong heating of a moist boundary layer (temps rising into
   the 90s with surface dew points in the mid 60s to around 70F)  may
   contribute to moderate CAPE (on the order of 1000-2000 J/kg) along
   the front and pre-frontal surface trough, inland of the northern Mid
   Atlantic into southern New England coast by Tuesday afternoon.  It
   appears that this will be sufficient to support widely scattered to
   scattered thunderstorms.  Although deep-layer shear will be weak,
   model forecast soundings indicate southwesterly to westerly flow
   around 20 kt in the 850-700 mb layer.  This may be enough, coupled
   with the fairly steep low-level lapse rates and potential heavy
   precipitation loading, to support the risk for a few potentially
   damaging wind gusts before storms weaken by Tuesday evening.

   ...Central Oregon (near/east of the Cascades)...
   Downstream (to the northeast of the approaching mid-level low),
   forcing for ascent is generally forecast to contribute to
   considerable thunderstorm development Tuesday afternoon into Tuesday
   evening.  Forecast soundings indicate that CAPE may remain limited
   to 500-1000 J/kg or less, but beneath 30-70 kt southerly flow in the
   500-300 mb layer, strong deep-layer shear will be at least
   conditionally supportive of isolated supercells posing a risk to
   produce severe hail and locally strong surface gusts.

   ..Kerr.. 08/08/2022

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