SPC 0730Z Day 3 Outlook

Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0149 AM CDT Mon Oct 05 2020

Valid 071200Z - 081200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS WEDNESDAY ACROSS
MUCH OF UPSTATE NEW YORK...VERMONT...NEW HAMPSHIRE...PARTS OF
NORTHERN MASSACHUSETTS AND SOUTHERN MAINE...

...SUMMARY...
Thunderstorms may overspread parts of Upstate New York through
northern New England Wednesday afternoon and evening, accompanied by
a risk for potentially damaging wind gusts.

...Synopsis...
A seasonably strong mid/upper jet across the northern mid-latitude
Pacific appears likely to become more zonal while nosing into the
northeastern Pacific during this period.  As this occurs, within
branching downstream flow across North America, another modestly
amplified, strong mid/upper jet is forecast to progress eastward
across Canada and the northern tier of the U.S.  This will include
broad ridging gradually shifting east of the Canadian Rockies,
through the Canadian Prairies, and broad troughing shifting across
eastern Canada and the Northeast.

In lower latitudes, mid/upper ridging will persist across the
subtropical western Atlantic into Florida and adjacent portions of
the Southeast, with several tropical perturbations progressing
around its southern/southwestern periphery.  It appears that this
will include a hurricane (currently Tropical Depression Twenty-Six) 
migrating slowly northwestward across the central Gulf of Mexico,
within a plume of tropical moisture largely confined to the Gulf of
Mexico.

Within the westerlies, a strong short wave perturbation, including a
100 kt northwesterly mid-level (around 500 mb) jet streak, is
forecast to dig east-southeast of the lower Great Lakes region,
before turning eastward across New England by Wednesday night.  It
appears that this will be accompanied by substantial further
deepening of a surface cyclone, across southern Quebec through the
Canadian Maritimes.  

Beneath an increasingly confluent regime in the wake of the
mid-level perturbation, cold surface ridging is forecast to build
across and east of the Mississippi Valley, and southward into the
Gulf Coast states, by late Wednesday night.  This will contribute to
the maintenance of dry and/or stable conditions across most areas
east of the Rockies.

...Upstate New York into northern New England...
Boundary-layer moisture within the warm sector of the surface
cyclone likely will be rather marginal for vigorous convective
development.  However, thermodynamic profiles probably will become
conducive to convection capable of producing lightning, aided by
forcing for ascent and cooling to the north of the strong cyclonic
mid-level jet.  Even with mixed-layer CAPE on the order of 250-500
J/kg, storms may become sufficiently strong to aid the downward
transfer of higher momentum to the surface.  With model forecast
soundings indicating 40-50+ kt mean ambient flow in the lowest 5-6
km AGL, at least a few gusts exceeding severe limits appear
possible.  This may commence on the nose of a developing mid-level
dry slot east of Lake Ontario Wednesday afternoon, before spreading
eastward across parts of northern New England by Wednesday evening.

..Kerr.. 10/05/2020

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