SPC 0600Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1145 PM 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...NORTHERN
MASSACHUSETTS...AND SOUTHERN MAINE...

...SUMMARY...
Thunderstorms may contribute to a risk for potentially damaging wind
gusts across parts of Upstate New York through northern New England
Wednesday afternoon and evening.

...Synopsis...
One seasonably strong and modestly amplified mid/upper jet appears
likely to continue progressing across Canada and the northern tier
of the U.S., as a somewhat stronger, more zonal upstream jet noses
across the northern mid-latitude Pacific during this period.  While
broad mid-level ridging shifts east of the Canadian and northern
U.S. Rockies, through the Canadian Prairies and northern U.S. Great
Plains, similar amplitude downstream troughing is forecast to
continue to evolve across the eastern Canadian Provinces and
Northeast.  

Models still indicate that the eastern troughing will include a
strong short wave perturbation, with a 100+ kt northwesterly
mid-level jet streak digging east-southeast of the lower Great Lakes
region and across the northern Mid Atlantic/southern New England
coast vicinity Wednesday through Wednesday night.  This is forecast
to be accompanied by a significant surface cyclone, which may
undergo substantial further deepening as it migrates from
southeastern Ontario/southwestern Quebec into the Canadian Maritimes
by 12Z Thursday.

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 is expected to
contribute to the maintenance of dry and/or stable conditions across
most areas east of the Rockies.

In lower latitudes, mid/upper ridging likely will persist across the
subtropical western Atlantic into Florida and adjacent portions of
the Southeast, with several tropical perturbations within the
easterlies on its southern and southwestern periphery.  This will
include Hurricane Delta migrating northwestward into the south
central Gulf of Mexico, within a plume of tropical moisture largely
confined to the Gulf of Mexico.

...Upstate New York into northern New England...
Thermodynamic profiles supportive of convection capable of producing
lightning probably will be confined to areas along and north of the
strong, digging cyclonic mid/upper jet streak.  This will be aided
by forcing for ascent and cooling within its left exit region, with
subsidence and warming aloft suppressing deeper convection to the
south.  

Boundary-layer moisture in the warm sector of the surface cyclone
will probably be rather marginal for vigorous thunderstorm
development, and mixed-layer CAPE may only peak around 250-500 J/kg.
However, given cool thermodynamic profiles and strong deep-layer
vertical shear, this may be sufficient to contribute to storms with
small hail.  Melting and evaporative cooling in downdrafts should
enhance the downward transfer of higher momentum to the surface. 
Potentially damaging surface gusts appear possible in stronger
convection, particularly where mean ambient west-northwesterly flow
in the lowest 5-6 km AGL is forecast on the order of 40-50+ kt, in a
rough corridor east-southeast of Lake Ontario through portions of
northern New England.

..Kerr.. 10/06/2020

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