SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0228 AM CDT Thu Jun 30 2022
Valid 021200Z - 031200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SATURDAY ACROSS
MUCH OF EASTERN PENNSYLVANIA...NORTHERN NEW JERSEY...SOUTHEASTERN
NEW YORK AND MUCH OF LONG ISLAND...CONNECTICUT...RHODE ISLAND AND
MUCH OF MASSACHUSETTS...
...SUMMARY...
Strong thunderstorms are expected to develop and overspread much of
the Northeast urban corridor Saturday afternoon, accompanied by a
risk for damaging winds and hail. A cluster of strong thunderstorms
might also develop across parts of the northern Great Plains late
Saturday afternoon and evening, and pose at least some risk for
severe weather.
...Synopsis...
Little appreciable change to the large-scale flow is forecast
through this period. Blocking with amplified split flow appears
likely to remain prominent across the eastern Pacific into western
North America. To the southeast of the persistent mid/upper high
over the Canadian Yukon and Northwest Territories, broad troughing
will remain entrenched across much of Canada and the adjacent
northern tier of the U.S. to the east of the Rockies. However, the
deep embedded mid-level low of Canadian Arctic origins is forecast
to slowly progress east of the southern Hudson/James Bay vicinity,
while several less prominent trailing perturbations dig across the
Canadian Prairies and south of the central Canadian Arctic
latitudes. Farther south, lower/mid tropospheric ridging extending
from the southwestern Atlantic through the southern Rockies likely
will be maintained.
...Northeast...
Associated with the deep mid-level low shifting into Quebec, a cold
front probably will already be advancing southward across northern
New England and to the east of the lower Great Lakes by 12Z
Saturday, before slowly continuing into southern New England and
northern Mid Atlantic coastal areas by the end of the period. In
advance of the front, it appears that a pre-frontal surface trough
will become a focus for stronger boundary-layer heating and mixing
across and just inland of much of the Northeast urban corridor,
where surface dew points in the mid 60s to near 70F may contribute
to moderate mixed-layer CAPE up to 1500-2000 J/kg. Thunderstorm
activity likely to develop along or ahead of the cold front probably
will intensify as it advances east-southeastward and encounters
increasing inflow of this air mass. It appears this may occur
coincident with 30-50 kt flow in the 700-500 mb layer, on the
southern fringe of the stronger westerlies, with associated shear
providing support for convective organization and potential for
damaging wind gusts and hail.
...Northern Great Plains...
A short wave impulse rounding the crest of the mid-level ridging
across the northern Rockies, in advance of a stronger impulse
digging within the cyclonic flow across the Canadian Prairies, may
contribute to forcing for convective development across eastern
Montana into the Dakotas by Saturday evening. Spread among the
various model output remains sizable, but boundary-layer moistening
beneath at least modestly steep mid-level lapse rates may contribute
to CAPE on the order of 1000-2000 J/kg within the lee surface
troughing across the northern Great Plains. Although it currently
may be an outlier, the 30/00Z NAM indicates a rather substantive
convective signal, suggestive of potential for the evolution of a
rather strong, organized and progressive convective system capable
of producing strong wind gusts.
..Kerr.. 06/30/2022
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