RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Wed Sep 22 11:47:02 UTC 2021.
No Mesoscale Discussions are in effect as of Wed Sep 22 11:47:02 UTC 2021.
SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0201 AM CDT Wed Sep 22 2021
Valid 241200Z - 251200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY ACROSS
MUCH OF NEW
HAMPSHIRE...VERMONT...MASSACHUSETTS...CONNECTICUT...RHODE
ISLAND...LONG ISLAND...PARTS OF FAR EASTERN NEW YORK AND FAR
WESTERN MAINE...
...SUMMARY...
Strong thunderstorms may impact southern and western portions of New
England Friday, accompanied by at least some risk for severe
weather.
...Synopsis...
Mid-level ridging may flatten some across the Canadian Prairies
during this period, but models indicate that broad mid-level ridging
will prevail across the British Columbia and Pacific Northwest coast
through the Canadian Prairies and northern U.S. Rockies. However,
downstream flow across eastern North America and the Atlantic
appears likely to continue to amplify. This will include digging
large-scale mid-level troughing southeast of the northern Great
Plains, through much of the Upper Midwest/Great Lakes and middle
Mississippi through Ohio Valley region.
Within the evolving large-scale troughing, it appears that a couple
of initial embedded mid-level lows will pivot around each other,
generally near and north of the Great Lakes vicinity. This includes
one emerging from the lower Ohio Valley in preceding days, which may
continue north of Lake Huron through southern Hudson Bay Friday
through Friday night. This may be accompanied by continuing
significant surface cyclogenesis near/northwest of James Bay, with a
broad, deep, occluded cyclone across southwestern Hudson Bay by 12Z
Saturday.
The trailing lead cold front is forecast to slowly continue east of
the Champlain/Hudson Valleys, and much of the middle/southern
Atlantic coast through the central Florida Peninsula. Another
reinforcing intrusion of cooler air may surge southeast of the Upper
Midwest through the lower Great Lakes and middle Mississippi/lower
Ohio Valleys, with yet another advancing into the Upper Midwest and
adjacent Great Lakes region by late Friday night.
Although mid-level cooling across parts of the Upper Midwest into
lower Great Lakes and Ohio Valley may contribute to scattered
convection capable of producing lightning, much of the nation, in
the wake of the lead cold front, will remain generally dry. Ahead
of the lead cold front, a narrow plume of higher moisture content
will continue to provide a focus for highest thunderstorm
probabilities Friday through Friday night.
...Parts of southern and western New England...
Despite a narrow pre-frontal corridor of mid 60s to near 70F surface
dew points, weak lower/mid tropospheric lapse and mid/high-level
cloud cover may only allow for the development of weak CAPE by peak
daytime heating. However, various forecast soundings indicate that
this may continue to coincide with moderate southerly flow in the
850-700 mb layer, which could contribute to sizable,
clockwise-curved low-level hodographs. While the NAM might be too
aggressive concerning this, it is possible that the environment may
still become conducive to organized convection, including
supercells, with the potential to produce damaging wind gusts and
perhaps a tornado or two.
..Kerr.. 09/22/2021
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Day 4-8 Outlook
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0318 AM CDT Wed Sep 22 2021
Valid 251200Z - 301200Z
...DISCUSSION...
The latest medium-range guidance suggests that amplifying mid/upper
flow may progress toward a pattern with increasingly prominent
blocking over the mid to higher latitudes of interior North America.
There is considerable spread concerning the short wave developments
within this evolving regime through the period. Regardless, given
initially dry conditions across much of the U.S., and apparent low
potential for significant surface cyclogenesis to the lee of the
Rockies, the potential for organized severe thunderstorms also
appears likely to remain low next weekend through at least the
middle of next week.
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