SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0312 PM CDT Thu Sep 07 2023
Valid 072000Z - 081200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE NORTHEAST...
CORRECTED THUNDER LINE
...SUMMARY...
Thunderstorms -- some capable of producing locally damaging wind
gusts and marginally severe hail -- will continue across portions of
the Mid-Atlantic region and into New England into this evening.
...Discussion...
Current expectations with regard to the convective scenario through
tomorrow morning remain in line with prior reasoning. As such,
aside from minor line adjustments, the overall forecast will remain
unchanged with this outlook update.
..Goss.. 09/07/2023
.PREV DISCUSSION... /ISSUED 1110 AM CDT Thu Sep 07 2023/
...Synopsis...
A mid-level high, centered over the southeastern New Mexico
vicinity, appears likely to remain prominent through this period,
with large-scale ridging building to its north, through much of the
Rockies and adjacent Great Plains today through tonight.
Downstream, several perturbations, comprising weak but amplifying
larger-scale mid-level troughing east of the Mississippi Valley, are
forecast to remain generally progressive, though mid-level ridging
may continue to build near/east of the middle and northern Atlantic
Seaboard, in the wake of a modest cyclone migrating eastward across
portions of the Canadian Maritimes.
The two more significant perturbations include a remnant mid-level
trough forecast to slowly accelerate northeast of the lower Great
Lakes region through southern Ontario and Quebec, and a weak
developing mid-level low forecast to dig south-southeast of the
lower Ohio Valley through Alabama/Georgia by 12Z Friday. East of
these features, and ahead of a cold front which has already advanced
into the Appalachians vicinity (while stalling across parts of the
lower Mississippi Valley into southern Great Plains), deep-layer
southerly mean flow and shear will likely remain mostly rather
modest to weak (less than 20 kt). However, models do suggest that a
more subtle perturbation migrating north-northeast of the Blue Ridge
might contribute to a belt of modest south-southwesterly mid-level
flow along the western periphery of the building ridge, with at
least some signal that this could also become convectively augmented
by tonight.
...Atlantic Seaboard...
Seasonably moist air, beneath relatively steep
lower/mid-tropospheric lapse rates, likely will contribute to
sizable mixed-layer CAPE to the east of developing surface troughing
to the lee of the Appalachians. This could become supportive of
developing clusters of storms with potential to produce strong wind
gusts, as convection initiates and slowly propagates off the higher
terrain this afternoon. The most prominent and concentrated area of
thunderstorm development still appears likely to be focused with the
increasingly sheared short wave impulse and modestly strengthening
southerly mid-level flow (30+ kt in the 700-500 mb layer) across
eastern Pennsylvania and New York, and adjacent portions of the Mid
Atlantic and New England, through early evening. This may include
an upscale growing, and gradually organizing, thunderstorm cluster
or two which may eventually pose a risk of producing a swath of
strong to severe surface gusts.
...Lower Mississippi Valley/Gulf Coast vicinity...
Destabilization associated with a corridor of strong pre-frontal
daytime heating may become sufficient for thunderstorms capable of
producing damaging wind gusts, perhaps aided by modest deep-layer
shear near the leading edge of strengthening north-northwesterly
mid/upper flow.
...Southern Great Plains...
Potential for sustained convective development within a very warm
and deeply mixed boundary across the Texas Panhandle into western
Oklahoma late this afternoon remains uncertain. However, to the
east of the lee surface trough, warm advection and lift associated
with a nocturnal strengthening south-southwesterly low-level jet
will pose better potential for thunderstorm development across
northern/eastern Oklahoma tonight. It is possible that elevated
instability and unsaturated sub-cloud air may be sufficient to
contribute to potential for hail and gusty surface winds with some
of this activity.
...Northern Great Plains...
Models suggest that daytime heating may contribute to a deep mixed
boundary layer with modest CAPE, along and south of a developing
zone of stronger differential surface heating, southeast of the
Black Hills into central Nebraska. Aided by forcing for ascent
associated with a short wave digging around the northeastern
periphery of the building larger-scale ridging, isolated strong
thunderstorm development posing a risk for producing strong surface
gusts is possible for a period late this afternoon and evening.
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