SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0739 AM CDT Mon Sep 09 2024
Valid 091300Z - 101200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN PARTS OF NEW
YORK...
...SUMMARY...
Isolated damaging thunderstorm gusts are possible in parts of New
York.
...Synopsis...
Mid/upper-level flow will become more zonal across most of the
northwestern and north-central CONUS, as a series of embedded
shortwave troughs penetrates/flattens antecedent ridging over the
Intermountain West and central/northern Rockies. Downstream, a
substantial cyclone -- initially centered near the southwestern edge
of Labrador -- anchors mean troughing that extends southwestward
down the Appalachians. The cyclone will eject northeastward over
Labrador through the period. In its southwestern quadrant, a
shortwave trough was apparent in moisture-channel imagery over
northeastern ON, approaching Georgian Bay and the neck of ON. This
feature should move southeastward to the upper St. Lawrence Valley,
eastern Lake Ontario and western NY by 00Z, then across southern New
England and offshore from the northern Mid-Atlantic Coast overnight.
The 11Z surface analysis showed a weak cold front from southern QC,
through a frontal-wave low over northern Lake Huron, then across
northern parts of WI/MN. The low should move east-southeastward
toward Lake Ontario and weaken through the day, while the cold front
and associated veering wind shift cross the remainder of ON and
start moving into NY. The front should cross the remainder of NY
and most of New England and PA overnight. An older, quasistationary
front was drawn across north-central FL westward over north-central
Gulf shelf waters, then bending southwestward into the western parts
of the developing tropical cyclone in the western Gulf.
Potential TC 6 -- now offshore from the Mexican Gulf Coast -- is
forecast by NHC to organize into a tropical storm this period.
Given the forecast track, intensity and wind radii, any developing
favorable sector for supercells/tornadoes will remain well out in
the Gulf day-1, and not an overland tornado concern until day 3,
when a risk area has been introduced northeast/east of the forecast
center track. See NHC advisories on this system for latest tropical
watches/warnings, and path/strength forecasts.
...NY...
Widely scattered to scattered thunderstorms are expected to move
southeastward to eastward across the outlook area from early
afternoon into early evening. Isolated damaging gusts, and perhaps
a gust or two near severe limits, may occur from the most vigorous
embedded cells.
This convection will be related to a compact (mesoscale) but strong
field of large-scale ascent preceding the shortwave trough, related
to its progressive field of DCVA, and forcing in the left-exit
region of a cyclonically curved speed max in the 250-500-mb layer.
The UVV field likely is manifest already by convection now over
Georgian Bay and vicinity, moving toward what should become a more
unstable environment over the outlook area. Deep-layer mean lapse
rates likely will never get steeper than about 6.5 C/km in this
setting. Still, the combination of subtle cooling aloft, weak but
sufficient boundary-layer moisture, and some diurnal heating ahead
of the UVV field, should deepen the buoyant layer enough to yield
pockets of 500-700 J/kg MLCAPE. Weak low-level shear, and 25-30 kt
effective-shear magnitudes in forecast soundings, indicate activity
should be multicellular. A shallow but well-mixed subcloud layer --
containing around 7 C/km lapse rates -- will support strong
downdraft accelerations in some of the cores.
..Edwards/Kerr.. 09/09/2024
Read more
