Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0750 AM CDT Tue Oct 10 2023
Valid 101300Z - 111200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Severe thunderstorms are not expected through tonight.
...Synopsis outside Northwest...
A large, deep-layer cyclone -- which is occluded in low levels --
continues to cover much of the east-central/northeastern CONUS,
Great Lakes region, and eastern Canada. The center should continue
to meander around northeastern ON/western QC south of James Bay
through the period, while continuing to fill slowly throughout its
depth. The associated surface frontal zone is well offshore from
the entire Atlantic Coast except for having stalled near south FL
and the Keys. There, isolated thunderstorms may occur amid modest
deep-layer lapse rates and frontal lift, but also, rich moisture and
weak MLCINH.
To the west, a frontal-wave low over the northwestern Gulf, and
associated warm/moist advection in low levels, may support isolated
thunder from the TX coastal bend to the lower Rio Grande Valley.
Ongoing eastern Pacific Hurricane Lidia and its eventual inland
remains in low levels will stay well southwest of this area through
the period, based on NHC forecasts. Its separating remnants aloft
may influence low-level frontal-wave cyclogenesis over the
northwestern Gulf near the end of this period and especially day 2,
but any even indirectly associated/overland severe potential is
expected to wait until after this period. Well upstream on the Rio
Grande -- over the Big Bend/far west TX region and northward over
the southern High Plains -- isolated, weak, high-based thunderstorms
may develop this afternoon amid favorable heating and marginal
moisture.
...Northwest...
A substantial cyclone -- not as vast/intense as the one in eastern
North America but still formidable in satellite appearance -- was
evident in moisture-channel imagery over the northeastern Pacific,
centered along 50N about 375 nm west of Vancouver Island. Its
500-mb center is expected to move eastward to east-southeastward
through the period, reaching the Northwest Coast near UIL around 12Z
tomorrow. A progression of basal shortwave perturbations and
related height falls will impart a net negative tilt to the
accompanying synoptic trough, which should extend southeastward from
the low to northern NV by that time. Two primary, associated
frontal bands of precip, with isolated embedded thunderstorms,
should move ashore: the first ongoing, with shallower/weaker
buoyancy, and a second, broader convective area from midafternoon
into early evening local time. Time series of forecast soundings
through the passage of the second area suggest hodograph size
decreasing as cooling aloft increases and deepens the buoyant layer;
however, a brief overlap window may develop where storm-scale
rotation can be sustained in at least marginally favorable low-level
shear environment. At this time, near-coastal tornado probabilities
are not zero, but appear too conditional and uncertain for a
categorical outlook.
Farther inland over the northern Rockies and vicinity, shots of
large-scale ascent preceding the main synoptic trough -- and
associated with several preceding vorticity lobes -- will maintain
favorable instability aloft. Overlap of that with weak but
sufficient low/middle-level moisture, in tandem with a diurnally
heated boundary layer, will support isolated thunderstorm potential
late this afternoon into early evening.
..Edwards/Broyles.. 10/10/2023
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