SPC AC 200726
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0226 AM CDT Sun Sep 20 2020
Valid 221200Z - 231200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
The severe potential associated with Tropical Cyclone Beta appears
too limited on Tuesday to include any severe probabilities across
southeastern Texas or Louisiana at this time.
...Southeastern Texas into Louisiana...
Tropical Storm Beta should be located along/near some portion of the
middle TX Coast Tuesday morning per latest NHC forecast. Most 00Z
guidance indicates that Beta will remain over land while slowly
weakening through the period. The low-level wind field associated
with Beta should likewise slowly diminish through Tuesday afternoon,
with southeasterly 850-mb winds around 15-25 kt across southeastern
TX and LA. The flow field should further weaken through mid levels.
The forecast vertical wind profile across this region appears quite
marginal to support organized storms. Dry low/mid-level air is also
forecast to wrap around the eastern half of Beta's circulation,
which may further hinder already weak forecast instability. At this
point, there appear to be too many limiting factors to include any
severe probabilities across southeastern TX and LA for Tuesday, but
this potential will be reevaluated in subsequent outlooks.
Farther north, a shortwave trough embedded within mid-level westerly
flow is forecast to move eastward along the U.S./Canada border from
the Pacific Northwest to the northern Plains through the period.
Low-level moisture is forecast to remain quite meager ahead of this
feature until it reaches the vicinity of ND late Tuesday night,
where low to mid 50s surface dewpoints may be present. A modest
southerly low-level jet along with a southeastward-surging cold
front may aid convective initiation late Tuesday across northern ND
into south-central Canada. Steep mid-level lapse rates should also
be present over this region, and potential exists for mainly
elevated storms to produce some hail given the forecast combination
of weak to locally moderate instability with strong deep-layer
shear. Regardless, will defer inclusion of any severe probabilities
across northern ND for now, as guidance differs on both the degree
of low-level moisture present and overall storm coverage.
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z