SPC 0830Z Day 3 Outlook

Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0225 AM CST Sun Nov 22 2020

Valid 241200Z - 251200Z


Isolated strong to severe thunderstorms appear possible Tuesday into
Tuesday night across portions of the southern/central Plains,
Ozarks, Mid-South, and lower Mississippi Valley.

...Southern Plains into the Ozarks and Lower Mississippi Valley...
An upper trough/low initially centered over the southern/central
Rockies should eject eastward across the southern/central Plains on
Tuesday, eventually reaching the lower/mid MS Valley by the end of
the period. Enhanced (50-60+ kt) mid-level southwesterly winds will
likely overspread much of the developing warm sector across the
southern/central Plains by Tuesday evening. A surface low over the
vicinity of western KS/NE Tuesday morning is forecast to develop
eastward towards the mid MS Valley through the period. Pronounced
low-level warm/moist advection will likely be ongoing across the
southern/central Plains Tuesday morning, with a 40-50+ kt
south-southwesterly low-level jet present over this region. As this
low-level jet shifts eastward across the Ozarks and lower/mid MS
Valley through the day, partially modified Gulf moisture will
likewise return northward.

Elevated convection may be ongoing Tuesday morning across the
southern/central High Plains associated with low-level warm
advection. As mid-level temperatures cool with the approach of the
upper trough and low-level moisture continues streaming northward
across the southern Plains, at least weak instability should develop
by late Tuesday afternoon along and east of a surface cold front and
dryline. Somewhat steepened mid-level lapse rates and strong
deep-layer shear may support isolated, marginally severe hail with
any initially discrete storms across OK and perhaps south-central
KS. By Tuesday evening, any storms that do form will likely grow
upscale into a line along the advancing cold front. Given the
predominately linear mode and enhanced low-level wind field,
isolated strong to damaging winds should become the main threat
across the Ozarks, Mid-South, and lower MS Valley region Tuesday
night into early Wednesday morning.

There is uncertainty regarding the quality and northward extent of
greater low-level moisture return, with the 00Z GFS/ECMWF suggesting
mid to perhaps upper 50s surface dewpoints may reach as far north as
south-central/southeastern KS into southern MO and the Mid-South.
The 00Z NAM shows less low-level moisture return across these areas.
Regardless, there will probably be enough low-level moisture and
related weak instability to support surface-based storms and
isolated strong/gusty wind potential with a low-topped convective
line. Farther south into parts of central/eastern OK, AR, northeast
TX, northern LA, and MS, the presence of somewhat higher dewpoints
along with enhanced low-level shear may support a slightly greater
tornado threat compared to locations farther north. Model
differences regarding the degree of low-level moisture return and
weak forecast instability suggest there is too much uncertainty to
include more than a broad Marginal risk area at this time.

..Gleason.. 11/22/2020

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