SPC MD 1433


MD 1433 Image

Mesoscale Discussion 1433
NWS Storm Prediction Center Norman OK
1230 PM CDT Sun Aug 09 2020

Areas affected...Portions of far eastern MN into northwestern and
north-central WI

Concerning...Severe potential...Watch possible 

Valid 091730Z - 092000Z

Probability of Watch Issuance...60 percent

SUMMARY...The severe threat should gradually increase this
afternoon, with a few tornadoes, damaging winds, and large hail all
possible. Watch issuance may be needed in the next couple of hours
to address this threat.

DISCUSSION...Recent visible satellite and radar imagery show a
well-defined MCV circulation over central MN. This mid-level
circulation appears to be somewhat displaced to the northwest of the
related surface meso-low near the Twin Cities, and this displacement
may affect the low-level wind fields and limit the severe threat in
the near term. Still, some cloud breaks to the east of the MCV
across far eastern MN into northwestern/north-central WI are
allowing surface temperatures to slowly warm into the upper 70s and
80s. Coupled with surface dewpoints in the upper 60s to lower 70s,
this modest diurnal heating should support the development of
1500-2000 J/kg of MLCAPE by mid afternoon, with locally stronger
instability possible.

Some uncertainty remains regarding the placement of greater storm
coverage, as the mid-level vorticity maximum associated with the MCV
should move quickly northeastward along the northern fringes of the
stronger instability this afternoon. Earlier VWPs from KMPX showed
considerable veering/strengthening of the low and mid-level wind
field ahead of the MCV. Forecast soundings from the RAP across
northwestern WI and vicinity suggest a sufficiently strong wind
field through mid levels to support organized severe thunderstorms,
including the potential for supercells initially.

With effective SRH of 150-200 m2/s2 forecast across this area, a few
tornadoes appear possible if the storm mode can remain at least
somewhat discrete. Isolated large hail may also occur with this
initial activity given the favorable forecast instability and shear.
Convection should tend to form into one or more small clusters later
this afternoon across northern WI, and damaging winds may eventually
become the primary threat. Trends will continue to be closely
monitored for signs of increasing storm coverage and intensity
across far eastern MN into northwestern WI, and watch issuance may
be needed in the next couple of hours.

..Gleason/Grams.. 08/09/2020

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   44469205 44709297 45529318 46159275 46639211 46669124
            46419017 46168966 45618933 44848955 44669017 44519095

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