539
ACUS02 KWNS 130551
SWODY2
SPC AC 130550

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1250 AM CDT Sat Jul 13 2024

Valid 141200Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM
NORTHERN/EASTERN ND INTO NORTHWEST MN...

...SUMMARY...
Strong to severe thunderstorms are possible from the northern Plains
into the Upper Midwest on Sunday.

...Synopsis...
Upper ridging is forecast be over the Four Corners early Sunday
morning, with a belt of westerly flow aloft to its north extending
across the northern tier of the CONUS (i.e. from the Pacific
Northwest through the Upper Midwest and Upper Great Lakes into the
Northeast). The upper ridging is expected to remain in place while a
series of low-amplitude shortwave troughs move quickly through the
belt of westerly flow aloft. The strongest of these shortwaves is
forecast to move southeastward across central and southern
Saskatchewan into the northern Plains late Sunday night/early Monday
morning. Subtropical ridging will continue to influence the sensible
weather across the Southeast.

The surface pattern early Sunday morning is less predictable,
particularly across the Upper Midwest where antecedent thunderstorms
and the potential influence of associated outflow on the cold front
introduce uncertainty. Current expectation is for a surface low to
be near the NE/SD/IA border intersection, with an outflow-augmented
cold front extending northeastward from this low across the IA/MN
border vicinity through east-central WI. The cold front will also
extend northwestward from the NE/SD/IA border low to another surface
low in northeast MT. The eastern portion of this front may shift
gradually southward into more of northern IA and southern WI
throughout the day, while the western portion remains largely in
place.

...Southern MN/Northern IA into Southern WI/Northern IL...
Strong buoyancy is expected to build near the composite outflow/cold
front throughout the morning and afternoon, supported by
temperatures in the upper 80s/low 90s and dewpoints in the low 70s.
Most guidance suggests MLCAPE will exceed 3000 J/kg across the
region by the late afternoon. However, large-scale forcing for
ascent will be nebulous and convergence along the front will be
modest, casting doubt to whether the convective inhibition expected
to be in place can be overcome. Robust updrafts are possible if
convective initiation is realized, with a conditional threat for
large hail and/or damaging downbursts. There is even some potential
for the development of an organized MCS if enough storms develop.
However, given the current uncertainty regarding initiation, only
low severe probabilities will be outlooked. Higher probabilities may
be needed if thunderstorm development appears more probable in
future outlooks.

...Far Eastern MT into the Dakotas and Northern NE/NE Panhandle...
The stalled front mentioned in the synopsis will likely sharpen
throughout the day as strong heating occurs to its west and modest
low-level moisture advection occurs to its east. Like areas farther
east, warm temperatures aloft and limited large-scale forcing for
ascent limit the predictability of convective initiation during the
afternoon and evening. Moderate to strong vertical shear suggests
that any storms that do develop could have fairly persistent
updrafts. High cloud bases and steep low-level lapse rate also
suggest that strong outflow is possible.

A more predictable severe threat is anticipated later in the evening
and overnight as the shortwave trough moving southeastward across
southern Saskatchewan moves into northeast MT and ND. Ascent
attendant to this system is expected to lead to elevated
thunderstorm development, with moderate buoyancy and shear promoting
organized storms. Large hail is possible with the initial
development, but a trend towards a more linear mode is anticipated
over time. Strong outflow should be able to penetrate any low-level
stability, with damaging gusts become the primary severe threat
Monday morning across ND and northwest MN.

...Lower MI into the Middle OH Valley...
Thunderstorms may be ongoing early Sunday morning across Lower MI,
remnant from overnight development across the Upper Midwest.
Isolated hail and/or damaging gusts are possible within the
strongest storms.

A convectively augmented vorticity maximum may move across the
region Sunday afternoon, contributing to the potential for afternoon
thunderstorm development within the moist and moderately unstable
airmass in place. A damaging gust or two is possible, but weak
vertical shear is expected to mitigate the overall severe-storm
potential.

..Mosier.. 07/13/2024

$$