355
FXUS63 KFGF 122326
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
626 PM CDT Fri Jul 12 2024

.KEY MESSAGES...

- Heat related impacts are expected this weekend, especially
  Saturday afternoon. Impacts will be highest for heat sensitive
  or vulnerable groups and anyone without effective cooling or
  hydration.

- There is a level 1 out of 5 risk for severe thunderstorms after
  8 PM tonight for eastern North Dakota into far northwest
  Minnesota.

- There is a level 2 out of 5 risk for severe thunderstorms
  across the region Saturday afternoon into overnight, and again
  Sunday night.

&&

.DISCUSSION...
Issued at 231 PM CDT Fri Jul 12 2024

...Synopsis...

Overall synoptic pattern this weekend will consist of large
upper ridging over the Great Basin and an upper trough
progressing eastward within the Canadian interior. Between these
two synoptic features, increased wind field/jet aloft will
promote progressive shortwave trough passages in addition to
upper divergence in the exit region of the jet. More
concentrated and trackable synoptic forcing comes with a
shortwave trough passage late Sunday, although subtle waves
within the flow are expected (and viewable via satellite)
tonight through Saturday. These waves aloft will provide the
synoptic forcing background to allow for several bouts of
thunderstorms within the Northern Plains into Upper Midwest this
weekend.

Ahead of these features, rich moisture content in the lower
levels are already in place over the Dakotas into Minnesota as
comprised of widespread 70s dew points. This sits underneath
extensions of an EML breaking out of the Great Basin into the
Northern Plains and Upper Midwest escaping the upper ridge`s
grasp as advected by upper westerly flow aloft. This is
contributing to a moderate to strongly unstable air mass that
will support the fuel needed for robust thunderstorm
development. Despite increased winds aloft, they aren`t overly
strong (on the order of 30-50kt at 500 mb), with less wind in
the lower levels. Despite the lackluster wind shear, effective
shear around 30-45kt should still provide enough to allow for
some organization of thunderstorms, especially considering the
moderate to strong instability, supporting severe potential.

High temperatures trapped within the upper ridging also spread
into our area (already seen today in the Dakotas), bringing the
high chance of high heat today through Saturday, possibly into
Sunday. These high temperatures and the high dew points/moisture
content in the lower levels bring high confidence in seeing
heat-related impacts to our region.

...Potential Heat Impacts This Weekend...

Forecast temperatures well into 80s and 90s combined with high
humidity as achieved by dew points into the 70s will contribute
to a period of above average warmth today into Sunday. With
recent warm conditions this week followed by hot conditions this
week, the chance for increased heat stress is increased than say
if this was just one or two days of warmth. Saturday will see
warmest conditions with apparent temperatures nearing or just
exceeding 100 F.

A Heat Advisory has been issued for areas that would see best
chance for seeing these apparent temperatures, although may not
actually meet criteria. Despite not technically meeting
criteria, the combination of hot temperatures in the 90s, high
humidity, ample sunshine, and lower wind will all contribute to
higher than average heat risk. This can be seen in wet bulb
globe temperatures reaching into the Extreme category for a
period in the southern Red River Valley Saturday afternoon.

Lower humidity will lessen chance for impacts Sunday, although
temperatures will be well into the 80s. Cooler temperatures are
forecast Monday into next week.

...Several Chances for Severe Thunderstorms...

As mentioned in the Synopsis section, moderate to strong
instability combined with sufficient shear and several shortwave
troughs will drive chances for strong to severe storms starting
tonight lasting into Sunday night. Trying to time and track
each shortwave passage has continued to be difficult with
several suites of guidance have differing opinions on convective
evolution. However, general consensus can be described as
increased chance for strong to severe storms starting tonight
after 8 PM, lasting through the overnight. A thunderstorm
complex could move out of Canada through the Red River Valley
and/or a cluster of thunderstorms moving out of western/central
North Dakota may move through eastern North Dakota into the Red
River Valley. Both would support the potential for wind gusts
50-70 mph and hail to the size of quarters. Complicating
factors like remnant boundaries from morning convection may
augment low level wind shear and/or areas that would see
thunderstorms, lowering confidence in location and magnitude of
hazards.

Getting into Saturday, guidance highlights areas within
Minnesota by mid afternoon may see a collection of high
precipitation supercells, which would bring potential for large
hail, gusty winds, and potential for tornadoes. Heavy rainfall
rates and potential training of thunderstorms may also bring
some minor flooding impacts as well. Another complex of
thunderstorms may exit western/central North Dakota late
Saturday night into eastern North Dakota into the Red River
Valley (again), bringing another chance for gusty winds and
perhaps embedded QLCS-type tornadoes.

Finally, a more congealed and trackable wave moves into western
Dakotas late Sunday. This may again bring a complex of
thunderstorms into our area Sunday night. This again would bring
chance for severe wind gusts and perhaps hail and embedded
tornadoes.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 626 PM CDT Fri Jul 12 2024

Look for VFR ceilings through the TAF period at all sites.
Impacts to aviation will surround the potential for
thunderstorms starting later this evening, then traversing the
area into the overnight period. The best chances for
thunderstorm activity will be at KDVL, KGFK, and KFAR, with
lower chances elsewhere. Strong to severe thunderstorm impacts
are possible, and could include gusty winds and/or wind shifts
and hail up to 1 inch.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Heat Advisory from noon to 8 PM CDT Saturday for NDZ030-038-
     039-049-052-053.
MN...Heat Advisory from noon to 8 PM CDT Saturday for MNZ002-003-
     029-030-040.

&&

$$

DISCUSSION...CJ
AVIATION...Lynch