466
FXUS63 KFGF 130758
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
258 AM CDT Sat Jul 13 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 2 out of 5 risk for severe thunderstorms
  across northwest Minnesota and southeast North Dakota. A level
  1 out of 5 risk exists in northeastern North Dakota.

- There is a level 2 out of 5 risk for severe thunderstorms
  Sunday night into Monday morning.

&&

.DISCUSSION...
Issued at 147 AM CDT Sat Jul 13 2024

...Synopsis...

The overall synoptic pattern should continue through the
remainder of the weekend into early next week, with a large
anticyclone over the desert southwest and frequent shortwaves
generating convection. These shortwaves are fairly weak until
Sunday night, which is why we have such high uncertainty in the
voltuion of convection through the weekend. Towards Sunday night
into Monday, a cold front should remove instability from our
area through next week, giving way to much quieter weather after
Monday. Large scale ridging with almost no flow aloft will
replace the current pattern, ending our chances for more
organized severe convection.

...Heat Risk This Weekend...

Forecast highs will rise into the 80s and 90s this afternoon
with dew points ranging from the 60s to 70s. This will increase
the risk for heat stress and allow heat index values to approach
the triple digits in the southern Red River Valley. Lack of wind
and ample sunshine behind the convection this morning should
push Wet Bulb Globe Temperatures into the Extreme category this
afternoon in the south. For this reason, the Heat Advisory will
continue through the day today. Heat issues will persist into
Sunday, albeit with cooler temperatures with less impact, but
heat stress could continue for vulnerable populations due to
repeated days of higher temperatures. Excessive heat is unlikely
to develop due to recovery overnight. As humidity exits Monday,
conditions for heat should improve.

...SEVERE STORMS TODAY...

A very complicated environment exists for us today with very low
confidence in how convection will evolve through the day. As of
07z, surface analysis indicates a developing MCV over
Griggs/Steele Counties, which is also confirmed via Nightime
Microphysics RGB indicating cyclonic rotation over the area.
This has developed in the wake of elevated convection that is
along a line from Fargo to the tri-state borders.

To keep things simple, we will start with the ongoing
convection. This is expected to translate eastward through the
day today, aided primarily by persistent elevated instability
from southwesterly winds aloft. There is a pocket of enhanced
effective bulk shear along western Minnesota with this
convection, so it is feasible we may see some intensification.
Given the linear structure of ongoing convection, if we do see
intensification as this line translates east, the primary hazard
will be damaging wind gusts. Some cores have gone up along the
outflow boundary, so there may be a brief chance of severe hail,
but the main hazard will be wind. As the sun rises today, an
eroding surface inversion should allow for convection to become
more surface-based, however the question is will this occur
before it exits our area. Again, primary hazards are likely to
be damaging wind gusts.

This afternoon is where things become really complicated. There
is low confidence right now in how much instability return we
see today thanks to the ongoing convection across the south and
the development of an MCV over eastern North Dakota. Dew points
right now range in the upper 50s to low 60s, which are heavily
under what most CAMs have around this time. However, there is a
reservoir of 70+ dewpoints remaining across South Dakota and
Nebraska. The main question right now is how much this ongoing
convection scours that 70s reservoir away from our area. In any
case, it is very likely we will see strong to potentially
extreme instability develop across the region this afternoon.
Forcing, however, is very nebulous and this is where the
dewpoint question becomes much more precarious. There are a wide
array of potential forcing mechanisms ranging from the ongoing
MCV to outflow boundaries to potential inverted troughs. As a
result of this low predictability, it is not possible at this
time to really say exactly where storms will develop. What we
can say is where they will most likely develop, which is in
west-central Minnesota later this afternoon. Confidence
decreases as you head further north as forcing becomes much more
nebulous. However, with how much we could potentially
destabilize today, the lightest tap will likely send parcels
going. In any case, if storms do develop this afternoon and
evening, supercells initially are possible, but should congeal
more into multicellular to linear mode. Bulk shear around 40
knots should be enough to generate solid wind production to 70
mph and hail to 2". Tornado issues should be limited thanks to
very limited surface flow (and 0-1km shear primarily in the
single digits). Severe convection should exit the area just
before midnight.

Attention will then turn upstream where severe convection is
likely to be pushing from Montana into western North Dakota.
HREF members primarily keep this activity away from our area,
but we could see this scraping our southern counties overnight.
If this occurs, the primary hazards by then should be damaging
winds with a very low chance for a QLCS tornado.


...SEVERE THREAT SUNDAY NIGHT INTO MONDAY...

There is much better confidence thanks to stronger synoptic
forcing on Sunday. A much stronger wave with a cold front will
progress through the region Sunday night. With stronger shear
pushing 50 knots, supercells are possible in advance of the
frontal boundary, likely capable of severe hail to 1.75" and
damaging wind gusts. Eventually, we expect upscale growth to
occur, allowing for the threat to transition to wind to 70 mph.
A lot of what happens today may impact this, so stay tuned for
further updates as we get closer. Right now, this looks to be
the highest confidence risk for our area.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1155 PM CDT Fri Jul 12 2024

VFR ceilings continue through the overnight period and into
Saturday morning. Look for isolated thunderstorms overnight,
with the possibility of a strong to severe thunderstorm or two.
The primary concern with these stronger storms will be gusty
winds and hail. Heading into Saturday, there is another chance
for scattered showers and thunderstorms, with isolated severe
storms possible once more. Confidence is very low regarding
exact location, thus left out VCTS until we get a bit closer and
have more updated data. Impacts are possible during the
afternoon and evening hours at all sites, with KGFK, KTVF, and
KBJI seeing the greatest chances at this time.

&&

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

&&

$$

DISCUSSION...Perroux
AVIATION...Lynch