838
FXUS63 KFGF 220936
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
436 AM CDT Sat Jun 22 2024

.KEY MESSAGES...

- Scattered thunderstorms are forecast in the Devils Lake Basin
  and northern Red River Valley regions this afternoon into
  early evening. A few these storms may become strong to
  briefly severe.

- Severe storms may develop Monday afternoon and evening.

&&

.DISCUSSION...
Issued at 425 AM CDT Sat Jun 22 2024

...Synopsis...

Early this morning, water vapor imagery depicts broad upper
troughing making its way into the Northern Plains, with at
least a couple of mid level shortwave troughs working their way
east within eastern MT/western Dakotas and within AB/SK.
Objective analysis still suggests there is still some connection
of a departing upper jet to keep divergence aloft over our area
through the morning. As seen on microwave satellite imagery, overall
low-mid level moisture content ahead of these shortwaves and
underneath upper divergence will remain sufficient enough to
allow continued areas of weak convection in the absence of
better instability. Easterly flow in the lower levels will also
continue drizzle/fog chances west of the Red River Valley in
eastern ND.

Getting into this afternoon, guidance suggests the influence
from the entrance region of upper jet is replaced by incoming
shortwave trough out of Canada. Cooling temperatures aloft and
sufficient low level moisture coupled with daytime heating will
support weak instability ahead of an incoming weak cold front
attendant to its parent shortwave. This will set the stage for
scattered thunderstorms forecast within the Devils Lake Basin
into northern Red River Valley. And with at least weak shear
associated with the approaching shortwave, there is a chance for
organization of storms allowing them to be strong to briefly
severe this afternoon into early evening.

As Saturday`s shortwave trough exits east, Sunday will see a
post-frontal air mass and shortwave ridging over our area keeping
conditions dry. This is ahead of another approaching mid-upper
level shortwave trough traveling east through the southern tier
of Canada. Increasing warmth and instability builds ahead of
this next shortwave trough as it approaches our area Monday,
allowing Monday`s temperatures to reach into the 80s and 90s
amid higher humidity. This coupled with sufficient shear will
allow the opportunity for severe storms on Monday, of which may
be significantly severe. However, there are uncertainties
revolving around this potential, of which will be discussed in
more detail below. Depending on Monday`s convective evolution
and timing/speed of surface trough, Tuesday may hold a chance
for strong to severe storms in portions of Minnesota. This is
also very uncertain.

Getting into mid next week, post frontal air mass and upper
ridging aloft extending out of broad upper anticyclone over the
majority of the central and western CONUS will favor mostly dry
conditions and near average temperatures.

Late next week, ensemble guidance is starting to hone in on the
next shortwave trough that should influence our region`s
weather, similar to Monday`s ridge riding fashion. This would
favor at least one period of increased chance for showers and
thunderstorms, along with average to potentially above average
temperatures.

...A few strong to briefly severe storms later today....

Overall, today`s severe potential looks meager given the
persistence from majority of guidance to keep instability and
shear on the lower end, but still sufficient to allow
opportunity for some thunderstorm organization. Unidirectional
shear around 35 kt coupled with weak instability between
500-1200 J/kg will allow for transient mesocyclone development
within strongest storms. Most shear is displaced within the
mid-upper portions of the updraft, which would support hail
production. Based on thermodynamic and kinematic spacing, hail up
to the size of quarters seems reasonable. Cooler temperatures
aloft will also allow for gusty winds between 40-60 mph through
evaporative cooling of downdrafts. Coverage of thunderstorms
may range from isolated to scattered, favored to be within
northeast ND into northwest MN closer to better forcing somewhat
displaced into Canada. Given dependency on daytime heating,
lessening cloud cover will also be necessary to support building
instability. Most guidance depicts this occuring closer to
central ND into southwest MB this afternoon, and seems
reasonable based on the expectation of exiting upper divergence.
Best timing for potentially strong to severe storms exists
between 5 PM - 10 PM.

...Severe storm potential Monday...

As the shortwave trough skirts across the southern tier of
Canada, it will drag a notable portion of an already established
EML out of the Great Basin into the Northern Plains Monday. This
is atop enriched boundary layer moisture comprised of dewpoints
in the 60s to potentially low 70s. This will contribute to high
confidence of high to very high instability within a warm
sector overspreading ND into MN on Monday. The aforementioned
stout EML will however also bring strong capping. This is
important as it may subdue the chance for thunderstorms to
develop altogether given better synoptic forcing expected to
remain in Canada. This is where majority of uncertainty comes
in: amount and location of forcing to overcome capping.

While best forcing for ascent aloft will remain in Canada, there
will still be some surface/low level features to perhaps focus
forcing for ascent. This comes in the form of a warm front and
surface trough/weak cold front bounding the warm sector as it
moves through our area. Most guidance still times the surface
cold front to pass through our area during the day Monday, with
favored passed during peak heating (when capping will be at its
weakest) within Minnesota. Additionally, there may be another
opportunity to develop thunderstorms near and north of the warm
front through low level isentropic lift/WAA. This supports the
chance of robust thunderstorm development on Monday.

Given the presence of sufficient shear associated with
increasing wind field ahead of the approaching shortwave trough
and likely very unstable air mass, any thunderstorms that can
sustain themselves will likely be severe. This includes the
potential for supercells, allowing for damaging winds, large
hail, and possible tornadoes. Of course, mesoscale and finer
details such as early day convection, orientation and timing of
surface fronts, and influence of evapotranspiration this time
of year introduces that much more uncertainty.

Ultimately to say, should robust thunderstorms develop Monday
in our area (still uncertain), they will hold a higher than
normal chance of becoming severe, potentially significantly
severe.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1155 PM CDT Fri Jun 21 2024

Scattered light showers/sprinkles continue across parts of
eastern ND and northwest MN, as several waves split around the
region. MVFR (and a few pockets of IFR) stratus are beginning
to develop in southern ND and guidance is starting to better
reflect timing expanding north and northeast through the early
TAF period. Eventually all sites should drop below VFR but
confidence in widespread/prevailing IFR is still low (except at
KBJI) based on trends. Eventually guidance supports all
locations in ND improving to VFR by Saturday evening. Weak
surface gradient is keeping light winds in place (less than 10
mph, with a tendency fro easterly or southeasterly directions
(though prevailing calm or variable conditions are just as
likely).

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.

&&

$$

DISCUSSION...CJ
AVIATION...DJR