931
FXUS63 KFGF 032102
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
402 PM CDT Mon Jun 3 2024

.KEY MESSAGES...

- Widespread showers and thunderstorms move through the area
  late tonight into Tuesday afternoon. Some storms may be
  strong to severe, bringing hail up to 1 inch, 60 mph winds,
  and isolated tornadoes.

- Gusty winds 40-50 mph with scattered showers and
  thunderstorms are anticipated Wednesday into Thursday.

&&

.DISCUSSION...
Issued at 213 PM CDT Mon Jun 3 2024

...Synopsis...

Water vapor satellite imagery Monday afternoon reveals large upper
troughing extending from the Pacific Northwest into the
Intermountain West. Moisture wrapping around the base and exit
region of the trough within the moist conveyor is creating
widespread convection/cloudiness into the northern High Plains.

All ensemble guidance agrees this trough will strengthen notably
as it migrates into the southern Prairie Provinces of Canada. Plenty
of large scale forcing from embedded shortwaves, jet dynamics,
and attendant fronts will drive showers and thunderstorms
tonight into Tuesday within the Dakotas and northern Minnesota.
Some thunderstorms are expected to be strong to severe.
Relatively rich moisture content feeding into strong forcing
from this trough along with sufficient instability will help
bring areas of moderate to heavy rainfall between 0.5-1.5
inches.

There is however some lingering uncertainty in smaller
scale features like more specific orientation, location and
timing of strongest forcing as well as amount of daytime heating
during the day Tuesday that would influence coverage and type
of favored severe hazards. This also would influence the chance
for small areas of heavy rainfall, possibly up to 2-3 inches
(10% chance of occurring), of which may result in localized
flooding if it occurs on saturated soils currently present in
some areas and/or over an urban area.

As the trough strengthens in southern Canada Wednesday and
Thursday, a belt of strong winds aloft will round the base of
the mid/upper circulation within its dry slot. This will allow
gusty winds over 40 mph across much of the region during the
day Wednesday and Thursday. There is still some uncertainty in
how high wind gusts will reach, with gusts to 55 mph not out of
the question.

Getting into mid to late this week, ensemble guidance then
suggests a weather pattern that favors relatively drier
conditions for our area compared to recent weeks amid northwest
flow aloft. Near to slightly below average temperatures are
also favored throughout the week in this pattern.

...Strong to severe storms late tonight into Tuesday...

Scattered to widespread showers and thunderstorms will move out
of central North Dakota into eastern North Dakota tonight around
10pm to 2am. This convection will be driven by an initial
shortwave impulse and moisture within the exit region of the
broader scale trough. Convection is strongly favored to be
elevated in height atop the nocturnal inversion, with
instability feeding into convection via a low level jet and
focused warm air advection.

While the overall wind shear within the cloud bearing layer is
weaker (around 30 kt), it should be enough to give convection at
least some chance to organize into clusters with transient
mesocyclone features. The elevated nature of convection should
also allow sufficient updraft depth into the hail growth zone.
Both factors will allow for the hail potentially up to 1-1.5
inches within strongest and/or shielded updrafts tonight in
portions of eastern North Dakota. This activity may push into
the Red River Valley late tonight into Tuesday morning generally
between 3am - 11am.

Early morning convection will continue to push east into
Minnesota after sunrise Tuesday. Most CAMs and ensemble guidance
suggest some window of opportunity for increased heating and
moisture increase in the boundary layer by Tuesday midday for
portions of Minnesota. This would allow initially elevated
convection from the early morning to become more surface based.
This along with strong storm relative shear in the lowest 1 km
introduces the potential for gusty winds to 60 mph and an
isolated tornado risk to accompany continued hail potential.
Tornado potential would be more tied to storms that can latch
themselves onto a northward advecting warm front during late
morning into early afternoon, currently favored to move through
the Bemidji to Lake of the Woods region.

There is still some uncertainty as to the degree of daytime
heating in the morning to early afternoon hours that would drive
the wind and tornado potential in Minnesota. Should more daytime
heating occur (resulting in temperatures pushing into the mid
70s), gusty wind and tornado potential would increase.
Otherwise, hail would be the favored hazard.

A fast moving cold front will eventually whisk away moisture to
feed storms out of our area by 3pm Tuesday, ending the threat
of strong to severe storms.

...Gusty winds with showers/storms Wednesday into Thursday ...

Ensemble guidance strongly agrees in a seasonably strong
trough/low into Canada by Wednesday and Thursday. When compared
to climatological standards, it could rival deepest troughing
and/or lowest surface pressure in its region for this time of
year (as offered by NAEFS). This increases confidence in a
widespread increased wind field over Northern Plains. Increased
winds aloft and tightened pressure gradient within the dry slot
of this system increases confidence in gusty winds over the
Dakotas Wednesday, and extending into Minnesota as well as the
Dakotas Thursday. Efficient mixing and continued waves of cold
air advection aloft within the dry slot during the day
Wednesday and Thursday will help transfer winds over 40 mph,
generally out of the northwest. Depending on how deep mixing
gets will dictate how high winds can be transferred (which still
remains in question). Winds up to 55 mph are still possible
should deep mixing occur (20% chance).

Most guidance also allows steepening lapse rates amid sufficient
moisture to allow for daytime showers and thunderstorms.
Thunderstorms may also help transfer higher winds aloft to the
ground, strongest of which may push wind gusts to the 50-60 mph
range.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 128 PM CDT Mon Jun 3 2024

MVFR CIGs continue at sites like KGFK, KFAR, KTVF, and KDVL
until around 20Z. An additional round of lowered MVFR to IFR
CIGs accompanied by rain showers and/or thunderstorms will
become possible after 09Z associated with a passing low pressure
system across the Dakotas into Minnesota tonight through
Tuesday. There is lowered confidence in location and timing of
thunderstorms after 09Z, so opted to leave out of TAFs for now.

Winds will remain light, under 10kt, through 06Z before
gradually increasing in the 10-20kt range out of the south and
southwest into Tuesday morning. A cold front will eventually
sweep across the region Tuesday, shifting and increasing winds
out of the west, potentially as early as 15Z at KDVL.

&&

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

&&

$$

DISCUSSION...CJ
AVIATION...CJ