255
FXUS63 KFGF 180028
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
728 PM CDT Mon Jun 17 2024

.KEY MESSAGES...

- Widespread thunderstorms will envelope the region tonight into
  Tuesday morning. Some of these thunderstorms will be strong to
  severe thunderstorms bringing isolated to scattered instances
  of strong winds, hail, and flash flooding between 9pm tonight
  to 7am Tuesday morning.

- Additional round of unsettled weather is forecast Thursday-
  Friday, including the potential for isolated strong to severe
  storms.

&&

.UPDATE...
Issued at 728 PM CDT Mon Jun 17 2024

There is one cluster of showers/isolated thunderstorms that
developed north faster over the Devils Lake Basin) close to the
inverted surface trough axis where WAA and synoptic ascent from
the upper jet to the northeast aided in expansion. Impacts are
minimal as instablity remains under 500 J/KG. The main area of
showers/storms is still on track for arrival in the later part
of the evening (some indications of this starting to fill in
across southern MN. Forecast is on track, with only adjustments
to add timing to the near term precip trends, blending into
previous forecast. No change in thinking for impacts late
evening- overnight at this time.


&&

.DISCUSSION...
Issued at 420 PM CDT Mon Jun 17 2024

...Synopsis...

Within the Northern Plains and Upper Midwest, southwest flow
aloft between upper ridging in the eastern CONUS and upper
troughing within CAN into the western CONUS is being noted via
water vapor imagery. This synoptic regime is allowing moisture
transport into the Northern Plains/Upper Midwest from the Gulf
of Mexico/southern CONUS in the lower levels, with a connection
to Pacific moisture in the upper levels. Enhanced southwest
flow aloft downstream of the upper trough`s axis is also
contributing to lee troughing/cyclogenesis at the surface in
the High Plains from eastern MT to CO. A surface warm front
extends from High Plains of WY/CO through NE into IA.

All guidance progresses this surface warm front and supporting
moisture/instability further north into the Dakotas and
Minnesota with the help of a better consolidated shortwave
trough pushing out of Four Corners to Northern Rockies region
tonight into the Dakotas on Tuesday. This will allow ingredients
for widespread thunderstorm development via synoptic forcing
aloft, frontal and dynamic forcing in the lower levels near and
north of the warm front, and increased instability and shear
into our area. This brings the likely chance for organized,
robust thunderstorms into our area tonight into Tuesday morning.

The surface low and attendant cold front will be pushing
through the area Tuesday, with guidance suggesting
reinvigorate of robust, organized convection along the cold
front within Minnesota as it migrates east. This activity has
the potential to be strong to severe bringing hail to the size
of ping pongs and wind gusts to 60 mph. Timing of potentially
severe storms Tuesday is between 10a-3p before exiting east of
our area, best chance east of US Hwy 59.

Behind the departing surface fronts, surface high pressure will
likely influence the region Wednesday into Thursday. The flow
aloft is progged to become more zonal mid to late this week,
with embedded shortwaves moving through the flow helping re-draw
moisture/instability back into the region, along with forcing
for ascent. This brings the next chance for strong to severe
storms late Thursday into Friday.

Confidence in synoptic pattern degrees notably after Friday,
with ensembles depicting continued chances for showers and
thunderstorms along with average temperatures under zonal flow
aloft.

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

Getting into this evening, high res CAMs depict a strong to very
strong low level jet of 50-70kt nosing into the Red River Valley
from the south. This will provide very strong inflow of weak to
moderate instability (1000-2500 J/kg MUCAPE) along with high
moisture content (PWATs 1.5-2.0 inches) to feed widespread
thunderstorms amid isentropic lift from WAA north of the surface
warm front. This pinpoints it within eastern ND into northwest
and west-central MN.

While the majority of lowest shear will not be realized for
thunderstorm development, strong storm relative flow within the
low levels along with elevated updrafts deeper into the hail
growth zone will support hail production. Expectation is for
lots of updrafts pulsing up will mitigate potential for
significant hail sizes, with expected maximum size being golf
ball sized, but more likely scattered instances of quarter to
ping pong ball sized hail.

Also, while there will be a low level stable layer underneath
robust thunderstorms, the magnitude of strong winds in the low
levels allows the potential for these winds to reach the ground.
Thus, wind gusts up to 70 mph can be anticipated tonight,
especially if thunderstorms can arch into bowing segments that
propagate north and/or east.

With strong feed of rich moisture and sufficient instability,
convective rainfall rates exceeding 1 inch per hour at times
will allow the opportunity for flash flooding. This is
especially true if these highest rainfall rates can sit over an
area for more than 1-2 hours. Relatively more susceptible areas
to see flooding include the central REd River Valley into
northeast North Dakota where recent rainfall has saturated the
top layer of ground, in addition to urban areas. Widespread 1-3
inches of rainfall can be expected, with locally 4-5 inches.
This may also impact riverine potential flooding in the coming
days as well.

...Additional chance for strong to severe storms Thursday-Friday...

Zonal flow aloft allows moisture/instability to re-enter our
area late Thursday into Friday. Ensemble guidance suggests one
or more shortwave troughs moving through the Northern Plains
during this timeframe, bringing forcing for ascent and increased
kinematics that may organize convection. This introduces the
next opportunity for strong to severe thunderstorms. This is
reflected in guidance like CSU ML severe forecasts. Confidence
in coverage and magnitude is still in question however. At this
time, a significant severe weather episode is not likely.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 713 PM CDT Mon Jun 17 2024

Shower/thunderstorm coverage is expected to increase across
eastern ND and northwest MN later this evening south to north (after
03Z), with rain/thunder impacts at all terminals. There is some
early activity at KDVL that is quickly transitioning north and
a lull will be expected after it passes at that site before the
main activity gets underway. The activity later tonight carries
a low chance for severe wind/hail at TAF sites and a higher risk
for heavy rain, and that will need to be monitored. MVFR (and
eventually IFR) stratus spreads north as well due to increasing
moisture and where heavier rain occurs visibility may briefly
drop below 3sm. Showers and thunderstorms transition east but
stratus is shown to linger into the afternoon (high chance for
MVFR into the evening).

A strong low level jet develops late this evening as well, and
low level wind shear (2kft agl or lower) in the 40-50kt range
should be expected. Winds above this layer increase
substantially overnight (55-70kt).


&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Flood Watch through Wednesday morning for NDZ007-008-014>016-
     024-026>030-038-039-049-052>054.
MN...Flood Watch through Wednesday morning for MNZ001>009-013>017-
     022>024-027>032-040.

&&

$$

UPDATE...DJR
DISCUSSION...CJ
AVIATION...DJR