Severe Thunderstorm Warning 14, NWS Grand Forks, ND

Area Forecast Discussion
National Weather Service Grand Forks ND
351 PM CDT Tue May 30 2023

.SHORT TERM...(This afternoon through Wednesday night)
Issued at 351 PM CDT Tue May 30 2023

-Scattered thunderstorms are expected this afternoon and evening,
with a low probability for a strong to severe thunderstorm in our
far southeast (generally less than 5%).

-Additional thunderstorms are possible Wednesday (mainly
afternoon/evening). Severe thunderstorms are not expected (even
lower probabilities than today).

A slow moving mid level shortwave is centered along the US/Canada
border in our south, while a surface trough/frontal zone is slowly
moving east (currently along the Red River Valley). ML CAPE around
1000 J/KG is in place over most of our area, with slightly higher
values (1500 J/KG) and effective shear 30-35kt over west central MN
where more organized updrafts have the potential for maintain
themselves. Mid level lapse rates are relatively weak (less than
7C/km) and shear profiles are top heavy where effective shear is
favored, with weak low level shear. The amounts of shear/instabilty
ahead of this frontal zone appears to be enough to support isolated
severe potential (some supercellular characteristics at times), and
due to the nature of the shear/skinny cape profiles hail around 1
inch will probably remain the main threat. DCAPE is borderline (800-
1000 J/KG range) ahead of this frontal zone, and with 0-3km shear
20kt or less severe wind potential is lower. I wouldn't rule out
severe potential though with enough rain loading or RFD potential on
sponger organized cells. Storm scale interactions of course could
still result in very low tornado threat, but the background
environment doesn't support this. Much weaker shear behind this zone
and less instability should favor sub severe cells.

Due to the timing of this wave and weaker mid level lapse rates
thunderstorm coverage should follow diurnal trends dissipating/moving
east around sunset.

Wednesday-Wednesday night: As low level flow will tend to be out of
the northeast and the main theta-E axis farther south placing higher
ML/MU CAPE outside of our CWA (lowering severe potential). Guidance
is resolving a mid level wave roding through southwest flow into the
region, with increasing probabilities for showers/thunderstorms
during the afternoon. Coverage/timing will be dependent on this wave,
and there is still quite a few ensemble members that are much
weaker. Trend in NBM/HREF has been for increasing
shower/thunderstorm probabilities and with PWATs still forecast to
exceed 1" brief heavy rainfall will be possible.

.LONG TERM...(Thursday through Tuesday)
Issued at 351 PM CDT Tue May 30 2023

- High confidence in hot temperatures (90+ degrees) through the long
term period.

- Lower confidence in precipitation through the long term, however
the probability of elevated impacts will decrease.

DISCUSSION...

Clusters indicate upper ridging over the northeastern United States
retrograding westward back over our area through the week. This
breeds high confidence for increasing temperatures through the long
term period. Clusters indicate roughly similar 500mb height
magnitudes, so there is at least some higher confidence in high
temperatures through the weekend. Given height magnitudes are
similar to what we had over the past weekend, high temperatures
should generally fall within the NBM 25 to NBM 50th percentile
ranges, which pegs high temperatures by this weekend pushing the low
to mid 90s. With dewpoints being fairly stable and with a lack of
evapotranspiration, heat index values should stay sub-advisory
criteria as they will fall similar to air temperatures.

With the large scale ridging across the area, shear will diminish
significantly. This would temper chances for strong/severe
thunderstorms, but wouldn't necessarily make thunderstorm chances
zero. Continued chances for showers and thunderstorms will exist for
the long term period but the chances for higher impacts from these
storms are low.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 112 PM CDT Tue May 30 2023

VFR conditions should prevail through the TAF period across
eastern ND and northwest MN, with lighter southwest winds
(generally under 12kt during the daytime periods). Main aviation
impacts will be related to where showers/thunderstorms develop
with an upper wave today, and scattered coverage is favored
mainly in northeast ND and northwest MN during the afternoon
through early evening (activity dissipating with sunset). Where
these storms develop brief gusty winds to 50 mph can't be ruled
out (along with smaller hail). The better chances for severe
hail/wind would be in west central MN but even the those chances
are very low.

&&

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

SHORT TERM...DJR
LONG TERM...Perroux
AVIATION...DJR

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Special Weather Statement
National Weather Service Grand Forks ND
307 PM CDT Tue May 30 2023

MNZ001-002-015-302030-
West Polk MN-Norman MN-East Polk MN-
307 PM CDT Tue May 30 2023

...A strong thunderstorm will impact portions of northeastern Norman
and south central Polk Counties through 330 PM CDT...

At 307 PM CDT, Doppler radar was tracking a strong thunderstorm near
Flaming, or 44 miles northeast of Fargo, moving northeast at 15 mph.

HAZARD...Wind gusts up to 50 mph and nickel size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Fertile and Flaming.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4739 9646 4751 9647 4760 9625 4741 9613
TIME...MOT...LOC 2007Z 243DEG 11KT 4745 9637

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH

Perroux

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