Special Weather Statement, NWS Grand Forks, ND

Area Forecast Discussion
National Weather Service Grand Forks ND
332 PM CDT Tue Aug 8 2023

.SHORT TERM...(This evening through Wednesday night)
Issued at 332 PM CDT Tue Aug 8 2023

Convective strength this afternoon and evening will be the main
challenges for the period.

Upper low continues to spin over southern Manitoba/Ontario, with a
decent vort coming down and bringing a cold front for our CWA. Pre-
frontal trough has been swinging through east central ND and
northwestern MN, with thunderstorms across much of our southern
and eastern CWA. The first round that developed along the Highway
2 corridor earlier has nearly fizzled out, but some additional
storms have been developing further south near Highway 200 and
Highway 10 where ML CAPE values have been getting to around 2000
J/kg. Effective bulk shear is around 20 kts with the better values
further north, and low level shear is even less impressive,
around 10 kts. Cannot completely rule out an isolated storm
pulsing upward and producing some marginal hail around an inch or
a quick downburst, but not very impressed with widespread severe
risk at this point. Storms will continue into this evening as the
main cold front comes down into region. Some smoke getting mixed
down behind the frontal boundary, so will keep patchy mention
going.

Northwesterly flow will continue into tomorrow, with a reinforcing
vort on the backside of the low moving through Canada. CAMs as
well as global models have some shower activity tomorrow as the
vort moves through, so have some 20 to 30 POPs going. Instability
behind the cold front is pretty weak, so thunder chances will be
mainly near the SD border. Overall, Wednesday should be cool and
breezy with highs in the 70s and chances for showers.

.LONG TERM...(Thursday through Tuesday)
Issued at 332 PM CDT Tue Aug 8 2023

Thursday and Friday...A fairly vigorous shortwave is expected to
move through southern Canada and ND Thursday, with a another
reinforcing shortwave coming down out of Canada on Friday as the
first system pulls east. Southeasterly winds at the surface get
going on Thursday ahead of the surface trough which will swing
through Thursday night. Many of the ensemble members are not too
impressive with surface based CAPE over our CWA except in a very
limited area near the SD border. There is some sign of elevated CAPE
around 1500 J/kg possible during the overnight hours as the system
swings through, along with some 40 to 50 kts of deep layer bulk
shear. Of course, that is only one model solution and even the
elevated instability is fairly conditional, but think there could be
some isolated severe cells possible Thursday. There is a strong
signal from the GEFS and ECMWF, and NBM probabilities of at least a
tenth of an inch in 12 hours is at least 60 to 70 percent.
Precipitation chances continue to be fairly decent into Friday as
the reinforcing shortwave comes through. The NBM mean surface based
CAPE is even higher Friday afternoon than Thursday for portions of
our CWA, but seems odd with northwesterly flow at the surface on the
backside of the surface trough. Will continue to monitor as the
period grows closer.

Saturday through Tuesday...Northwesterly flow returns with various
weak shortwaves coming through. There isn't much in the clusters to
hang our hat on and predictability is pretty low for these kind
of features his far out. Near seasonal temps and POPs in the 20 to
50 percent range as various shortwaves move through seems
reasonable.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1248 PM CDT Tue Aug 8 2023

VFR conditions for all TAF sites as smoke has been a bit less
dense than expected, although still could see some vis reductions
to 4-6SM as a cold front comes through and helps elevated smoke
get to the surface. Showers and thunderstorms also possible along
the front, with some VCTS or VCSH through this afternoon and
evening as the boundary pushes southeastward. Most of the precip
should be done by late evening, with winds becoming more northerly
behind the front.

&&

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

SHORT TERM...JR
LONG TERM...JR
AVIATION...JR

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Special Weather Statement
National Weather Service Grand Forks ND
333 PM CDT Tue Aug 8 2023

MNZ002-015-022-082100-
Mahnomen MN-Norman MN-East Polk MN-
333 PM CDT Tue Aug 8 2023

...A strong thunderstorm will impact portions of east central Norman,
southeastern Polk and Mahnomen Counties through 400 PM CDT...

At 332 PM CDT, Doppler radar was tracking a strong thunderstorm near
Bejou, or 41 miles north of Detroit Lakes, moving east at 40 mph.

HAZARD...Winds in excess of 40 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...
Mahnomen, Island Lake in Mahnomen County, Bejou, Lengby, Roy Lake,
Beaulieu and Pine Bend.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4726 9555 4732 9611 4748 9611 4755 9555
TIME...MOT...LOC 2032Z 271DEG 35KT 4740 9600

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...40 MPH

Lee

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