176
FXUS63 KFGF 280248
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
948 PM CDT Thu Jun 27 2024

.KEY MESSAGES...

- There is a level 1 out of 5 risk for severe thunderstorms for
  all of eastern North Dakota tonight.

- There is a level 1 out of 5 risk for severe thunderstorms across
  the region Friday afternoon and evening.

- There is a low chance for severe thunderstorms again Monday
  across the region.

&&

.UPDATE...
Issued at 948 PM CDT Thu Jun 27 2024

Showers and Thunderstorms continue to push across the area this
evening. The severe risk continues for the Devils Lake Basin,
but appears to be losing steam. Forecast remains on track.

UPDATE
Issued at 635 PM CDT Thu Jun 27 2024

Severe weather is starting to our west in western and central
North Dakota. Currently in our area, we have majority showers
and some embedded thunderstorms moving through. The severe
weather should become elevated into this evening as it
approaches our area, but the Devils Lake Basin is under a level
1 out of 5 (marginal) risk for severe storms so not out of the
question we could have a few. Forecast remains on track.

&&

.DISCUSSION...
Issued at 247 PM CDT Thu Jun 27 2024

...Synopsis...

Ridging is propagating eastward, with a mid/upper low
propagating eastward from the Pacific NW. Ensemble guidance in
good agreement depicting the upper level pattern to remain
progressive through the period. Ensemble members do show
variances with timing, track, strength of each passing mid level
trough and associated surface low/front evolution which leads
to variances in timing, location, and magnitude of any severe
impacts or heavy rain. Temperatures vary with passing shortwave
ridges/troughs with a tendency for below average temperatures at
time (notably this weekend behind the trough on Friday). Each
passing trough carries at least some potential for severe
thunderstorms, with details tied to the mentioned uncertainties.

...Severe threat overnight...

Mid-level warm air advection currently propagating into the
region leading to scattered showers. Instability is very weak,
so not much for thunder at this point, although do anticipate at
least isolated thunder at times. This activity will continue to
move northeast into the evening hours.

The more widespread coverage overnight will be associated with
stronger 850mb WAA associated with a stronger low level jet.
With this stronger forcing, SPC indicates the marginal risk for
severe severe storms (at least for eastern North Dakota),
although instability quickly wanes after sunset - and forcing
arrives after sunset. Given lack of instability most convection
will be weaker, although strength of forcing and strong deep
layer shear will lead to a stronger storm or two. Primary
threats remain hail, and wind where momentum transfer of heavy
rain/elevated downdrafts can mix down higher gusts in the higher
low level shear environment.

Will also need to monitor for stronger wake low winds as the
convection tonight propagates eastward - the latest runs of the
HRRR indicate this potential. At this point predictability is
very low - especially considering the weaker nature of the
anticipated convection.

...Severe threat Friday afternoon/evening...

Deformation zone is favored by latest trends to shift north through
Friday morning towards the US/Canada border, lingering into the
afternoon. A mid level dry slot is shown to allow for clearing
across much of the region. Latest guidance in good agreement
indicating the main axis of instability will be east of the CWA
by mid-afternoon. However, there is a signal for MLCAPE up to
1000 J/KG along and just ahead of an inverted trough which
connects back toward the mid-upper low which will still be
approaching from the west. This will tend to be in a post
frontal shear environment (backing low levels) but deep layer
shear remains high (top heavy shear profiles). Due to the
strong effective shear we could see low topped supercell
development. If clearing and enough instability builds along and
ahead of the inverted trough, low level vorticity along with
stronger low level lapse rates/CAPE and slower propagating
frontal boundary could lead to a conditional tornado threat.
Given lower freezing levels, hail up to 1.5 or so inches also
would be a threat.

...Severe threat Monday....

Another mid/upper wave follows a very similar track and evolution
as the system Friday, with a period of widespread showers or
embedded thunderstorms. There is a signal for a deeper warm sector
building into our region within most clusters, and higher probs for
SB CAPE to exceed 1000 J/KG during the peak heating/diurnally
favored period of the afternoon/evening. CSU GEFS based machine
learning (15-30% severe probs) are supported by 100% chance for
greater than 55 NBM CWASP and 50-60% probability for NBM CWASP
values exceeding 65. That aligns with a threat for isolated to
scattered severe convection. This is still farther out, so
details/impacts are still inherently uncertain.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 635 PM CDT Thu Jun 27 2024

MVFR to IFR and eventually LIFR conditions expected through
tonight into Friday evening. With the TSRA moving through,
ceilings are forecasted to drop to around 005 into Friday
morning and remain there for the TAF period. Winds will lessen
to around 10 knots, but before then they will be gusting up to
20 - 25kts and sustained around 15 kts. Winds will shift into
Saturday morning, but that is outside the current TAF period.

&&

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

&&

$$

UPDATE...AH
DISCUSSION...TG
AVIATION...AH