842
FXUS63 KFGF 111928
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
228 PM CDT Tue Jun 11 2024

.KEY MESSAGES...

- Scattered severe thunderstorms are possible tomorrow afternoon
  in northwest Minnesota. Significant hail (2+") and damaging
  wind gusts (up to 70 mph) are possible.

&&

.DISCUSSION...
Issued at 130 PM CDT Tue Jun 11 2024

...Synopsis...

Surface analysis at 18z indicates the center of the low that
brought us rain over southern Manitoba and Ontario. A relatively
enhanced region of a stronger pressure gradient has developed on
the backside of this low as a result, and is giving us sustained
winds between 20-30 mph. Winds will diminish as this low
continues to exit the region through the day today, so headlines
are not likely (5% chance of Wind Advisory).

A progressive shortwave trough will sweep through zonal flow
aloft tomorrow afternoon, bringing the potential for severe
thunderstorm development. There are a myriad of uncertainties
outlined below, but at this point in time expect the potential
for severe thunderstorms in northwest Minnesota.

Upper air flow towards late week shifts to northwesterly as an
intensifying ridge sets in. This should keep us quiet at least
through Friday until southwesterly flow replaces it and gives us
increased chances for widespread rainfall. How much rain falls
is dependent on intensity and track of the system, of which
ensembles are significantly struggling to get a handle on. At
this point in time, NAEFS percentiles do have an enhanced
corridor of IVT in the 99th percentile across the northern
plains from South Dakota to SW Minnesota with diminishing
probabilities radially away. This gives us solid confidence in a
more widespread rain event but also the potential for more
focused moisture advection across the northern plains.

After this system, ensemble guidance falls apart and
predictability for impacts next week is low. There is a strong
signal for another wave to move through early next week,
although the potential range of outcomes is very wide and
predictability needs to increase to ascertain potential impacts.

...SEVERE THUNDERSTORMS TOMORROW...

A rather complex convective scenario is expected to develop
across the region tomorrow. In advance of a progressive
shortwave trough (centered over the Pacific Northwest per WV
satellite), a modest 850mb low level jet is expected to provide
meaningful moisture advection to the area overnight tonight into
tomorrow morning. Elevated convection is likely to develop with
this low level jet, but at this point in time the most likely
zone of this occurring is south of the area.

As we progress through the morning and early afternoon, strong
theta-e advection in advance of the surface low propagating
through the southern Canadian Prairie will create a surface
theta-e boundary. This will serve as the initiating boundary for
convection tomorrow afternoon. Hodographs along the initiating
boundary are effectively straight but have ample deep layer
shear (exceeding 50 knots thanks to a strong 250mb jet) to
facilitate supercell development. Both mean wind and Bunkers
right vectors are effectively parallel to the initiating
boundary so initial discrete mode should be anticipated. Within
supercells that remain discrete, strong CAPE within the hail
growth zone coupled with modest storm-relative flow will allow
for significant hail to develop. With strong vertical mixing
anticipated tomorrow as well, it is very likely we will see very
cold RFDs from any supercells so the potential for wind to 70
mph is also there.

With the cooler RFD potential and straight hodographs
facilitating splitting, there is the potential for upscale
growth/clustering to develop. If this does occur in our area,
expect the potential for significant hail to increase as updraft
width increases. An attendant stronger wind threat may develop
although confidence is low due to the potential for fast
developing surface inversions from outflow/RFD.

Lastly, the tornado threat tomorrow should remain fairly
limited. Very deep vertical mixing and drier profiles (LCLs
approaching 1500m) should make it difficult for a tornado threat
to arise. Additionally, streamwise vorticity in the lowest 1 km
is very limited except where guidance has a more zonal component
of the theta-e gradient in southern Manitoba. Here winds become
more backed at the surface, allowing for slightly better
streamwise vorticity. The potential for significant tornadoes
should be kept to a minimum thanks to very poor thermodynamics.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1213 PM CDT Tue Jun 11 2024

VFR ceilings will prevail for the TAF period, with isolated MVFR
for all TAF sites except FAR possible through 00z. After that,
winds will diminish this evening and skies will remain VFR. Low
level wind shear will arise after 06z and last through at least
14z. Thunderstorms may develop around 16-18z near GFK/FAR but
confidence is too low to add TSRA to the TAF.

&&

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

&&

$$

DISCUSSION...Perroux
AVIATION...Perroux