822
FXUS63 KFGF 222355
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
655 PM CDT Wed May 22 2024

.KEY MESSAGES...

- Isolated severe thunderstorms remain possible Thursday between
  4 PM and 10 PM mainly south of Highway 2. Potential hazards
  include hail up to the size of ping pong balls (1.5"), 60 mph
  winds, as well as possible tornadoes.

- Potentially heavy rain late Thursday into Friday may
  contribute to additional rises on rivers within the Red River
  basin.

- Patchy frost is possible Saturday morning, with the best
  chances across the Devils Lake basin.

&&

.UPDATE...
Issued at 655 PM CDT Wed May 22 2024

Reflectivity is diminishing across the area this evening, with
only a couple of showers now in Walsh, Pennington, and Beltrami
Counties. North to northwest winds are expected to become light
and variable as the evening progresses. Temperatures are in the
60s to near 70 from north to south. Overall, the forecast
remains on track this evening; however, a few adjustments were
made to PoPs to reflect current conditions.


&&

.DISCUSSION...
Issued at 245 PM CDT Wed May 22 2024

Synopsis:

Upper troughing lingers across southern Canada into the northern
tier of the CONUS. Yesterday`s upper low currently stalled in
western Ontario continues to fill in/weaken, with another
upstream upper low in the PacNW as seen on water vapor imagery.
At the surface, northwest winds behind the weakening upper low
in ON resides over our ND and MN, with a cold front in SK/MB
making its way southward. Scattered showers with isolated weak
thunderstorms will remain possible this afternoon, particularly
around surface convergent line from northeast ND into the Red
River Valley and west-central MN.

The cold front is progged to move into our area late afternoon
and evening, stalling near the I-94 corridor by Thursday
morning. There is a chance for fog near this front in northwest
and west-central MN Thursday morning given recent moisture and
a chance to calm winds with clear skies.

This stalled cold front turns into a warm front as the PacNW
upper low starts to push east toward the Dakotas Thursday.
Placement of the warm front by Thursday afternoon has
implications on strong to severe storm potential and location by
Thursday afternoon/evening. See below for more details.

Upper low now moving through the Dakotas Thursday into Friday
will bring high confidence in showers and thunderstorms, with
potential areas of heavy rainfall. There is a small chance rain
Friday turns to snow, especially if colder air collocates with
area of precipitation. However at this time, the chance for
precipitation transitioning to snow is low (10%), along with any
potential snow that would fall during the day Friday is likely
to melt on warm surfaces like roadways (limited mainly to grassy
surfaces). Areas that hold this small chance for snow reside in
eastern North Dakota and northwest Minnesota.

Colder air behind this low may allow a chance for frost
Saturday. Upper troughing lingers over our region into next
week, continuing the chance for showers and thunderstorms along
with near to slightly below average temperatures. An eventual
transition to upper ridging is suggested by ensembles mid to
late next week.

Isolated severe storms Thursday afternoon- evening:

Guidance continues to support the cold front stalling and
retreating northward as a warm front by Thursday afternoon
within our area. South of this warm front, increasing low level
moisture and temperatures will aid in increasing instability.
Winds increase in magnitude as the aforementioned upper low
approaches, increasing shear. This approaching upper low will
help the formation of surface low pressure and attendant cold
front in the central Dakotas with eventual movement toward
eastern ND and northwest MN by late Thursday/early Friday,
aiding in synoptic forcing/lift for the development of
thunderstorms, some of which should be strong to severe. Favored
timing of expected strong to severe thunderstorms resides
between 4-10 pm.

There remains some uncertainty in the orientation and how far
north the warm front will reach, but at this time all guidance
keeps it south of US Highway 2, helping increase confidence that
severe potential remains south of US Highway 2.

Sufficient magnitude of shear juxtaposed with instability aloft
should support the potential for hail up to 1.5 inches within
discrete and/or clusters. Wind to 60 mph will also remain
possible, and more favored within clusters and/or linear
segments, particularly if stronger heating in the warm sector
occurs. Tornadoes will also be possible given the potential
strength and orientation of low level shear along with
increasing low level moisture. This may become more favored for
storms that linger around the warm front for an extended period
of time as well as should stronger heating pushing temperatures
into the mid to upper 70s in the warm sector occur.

Heavy rainfall Thursday-Friday leading to potential river rises:

The PacNW upper low now pushing through the Dakotas Thursday
will bring high confidence in widespread showers with scattered
thunderstorms late Thursday through Friday over portions of
eastern ND into northwest MN. In general, 0.5 inches to 1.0
inches can be anticipated (greater than 60% chance), with
between 1-2 inches possible (40%). Higher amounts under
thunderstorms up to 3 inches also remains possible in localized
areas.

Given soils near to completely saturated, additional river rises
may ensue. Some of which may be pushed into flood stage should
heavy rain fall over more sensitive basins like the southern Red
River Basin. There is low confidence in this occuring however.
Additionally, there is very little chance in seeing major
impacts from flooding regardless of any scenario unfolding with
this system.

Frost potential Saturday morning:

There continues to be a strong signal for below average
temperatures aloft on the back side of the departing mid/upper
low (as low as-2C) late Friday into Saturday. NBM shows high
probability (60% or greater) for lows below 36F. For actual
frost impacts though, it may be less certain as recent rains may
hold surface dewpoints above freezing. Still, within ensembles
there is a 20-30% chance for 32F temps, with better probs
towards the traditional cold spots near the Devils Lake Basin.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 628 PM CDT Wed May 22 2024

VFR conditions prevail at all TAF sites this evening. Isolated
light showers are continuing to diminish at this time and are
not expected to cause any impact to aviation tonight into
Thursday morning. The primary concern for this update will be
the low chance for patchy fog along a stalled frontal boundary
early Thursday morning. The best chances for this to occur will
be at KBJI, with lower chances elsewhere. Otherwise, look for
minimal impacts through the period. Further into Thursday, there
will be a chance for showers and thunderstorms; however,
confidence is low regarding impacts to any single location at
this time.

&&

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

&&

$$

UPDATE...Lynch
DISCUSSION...CJ
AVIATION...Lynch