251
FXUS63 KFGF 220906
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
406 AM CDT Wed May 22 2024

.KEY MESSAGES...

- Isolated severe thunderstorms are possible Thursday late
  afternoon and evening, mainly south of Highway 2. Hail up to
  the size of ping pong balls (1.5") and 60 mph winds are the
  main threats.

- Another period of 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.

&&

.DISCUSSION...
Issued at 344 AM CDT Wed May 22 2024

The main low pressure system responsible for rain and wind impacts in
the previous 24hr has transitioned east of the region, with lingering
light rain within the cyclonic flow aloft on the back side of this
system. Shortwave ridging eventually amplifies over our region
ahead of the next approaching mid/upper level low that arrives later
Thursday night shifting east Friday. This upper low has a stronger
period of CAA and well below average temperatures are forecast
Friday into Saturday morning. A complicated quasi-zonal pattern
persists beyond this, allowing for additional mid level waves to
pass through the Northern Plains before ensembles indicate a trend
towards ridging next week (putting an end to our more
active/cooler pattern).

Severe threat Thursday:

As southwest flow builds on the back side of the shortwave ridge
ahead of the next developing mid/upper low, a theta-e gradient
tightens and a warm front possibly lifts into southern ND/west
central MN. South of this frontal zone increasing BL Tds will
support potential for MLCAPE 1000-2000 J/KG (HREF shows
probabilities for 1500 J/KG MLCAPE 30-60% along and south of I-94).
CAPE becomes increasing elevated with stronger capping north of this
front as BL will be much cooler (and possibly cloudier). Veering
profiles with effective shear 30-40kt would support organized cells
if they develop near that frontal zone, and about 30% of HREF
members show brief UH tracks greater than 75 m2/s2 aligned with that
region (a few outliers with longer stronger tracks). Timing of cap
erosion, uncertainty regarding synoptic forcing due to mid level
shortwave riding, and frontal position (which has varied over the
last few days) will be complicating factors on coverage. Still,
there is a window for severe storm development with all hazards
being possible along/south of I-94 based on the current favored
frontal position.

Heavy rain impacts Thursday-Friday:

The most organized period of rain will be with the mid/upper low
passage Thursday night into Friday, with a broad area of rain
expected to move over the region. Highest rates as usually will be
with convection earlier in the event when coverage will be less
certain, before a transition to more light/moderate stratiform rain.
Ensemble probs for 1"+ 2hr rain are in the 50-60% (both raw ensemble
probs and NBM), with the probability for 2"+ less than 20% and likely
tied to convective components earlier on. As this wave will be
relatively quick and there isn`t a signal for slower/back building
convection flash flood threat isn`t highlighted. Where higher rain
totals do occur though, they could contribute to eventual rises on
rivers, though this will be directly related to where and how
widespread the heavier rain is.

Frost potential Saturday morning:

There is a strong signal for below average 850MB temps on the back
side of the departing mid/upper low (as low as -2C) and 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 Tds 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 /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1123 PM CDT Tue May 21 2024

Look for IFR CIGs at KBJI through the early morning before
improving to MVFR conditions by mid to late morning Wednesday.
A brief period of MVFR conditions is possible at KTVF just prior
to sunrise. Look for VFR conditions elsewhere as rain continues
to work to the east and northeast through the period. Skies
will become mostly clear after midday.

&&

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

&&

$$

DISCUSSION...DJR
AVIATION...Lynch