Area Forecast Discussion
Issued by NWS Grand Forks, ND

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FXUS63 KFGF 292022

Area Forecast Discussion
National Weather Service Grand Forks ND
322 PM CDT Mon May 29 2023

.SHORT TERM...(This evening through Tuesday night)
Issued at 234 PM CDT Mon May 29 2023

Key Messages:

- Chance for scattered showers and thunderstorms continues this
  afternoon into this evening. After a lull in activity Tuesday
  morning, chances increase again Tuesday afternoon.

- There remains a chance for strong to briefly severe storms this
  afternoon into afternoon bringing gusty winds up to 60 mph,
  small hail up to the size of quarters, and locally heavy
  rainfall. Widespread or significant impacts are not expected
  from these hazards.


Water vapor imagery from geostationary and polar orbiting
satellites reveal a collection of low amplitude shortwave troughs
moving within quasi-southwesterly to zonal flow aloft across the
Northern Plains into southern SK/MB. A tongue of low level moisture
feeding into these troughs exists across the Great Plains. At the
surface, this moist air mass is advecting into our area as noted
by dew points into the upper 50s to lower 60s, along with a
surface trough extending through central North Dakota.

These features are leading to scattered showers and
thunderstorms, with focus near one shortwave trough within
northeast ND, as well as on the leading edge of the aforementioned
moisture plume. This will be the main driver of precip through
mid to late afternoon as it slowly pushes northeast, keeping best
chances up to 60% within northwest MN and northeast ND before 7 PM.

Another shortwave trough within eastern MT will continue east,
helping propagate the surface trough toward our area. By early
this evening, hi res guidance suggests a LLJ develops near the
tri- state to west-central MN area ahead of the approaching
trough. This is expected to help focus convection tonight
generally between 8 PM to 4 AM.

Despite the two synoptic troughs, overall wind shear is lacking
but still around 20 to 30 kt range. Additionally, mid level lapse
rates are marginally steep given a lack of notable EML. However,
there is enough low level moisture and cool temps aloft to allow
for weak instability with MLCAPE values around 1 to 1.5 kJ/kg.
Regardless of the lackluster parameter spacing, there may be just
enough instability and cell interactions to allow for strong to
briefly severe storms this afternoon and evening capable of
producing a few rogue wind gusts no more than 60 mph and some
brief instances of quarter sized hail.

There is a chance for heavy rainfall associated with training
and/or back building thunderstorms from the LLJ- driven
convection this evening. This is conditional upon clustering
thunderstorms consolidating an outflow boundary to push and match
the LLJ feeding and sparking convection upon this mesoscale
forcing mechanism. Latest CAMs suggest hourly rainfall rates up to
2 inches per hour are possible in this scenario, which may equate
to local minor flooding, especially if this occurs over any urban
or poor drainage landscapes. Guidance generally pegs this
potential around the tri-state into west-central Minnesota area,
although confidence is not lowered in this scenario given the
dependence on meso- to storm-scale factors necessary to anchor
convection for training/back building.

As of now, widespread or significant impacts from these hazards
are not expected.

Guidance suggests a lull in precip coverage during morning hours
Tuesday before the next diurnal uptick in chances ahead of the
aforementioned surface trough now into eastern ND utilizing a
similar environment as today.

Note on near critical fire weather conditions this afternoon
within northwest MN: moisture is moving faster into the area where
the related Special Weather Statement is currently valid quicker
than previously forecast this morning, helping close the window
for elevated fire weather conditions.

.LONG TERM...(Wednesday through Monday)
Issued at 234 PM CDT Mon May 29 2023

-Well above average temperatures continue to be favored through the
long range periods.

-Thunderstorms remain possible each day over parts of the region
next week, and there is a low probability for strong to severe
thunderstorms. Due to the nature of the pattern predictability on
coverage/impacts will remain low at this range.

The large scale blocking ridge is show to shift back towards the
west and again remain a dominate feature in our long range pattern.
There is strong clustering/consensus on the general evolution of
this pattern at least until early next week, with there is some
indication within several ensemble clusters showing some weakening
of the ridge due to stronger troughing (this is less than 25% of all
unified ensemble members). There should be a tendency for very
warm/above average temperatures in this pattern and based on biases
of the previous week and current ensemble member ranges we are
likely to see highs in the upper 80s to lower 90s. As would be
expected there is increased spread in potential temperatures early
next week (the stronger troughing would allow for temperatures
closer to seasonal averages).

One difference will the be degree of moisture transport along the
western extent of the ridge tapping into the higher Tds of the
southern CONUS. This lowers the potential for RH values to fall
within near critical or critical levels, but supplies the region with
higher PWATs (within the 99th percentile of NAEFS model climatology).
There is highly variable evolutions of the surface patterns/profiles
that play into severe potential/impacts. There is at least a 20-40%
probability based on the three main ensemble suites of 1500 J/KG of
SB CAPE. Synoptic forcing will tend to be disorganized, and
surface/boundary evolutions day to day will play a role in
shower/thunderstorm coverage/impacts. CSU/NBM machine learning do
not highlight one period/day in particular with a 5% or greater
probability for severe convection, however this is the type of
pattern where there is at least a conditional risk for strong to
severe storms (forcing, instability, shear all will remain
uncertain). It is safe to say though, that with higher PWATs/BL
moisture availability storms that do develop may carry a localized
heavy rain risk. Probability for 0.25"+ during any one 24hr period
is less than 30%.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1245 PM CDT Mon May 29 2023

Overall, VFR conditions are favored across the area, conditional
upon scattered thunderstorms impacting any TAF site within the
area. A couple of small systems move through the region today and
tonight bringing a chance for scattered showers and thunderstorms.
Some thunderstorms have contributed to MVFR CIGs in addition to
lowered vsby and attached CB. A lull in thunderstorm activity is
forecast between 10 UTC through the morning Tuesday.

There is a chance for MVFR CIGs for portions of northwest and
west-central MN, including KBJI, between 09-15 UTC Tuesday.

Otherwise, winds will be out of the south and southwest today.
Winds start gusty between 20-25 kt within the Red River Valley
and northwest Minnesota this afternoon before lessening to under
15 kt.




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