604
FXUS63 KFGF 120413
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
1113 PM CDT Thu Jul 11 2024

.KEY MESSAGES...

- Heat related impacts are expected into this weekend,
  especially Saturday afternoon. Impacts will be highest for
  heat sensitive or vulnerable groups and anyone without
  effective cooling or hydration.

- There is a level 1 out of 5 risk for severe thunderstorms
  Friday evening into the overnight for northeast North Dakota
  and far northwest Minnesota.

- There is a level 2 out of 5 risk for severe thunderstorms
  across the region Saturday afternoon into Saturday night.

&&

.UPDATE...
Issued at 1111 PM CDT Thu Jul 11 2024

High level smoke continues to move through the region this
evening, with shower and thunderstorm activity remaining north
of the International border. Overnight lows drop down to the
mid 60s. Heat continues to build into the region tomorrow and
into the weekend.

&&

.DISCUSSION...
Issued at 340 PM CDT Thu Jul 11 2024

Large scale mid/upper ridging centered over the SW US will
continue to be a factor in the evolution of the pattern over the
Northern Plains over the next 7 days. Initially the amplitude
of the ridge will have pushed far enough north, with higher
heights in westerly flow bringing the hottest air mass of the
season so far into our CWA. A combination of southerly BL flow
and seasonally high evapotranspiration will result in higher Tds
advecting northward exacerbating heat impacts. The ridge does
become more depressed as a stronger mid/upper trough passes
north then deepens near Hudson bay early next week, allowing for
north-northwest flow to build back into the Northern
Plains/Upper Midwest. This results in a downward trend in
temperatures near or slightly below seasonal averages. The
pattern supports periodic shower/thunderstorm chances in both
cases as mid level trough passages propagate around the top of
the ridge or within north-northwest flow. Confidence and the
potential for impacts decrease as the pattern shifts next week,
and drier/cooler flow arrives.

...Heat impacts through this weekend...

Temperatures each day are shown by NBM to reach the upper 80s
and lower 90s, with highest values Saturday in the southern Red
River Valley. NBM hasn`t shown as strong of a low bias as during
transition seasons when the mixed layer was deeper and surfaces
drier, and the spread between the 25th and 75th is 4-5F, which
ultimately isn`t much of a spread considering the base NBM
Saturday is generally close to the median or even 75th. Due to
the degree of BL Tds advecting north (and potential for these
values to be even higher) heat indicies (along with other heat
impact indicies) will approach criteria in line for advisory
consideration Saturday afternoon especially in the southern Red
River Valley (wet bulb globe temperatures actually forecast into
the extreme category). Where the frontal zone ultimately sets
up, along with any other cloud/precipitation impacts will play
into where impacts ultimately occur and the magnitude of these
impacts.

...Severe threat Friday evening and overnight...

Strong capping and lack of organized forcing will play a role in
limiting local thunderstorm initiation despite high instability in
place Friday afternoon. This changes some by Friday evening, as
upstream activity in western ND or the southern prairies of Canada
may spread east-southeast towards our northwest. An axis of modest
elevated instability remains in place after sunset with good effective
shear (35-40kt), so if activity does hold together it could maintain
a marginal severe threat into northeast ND and far northwest MN.
Currently there is a relatively high spread in CAMs/HREF
membership on how that activity may evolve as is moves east, but
wind and marginal hail would be the most likely impacts.

...Severe threat Saturday afternoon into Sunday morning...

A deeper plume of rich moisture rotates into the region ahead
of another mid level trough riding around the northern extent of
the ridge. Very high CAPE values and deep layer shear are shown
across our area centered along a theta-e axis, with several
fronts stalled within our CWA. Initially capping may limit
initiation, but considering surface low pressure proximity and
at least some local low level convergence there is potential as
shown by some guidance for discrete initiation earlier in the
day and eventually upstream activity may once again merge into
one or more MCS clusters. Due to the nature of the air mass and
potential for better forcing impacts/coverage may be higher.
The signal for wind is strongest (with DCAPE over 1500 J/KG) but
the magnitude of instability and deeper layer shear raises
potential for larger hail to around ping pong ball size if
discrete storms were to develop.

...Low chance severe Sunday...

A stronger mid/upper wave approaches the region from Canada late
Sunday afternoon into Sunday evening, and while the main theta-e
axis and frontal zone will have shifted southeast, we may have a
window for severe potential as highlighted by 5% severe probability
in GEFS based CSU machine learning.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1038 PM CDT Thu Jul 11 2024

Conditions remaining ideal through the night with VFR skies and
light southerly winds. Good low level moisture should support
cumulus formation by the afternoon leading to FEW at MVFR
levels. Poor winds aloft will not support strong gusts tomorrow
but still monitoring for evening convection moving out of
southern Manitoba impacting northern areas potentially by the
end of the TAF period.

&&

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

&&

$$

UPDATE...Spender/TT
DISCUSSION...DJR
AVIATION...TT