664
FXUS63 KFGF 112041
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
341 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.

&&

.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 show 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 ultimate 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 relative 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...

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 ore 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 ball 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 /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1240 PM CDT Thu Jul 11 2024

VFR conditions are expected to prevail through the TAF period
across eastern ND and northwest MN. A thin layer of high level
smoke is still moving thorugh the region, while a scattered layer
of shallow CU (4000-6000 FT AGL) is forming from southeast ND
and across northwest MN. Winds are generally of the the south to
southwest 7-13kt (highest in northeast ND), with some gusts this
afternoon around 20kt. Winds should follow a standard daytime
trend, decreasing below 12kt at sunset before increasing from
the south-southeast Friday.

&&

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

&&

$$

DISCUSSION...DJR
AVIATION...DJR