885
FXUS63 KFGF 112324
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
624 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 624 PM CDT Thu Jul 11 2024

Afternoon cumulus are beginning to fade preceding mostly clear
skies tonight if you ignore the lingering smoke which per area
sensors seems to be staying off the sfc with air quality in the
acceptable range. Remainder of the forecast remains on track for
tonight with lows only dropping into the mid 60s an low 60s Tds
making it a good night to possibly leave the AC running for the
heat sensitive folks.

&&

.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 /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 624 PM CDT Thu Jul 11 2024

Minimal aviation concerns with afternoon gusts dropping off by
10pm and clear skies tonight. VFR conditions at all sites
through Friday AM with gusts returning between 15-18Z. Expecting
minimal cumulus tomorrow but FEW040 if anything. Low (20%
chance) for some convection beyond the TAF period tomorrow
night.

&&

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

&&

$$

UPDATE...TT
DISCUSSION...DJR
AVIATION...TT