024
FXUS63 KFGF 200920
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
420 AM CDT Thu Jun 20 2024

.KEY MESSAGES...

- Periods of scattered showers and thunderstorms are forecast
  tonight into Saturday. There is a low chance for isolated
  severe storms south of the I-94 corridor late Friday into
  early Saturday.

- Unsettled weather continues into next week, with potentially
  strong to severe storms Monday.

&&

.DISCUSSION...
Issued at 410 AM CDT Thu Jun 20 2024

...Synopsis...

Southwest flow aloft continues over the Northern Plains and
Upper Midwest sandwiched between broad upper ridging over the
eastern CONUS and upper troughing in the West. This continues
through Friday, allowing embedded waves to move through flow
aloft over the region. Additionally, upper level divergence
resides over the region as entrance region of an upper jet
connects the two synoptic features.

At the surface, post-cold frontal air mass and high pressure
over northern MN/western ON is helping keep conditions mostly
dry over our area today (save some very light rain showers in
far southern Red River Valley and west-central MN this morning).

A warm front is forecast to slowly migrate northward out of NE
into SD separating richer moisture content and a more buoyant
airmass to its south. With a lack of more focused forcing aloft
as well as general parallel orientation of the front to flow
aloft, the warm front is not expected to make much progress
northward, keeping much of the potentially robust convection
south of our area today into Friday. There is however an
opportunity for scattered showers and thunderstorms to form on
the nose of a low level jet late tonight in southeast ND and
west-central MN. This activity is expected to be progressive
with the help of progressive and transient nature of embedded
waves aloft. There is very little chance this activity will
result in strong to severe convection with very little support
in sufficient instability feeding convection.

Friday into Saturday, the upper pattern starts to change as
upper ridging retrogrades out of the eastern CONUS into the
Intermountain West, with upper troughing migrating east into the
Northern Plains. This will provide better focus for showers and
thunderstorms to develop within the Dakotas into Minnesota.
However, the vast majority of guidance continues to keep the
warm front south of the area within SD, as well as track of
eventual surface low pressure underneath the shortwave trough.
An inverted trough/surface front does extend northward out of
this surface low moving through our area late Friday into
Saturday. This latter feature will provide the focus for
scattered showers and thunderstorms in our area during this
time, including a low chance in brief, isolated severe storms
in southeast ND into west-central MN.

Getting into next week, the flow aloft becomes more zonal with
progressive upper waves moving across the northern tier of the
CONUS/southern tier of CAN. One such wave is well advertised on
Monday. This synoptic forcing along with potentially favorable
instability and wind shear for organized, robust convection
introduces the potential for severe storms on Monday. Confidence
degrades in details regarding timing and amplitude of waves that
would drive precipitation chances and potentially impactful
weather. Temperatures are forecast to be generally near
average, with a brief opportunity for above average
temperatures Monday into Tuesday.

...Low chance for severe storms late Friday into early Saturday...

Available guidance from ensembles and CAMs continue to keep at
least a low chance for brief, isolated severe storms south of
the I-94 corridor late Friday into early Saturday. Limiting
factors in higher chances and/or more robust organization of
thunderstorms include lack of better instability as well as
lackluster organization from marginal shear and messy storm
mode. The low chance is mainly stemmed from the potential
scenario of the aforementioned warm front being further north
toward our area allowing better opportunity of instability to
feed into convection as it enters our area from the south and
west. Even with this scenario, hail up to the size of quarters
would be the main hazard given the elevated nature of
thunderstorms and lack of better shear/magnitude of wind.

...Potentially strong to severe storms Monday...

While Monday is still 5 days out, ensemble guidance is in
surprisingly good agreement in a notable shortwave trough moving
through North Dakota into Minnesota within zonal flow aloft.
This shortwave trough has a better chance of bringing increased
winds aloft out of the west, including high chance of at least a
50kt mid level jet. Staying in the mid levels, guidance is also
supporting the idea of steep lapse rates advecting into the
region as an EML develops in the Intermountain West, with a
branch breaking away out of MT/WY/CO into the Dakotas with the
help of the shortwave. At the surface, the vast majority of
guidance also allows for a moist and buoyant warm sector to
initially advect into the High Plains and eventually eastward
into/near our area by Monday. Both steep lapse rates aloft and
very buoyant low levels support most ensemble guidance favoring
high chance in moderate to highly unstable air mass within this
warm sector.

Orientation of the warm sector and bounding fronts will be
important in determining storm mode (which in turn will modulate
hazards). But most guidance depicts a scenario where increasing
flow aloft overruns frontal orientation to allow the potential
for discrete supercells and/or well organized convective
complex. This increases the chance in potentially significant
hazards given the likelihood of very unstable air mass
juxtaposed with increased winds aloft with favorable storm mode.

While mesoscale specifics remain unclear at this time, severe
storms with the potential for significantly severe hazards
appears to be a plausible outcome.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1148 PM CDT Wed Jun 19 2024

VFR conditions should prevail through the TAF period, though
there is a low (less than 10%) chance for ground fog development
early Thursday morning if skies remain clear overnight. Surface
high pressure remains in place, resulting in calm or light and
variable winds (5 mph or less) through Thursday morning. Weak
gradient begins to build ahead of low pressure and southeast
winds prevail 5-10kt during the day Thursday. A few
sprinkles/light showers or virga may move over southeast ND and
west central MN through Thursday morning. Better rain chances
(and thunderstorm chances) arrive later Thursday night after the
current TAF period.

&&

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

&&

$$

DISCUSSION...CJ
AVIATION...DJR