487
FXUS63 KFGF 291203
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
703 AM CDT Tue Sep 29 2026

.KEY MESSAGES...

- Rain ends from west to east during the day. Localized flooding
  impacts may be found this morning in a zone from Thief River
  Falls to just south of Grand Forks to north of Valley City.

&&

.UPDATE...
Issued at 449 AM CDT Tue Sep 29 2026

Flood watch for parts of southeast ND including Fargo-Moorhead
will expire on schedule. The heaviest rainfall overnight fell
more north of the watch area, with the exception of Barnes
county. Overnight the heaviest rainfall with amounts of 1.50 to
2.50 inches 06z-09z fell from near Valley City northeast to
just south of Grand Forks to near Thief River Falls. Since 08z
the rates of rainfall have diminished greatly with 1 hour
rainfall rates from radar showing 0.10 to 0.20 inch. Will
continue current areal flood warning and flood advisory for
parts of the Sheyenne River basin where total rainfall of 4-6
inches has fallen in the last 24 hours. Rainfall will end from
west to east gradually today...taking the longest to exit
Bemidji-Fergus Falls which wont be til later afternoon. But also
this area has received much lighter amounts of rainfall so far.

&&

.DISCUSSION...
Issued at 301 PM CDT Mon Sep 28 2026

...Synopsis...

Broad southwest flow aloft currently resides over the Northern
Plains and Upper Midwest as a result of longwave upper troughing
in the West. This is helping draw northward increasing moisture
content, while also allowing several shortwave troughs embedded
within the flow aloft to provide forcing for ascent to drive
widespread rainfall into the eastern Dakotas and northern
Minnesota this afternoon through tonight. Weak but sufficient
instability accompanying the surge in moisture will also allow
embedded thunderstorms to be present, especially tonight. Two or
more "waves" of rainfall with embedded thunderstorms will drive
potential for training higher rain rates - bringing potential
for localized flooding impacts. More details on this potential
found below.

Tuesday morning, rainfall should end west to east, with most/all
of the area becoming dry by the afternoon. This will usher in a
relatively dry period through the remainder of the week, with
the exception of some transient showers potentially late
week/weekend, but ultimately resulting in little rainfall
amounts, if any. This is a result of generally zonal to
northwest flow aloft amid upper ridging building over the High
Plains/Intermountain West. Near to above average temperatures
are forecast through Wednesday, turning average to below average
temperatures late this week.


...Potential flooding impacts this afternoon & tonight...

There remains potential for an additional 3 to 6 inches of
rainfall this afternoon through tonight in portions of southeast
ND, central/southern Red River Valley, into northwest MN. The
majority of CAMs continue to paint this scenario somewhere
within the aforementioned areas, but each with their own variety
of exactly where this will occur. Locations that experience
these amounts are liable to see flooding impacts.

Confidence is relatively high in this output based on the
presence of a stationary boundary extending southwest to
northeast generally from the southern James River Valley in
southeast ND into the central Red River Valley into northwest
MN. This sets the stage for additional upper forcing to act
upon, which is well advertised to resurge tonight in the form of
a shortwave trough propagating out of the High Plains of WY/SD,
through the Dakotas, and into northwestern ON by Tuesday
morning. This will help reinvigorate the low level jet within
the "warm sector" of the aforementioned stationary front -
suggested to generally remain in this orientation/position
through the event, with some eventual movement eastward Tuesday
morning.

Abnormally high moisture content (~1.5 inches of PWATs)
coupled with weak but sufficient instability (MUCAPE ~800 J/kg),
and storm motion generally parallel to frontal orientation will
drive high rain rates. Rain rates like 0.5-1" per hour and/or
2-4" per 6 hours will result in areas that see repeated
thunderstorms move over any particular location for at least 2
hours.

Pre-conditioned areas that have recently experienced soaking
rainfall is also important to consider when identifying
potential areas for subsequent flooding impacts. While these
advertised highest rain rates may occur in northwest MN, higher
rain amounts from this morning have generally missed this area.
Conversely within southeast ND, rainfall from this morning in
the 1-2 inch range have already occurred, with continued
convective rates from thunderstorms still ongoing in southeast
ND at the time of this Forecast Discussion issuance. Despite
this area in drought, higher rain rates coupled with
previously/currently received rainfall still allow for excessive
runoff.

Of course, urban areas are relatively more susceptible to these
higher rain rates; this includes cities like Fargo-Moorhead
and/or Valley City.

While the overall area of concern holds generally medium to high
confidence, more precise location of highest rainfall amounts
remain in question. Because of this, have opted to not issue a
Flood Watch; however, a Flood Watch may be issued should
confidence increase in more precise location of potential area
of concern later this afternoon/early evening.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 657 AM CDT Tue Sep 29 2026

Lots of variety around the area.....For the most part IFR to
lower end MVFR ceilings. Rain area is moving east and will end
in the far eastern fcst area 19z-21z. Winds will eventually turn
become westerly 5 to 12 kts today. Watching expanse of fog
northwest of Devils Lake as it may well move into the airport
area just after 12z. Tempo group for 3/4sm br for KDVL for this,
but it could be 1/4sm FG.

&&

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

&&

$$

UPDATE...Riddle
DISCUSSION...CJ
AVIATION...Riddle