309
FXUS63 KFGF 202029
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
329 PM CDT Mon May 20 2024

.KEY MESSAGES...

- Potential heavy rainfall may lead to overland flooding Tuesday
into Wednesday for the Southern Red River Valley into Minnesota.

- If heavy rainfall does happen then River flooding could start as
early as Thursday for some areas along the southern Red River.

- Chance for strong to severe thunderstorms Thursday.

&&

.DISCUSSION...
Issued at 329 PM CDT Mon May 20 2024

Tonight will be the calm ahead of the storm Tuesday
afternoon into the evening. There will be a bowling ball of a low
pressure system coming up from the southwest and eventually merging
with another system moving east through the Canadian Providences.
Winds may be gusty and potential reach Advisory levels in southeast
ND however there is some uncertainty as to whether or not those
winds will reach the surface due to mixing potential or even if the
rainfall will be strong enough to drag the wind down to the surface
as well. The clusters are currently split on how these storm tracks
will impact our area. A more northwestern track through our forecast
area will bring higher rain accumulations into the valley and into
the devils lake basin. Looking at cluster consensus there is more
confidence for West-central Minnesota to receive the higher rain
totals for our area.

Potential Riverine Flooding Later This Week into Next Week:

Heavy rainfall from strong low pressure system moving into the Upper
Midwest remains possible over southern and eastern portions of the
Red River Basin Tuesday. This brings a chance to push river levels
into flood stage as early as mid week or as late as early next week,
particularly within the southern Red River Basin. While there is
still some uncertainty in where excessive rain falls within our
area, there is a scenario where 1-3 inches with locally higher
amounts falls over the far southern Red River Valley and west-
central into northwest Minnesota. There are additional chances for
rainfall later this week, however details are too uncertain to
comment on their amounts and locations.

Given soils that are near to completely saturated in these areas,
much of this rainfall would runoff into river systems. Additionally,
river levels are slightly elevated from recent bouts of rainfall
over the last month.

The chance for reaching flood categories in the southern Red River
Basin through early next week is as follows:

Minor Flooding: 20-40%
Moderate Flooding: 10-30%
Major Flooding: Less than 10%

For the Red River at Fargo (FGON8) specifically, one can add 10-30% to Minor and
Moderate values, with chance for Major around 10%.

Low probability severe potential Thursday (less than 5%):

Most ensembles favor a period of shortwave ridging in the wake of
the departing mid/upper low before the next organized wave arrives
Thursday night. There is a signal along the western axis of this
ridging for SW return flow ahead of the next wave. This may result
in increasing BL Tds and steepening mid level lapse rates.
Deterministic GFS (Day 4) shows MLCAPE in the 1000-1700 J/KG range
across our south and west during peak heating Thursday afternoon. At
this range there isn`t a strong signal in SB/MU CAPE from ensembles
during the same period (7% prob for 1000 J/KG SB CAPE near SD/ND
state line). Veered hodographs and effective shear in excess of 40kt
as shown would support of organized convection/supercells "if" that
pattern sets up and there is forcing available to initiate
convection/overcome capping. There is no signal in ensemble based
machine learning, analogues, Tonight will be the calm ahead of the storm Tuesday
afternoon into the evening. There will be a bowling ball of a low
pressure system coming up from the southwest and eventually merging
with another system moving east through the Canadian Providences.
Winds may be gusty and potential reach Advisory levels in southeast
ND however there is some uncertainty as to whether or not those
winds will reach the surface due to mixing potential or even if the
rainfall will be strong enough to drag the wind down to the surface
as well. The clusters are currently split on how these storm tracks
will impact our area. A more northwestern track through our forecast
area will bring higher rain accumulations into the valley and into
the devils lake basin. Looking at cluster consensus there is more
confidence for West-central Minnesota to receive the higher rain
totals for our area.

Potential Riverine Flooding Later This Week into Next Week:

Heavy rainfall from strong low pressure system moving into the Upper
Midwest remains possible over southern and eastern portions of the
Red River Basin Tuesday. This brings a chance to push river levels
into flood stage as early as mid week or as late as early next week,
particularly within the southern Red River Basin. While there is
still some uncertainty in where excessive rain falls within our
area, there is a scenario where 1-3 inches with locally higher
amounts falls over the far southern Red River Valley and west-
central into northwest Minnesota. There are additional chances for
rainfall later this week, however details are too uncertain to
comment on their amounts and locations.

Given soils that are near to completely saturated in these areas,
much of this rainfall would runoff into river systems. Additionally,
river levels are slightly elevated from recent bouts of rainfall
over the last month.

The chance for reaching flood categories in the southern Red River
Basin through early next week is as follows:

Minor Flooding: 20-40%
Moderate Flooding: 10-30%
Major Flooding: Less than 10%

For the Red River at Fargo (FGON8) specifically, one can add 10-30% to Minor and
Moderate values, with chance for Major around 10%.

Low probability severe potential Thursday (less than 5%):

Most ensembles favor a period of shortwave ridging in the wake of
the departing mid/upper low before the next organized wave arrives
Thursday night. There is a signal along the western axis of
this ridging for SW return flow ahead of the next wave. This may
result in increasing BL Tds and steepening mid level lapse
rates. Deterministic GFS (Day 4) shows MLCAPE in the 1000-1700
J/KG range across our south and west during peak heating
Thursday afternoon. At this range there isn`t a strong signal
in SB/MU CAPE from ensembles during the same period (7% prob for
1000 J/KG SB CAPE near SD/ND state line). Veered hodographs and
effective shear in excess of 40kt as shown would support of
organized convection/supercells "if" that pattern sets up and
there is forcing available to initiate convection/overcome
capping. There is no signal in ensemble based machine learning,
analogues, and NBM CWASP. The lack of ensemble support lowers
confidence enough to hold off on messaging a severe threat, but
it is still worth monitoring.


&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1253 PM CDT Mon May 20 2024

VFR conditions will be predominant throughout the period. There
will be an occasional MVFR ceiling to develop but that has been
trending to only last about an hour or so and is hard to gauge
looking at satellite. Winds will become variable starting this
evening until tomorrow morning however winds speeds are expected
to be 6kts or less.

&&

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

&&

$$

DISCUSSION...CJ/MM
AVIATION...MM