360
FXUS63 KFGF 211153
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
653 AM CDT Tue May 21 2024

.KEY MESSAGES...

- Northerly winds gusting to 50 mph are expected across the
  southern  Red River Valley this afternoon and evening. There
  is a 20 percent chance for gusts around 60 mph.

- Heavy rainfall may lead to localized overland flooding this
  afternoon into Wednesday for the Southern Red River Valley
  into Minnesota.

- Depending on the extent of heavy rain, river flooding could
  start as early as Thursday for some areas along the southern
  Red River basin.

&&

.UPDATE...
Issued at 652 AM CDT Tue May 21 2024

The initial areas of rain associated with the approaching
system is spreading into our south matching up with timing from
earlier. Lighting activity is mimnimal and most reports so far
for the activity alighned with our region are in the light to
moderate range (again within expectations). So far forecast
appears to be on track.


&&

.DISCUSSION...
Issued at 416 AM CDT Tue May 21 2024

A strong Colorado low type system is developing currently over
eastern Colorado with SW flow increasing deep moisture advection
into the Northern Plains this morning. This system will be
responsible for wind, rain, and potential excessive rain impacts
today into Wednesday. As this system transitions east an active
quasi-zonal pattern with additional organized mid/upper lows moving
out of the Pacific NW or Canadian Prairies will remain in place over
the next 7 days with additional rain events possible but lower
confidence/predictability regarding impacts at this time.

Regarding Winds today: As the surface low deepens and moves north,
strong gradient will support increased winds and while mix layers
are deep, model mixed layer winds show maximum values in the 40-
47kt range in the southern Red River Valley this afternoon into the
early evening and this is a consistent signal between current
deterministic models. A little better mixing 50kt (warning impact)
winds may develop and NBM probs highlight around a 20% probability
for this in the far southern Red River Valley.

Regarding rain/flooding potential: There is strong consensus for the
700 MB low track to support a prolonged period of deformation lining
up from the southern Red River Valley into west central MN. Main
instability axis is well to the south (MUCAPE may only be around 100-
200 J/KG at the most) and HREF shows any signal for higher rates
(1"+/hr) to the southeast. Still, forcing and instability (as it is)
will be enough for periods of light to moderate rain and occasional
convective pocket of brief heavier rain to track over a lot of our
area. Heaviest rain axis is more likely to linger longer in MN than
in the southern RRV, and probs from NBM and HREF support this trend.
HREF PMM would indicate the heaviest rain axis supporting 2-4" over
6hr periods, though higher amounts are still possible especially if
considering the length of the event. Adjusted FFG would require
almost double those values for more than localized runoff and as
rates are not favorable for actual flash flooding. Localized
overland/areal type flooding would be favored (ponding/more
gradual runoff). Depending on the extent of the higher totals
riverine flooding is possible with a delay in responses
(responses on rivers by Thursday from this rain event).

River probabilities relayed from RFC coordination on Mon day shift:

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%.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 653 AM CDT Tue May 21 2024

Aviation impacts will increase across southeast ND and northwest
MN through the day as rain showers and eventually MVFR stratus
overspread those regions. Northeast ND should remain VFR through
the TAF period. Winds increase as this low pressure system
moves through the region, with the strongest winds in southeast
ND and parts of west central MN where gusts around 40kt are
possible this afternoon and evening. Low level wind shear
(around 50kt) will be possible at KBJI late in the TAF period.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Wind Advisory from noon today to 11 PM CDT this evening for
     NDZ039-049-052-053.
MN...Wind Advisory from noon today to 11 PM CDT this evening for
     MNZ003-029-030-040.

&&

$$

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