-- Discussion containing changed information from previous version are highlighted. --
097
FXUS63 KFGF 220322
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
1022 PM CDT Sat Sep 21 2024

.KEY MESSAGES...

- There is potential for localized frost in portions of west-
  central Minnesota Sunday night into Monday morning.

&&

.UPDATE...
-- Changed Discussion --
Issued at 1022 PM CDT Sat Sep 21 2024

Skies are almost completely cleared with only a few pockets of
lingering mid level clouds in the region and sky trends were
adjusted to reflect this. Tds have dropped to the upper 30s to
lower 40s and temperatures are rapidly falling with ideal
radiational conditions in place. Based on the current trends
low temps were adjusted to the NBM 25th percentile with matches
up with the idea of colder spots in the upper 30s and most
locations falling to the lower 40s by sunrise Sun morning.
Otherwise, the forecast for the rest of the night remains on
track.

Issued at 640 PM CDT Sat Sep 21 2024

Most CU is transitioning east or dissipating with the setting
sun, and winds are on the expected downward trend. Very dry air
arrives with the northwest flow aloft, so while radiational
conditions are good, there isn`t a signal for fog development.
Shallow/ground fog may still develop near sunrise Sunday, but
impacts are highly uncertain/limited. Guidance doesn`t support
adding fog at this time, so I held off with this update. There
are no other changes from previous forecast/discussion.
-- End Changed Discussion --


&&

.DISCUSSION...
Issued at 241 PM CDT Sat Sep 21 2024

...Synopsis...

Post cold frontal, continental air mass is infiltrating the
Northern Plains with surface high pressure building into the
region from the northwest. This is bringing in drier air with
closer to average temperatures for this time of year. Winds
decrease around sunset this evening, with calm and clear
conditions tonight promoting some ground fog Sunday morning.
Although a lack of higher moisture content should prevent more
widespread chance for dense fog. Surface high pressure moves
into Minnesota late Sunday into Monday. This may help bring some
localized frost to some areas in Minnesota late Sunday night
into Monday morning.

Quasi-zonal flow aloft with progressive shortwave trough early
next week will bring a period of breezy winds, but lack of
moisture keeps dry conditions favored. Mid to late week,
anomalously strong upper ridging builds into the Intermountain
West and Canadian Prairies. This will eventual lean into the
Northern Plains and Upper Midwest, promoting another period of
above average temperatures at least into the 70s and 80s. As
this ridging builds, continued lack of moisture and forcing for
ascent will keep conditions dry.

...Sunday Night Frost Potential...

Dry air mass comprised of dew points into the mid to upper 30s
will overspread the region Sunday night into Monday. Surface
high pressure will be migrating into Minnesota by this time,
with a increasing surface pressure gradient and cloud cover from
the west into North Dakota and Red River Valley SUnday night.
Areas that can remain calm and clear to mostly clear hold the
chance of efficient radiational cooling, bringing temperatures
below 40, and potentially to the mid 30s. Current guidance
presents areas within west-central Minnesota hold potential for
localized frost conditions Sunday night into Monday morning.
Uncertainty in whether or not this happens (and more precise
locations) stems from differences in guidance with respect to
cloud cover and surface winds.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 640 PM CDT Sat Sep 21 2024

VFR conditions should prevail through the TAF period as CU
dissipates with the setting sunset and much drier air arriving
in northwest flow. Gusty winds northwest winds are already
decreasing, and the approach surface high pressure and loss of
mixing should result in light and variable if not calm winds
later tonight/Sunday morning. Clearing skies/light winds do
raise the potential for patchy fog, but the amount of dry air
immediately off the surface (and no guidance highlighting
development) lowers confidence in impacts/coverage.

Surface gradient remains weak through the day Sunday, with dry
air aloft. Prevailing winds should increase with mixing in the
west-northwest direction (6-10kt) for most locations and there
is a a low chance for 5000 FT AGL CU redeveloping in northeast
ND (ceiling development unlikely).

&&

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

&&

$$

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