615
FXUS63 KFGF 122027
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
327 PM CDT Sun May 12 2024

.KEY MESSAGES...

- Smoke from Canadian wildfires will continue to impact the
  region into Monday morning.

- Areas of frost are expected for areas mainly north of US
  Highway 2 late tonight into Monday morning.

&&

.DISCUSSION...
Issued at 327 PM CDT Sun May 12 2024

Northwest flow on the back side of a mid/upper low centered over
northwest Ontario is in place currently with surface ridging
building south behind the cold front (now south of our forecast area
in SD/central MN). The larger scale pattern becomes progressive and
quasi-zonal with broad troughing developing in Canada, which results
in  a series of mid level shortwave ridges and troughs passing
through the Northern Plains next week. This pattern will tend to
support temperatures varying from the 60s to 70s each day as
ridging/troughing passes which is within a standard deviation of
climate averages (basically seasonal). There will also be increasing
chances for light showers (and enough instability for low non-severe
thunderstorm potential). The best resolve mid level wave arrives
late Monday night through Tuesday, with likely rain showers and
closer a 50-70% chance for at least 0.1" rainfall during that
period. Excessive rainfall and severe thunderstorms are not expected
based on analogues and ensemble based machine learning during the
next 7 days.

Regarding smoke timing/impacts:

Northwest flow continues to bring reinforcing periods of smoke into
the region today, with the highest smoke concentrations closer to
the frontal zone and wrapping up into the mid level low to our
northwest. This smoke is originating from fires located over norther
Alberta, Saskatchewan and Manitoba. Satellite (matching up with
latest HRRR/RAP smoke models) indicates a period of improvement
possibly arriving this evening, though additional pockets of smoke
may continue to rotate into the region through Monday morning
becoming trapped below the nocturnal inversion. The shift in flow as
the next mid level shortwave should result in surface smoke impacts
eventually ending Monday, though the back side of that system could
bring smoke right back as flow shifts back out of Canada later
Tuesday night.

Regarding frost impacts tonight:

As smoke allows for long wave radiation to escape, it will not
factor into low temperatures tonight the way clouds would. As
actual cloud cover should remain mostly clear and winds should
decrease, we should see good radiational conditions. Surface Tds
are forecast to be in the 32-35F range during peak radiational
cooling across our north-northeast, so the floor for our lows
will be within range for frost conditions. NBM probs are low
regarding the potential for widespread lows 35 or lower, however
the pattern should support our traditional colder/outlying
locations dropping to the 33-36F range supporting frost
formation on surfaces. Based on experience of seeing those
locations drop lower than guidance in similar patterns,
confidence was high enough to issue a Frost Advisory (3am-8am)
along the US/Canada border and near the Hwy 2 corridor in MN
(where traditional colder spots are most likely to have frost
impacts). In similar patterns the immediate Red River Valley
(and urban areas) tend to remain higher, but there is still
potential (less than 30% chance) for frost in outlying parts of
counties just south of the current advisory where Tds may be
near 36F.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1237 PM CDT Sun May 12 2024

MVFR to VFR conditions due to the wildfire smoke. Visibilities are
going to hard to predict as there are some patches of thicker smoke
moving through. Overall the visibilities should improve by the
evening and with the smoke moving out completely later tonight.
Winds will remain out of the north through tonight, but KDVL will
begin shifting to the east around 05z while the rest of the TAF
sites remain northerly.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Frost Advisory from 3 AM to 8 AM CDT Monday for NDZ006>008-016-
     054.
MN...Frost Advisory from 3 AM to 8 AM CDT Monday for MNZ004>009-
     013>017.

&&

$$

DISCUSSION...DJR
AVIATION...MM/DJR