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098
FXUS63 KFGF 201154
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
654 AM CDT Mon May 20 2024

.KEY MESSAGES...

- The probability for greater than 1 inch of rainfall is 60%
  Tuesday into Wednesday across parts of northwest and west
  central Minnesota.

&&

.UPDATE...
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Issued at 654 AM CDT Mon May 20 2024

Patchy shallow/ground fog has develops in areas of clearing
across parts of the southern Red River Valley and a few
locations have reported visibility drops to 1/4 mile, though
webcams show limited impacts due to the very shallow nature of
most of this fog. I made some adjustments to add patchy fog to
the morning period and issued a Special Weather Statement
through 8am when daytime mixing should allow this fog to burn
off or lift.
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&&

.DISCUSSION...
Issued at 347 AM CDT Mon May 20 2024

Southwest flow remains in place with mid/upper troughing to the west
centered across the US Norther Rockies towards the Great Basin. As
this trough shifts east, a more organized/stronger mid/upper low
develops into the Northern Plains/Upper Midwest to our southeast and
brings a widespread rain event to parts of our region. Following this
the pattern becoming more disorganized with some variation of either
zonal  as a series of additional waves are resolved to move west to
east through an active northern jet stream. There is higher
variation in timing/evolution of these features but there is a
growing consensus on another period of organized rain/embedded
thunderstorms Thursday night into Friday. Temperature trends vary
from seasonal in the 60s/near 70 (like today) to below normal
particularly on days like Tuesday when rainfall/cloud cover could
limit daytime heating (50s for highs where rain occurs).

Tuesday-Wednesday Rain:

Guidance continues to show general consensus of a "Colorado-low" type
pattern Tuesday into Wednesday with an organized deformation rain
band forming a swath of moderate to heavy rain primarily in west
central/northwest MN. Subtle shifts/differences in strength/position
of the mid level wave and interaction/position of a stalled frontal
zone could shift this axis a bit farther west like some guidance
shows, however a growing consensus of ensemble data continues to
favor our east/southeast for highest precip chances/amounts and our
west-northwest (Devils Lake Basin) may remain mostly dry for the
event. Duration of rainfall lowers any risk of excessive runoff, so
the main impacts will be to outdoor plans/agriculture planting.
Probability for 0.5"+ for the event now ranges from near 60% around
Fargo to over 80% in west central MN (near zero in Devils Lake). In
our east/southeast locations of MN the probability for 1"+ is a bit
higher than 24hr ago (now 60%).

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 /12Z TAFS THROUGH 12Z TUESDAY/...
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Issued at 654 AM CDT Mon May 20 2024

Flight conditions remain variable this morning across eastern
ND and northwest MN with several developing pockets of MVFR
stratus and patchy shallow/ground fog. Conditions have varied
from VFR to LIFR over short periods and while the fog should
lift by 13Z stratus may fill in and persist before finally
pushing east mid to late morning when prevailing VFR conditions
become more likely. Winds are light and variable but should
increase from the northwest 10-13kt during the daytime period as
low pressure shifts east and high pressure builds to the north.
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&&

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

&&

$$

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