Area Forecast Discussion
Issued by NWS Grand Forks, ND

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FXUS63 KFGF 270451

Area Forecast Discussion
National Weather Service Grand Forks ND
1151 PM CDT Sat May 26 2018

Issued at 1026 PM CDT Sat May 26 2018

Regarding thunderstorm potential tonight: Thunderstorm activity
over Eastern Montana is shown to spread eastward, with a general
agreement in CAMs of arrival in our far western CWA after 7Z, and
the Red River Valley around 12Z. This may be optimistic on timing
based on current regional radar trends. Evolution and intensity
are still uncertain, and there is not a lot of agreement on that
side of things at this point. RAP shows MU CAPE potentially in the
1500-2000 J/KG range in our far west by 12Z as warm front moves
northward and southerly flow begins to develop, while values
remain lower to northeast. At the very least keeping thunder in
the forecast and adjusting timing of PoPs seemed reasonable. Any
thunderstorms would become elevated and if low levels remain
decoupled it will be hard to anticipate potential for any severe
wind. Also, if activity outpaces increase in instability stronger
updrafts necessary for larger hail may not be supported. Potential
is there and this should be monitored, but overall confidence in
impacts is low.

UPDATE Issued at 645 PM CDT Sat May 26 2018

Only minor adjustments to near term trends, otherwise monitoring
upstream activity for possible adjustments to PoP/Wx for later
tonight/tomorrow. Elevated instability (MU CAPE 500-1500 J/KG)
should be in place so while PoPs weren`t adjusted, I added thunder
mention to late night/Sun morning grids.


.SHORT TERM...(This evening through Sunday)
Issued at 246 PM CDT Sat May 26 2018

Mostly sunny skies are expected through the remainder of the day
across much of the forecast area. The only exception will be
across north and northwest Minnesota where a persistent cumulus
field has developed in a less stable airmass influenced by a weak
upper level shortwave north of the Great Lakes region. Slight
instability of 500-1000 J/kg MUCAPE in this region may allow for
an isolated thunderstorm or two in this region later this evening.

Otherwise, a few clouds and breezy conditions will persist across
eastern ND/western MN. Winds are expected to gradually diminish
through the evening and overnight hours as surface high pressure
shifts to the east.

Rain chances will increase across eastern ND early Sunday morning
as precipitation associated with a subtle mid level wave propagate
into the region around an upper level ridge axis. This early
morning precipitation is expected to move out of the region and
make way for a second round of showers/thunderstorms Sunday
afternoon. A deepening surface low across central SD will cause a
northward flux of higher theta-E air into the southeast ND/west MN
region. Deterministic and short- range ensemble guidance suggest
a boundary layer airmass characterized by dewpoints in the upper
50s/low 60s will support moderate instability of 1.5-2.5 kJ/kg
MLCAPE by the afternoon and evening hours. 0-6 km Bulk Shear
values of 30-40 knots will support organized convection that will
pose a threat for severe hail up to one inch and strong wind gusts
up to 60 mph. While convection will likely be focused a surface
warm front across the southern River Valley, uncertainty remains
as to the degree of destabilization from daytime heating due to
early morning showers/cloud cover and whether forcing along the
front will be sufficient to initiate convection. As such,
trends in surface dewpoints and cloud cover will have to be
monitored to assess the afternoon severe potential.

.LONG TERM...(Sunday night through Saturday)
Issued at 246 PM CDT Sat May 26 2018

Temperatures... Hot weather continues Monday for the Memorial Day
Holiday. Cooler temperatures begin to move in Monday with 70s and
the low 80s in the Devils Lake Basin and along the international
border. Cooler weather moves across of the rest of eastern North
Dakota and northwest Minnesota Tuesday with temperatures still above
normal but not like the recent record setting temperatures. By late
next week temperatures could even to fall to close to normal as a
cooler air mass moves in.

Thunderstorm Potential... Thunderstorms and showers on Monday with
potential for strong to severe storms. This will depend on what
happens Sunday as any significant convection on Sunday will reduce
the chance for strong to severe storms Monday. Bulk shear values on
Monday across eastern North Dakota and northwest Minnesota in the
NAM are in the 30 to 55 kt range which would support strong to
severe storms. What is more in question is the instability,
especially after potential Sunday convection. MU CAPE varies
significantly from near 0 up to 3500 J/kg, but in the areas with the
better shear values go up to closer to 2300 J/kg in the NAM and GFS.
Thunderstorms will again be possible Tuesday and Wednesday but it is
too early to say much about thunderstorm strength for those days.

Excessive Rainfall Potential... Monday into Wednesday high
precipitable water values in the NAM and GFS are above the 90th
percentile for nearby sounding climatologies (BIS, ABR, and INL).
This is supported by the previous upper low becoming dislodged and
the trough moving towards the Northern Plains. Dryer weather
expected Thursday before another chance for rain Friday into
the next weekend as an upper level trough moves into the region.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1149 PM CDT Sat May 26 2018

VFR condtions should preavil acros eastern ND and northwest MN
through the TAF period. Primary avaiation concern continues to be
potential for showers/thunderstorms of an on thorughout the TAF
period with lingering front and series of disturbances. Best
chance overall is with activity expected to spread from far
western ND across the state an into eastern ND between 7Z and 12Z.
KDVL and KFAR appear to have best chance for thunder and VCTS was




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