Area Forecast Discussion
Issued by NWS Grand Forks, ND

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FXUS63 KFGF 212020

Area Forecast Discussion
National Weather Service Grand Forks ND
320 PM CDT Mon May 21 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 320 PM CDT Mon May 21 2018

Precip chances this evening and tomorrow will be the main
challenges for the period.

Light rain showers have continued to rotate through our
southeastern counties as a weak upper low rotates near the SD/MN
border. SPC meso page shows that the atmosphere is pretty stable,
so precip will remain as showers. The high res models continue to
have spots of some 0.1 or more QPF, but given recent trends think
this is overdone and we will most likely see some sprinkles at
best. The CAMs are pretty consistent on taking the showers off to
the east sometime around the 02 to 03Z time frame, so we should
dry out fairly quickly later this evening. Southeasterly winds
will become more southerly, and higher dewpoints in the 40s and
50s will move north tonight. A few of the models bring some fog
into our southern counties, but not confident enough to include in
the grids at this point as it is not the greatest setup for
advection fog. Lows should be in the upper 40s to low 50s.

Tomorrow, the weak upper low will be well off to the east and we
will be under some shortwave ridging during the day. With a trough
of low pressure to our west, southeast winds will continue. There
will be decent moisture, and a few of the models have some
500-1000 J/kg of CAPE developing. However, there is no good
forcing with the ridge overhead so think we will stay dry
throughout the day, with afternoon highs in the upper 70s to low

.LONG TERM...(Tuesday night through Monday)
Issued at 320 PM CDT Mon May 21 2018

Thunderstorm chances return to the forecast for the second half of
the work week. A weak upper level low transversing across northwest
Canada can be seen in water vapor imagery this afternoon. This
feature is expected to continue to move eastward over the next
couple of days and induce weak pressure falls at the surface. During
the day Wednesday, this surface low, along with lee troughing
associated with weak zonal upper level flow across the northern
Rockies, will cause a poleward moisture flux with dewpoints across
ND expected to reach into the mid to upper 50s.

A mid level impulse advecting northeastward in the upper level flow
is expected to cause a lee low to propagate into the western Dakotas
late Wednesday. Thunderstorm initiation will be possible in the
vicinity of this low and to the east along a weak warm frontal
boundary. Locally, thunderstorms chances will initially be best
across south central ND and into far western MN and spread into
northeast ND/northwest MN through the evening as showers/storms
advect northeast. MUCAPE values of 1-2k J/kg and roughly 30 knots of
0-6 km bulk shear suggest some severe potential, uncertainty exists
pertaining to the strength of the capping inversion and forcing for

Storm chances remain in the region for Thursday afternoon/evening.
The boundary layer airmass is expected to recover during the first
half of the day as southerly flow continues across the region.
Forcing for ascent will be provided by a weak upper level shortwave
on top of a surface trough positioned across the eastern half of ND.
Moderate instability values and weak convective inhibition support
storm development, but weak 0-6 km bulk shear may limit organized
severe potential. However, this day will need to be monitored for
the possibility of severe thunderstorms.

A zonal to northwesterly flow regime is expected to emerge for the
end of the week. Thunderstorms will be possible again Friday evening
and into Saturday as an upper level shortwave propagates across the
northern Plains. Shower/storm chances diminish heading through the
weekend as surface high pressure moves back into the region.

Temperatures during the extended period are expected to be seasonal
with highs in the mid to upper 80s across much of the region.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1228 PM CDT Mon May 21 2018

All sites are VFR as mid and high clouds move into the
southeastern forecast area. Some showers will move into the KBJI
area later this afternoon, so have VCSH into the early evening.
KFAR has some guidance showing some MVFR ceilings coming in late
in the period, with others keeping them VFR. Have ceilings
lowering to around 6000 ft this evening and will keep the morning
at around 3500 ft and adjust as we get closer. KBJI is more
certain to go MVFR by tomorrow morning. Northern and western TAF
sites will stay VFR. Winds will be from the southeast and then
south to southwest late in the period.




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