Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 202352

Area Forecast Discussion
National Weather Service Bismarck ND
652 PM CDT Tue Jun 20 2017

Issued at 623 PM CDT Tue Jun 20 2017

Trimmed the early evening POPs back based on current CAM models
and satellite and radar trends. Will see more showers and
scattered thunderstorms develop as upstream shortwave and low to
mid level warm advection develop around or after midnight.
Otherwise current forecast looks good.


.SHORT TERM...(This evening through Wednesday)
Issued at 256 PM CDT Tue Jun 20 2017

Highlights of the short term forecast period include isolated to
scattered showers and thunderstorms tonight and early Wednesday,
followed by a warm and breezy Wednesday afternoon.

As of 19 UTC, isolated and high-based showers continue moving to
the southeast and extend from about Watford City to New Salem and
Fort Yates. Despite a dry lower atmosphere as sampled by the 12
UTC Bismarck and Glasgow RAOBs, some precipitation is reaching the
ground per ASOS/AWOS observations and thus we have extended low-
end precipitation chances through late afternoon in south central
ND. Overall, the weak vorticity maximum embedded in northwesterly
flow aloft on the leading edge of 500 mb height rises that seems
to be driving this activity is forecast by recent RAP iterations
to shear southeast and weaken by 00 UTC.

Synoptically, a shortwave trough is expected to strengthen as it
rapidly moves from western British Columbia this evening and into
southern Manitoba by Thursday evening. A 35-45 kt southerly low-
level jet is forecast to develop in advance of that wave tonight,
and ascent based near 850 mb related to that wind maximum and the
associated warm air advection will likely be sufficient to yield
isolated to scattered showers and thunderstorms, mainly after 05
UTC and mainly from Minot to Jamestown per CAMs through the 18 UTC
HRRR and 15 UTC ESRL HRRR. Forecast soundings show steepening mid-
level lapse rates associated with an elevated mixed layer. We will
lack rich moisture and MUCAPE for parcels lifted from about 850 mb
will generally peak from 500 to 800 J/kg, so while a strong storm
or two is possible, the probability of severe weather appears low
at this time despite strengthening wind fields aloft.

A mid-level thermal ridge will cross the region Wednesday ahead of
a cold frontal passage that is expected during the afternoon. We
leaned on the warmer edge of of model temperature forecast output
for highs on Wednesday given expected deep mixing along and to the
west of the frontal zone, and in respect to recent model biases. A
low probability of convection will exist in the James River Valley
during the afternoon, but we are downplaying any risk of strong or
severe storms because we believe the prospects of deep convective
development are highest east of the area per the 12 UTC NAM, GFS,
and ECMWF simulations. The 09 UTC SREF calibrated severe storm
guidance is also very low in our area Wednesday. Behind the front,
northwest wind gusts to 30 mph are forecast with momentum transfer
via cold advection in a deep boundary layer. Low humidities near
20 percent will yield some elevation in fire concerns, but fuel
status may not yet support critical (red-flag type) designation.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 256 PM CDT Tue Jun 20 2017

Much cooler, below-normal temperatures are expected late this week
and into the weekend.

The 12 UTC global model suite continued to advertise a trough at
500 mb developing over the region by Friday and lingering through
the weekend. In general the last few GFS and ECMWF cycles have
been trending drier during this time period, with a tendency for
shortwaves embedded in the mean trough to be open waves instead of
closed with deeper dynamics as some earlier iterations suggested.
Thus, our forecast stayed the course with only a chance of showers
in this period. Instability per model-derived CAPE fields is low
and thus the probability for thunderstorms is low. Our confidence
remains high in highs only staying in the 60s F in many areas on
Friday and Saturday, before mid-level heights begin to rebound and
yield a warming trend again by early next week.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 623 PM CDT Tue Jun 20 2017

A warm front extended from low pressure in Alberta southeast
through eastern Montana. The warm front will be the focus for
scattered showers and thunderstorms tonight northwest around 06Z
moving into the central between 09-15Z. Otherwise VFR at all TAF
sites through the 00Z period.




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