Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 212000
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
300 PM CDT Wed Jun 21 2017

.SHORT TERM...(This evening through Thursday)
Issued at 300 PM CDT Wed Jun 21 2017

A cold frontal passage this afternoon will be followed by another
surge of cold air advection and gusty northwest winds Thursday.

We continue to downplay the potential for surface-based storms in
our area of responsibility this afternoon since the current pace
of a southeast-moving pre-frontal trough and cold frontal boundary
suggests they will be mostly east of the area by the time capping
is sufficiently eroded for convective initiation. However, there`s
been just enough run-to-run consistency in HRRR iterations through
its 18 UTC cycle to carry a slight chance of thunderstorms across
Dickey County for a brief window in the late afternoon. Forecast
soundings do suggest MLCAPE of 1000-1500 J/KG and deep-layer speed
shear of 50 kt, sufficient for marginally-severe storms, but again
we believe the probability of convective initiation in our area
is low since the primary low-level confluence region will quickly
be shifting east of the area.

Today`s global and CAM model suites suggest another frontal surge
marked by additional thermal packing in the 850 mb isotherms will
push into northwest and north central ND tonight. Vertical motion
associated with a strong but transient 140 kt 300 mb jet streak is
expected to move eastward along the international border overnight
and will likely yield a deep enough ageostrophic circulation atop
the mid-level baroclinic zone in support of scattered showers. That
frontal zone and its following cold air advection is then expected
to continue southeast across the area early Thursday, away from the
deeper forcing aloft associated with the upper-level jet streak. A
dry forecast is thus in play tonight and Thursday in southwest
and south central ND.

Forecast soundings from the 12 UTC NAM and GFS both concur that we
will have deep mixing to around 650 mb on Thursday in the cold air
advection regime. Mean mixed-layer winds will be near 30 kt and
peak speeds at its top will near 40 kt, especially northwest and
north central. We weighted forecast winds toward the consensus of
12 UTC MOS guidance, which often verifies well in these cases.
Those numbers suggest that a wind advisory may be required with a
later forecast release if model trends hold steady, especially
from Williston toward Minot Thursday afternoon.

.LONG TERM...(Thursday night through Wednesday)
Issued at 300 PM CDT Wed Jun 21 2017

Much cooler weather is still expected Friday and Saturday, but
only a low chance of showers exists.

The 00 and 12 UTC GFS and ECMWF and their ensembles held steady in
forecasting a 500 mb trough across the region with temperatures at
850 mb in the 5 to 8 C range Friday and Saturday. Thus, highs will
likely struggle to get out of the 60s F and overnight lows will be
in the 40s F this weekend. Precipitation prospects will be limited
by lackluster tropospheric moisture content, especially since it
appears a stronger 500 mb low dropping through the trough may well
pass east of the local area.

A warming trend is still on track next week as flow aloft begins
to return to a more zonal and progressive nature.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 300 PM CDT Wed Jun 21 2017

VFR conditions expected through the period. A cold front will
continue eastward this afternoon, reaching KJMS by around 21z and
the Red River Valley around 00z. Northwest winds behind the front
should range from sustained at 15-25 knots with gusts to over 30
knots at times this afternoon. There may be some scattered to
isolated thunderstorm development east of KMOT and north and east
of KJMS by around 20z-22z, then mainly affecting the Red River
Valley late this afternoon and early evening. Winds decreasing
after 00z and becoming light and variable between 03z- 12z. There
is some hint of showers across northern ND after 06z with a
secondary cold frontal passage. Confidence is low at this time and
did not mention in TAFS for KISN-KMOT. Northwest winds pick up
again after 12z with that secondary cold frontal passage bringing
gusty northwest winds again on Thursday.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...CJS
LONG TERM...CJS
AVIATION...JV


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