Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 200443

Area Forecast Discussion
National Weather Service Bismarck ND
1143 PM CDT Tue Sep 19 2017

Issued at 1143 PM CDT Tue Sep 19 2017

Latest water vapor imagery shows the negatively tilted mid/upper
level shortwave trough aligned from southeast Saskatchewan through
the central North Dakota and eastern South Dakota. Main line of
significant thunderstorms now into western Minnesota and eastern
South Dakota. Still a weak line of showers across central ND, and
this will continue to wane as the upper trough shifts farther
east, and westerly winds and drier air advect in overnight.
Current forecast is on track.

UPDATE Issued at 933 PM CDT Tue Sep 19 2017

Convection waning across the southern James River Valley with the
last few weakening cells now exiting LaMoure County. After
coordinating with SPC, have cancelled the Tornado Watch from all
remaining counties across the James River Valley. Scattered
showers will end from southwest to northeast overnight with
decreasing clouds to follow the rest of the night. Text products
have been sent.

UPDATE Issued at 546 PM CDT Tue Sep 19 2017

So far this afternoon into this evening there has been one notable
storm that swept through the southern James River Valley,
otherwise the storms have stayed on the tame side. Parameters are
still in place for severe weather over James River Valley, but
with the frontal boundary making its easterly push, severe
potential will be on a gradual decrease. Convection allowing
models have been overplaying the the thunderstorm coverage so far
this afternoon/early evening, so will ease up a bit on
precipitation chances through the evening.


.SHORT TERM...(This evening through Wednesday)
Issued at 146 PM CDT Tue Sep 19 2017

Convection continues to track east across central ND this
afternoon. Greatest risk of severe storms looks to be along and
east of a line from around Harvey to Linton. Most mesoscale models
show rapid intensification near the current line of convection in
the next 1-2 hours as remaining cap dissipates. With a very strong
synoptic system, all threats remain: Large hail, Damaging winds
and even tornadoes. The severe threat will exit the eastern CWA
during the evening hours. Clearing from west to east tonight with
overnight lows dropping into the mid 30s possibly over the
southwest. Areal extent appears small for areas of frost. Will
mention some frost but advisory not anticipated at this time.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 146 PM CDT Tue Sep 19 2017

Cooler and much drier on Wednesday. Our main concern will be
possible fire weather issues in the southwest during the
afternoon. Minimum humidities are in the 20 to 25 percent range
with sustained winds around 20 mph. As was mentioned on the mid
shift, it still looks like marginal fire weather conditions may
exist for a brief period. With uncertainty in duration with only
marginal winds, we will not issue a fire weather watch at this
time. Overnight shift can re-evaluate. If we mix out more than
anticipated, fire weather hazards may still be needed.

Relatively dry period Wednesday and Thursday as the first upper
low lifts into Canada. The next round of active weather picks up
Thursday night and continues through the weekend as another upper
low deepens over the western U.S. keeping a southwest upper flow
over the northern plains. However, we also begin to cool down and
the thunder risk beyond today and tonight looks to be minimal
through the weekend. Highs mainly in the 60s and 70s Wednesday and
Thursday. A transition on Friday to cooler highs mainly in the 50s
over the weekend.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1143 PM CDT Tue Sep 19 2017

Expect vfr cigs/vsbys this TAF period. Low level windshear is
forecast at KBIS/KJMS near the end of the period with an increase
in low level southerly winds.




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