000
FXUS63 KBIS 191150
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
650 AM CDT Tue Sep 19 2017

.UPDATE...
Issued at 640 AM CDT Tue Sep 19 2017

Showers are becoming more numerous across eastern Montana with
several areas of mainly VIRGA across central North Dakota this
morning. Patchy fog and low clouds remain over the east.

The main focus for thunderstorms today will be along the cold
front now entering far western North Dakota. Current forecast
looks good with minimal changes.

&&

.SHORT TERM...(Today and tonight)
Issued at 353 AM CDT Tue Sep 19 2017

A Heads Up day, as a possible locally significant severe weather
event along and east of Highway 83, but highly favoring the James
River Valley, highlights the short term period. We will be doing
an 18Z Special Balloon launch in support of an Enhanced Risk for
Severe Thunderstorms across southeastern ND.

For the near term/early this morning, a narrow region of stratus/patchy
dense fog from the Turtle Mountains south into Jamestown should
continue to erode by mid morning as ascent/instability shifts into
this region.

Latest water vapor imagery shows a strong mid/upper level shortwave
trough shifting through south central Idaho early this morning.
Height falls underway and will increase across western and central
ND this afternoon. A strong surface cold front was located in
eastern Montana early this morning. Surface low pressure was
developing in southwest ND, with a 3hr pressure fall of around
4mb ahead of the front. This low will continue to deepen and lift
northeast today. With the increasing in vertical motion, clouds
and showers will also increase through the morning west, and into
the central this afternoon along and ahead of the cold front. The
cold front will reach the James River Valley early this evening.
Strong large scale ascent overlapping with low/mid level frontogenesis
and steep mid level lapse rates coincide over central ND beginning
at approximately 20z/3PM CDT, and gradually shifts east into the
James River Valley through 02Z/9PM CDT. Soundings and severe
weather parameters paint the James River Valley as a Tornadic
Supercell threat late this afternoon into the early evening. This
is in line with SPC Enhanced Severe Thunderstorm Risk. Along and
east of Highway 83, hail up to golfball size, damaging winds up to
70 mph, along with a few tornadoes are the main hazards. The
early afternoon balloon launch will be most helpful in verifying
how the severe parameters are coming together and if any adjustments
are needed in the current areal coverage. The showers/thunderstorms
will diminish by 06z, and exit the far southern James Valley shortly
thereafter.

Gusty southeasterly winds in central ND in the morning will
diminish this afternoon, as they veer around to the southwest and
west with the approach of the cold front. Winds will remain gusty
in the James River Valley through the afternoon with high
temperatures in the upper 70s across this region. In the west,
highs will be in the lower 60s.

.LONG TERM...(Wednesday through Monday)
Issued at 353 AM CDT Tue Sep 19 2017

Longwave trough in the west will continue through the long term period.

Wednesday and Thursday will be dry. Breezy, cooler for Wednesday
with highs in the  60s. A dry cold front will push through
Thursday, but slow up as it approaches the James River Valley.
Thus, the cooler temperatures of mid 60s for highs will reside in
western ND, while the James Valley will see highs in the upper
70s.

Shortwaves will begin to move into western/central ND Thursday
night through Monday with periodic chances for showers. A cooling
trend commences into the weekend with highs mostly in the mid to
upper 50s Sat/Sun, then lower 60s Monday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 640 AM CDT Tue Sep 19 2017

An increasing southeast windflow will favor stratus and fog
across eastern North Dakota this morning, impacting KJMS. Wind
shear from KBIS-KMOT this morning will end after 15z. The main
hazard to aviation after 18Z will be thunderstorms Tuesday
afternoon and Evening. For this used VCTS for KBIS-KJMS due to
timing uncertainty. But conditions favor a line of thunderstorms
with gusty winds, possibly impacting KJMS after 00Z.

&&

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

$$

UPDATE...WAA
SHORT TERM...KS
LONG TERM...KS
AVIATION...WAA