Special Weather Statement, NWS Bismarck, ND

Area Forecast Discussion
National Weather Service Bismarck ND
139 PM CDT Sat Jul 29 2017

.UPDATE...
Issued at 137 PM CDT Sat Jul 29 2017

Several thunderstorms have initiated across the west central
along the nearly stationary frontal zone. This is in an area of
near adiabatic low level lapse rates and decent 2000 MU Cape but
very little shear. Will update for these storms west central but
do not think they will grow to severe other than a quick pulse.

UPDATE Issued at 1232 PM CDT Sat Jul 29 2017

Latest NAM model sounding data suggests capping will erode around
20z across western North Dakota although a few storms could
preceed this time across the frontal zone north where boundary
may help to force the convection. Weak convection continues across
eastern Montana with mid level short wave and a few showers wil
cross the border this afternoon far west. Generally weak shear
with enough CAPE will keep the severe threat to marginal. SARS
sounding analogues fit a modest hail size around an inch or less.
High LFC's will mean a minimal tornado threat.

UPDATE Issued at 925 AM CDT Sat Jul 29 2017

Added some low POPs across the northwest where a stationary
front will become the focus for showers and thunderstorm
development. Otherwise current forecast looks good.

UPDATE Issued at 621 AM CDT Sat Jul 29 2017

Isolated thunderstorms continued to develop over southeastern
Saskatchewan - and remained north of the international border. This
convection was likely associated with a surface cold front extending
from a low near Hudson Bay southwestward across Manitoba to near the
border of Saskatchewan/Montana/North Dakota. Latest iterations of
the CAM models suggest this activity should wane over the next
couple of hours.

As this cold front moves east today, there will be a chance of
thunderstorms in its vicinity in north central North Dakota. A
cluster of upper level impulses moving into western ND this
afternoon will also be the focus of possible thunderstorm
development.

No big changes this update. Blended hourly observations with
forecast temps/dewpoints/winds.

&&

.SHORT TERM...(Today and tonight)
Issued at 328 AM CDT Sat Jul 29 2017

Currently, an upper level ridge over the Rockies had flattened with
a large shortwave moving east across northern/central Canada. A
trailing surface cold front extended from near Hudson Bay
southwestward across Manitoba and to the border of
Saskatchewan/Montana/North Dakota. A weaker upper level shortwave
was also in the flow over the intermountain west near
Idaho/Montana/Wyoming early this morning. Broad surface low pressure
remained over the eastern Rockies and Front Range.

A few isolated thunderstorms in southeastern Saskatchewan
developed in the past hour or so...and put a slight chance mention
in far northwestern ND before sunrise. This convection is likely
associated with the aforementioned trailing cold front across
northern/central Canada.

A cluster of upper level impulses associated with the intermountain
west shortwave were over western/central Wyoming/Montana early this
morning, and are forecast to move east today, entering the western
Dakotas this afternoon and expanding across the Dakotas tonight. The
lingering Canadian cold front is forecast to stall over southern
Manitoba/northwestern ND, and diminish/wash out with time by this
evening. There will be an increasing chance of shower and
thunderstorm development this afternoon across western and central
North Dakota associated with these surface and upper level features.

Enough lower level moisture for decent MU CAPE values around 2500
J/Kg this afternoon, but 0-6km bulk shear is weak. Thus good
potential for thunderstorms, but not expecting much in the way of
severe storms. SPC has western and central ND in the "general"
category for thunderstorms - meaning not in the marginal or slight
risk for severe storms today.

Another warm day today with highs from the mid 80s to lower 90s, and
lows tonight again in the 60s.

.LONG TERM...(Sunday through Friday)
Issued at 328 AM CDT Sat Jul 29 2017

Daily chances for showers and thunderstorms exist through mid-week.
An upper level ridge to the west will keep North Dakota firmly
entrenched in northwest flow, leading to frequent upper level waves
moving overhead. While this ridge remains west we will see a fairly
stagnant pattern with temperatures in the 80s/90s each day and
isolated to scattered showers and thunderstorms.

On Sunday the models are not forecasting much in the way of forcing
for shower or thunderstorm development. Plenty of low level moisture
with dewpoints in the 60s over much of western and central ND but
not seeing much in the way of upper level impulses or steep mid-
level lapse rates. Model consensus still yielded a slight chance
mention of thunderstorms southwest and south central.

On Monday a cold front moves into northwestern North Dakota in the
afternoon, reaching a Minot-to-Bowman line by evening, then making
its way south and east overnight. This front and associated upper
level impulses will be the focus for scattered showers and
thunderstorms - mainly across central and southwestern North Dakota
Monday afternoon/night. Forecast CAPE values above 2000 J/kg will be
present, but with low 0-6km bulk shear. However, shear values
increase in the vicinity of the front over north central ND and into
Manitoba by late afternoon/evening. SPC has placed north central and
northeastern ND in a "marginal" risk for severe storms on Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1232 PM CDT Sat Jul 29 2017

At noon CDT a nearly stationary frontal boundary across northwest
North Dakota will remain in place this afternoon then retreat
back north late tonight as warm air moves in associated with a
mid level ridge over the western CONUS. Scattered thunderstorms
will be the hazard to aviation this afternoon and tonight. VFR is
forecast for all TAF sites.

&&

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

UPDATE...WAA
SHORT TERM...JV
LONG TERM...JV
AVIATION...WAA

Hazardous Weather Outlook
National Weather Service Bismarck ND
1248 PM CDT Sat Jul 29 2017

NDZ001>005-009>013-017>023-025-031>037-040>048-050-051-301800-
Divide-Burke-Renville-Bottineau-Rolette-Williams-Mountrail-Ward-
McHenry-Pierce-McKenzie-Dunn-Mercer-Oliver-McLean-Sheridan-Wells-
Foster-Golden Valley-Billings-Stark-Morton-Burleigh-Kidder-
Stutsman-Slope-Hettinger-Grant-Bowman-Adams-Sioux-Emmons-Logan-
La Moure-McIntosh-Dickey-
1248 PM CDT Sat Jul 29 2017 /1148 AM MDT Sat Jul 29 2017/

This Hazardous Weather Outlook is for portions of north central
North Dakota, northwest North Dakota, south central North Dakota,
southeast North Dakota, and southwest North Dakota.

.DAY ONE...This Afternoon and Tonight

Isolated to scattered thunderstorms are possible late this
afternoon and tonight. A few storms could be severe west with
large hail and gusty winds the primary threat.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

There are daily chances for thunderstorms through Wednesday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

waa

Special Weather Statement
National Weather Service Bismarck ND
1220 PM MDT SAT JUL 29 2017

NDZ017-031-291845-
McKenzie ND-Golden Valley ND-
1220 PM MDT SAT JUL 29 2017

...A STRONG THUNDERSTORM WILL AFFECT NORTHERN GOLDEN VALLEY AND
SOUTHWESTERN MCKENZIE COUNTIES UNTIL 1245 PM MDT...

At 1219 PM MDT, Doppler radar was tracking a strong thunderstorm near
Trotters, or 23 miles northeast of Wibaux, moving northeast at 20
mph.

Half inch hail and wind gusts to 40 mph will be possible with this
storm.

This storm will remain over mainly rural areas of northern Golden
Valley and southwestern McKenzie Counties.

LAT...LON 4732 10405 4748 10365 4733 10365 4733 10367
      4718 10367 4717 10403 4725 10405
TIME...MOT...LOC 1819Z 246DEG 18KT 4726 10392

ABELING

Special Weather Statement
National Weather Service Bismarck ND
1228 PM MDT SAT JUL 29 2017

NDZ031-291845-
Golden Valley ND-
1228 PM MDT SAT JUL 29 2017

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN GOLDEN VALLEY
COUNTY UNTIL 1245 PM MDT...

At 1228 PM MDT, Doppler radar was tracking a strong thunderstorm 12
miles north of Sentinel Butte, or 16 miles northeast of Beach, moving
east at 20 mph.

Half inch hail and wind gusts to 40 mph will be possible with this
storm.

This storm will remain over mainly rural areas of northeastern Golden
Valley County.

LAT...LON 4717 10392 4722 10372 4718 10367 4703 10366
      4699 10369 4699 10391
TIME...MOT...LOC 1828Z 264DEG 19KT 4710 10379

ABELING

Special Weather Statement
National Weather Service Bismarck ND
106 PM MDT SAT JUL 29 2017

NDZ031-032-291945-
Golden Valley ND-Billings ND-
106 PM MDT SAT JUL 29 2017

...A STRONG THUNDERSTORM WILL AFFECT EAST CENTRAL GOLDEN VALLEY AND
SOUTHWESTERN BILLINGS COUNTIES UNTIL 145 PM MDT...

At 106 PM MDT, Doppler radar was tracking a strong thunderstorm 5
miles east of Sentinel Butte, or 13 miles east of Beach, moving east
at 15 mph.

Half inch hail and wind gusts to 50 mph will be possible with this
storm.

This strong thunderstorm will be near...
  Medora around 145 PM MDT.

LAT...LON 4683 10381 4701 10383 4708 10343 4678 10341
TIME...MOT...LOC 1906Z 265DEG 12KT 4693 10372

ABELING

Special Weather Statement
National Weather Service Bismarck ND
208 PM MDT SAT JUL 29 2017

NDZ043-292045-
Bowman ND-
208 PM MDT SAT JUL 29 2017

...A STRONG THUNDERSTORM WILL AFFECT NORTH CENTRAL BOWMAN COUNTY
UNTIL 245 PM MDT...

At 208 PM MDT, Doppler radar was tracking a strong thunderstorm near
Rhame, or 10 miles west of Bowman, moving east at 10 mph.

Half inch hail and wind gusts to 50 mph will be possible with this
storm.

Locations impacted include...
Rhame and Griffin.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek shelter
inside a building or vehicle.

&&

LAT...LON 4611 10368 4620 10372 4628 10350 4628 10348
      4612 10342
TIME...MOT...LOC 2008Z 254DEG 7KT 4619 10361

AYD