Special Weather Statement, NWS Bismarck, ND

Area Forecast Discussion
National Weather Service Bismarck ND
1006 PM CDT Sun Aug 5 2018

.UPDATE...
Issued at 1006 PM CDT Sun Aug 5 2018

Multicellular convection from northwestern ND into northeastern MT
appears to be associated with a slightly stronger impulse aloft
based on earlier surface pressure falls focused in that area, and
recent observed propagation is directed southeastward along a weak
weak low- and midlevel frontal zone that extends from near Sidney,
MT, to Beulah and Jamestown, ND, as of 02 UTC. Weak frontogenesis
near that frontal zone and modest mass field responses aloft with
the approaching weak shortwave trough impulse will likely aide in
the continued east-southeast propagation and maintenance of that
area of showers and a few thunderstorms through the night, so we
used this update cycle to modify PoPs in line with that thinking,
spreading 40-50 percent probabilities into central ND after 05
UTC. The 00 UTC Bismarck RAOB captured multiple weak inversion
layers aloft and midlevel lapse rates around 6.5 C/km, and recent
KBIS and KMBX WSR-88D VWP data shows 0-6-km bulk wind differences
only around 20 kt in further support of multicellular convection.
Given locally amalgamating cold pools and residual steep low-
level lapse rates, a few strong storms -- possibly with both gusty
winds and some hail -- could occur in west central ND the next 90
minutes, but the overall risk of strong storms overnight will be
minimized by the lack of stronger instability and weak shear. Note
too that the lack of an appreciable low-level jet will further
hinder any notable theta-e response, tempering instability, and
negating any discernible improvement in shear profiles, as well.

UPDATE Issued at 706 PM CDT Sun Aug 5 2018

Little in the way of change was made with this update other than
to accommodate recent observational trends. Scattered convection
is ongoing early this evening, but is loosely focused along and
slightly to the cool side of a weak frontal zone extending from
near Rugby to Minot and Crosby per trends in GOES-16 images that
have shown more agitated cumulus in that vicinity during the last
few hours. Background ascent is modest -- though perhaps is a bit
more notable in northeastern MT per surface pressure falls, which
is likely reflective of an approaching impulse that should tend to
maintain at least a low-end chance of precipitation overnight as
it moves eastward. Another weak impulse is moving into western SD.
This scenario justifies an increasingly broad-brush approach to
the PoP forecast further from the near-term when extrapolation of
observational trends is appropriate. Mid-level lapse rates are on
the order of 6 C/km over most of the area, and surface dewpoints
are generally in the lower to middle 50s F save for the southern
James River valley, limiting instability and potential strength of
any storms. Recent 0-6-km bulk wind differences from the KBIS VWP
are also on the order of 20 kt, further suggesting that any storms
will likely have limited intensity, although a belt of slightly
stronger flow with 0-6-km bulk wind differences on the order of 30
kt may exist along the Highway 200 corridor per RAP analyses, in
support of a low-end probability of stronger storms in that area.

&&

.SHORT TERM...(This evening through Monday)
Issued at 143 PM CDT Sun Aug 5 2018

Latest water vapor imagery indicates a weak shortwave trough
located over southern Alberta/Saskatchewan and a couple of
shortwaves ejecting east from Wyoming. The northern stream trough is
forecast to slowly sag south through Monday, somewhat merging in
time and space with the aforementioned shortwaves in Wyoming as
they shift east. In doing so, low level cooling per a surface to 850mb
cold front on the NAM/GFS will shift a cold front from north to
south overnight into Monday morning. This will result in cooler
air with highs in the 70s Monday as well as generate the chance
for showers/thunderstorms this afternoon through Monday. Difficult
to pinpoint exact areas, but it would appear the north, southwest
and far south central may be more prone to the highest chances
based on the above thinking. Severe weather is not expected at
this time. Lows tonight will mostly be in the 50s, with lower 60s
south central.

.LONG TERM...(Monday night through Sunday)
Issued at 143 PM CDT Sun Aug 5 2018

Large upper ridge across the west will expand north and east with time
and envelop the northern high plains Tuesday through Saturday.
This will result in dry, along with warm to hot conditions,as
highs will range from the upper 80s to lower/middle 90s during
this time period. Differences arise late next weekend, as the GFS
advertises a cold front moving through Sunday/Sunday night, while
the ECMWF is slower and keeps the region warm and dry through
Monday night.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 1006 PM CDT Sun Aug 5 2018

VFR conditions will generally prevail through the 00 UTC TAF
cycle. However, scattered showers and a few thunderstorms will
move from northwest and west central ND late this evening into
the central parts of the state overnight. Radar trends could
necessitate amendments or adjustments with the 06 UTC TAFs to
reflect higher confidence in impacts at some terminals. Localized
sub-VFR conditions are possible with any storms. Otherwise, there
will remain a chance of showers and thunderstorms over southern
areas through Monday in association with a weak frontal passage.

&&

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

UPDATE...CJS
SHORT TERM...KS
LONG TERM...KS
AVIATION...CJS

Hazardous Weather Outlook
National Weather Service Bismarck ND
1016 PM CDT Sun Aug 5 2018

NDZ001>005-009>013-017>023-025-031>037-040>048-050-051-070330-
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-
1016 PM CDT Sun Aug 5 2018 /916 PM MDT Sun Aug 5 2018/

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...Tonight

A few thunderstorms are expected across western and central North
Dakota tonight, but severe weather is not expected.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

There is a chance of thunderstorms in southwest and south central
North Dakota on Monday. Severe weather is not currently expected.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected.

CJS

Special Weather Statement
National Weather Service Bismarck ND
906 PM CDT SUN AUG 5 2018

NDZ009-017-060230-
McKenzie ND-Williams ND-
906 PM CDT SUN AUG 5 2018

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT NORTHWESTERN MCKENZIE
AND SOUTHWESTERN WILLIAMS COUNTIES UNTIL 930 PM CDT/830 PM MDT/...

At 906 PM CDT/806 PM MDT/, strong thunderstorms were clustered near
Fort Union Trading Post, or 17 miles north of Sidney, moving
southeast at 15 mph.

Half inch hail and wind gusts to 40 mph will be possible with these
storms.

Locations impacted include...
Fairview, Fort Union Trading Post, East Fairview, Trenton, Cartwright
and Fort Buford State Historical Site.

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

&&

LAT...LON 4816 10405 4818 10401 4811 10346 4767 10404
TIME...MOT...LOC 0206Z 322DEG 15KT 4797 10413

HARGROVE

Special Weather Statement
National Weather Service Bismarck ND
915 PM CDT SUN AUG 5 2018

NDZ017-060245-
McKenzie ND-
915 PM CDT SUN AUG 5 2018

...A STRONG THUNDERSTORM WILL AFFECT SOUTHWESTERN MCKENZIE COUNTY
UNTIL 945 PM CDT/845 PM MDT/...

At 915 PM CDT/815 PM MDT/, a strong thunderstorm was located 11 miles
east of Sidney, moving southeast at 10 mph.

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

Locations impacted include...
Sather Dam.

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 4768 10404 4780 10389 4755 10333 4733 10371
      4733 10381 4759 10405
TIME...MOT...LOC 0215Z 296DEG 10KT 4766 10392

HARGROVE

Special Weather Statement
National Weather Service Bismarck ND
928 PM CDT SUN AUG 5 2018

NDZ009-017-060315-
McKenzie ND-Williams ND-
928 PM CDT SUN AUG 5 2018

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN MCKENZIE AND
SOUTHWESTERN WILLIAMS COUNTIES UNTIL 1015 PM CDT/915 PM MDT/...

At 928 PM CDT/828 PM MDT/, a strong thunderstorm was located near
East Fairview, or 14 miles north of Sidney, moving southeast at 15
mph.

Nickel size hail and wind gusts to 40 mph will be possible with this
storm.

Locations impacted include...
Fairview, Alexander, Fort Union Trading Post, East Fairview, Trenton,
Cartwright, Fort Buford State Historical Site and Charbonneau.

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 4811 10404 4802 10327 4759 10397 4767 10405
TIME...MOT...LOC 0228Z 315DEG 12KT 4791 10405

HARGROVE

Special Weather Statement
National Weather Service Bismarck ND
1020 PM CDT SUN AUG 5 2018

NDZ017-018-060400-
McKenzie ND-Dunn ND-
1020 PM CDT SUN AUG 5 2018

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN DUNN AND CENTRAL
MCKENZIE COUNTIES UNTIL 1100 PM CDT/1000 PM MDT/...

At 1020 PM CDT/920 PM MDT/, a strong thunderstorm was located near
Arnegard, or 7 miles southwest of Watford City, moving southeast at
40 mph.

Half inch hail and wind gusts to 55 mph will be possible with this
storm.

Locations impacted include...
Watford City, Alexander, Arnegard, Mandaree, Theodore Roosevelt
National Park North Unit, Grassy Butte, Charbonneau, Rawson and
Johnsons Corner.

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 4801 10362 4775 10250 4733 10309 4733 10338
      4780 10389
TIME...MOT...LOC 0320Z 302DEG 33KT 4775 10343

HARGROVE

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