Severe Thunderstorm Warning 4, NWS Bismarck, ND

Area Forecast Discussion
National Weather Service Bismarck ND
246 PM CDT Fri May 17 2024

.KEY MESSAGES...

- Severe Thunderstorm watch until 02z.

- Scattered severe thunderstorms are possible this evening. The
 expected hazards will be damaging winds up to 70 mph and hail
 up to quarter size.

- Windy and cooler on Saturday with highs mostly in the 60s.

- Daily chances (40%) for showers and thunderstorms continue
  through the weekend and into early next week.

&&

.UPDATE...
Issued at 241 PM CDT Fri May 17 2024

Quick update that there is now a Severe Thunderstorms watch for
most of western and central ND until 02z. Hazards are still
70mph winds and quarter sized hail. It may need to be expanded
into the far southeast, but we will see how the storms go.

&&

.DISCUSSION...
Issued at 200 PM CDT Fri May 17 2024

The upper level wave has started to move into the state, as seen
in satellite with agitated mid level clouds at 18z. Near the
Montana/North Dakota border near Glendive, MT, south to Bowman,
ND and over to Glen Ullin, ND cumulus has started. We should be
warmer than our convective temperature now, so more and more
cumulus should start to pop in the next hour, especially with
the diffluence over head from the upper level wave. The latest
SPC update at 1630z expanded the slight risk through the whole
CWA. Some CAMs have isolated storms forming now before the main
cold front moves through and forms a line. The main threat is
still 70mph winds because of a lack in CAPE, and the storm mode.
The storm mode is a line because the shear vector will be
parallel to the cold front, continuously allowing new convection
to form in the line. DCAPE look very favorable with values
around 1000 J/kg, and model soundings have an inverted V with
steep lapse rate. This allows the wind to mix down very easily.
So the isolated storms that form now, will then combine into a
line as the cold front moves in. Timing on the line forming
looks to sometime around 21-23z. The CAMs are all a little
different on the which storm mode they start as. The line will
move west to east, leaving our area around 03z. Most CAMs are
confident on that. Then on the back side of the front, more
showers and possibly thunderstorms will form again in the west,
lasting through the night.

Saturday will be breezy on the backside of this front with cold
air advection and a tight pressure gradient. Westerly winds
will gust to 40mph, with sustained winds at 30mph. We will most
likely need a Wind Advisory from Saturday morning, until around
00z. Since we have active storms today, we will wait until the
overnight period to issue that. Highs on Saturday will be much
cooler in the 60s, this cooler trend will continue through the
weekend. Flow aloft this weekend will remain southwest with
another low and wave moving through Sunday and Monday. Chances
for showers and thunderstorms will continue through the forecast
period with the highest chances ending Monday when the
southwest flow relaxes some. Mid next week the flow is weak in a
quasi-zonal flow. Another big low pressure possibly forms in
the Pacific Northwest Wednesday. This could bring another round
of storms with diffluence flow aloft and southerly flow at the
surface Thursday and Friday. Temperatures look to stay slightly
below average in the low to mid 60s through Friday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 200 PM CDT Fri May 17 2024

VFR this afternoon until strong thunderstorms move west to east
between 21 and 03z. Overnight light rain may continue until the
early morning. Winds will gust around 20kts today from the
southwest increasing to 35kts from the west by Saturday
morning. Skies will clear out by late morning Saturday except
near KMOT where 3kft ceilings could linger, left it as SCT for
now until we get more confidence.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
None.

&&

UPDATE...Smith
DISCUSSION...Smith
AVIATION...Smith

Hazardous Weather Outlook
National Weather Service Bismarck ND
249 PM CDT Fri May 17 2024

NDZ001>005-009>013-017>023-025-031>037-040>048-050-051-182000-
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-
249 PM CDT Fri May 17 2024 /149 PM MDT Fri May 17 2024/

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

Scattered severe thunderstorms are possible this evening. The
expected hazards are damaging winds to 70 mph and quarter sized
hail.

Severe Thunderstorm watch has been issued for western and central
North Dakota. See weather.gov/bis for details.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Strong westerly winds are possible on Saturday.

.SPOTTER INFORMATION STATEMENT...

Severe weather can be reported on social media, or by calling
701-223-4582.

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