993
FXUS63 KBIS 170257
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
957 PM CDT Thu May 16 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected this evening
  into the late overnight hours. A few stronger storms are
  possible this evening, with small hail and locally gusty
  winds.

- Isolated severe thunderstorms are possible Friday afternoon
  and evening. The expected hazards will be damaging winds up to
  60 mph and hail up to quarter size.

- Warmer on Friday (lower to mid 80s south, central, and east),
  followed by a cooldown with windy conditions Saturday.

- Daily low to medium chances for showers and thunderstorms
  continue through the weekend and into early next week.

&&

.UPDATE...
Issued at 955 PM CDT Thu May 16 2024

Aside from a mini-supercell in eastern North Dakota, the
intensity of convection has steadily diminished over the past
couple hours. The predominant line of showers and storms, now
moving through the James River Valley, is still capable of
producing gusts as high as 45 mph, as was observed at the
Jamestown Airport shortly after 9 PM. These storms will soon be
exiting our forecast area. The main area of focus for showers
and storms over the next few hours will be from northwest to
north central North Dakota, with elevated convection still
developing upstream in northeast Montana. However, the threat
for a stronger storm has greatly diminished with the loss of
diurnal heating.


UPDATE
Issued at 725 PM CDT Thu May 16 2024

At 7 PM CDT, a line of showers and thunderstorms from near Minot to
east of Bismarck to Fort Yates was tracking east at around 30 mph.
Several wind gust reports around 40 to 50 were received for the
portion of the line between Lake Sakakawea and Interstate 94 as it
approached Highway 83. Both radar and surface observations show a
decreasing trend in the strongest convection, but SPC mesoanalysis
maintains a similar CAPE/shear space downstream.

Back to the northwest, a couple of stronger storms have developed in
northeast Montana, moving southeast. While buoyancy is more
questionable there, with MLCIN likely to increase soon, effective
bulk shear is much stronger, on the order of 50 kts. The stronger
shear is forecast to spread into northwest North Dakota this
evening, so it is possible the intensity of the ongoing convection
could be maintained across the border. All measures of buoyancy are
forecast to decrease after sunset though.

&&

.DISCUSSION...
Issued at 245 PM CDT Thu May 16 2024

Currently diurnal cumulus is growing strong in the west and
southwest along the western side of the surface trough with a
few of them producing rain. The effective shear is up to 35
knots in the south central but mixed level CAPE is only around
500 J/kg. So there is enough shear to organized storms but we
need a little more energy to do it. All the CAMs have scattered
showers this late this afternoon in the west and east, then an
organized line moving west to east at 21z. Flow aloft this
afternoon is turning more and more zonal as a upper level low in
Canada moves closer. This will add some diffluence aiding in
more storm development through this evening. Storms today should
stay sub-severe, strong winds are possible and maybe small
hail. These showers and thunderstorms should continue all night,
moving west to east, clearing out by sunrise.

Friday looks like a higher risk of severe weather happening.
Flow aloft is southwest with good diffluence over the state. A
very warm thermal ridge also moves in, providing us with the
warmest day of the week with temperatures in the 80s. So as long
as parcels can gather enough energy from the surface to break
through this warm nose, storms can be expected. The SPC has us
currently in a marginal risk for Friday, mainly just a wind
threat and maybe a quarter sized hail stone or two. DCAPE looks
high enough to produce severe winds. Most of the CAPE is east
of the river in the afternoon on the lifting side of the surface
trough, showers and thunderstorms are possible through the
whole state however.

This weekend colder air aloft wraps around the low, bringing
surface temperatures down to the 60s. The combination of this
cold air advection and a pressure gradient off the low, will
create breezy winds CWA wide. Wind advisory level winds are
possible in the southwest. We will keep an eye on this to
potentially need a Wind Advisory Saturday. The chances of
showers and thunderstorms continue through the weekend. Saturday
the main chances will be along and north of HWY 2. Sunday it
will be east of HWY 83 and south of HWY 2. Sunday another upper
level low swings down from Canada through Montana, keeping us in
southwest flow through Monday. No severe weather is expected
for now. Sunday through monday the chances are more widespread.
Temperatures through the weekend will be mainly in the upper 60s
through the end of the forecast.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 955 PM CDT Thu May 16 2024

Scattered showers and isolated thunderstorms remain possible
across most of western and central North Dakota tonight. If a
storm moves over a terminal, erratic gusty winds up to around 40
kts and brief visibility reductions to MVFR/IFR levels can be
expected. VFR conditions and light southerly winds are otherwise
expected through tonight. Winds will turn southwesterly and
eventually westerly on Friday as a cold front approaches.
Showers and thunderstorms are expected to develop over western
North Dakota mid to late Friday afternoon, with higher TS
chances farther south.

&&

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

&&

$$

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