Severe Thunderstorm Warning 92, NWS Bismarck, ND

Area Forecast Discussion
National Weather Service Bismarck ND
347 PM CDT Fri Jul 12 2024

.KEY MESSAGES...

- Isolated severe storms are possible across all of western and
  central North Dakota late this afternoon and into tonight.
  Hail to the size of quarters and winds up to 60 mph will be
  the main hazards.

- Very warm temperatures through the weekend, with a Heat
  Advisory in Dickey and LaMoure counties 1 PM to 8 PM
  Saturday.

- Isolated to scattered severe storms are possible late Saturday
  afternoon and into the night. Hail to the size of golf balls
  and damaging winds up to 70 mph will be the main hazards. A
  tornado or two is possible northwest.

- Isolated to scattered severe storms will be possible once
  again on Sunday.

&&

.DISCUSSION...
Issued at 345 PM CDT Fri Jul 12 2024

Currently mostly clear skies are found across the state, with
some diurnal cumulus in the James River Valley. Scattered
thunderstorms have developed in far northwest North Dakota along
a weak surface front. Ahead of this front is a surface trough
orientated north/south across the west central part of the
state. Aloft the ridge is still flattening with a small
shortwave in eastern Montana. This wave will move east through
the evening, combining forces with the cold front, kicking off
convection. At the surface with this wave is much drier dew
points. Currently dew points in North Dakota are in the 60s and
70s. With these higher dew points CAPE values are very high,
however the is a strong cap in place, via our morning soundings.
This would be why there is no diurnal cumulus elsewhere. Models
have a pseudo-dry line moving in from Montana behind the cold
front this evening that storms will form on. As of 3pm CT
there's a storm trying to go up in southern Dunn county. This
will be a good indicator on the status of the cap. This storm so
far has only produced a quick weak tornado, no hail. Most CAMs
are very different a few isolated cells turning into an
organized line moving through the state, then the rest of them
keep the isolated cells. So if the line happens wind will be
more of a concern, especially with dew points dropping. That
will make an inverted V sounding, which is ideal for severe
wind. Otherwise if isolated cells, it will mostly be hail
around 1 inch. Shear is not very high, it looks to be around
20kts. CAPE is much high in the moist air but then drops off
rapidly west of the river where the storms will be forming.
Confidence in the storm mode is relatively low for a few hours
before the event unfortunately. The forecast may have lower PoP
values than expected because of this uncertainly in storm mode
and timing. The general timing for the main show is 23z
(starting in the west) to around 08z (ending in the east).
Wildfire smoke will continue to affect the upper atmosphere,
really just affecting the color of the clear sky you see.

Saturday is more of the same with possible severe storms. SPC
has a slight risk (level 2/5) across most of the area. Most
CAMs have a line moving in from Montana around 02z. CAPE looks
to be around 1500 J/kg with shear values around 40kts. 0-3km
shear is around 30kts, so wind will be a bigger concern if the
storm mode is a line, otherwise hail would be bigger in size
around golf balls. Sunday another chance of severe storms are
possible. SPC has a marginal from Williston to Bismarck over to
the Red River Valley. There is also a slight risk in the north
central down through Harvey and east. Currently for Sunday CAPE
and shear is very high in the slight risk area. We'll see how
that evolves.

Saturday will be the warmest day with the highest humidity. The
James River Valley will be the warmest spot. We have issued a
Heat Advisory for just Dickey and LaMoure counties from 1pm to
8pm Saturday for heat index values as high as 103 degrees.

The ridge through the weekend will continue to flatten and turn
zonal with slight waves of energy moving through. High
temperatures through the weekend will slowly cool to the 80s by
Monday as a front and wave dip down from Canada. Temperatures
look to stay in the 80s with a big upper low spinning farther
up in Canada before dipping into the Great Lakes Wedneday. This
will put us in northerly flow, aiding to the slightly cooler
temps.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 345 PM CDT Fri Jul 12 2024

VFR through most of the period. There's a chance of
thunderstorms late this evening through about 08z. Confidence
is a little low so kept it all VCTS for now. Clouds in the James
River Valley have formed as MVFR and should lift higher this
afternoon. Winds will be light, may be gusting to 20kts this
evening.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM to 8 PM CDT Saturday for NDZ048-051.

&&

DISCUSSION...Smith
AVIATION...Smith

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