420
FXUS63 KBIS 021727
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1227 PM CDT Sun Jun 2 2024

.KEY MESSAGES...

- Scattered severe thunderstorms today. Threats include hail up
  to the size of golf balls, damaging winds up to 60 mph, and a
  tornado or two possible.

- Chances for showers and thunderstorms continue through the
  first half of the week. Temperatures will be near to slightly
  above average, with highs in the lower 70s to lower 80s this
  week.

- Strong northwest winds are possible Tuesday through Thursday.

&&

.UPDATE...
Issued at 1208 PM CDT Sun Jun 2 2024

Scattered showers and thunderstorms continue to track north and
east from western into central ND. Latest surface analysis shows
low pressure over northwest South Dakota beginning to nose
northeast into central ND. There is also a local minimum in
MLCape over south central ND nosing into the Devils Lake Basin,
with an increase in low level moisture advection over the
far southwest and into central ND. This area seems to be favored
for convective initiation early this afternoon, which is
generally in line with our previous thinking. The initial threat
would probably favor large hail for any discrete cells that can
develop and then developing into more of a wind threat later
this afternoon. We sent updated pops and sky cover with the
early afternoon update.

UPDATE
Issued at 909 AM CDT Sun Jun 2 2024

Current surface analysis shows low pressure over northwest south
Dakota with a warm front extending east along the ND/SD border.
Isolated to scattered storms lifting northward, along and north
of this boundary are producing some small hail this morning in
the southern James River Valley. This is within an area of
around 35 knots of effective shear and MUCape of 500-1000J/kg so
an isolated strong to severe is not out of the question this
morning.

Farther north and west. The ongoing convection in the north
central continues to lift northeast into a more unfavorable
environment. The convection along the Montana border has also
diminished in intensity.

Looking ahead today, could still see a few stronger cells in the
JRV this morning. The convection in the west could percolate as
it tracks eastward this morning. We`re thinking the stronger
capping over the southwest/south central would help limit
convection while it would have a better environment in the
northwest/north central to linger through the morning and into
the early afternoon. For pops we utilized a blend of short term
guidance but leaned toward the HRRR guidance which seemed to
reflect our thinking. Convection lingering north and/or
developing central to north central late morning/early afternoon
and tracking off to the east and developing farther south during
the afternoon. Updated pops and sky cover this morning. latest
updates will be transmitted shortly.

UPDATE
Issued at 632 AM CDT Sun Jun 2 2024

Low level jet keep kicking up storms in the north central and
east, all have been non-severe. The CAMs actually have had the
line of storms in far eastern Montana so maybe they are
performing okay. That line will move in within the next hour,
so far it is non severe. The environment over there has about
500 J/kg MLCAPE and 35kts of shear so it could go severe. This
storm will be the start of it, still looking like the storms
will form an organized line east of the river in the afternoon.

&&

.DISCUSSION...
Issued at 300 AM CDT Sun Jun 2 2024

Showers and thunderstorms have developed in the south central
and James River Valley. They formed in the region of the low
level jet (LLJ). A few of the storms have been strong but not
severe so far. The RAP and HRRR have the LLJ increasing in
strength before sunrise, so maybe a storm could go severe. There
is a lot of shear (55kts) and some MUCAPE around 500 J/kg at
this time.

Aloft the main wave is starting to move through eastern Montana,
with the surface low over southeast Montana. The main front is
also in Montana, moving east. The low level jet is forecast to
stay over western and central North Dakota 11z when the wave
moves further east and pushes it east. None of the CAMs have
this early morning convection so it is hard to use them for
timing later today, but there might be a break between this
convection and the main show. They still have storms firing in
Montana this morning and moving east, forming into a line around
Highway 85. With CAPE around 1000 J/kg this morning and low
level lapse rates over 7 C/km and the high shear, storms
initially could be supercells with golf ball sized hail. Then
when they form a line it should mainly be a wind threat. DCAPE
values aren`t over 1000 J/kg so we will be sticking to 60mph
winds. The low level helicity in the southwest this morning is
over 200 m2/s2 then it moves over to the east and values
increase around 400! So there is a possibility of quick spin up
tornadoes east of the Missouri River along the line, with the
highest chance looking south of the Interstate. Timing for this
looks to be late afternoon when the cold front develops the
line. SPC still has the slight risk in the east almost to the
river, and a marginal for this morning`s storms in the west.
The storms should move out by sunset.


The first half of the week will continue to be active. Another
upper low develops in the Northwest and moves across bringing
more chances for thunderstorms Monday afternoon and Tuesday.
The CSU machine learning forecast has a small hail threat in the
south central for Monday afternoon and overnight, otherwise the
severe risk is low. Monday will be the warmest day of the week
with highs in the 80s, then as the upper low leaves cooler air
filters back in. Highs will be back below average in the lower
70s for the mid week and in the mid 70s for the end of the week.
Average temperatures are in the mid 70s for the week of June.
Wednesday night is when the upper low will start to spin away,
putting us in cyclonic northwest flow, with a big ridge building
in the west over a Four Corners high. So the weather will be
quiet except for breezy northwest winds Tuesday through Thursday
with low pressures moving through. Wednesday we may need a wind
advisory in the southwest, we`ll see.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1208 PM CDT Sun Jun 2 2024

Scattered showers and thunderstorms will track eastward across
central North Dakota this afternoon and early evening. These
storms will have the potential to produce MVFR-IFR visibilities
in heavy rain, in addition to strong winds and large hail. The
activity should exit the James River Valley by early evening.
Thereafter unless we see an are of patchy fog, VFR conditions
are expected through the rest of the 18Z TAF period.

&&

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

&&

$$

UPDATE...TWH
DISCUSSION...TWH
AVIATION...TWH