173
FXUS63 KBIS 171150
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
650 AM CDT Fri May 17 2024

.KEY MESSAGES...

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

- Warmer today with highs from the mid 70s northwest to the mid
  80s south central. Windy and cooler on Saturday with highs
  mostly in the 60s.

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

&&

.UPDATE...
Issued at 631 AM CDT Fri May 17 2024

Except for maybe a stray sprinkle, shower activity has either
dissipated or moved east of the forecast area. Mostly sunny
conditions should prevail this morning. We made some minor
adjustments to sky cover based on latest satellite imagery.
Otherwise no changes to the forecast early this morning.

Just looking at the more recent runs of the RAP, there is more
instability in the north and potentially a greater hail threat
north, but this is quite a switch from earlier and will wait for
additional 12Z guidance for any significant changes to threats.
Will continue with 1 inch hail and 70 mph winds.

&&

.DISCUSSION...
Issued at 332 AM CDT Fri May 17 2024

Isolated to scattered showers were moving across western and
central ND early this morning. Low pressure continues to spin
over southwest Saskatchewan, with surface pressures also
developing over central and eastern Montana, ahead of a strong
shortwave tracking across central/eastern Washington and Oregon.
As shower activity dissipates and or exits to the east, we
should see a quiet and mostly dry morning with temperatures
climbing well into the 70s most areas by midday.

This afternoon as temperatures climb into the lower and mid 80s
over southwest and central ND, we see steepening low and mid
level lapse rates and increasing instability over the forecast
area. Strong bulk shear will be present across the entire
forecast area today. The aforementioned shortwave and attendant
surface low pressure will catch up with the lingering frontal
boundary from the Saskatchewan low pressure system and push
quickly across the forecast area late this afternoon and this
evening. This will bring a chance of strong to severe storms to
most of the forecast area.

When looking at the potential for sever weather, just compared
to yesterday, the areal extent and the window of opportunity
looks a bit smaller (far southwest and south central then
lifting a little more north, east of the Missouri, into the JRV
from around 21Z-04Z). However, with the strength of the
shortwave, strong to possibly severe storms can`t be ruled out
pretty much anywhere across western and central ND (perhaps not
the far northwest which is currently in the general TSTM
risk).

As far as hazards, it seems like winds will be the main threat.
After coordination with FGF/ABR we bumped up the wind threat to
70 mph. There is an area of strong DCAPE over south central ND
this afternoon. However, it does begin to dissipate as
convective potential increases. Also, just with the strength of
the shortwave and the strong jet dynamics, a strong wind gust
seems possible. Bufkit soundings show the potential for 40-50
knot winds mixing down to near the surface just behind the cold
front. Any convection with the front would help to push this
cold air to the surface, and the Inverted V type soundings are
favorable for stronger winds mixing to the surface.

The hail threat seems lower with 1 inch hail a good upper limit
at this time. There is some instability ahead of the front this
afternoon and if there is convection there would be enough
instability for some marginally severe hail. This will be a
conditional threat given the capping that will exist ahead of
the cold front. If we do see convection develop ahead of the
front this afternoon we could see some hail to 1 inch. One
additional thought...Latest RAP guidance and NAM guidance is
showing some larger hail potential along the Canadian border.
This wasn`t the case earlier, so will continue to monitor.

Based on the storm mode, which would favor a linear or mixed
mode as the shear is mostly parallel to the cold front. Ahead of
the front, a better hail threat would exist with the potential
for a discrete cell if the cap can be overcome, as mentioned
earlier, but with that condition remaining, seems reasonable to
limit hail to 1 inch.

Also as mentioned earlier, environmental winds alone will be
strong behind the cold front tonight and added convection could
make for a windy overnight. There is another shortwave following
late tonight into Saturday morning. Shower/thunderstorm
activity with that wave could also mix down some stronger winds
aloft. Saturday looks to be windy across the forecast area and a
wind advisory may be needed for at least portions of the area
on Saturday. Saturday will also be much cooler, with scattered
showers mainly in the north.

Sunday will bring a modest warm-up with highs climbing back into
the 70s across most of the forecast area. A broad southwest
flow with an approaching shortwave could bring some shower and
thunderstorm activity once again. At this time it looks the
southeast CWA would be favored for thunderstorms. Monday and
through the remainder of the forecast period temperature look to
remain seasonable with near daily chances for showers and
thunderstorms.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 631 AM CDT Fri May 17 2024

VFR conditions to begin the 12Z TAF period with clear to partly
cloud skies ans light winds.

This afternoon and evening showers and thunderstorms are
expected to move through the forecast area from west to east. At
this time we included a TEMPO for Thunder at KBIS (23-03Z) and
KJMS (01-05Z) with gusty winds to 40 knots and MVFR Vsbys. At
the remaining TAF sites storms and timing are more uncertain so
for now just included a VCTS. Of course gusty and erratic winds
with MVFR vsbys can be expected in any storms that develop. In
the afternoon and evening winds will shift southwest then west
to northwest with the passage of a cold front. Scattered showers
with VFR Vsbys and moderate west to northwest winds at all
sites behind the cold front and through 12 UTC.

&&

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

&&

$$

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