862
FXUS63 KBIS 030833
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
333 AM CDT Fri May 3 2024

.KEY MESSAGES...

- Expect low to medium chances (20 to 60 percent) for rain
  showers through the day, mainly across the northern half of
  western and central North Dakota. Some light snow may mix in
  across the west this morning.

- Temperatures will warm through the weekend, with windy
  conditions on Sunday.

- Chances for rain return Sunday evening and continue through
  the work week. The wettest period will Monday through Tuesday
  when most of western and central North Dakota will see medium
  to high chances (60 to 90 percent) of rain.

&&

.DISCUSSION...
Issued at 333 AM CDT Fri May 3 2024

Early this morning, western and central North Dakota sits under
the influence of broad quasi-stationary troughing overhead. The
upper low that brought showers and thunderstorms to the region
yesterday will continue to eject out into Ontario to our
northeast as the next upper low rotates down into northwest
North Dakota from southern Saskatchewan later today. This low
will be the trigger for showers to develop through the day (20
to 60 percent chance), mainly across the northern half of the
forecast area (best chances along the International Border).
Some light snow may even mix in across the west briefly this
morning. RAP soundings suggest that instability will be limited
this afternoon and evening with MUCAPE values mainly maxing out
in the 100 to 200 J/kg range. While a stray rumble of thunder
or two cannot be ruled out, confidence is not high enough to
include mention of thunder in the gridded forecast at this time.

Precipitation chances will diminish to the northeast tonight as
the upper level trough finally starts to move out to our east,
transitioning western and central North Dakota into northwest
flow aloft on Saturday. Surface high pressure will also slide in
on Saturday, leading to diminishing clouds from west to east and
slightly warmer temperatures. Highs will remain cool today,
ranging from the mid 40s northeast to the mid 50s southeast and
then by Saturday, highs will range from the lower 50s to lower
60s.

An upper level ridge axis then approaches Saturday night and
crosses the state on Sunday. This will mean even warmer
temperatures with forecast highs ranging from the lower 60s to
lower 70s. Behind the ridge axis, a deep trough will approach
from the west, transitioning western and central North Dakota
into meridional flow aloft. As this trough approaches, a
surface low will deepen to around 990 mb or less over eastern
Montana. This will lead to strong warm air advection, pressure
falls, and a rapidly tightening pressure gradient on Sunday for
our area. So, while highs will be fairly mild, it will be windy
with soundings suggesting the potential for 40 knots or so
available to mix down from the top of the mixed layer. The
potential for gusts up to 45 mph seems reasonable for now and an
eventual Wind Advisory seems like a decent probability.

The story then turns to the approaching strong storm system and
widespread rain event Sunday night through the week. The sub
990 mb surface low will continue to deepen as the upper level
trough starts to take on a negative tilt and nudges into the
northern Plains. Widespread showers and some thunderstorms will
develop through the day and night, but dry slotting is likely to
setup somewhere depending on the eventual track of the low.
While thunderstorm chances will be better than in previous days,
instability still appears to be somewhat lacking. However we
could see some MLCAPE values up to 500 J/kg with deep layer
shear forecast to range from around 35 to 45 knots. So, the
severe weather potential appears to be fairly low but a couple
of strong storms may be on the table.

The wettest period will generally be Monday through Tuesday
(widespread 60 to 90 percent chances for showers) and another
potential hazard could be heavy rain, especially if heavier
showers/storms can train over some of the same areas. NBM
72-hour probabilities (ending 12z Thursday) don`t suggest
anything too dramatic with most of the west and central in
medium probabilities (40 to 70 percent) for an inch of rain or
more (the one exception being the James River Valley where the
consensus currently wants to place most of the dry slotting).
When we increase that threshold to two inches, the probabilities
fall off mainly into the 10 to 30 percent range. However, it is
worth noting that the NAEFS is showing Integrated Water Vapor
Transport, PWATs, and 850 mb specific humidity in the 97.5th
percentile or greater for this time of year in the Monday
through Tuesday time frame. Thus, there may be an opportunity
here for some heavier rainfall in a few locations.

The upper low will start to wind down by mid week but will be
slow to kick out into the Great Lakes region given a stubborn
east coast ridge. Low to medium chances (20 to 60 percent) for
showers will continue through at least Thursday.

Highs on Monday will not be quite as warm as Sunday given
widespread clouds and rain. However, we should still see highs
in the 60s. With the cool wet pattern continuing, highs will
mainly dip back into the lower 50s to lower 60s for most of the
rest of the work week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 117 AM CDT Fri May 3 2024

The next chance of rain will start to enter the northwest in the
next few hours, potentially impacting KXWA. More showers will
develop throughout the day on Friday but will generally be of
the hit and miss variety. With such uncertainty about eventual
location and tracks of these showers, we elected to keep mention
of rain out of any specific site forecast except for KXWA where
confidence is a bit higher. There is a small chance for a rumble
of thunder or two as well. IFR to MVFR ceilings will be likely
across the west and north through much of the period, including
KXWA, KDIK, and KMOT. For now, it appears that KBIS and KJMS
should remain in VFR categories through the period. Winds will
become a bit gusty out of the west Friday afternoon, when we
could see some gusts up to 35 mph.

&&

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

&&

$$

DISCUSSION...ZH
AVIATION...ZH