840
FXUS63 KBIS 181931
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
231 PM CDT Sat May 18 2024

.KEY MESSAGES...

- Gusty west winds will continue through the rest of this afternoon
  with sustained values up to 30 mph and gusts to 45 mph.

- Low to medium rain shower chances (20 to 40 percent) return
  late tonight into early Sunday morning.

- There is a Marginal Risk of severe weather (level 1 out of 5)
  late Sunday afternoon into the evening hours.

- High temperatures remain cool through the next work week,
  mainly in the 60s. Expect daily low to medium (20 to 40
  percent) chances for showers and thunderstorms through the
  week.

&&

.DISCUSSION...
Issued at 231 PM CDT Sat May 18 2024

An upper low continues to spin off to the east just north of the
Canadian border over eastern Manitoba. Associated light rain
showers continue over Bottineau and Rolette counties, but should
move out in the next hour or two.

Western and central North Dakota generally sits under the
influence of near zonal flow aloft but we will see some subtle
ridging move across the state through the rest of the day. While
visible satellite imagery shows a decent amount of fair weather
cumulus, this progressive ridging should lead to some
subsidence across the west, leading to some clearing.

The strongest cold air advection and pressure rises have mainly
moved off to the east, so while it will remain windy though the
rest of the afternoon (winds out of the west northwest), it
should very gradually diminish as we move towards sunset. Given
the tight pressure gradient, we are still expecting sustained
winds up to 30 mph and gusts to 45 mph for a few more hours.
Thus, the Wind Advisory still looks to be in good shape.

Late tonight and into Sunday morning, we will gradually
transition to southwest flow aloft as a Pacific Northwest trough
starts to approach. Warm air advection may lead to some low to
medium (20 to 40 percent) chances for hit and miss showers late
tonight into Sunday morning, mainly across the south central
and James River Valley. This activity should move north through
the morning and into the early afternoon but uncertainty remains
about how long it will be able to sustain itself.

A better chance for showers and thunderstorms (40 to 70 percent)
should start to develop over the south central and James River
Valley by late Sunday afternoon and into the evening hours. A
surface low will start to deepen over South Dakota with an
inverted surface trough extending to it`s north northeast. This
boundary should be the focus for thunderstorm development by the
late afternoon hours. Across the far south, RAP soundings
suggest the potential for up to 2000 J/kg of MUCAPE. However,
looking at MLCAPE, we generally max out in the 500 to 1000 J/kg
range. Still, with forecast deep layer shear will range from 45
to 55 knots over the same area. On paper, these parameters
should be more than enough for a strong to severe storm or two.
However, there are concerns with moisture quality and depth. It
is also worth noting that the RAP is a bit more bullish on
higher instability than most of the other short term models (but
the RAP still shows fairly "skinny" CAPE which may mean
relatively narrow updrafts). That being said, deep layer shear
vectors will mainly be orthogonal to the surface trough so
storms that do form could be discrete or semi- discrete. The
Storm Prediction Center has placed Emmons, Logan, McIntosh,
LaMoure, and Dickey counties in a Marginal Risk (level 1 of 5)
for severe weather. After analyzing soundings and the latest
CAMS, we have decided to message the marginal severe weather
potential up to Kidder, Stutsman, and Foster counties as well.
For now, we will message wind gusts up to 60 mph and hail to the
size of quarters. The one caveat is that if the RAP were to
verify, these thresholds would possibly be too low. However,
the RAP appears to be an outlier right now, maybe not mixing
out dewpoints enough.

Regarding temperatures, Sunday will be the warmest day of the
week with highs ranging from the lower 60s to the lower 70s. By
Monday we will only see lower 70s in our far southeast with
highs in the 60s elsewhere. Highs will mainly be in the 60s
through midweek. The coolest days will then be possible towards
the end of week (Thursday and Friday) when we could see some
highs in the upper 50s to lower 60s.

The active progressive flow will also continue through the week,
leading to daily low to medium (20 to 40 percent) chances of
precipitation at various locations across western and central
North Dakota. Thunderstorm potential will be limited given the
cooler temperatures but a slight chance seems warranted towards
the end of the week across the south as most models have a
potent trough moving into the region (Thursday-Friday). The
eventual track of this trough and associated upper low is still
a bit up in the air. Most models/ensemble members have this
feature but substantial uncertainty remains regarding the track
and strength. It may be worth nothing that CIPs extended analogs
suggest some severe potential across our south by the end of the
week, but CSU Machine Learning guidance is not showing the
potential at this point.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1228 PM CDT Sat May 18 2024

We will see widespread fair weather cumulus this afternoon but
should remain in VFR categories through the period. Some
isolated to scattered showers will develop across the south
central and James River Valley early Sunday morning before
lifting north. Due to the isolated to scattered nature and exact
location uncertainty, have not included mention in any site
specific forecast at this time. It will remain windy through
this afternoon with winds mainly out of the west northwest.
Sustained values may reach 30 mph with gusts to 45 mph.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 7 PM CDT /6 PM MDT/ this evening for
NDZ001>005-009>013-017>023-025-031>037.

&&

$$

DISCUSSION...ZH
AVIATION...ZH