379
FXUS63 KBIS 060945
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
445 AM CDT Mon May 6 2024

.KEY MESSAGES...

- Several rounds of showers with low to medium chances for
  thunderstorms across western and central North Dakota today
  through tonight.

- There is a conditional risk of a few strong thunderstorms this
  afternoon and evening, mainly across southwest and south
  central parts of the state.

- Strong southeast winds gusting to 50 mph expected across
  central and eastern North Dakota today.

- Strong westerly winds are possible in southwest North Dakota
  on Tuesday.

- Warmer and drier weather is favored later in the week.

&&

.DISCUSSION...
Issued at 444 AM CDT Mon May 6 2024

A strong low level jet resides over the Northern Plains early this
morning, downstream of a potent shortwave/closed low over the
Rockies. Poleward moisture transport over central South Dakota has
recently initiated an area of showers with occasional lightning
along and west of Lake Oahe. This activity will continue to spread
northward into south central North Dakota through mid morning. More
isolated shower activity has also been noted across the rest of the
western half of the state at times during the early morning hours.

The strong upstream mid level low will spin into the Northern High
Plains today, with surface cyclogenesis underway early this morning
across eastern Montana and eastern Wyoming. Expect several areas of
showers with embedded thunderstorms to develop over and track
through western and central North Dakota over the course of the day.
Strong southeast winds will focus more over central and eastern
parts of the state today as the surface low deepens near the Black
Hills. Previously issued Wind Advisories for today remain on track.
Afternoon temperatures are likely to reach the 60s.

We are still monitoring the potential for a few stronger storms this
afternoon and evening, with the primary hazard being a weak tornado
or two. The main area of concern is expected to be along a northward
advancing occluded front with a northwest-southeast orientation from
southwest into far south central North Dakota. It is not certain
that surface-based convection will initiate along this boundary
(although mid to upper level forcing should be substantial), nor that
uninhibited low level buoyancy will build directly ahead of the
occluded front. Having said that, there is now greater ensemble
support for a narrow ribbon of 500-1000 J/kg SBCAPE preceding the
occluded front. Any storms that form along this boundary would
likely experience 20-30 kts of 0-1 km shear, along with 100-200
m2/s2 of 0-500 m SRH. Given those shear parameters, coupled with
very low LCLs and large, looping hodographs showing ample streamwise
vorticity for ingestion by right-moving supercells, it stands to
reason that a couple of brief, weak tornadoes could occur. Once
again, this potential is reliant on the presence of SBCAPE on the
order of 500 J/kg in the storm inflow air mass. Other severe hazards
cannot be completely ruled out, but should be of lesser concern.

A nearly-stacked low will continue to spin over western North Dakota
tonight before it begins to broaden out on Tuesday. There is still
some uncertainty on where the surface low circulation will settle on
Tuesday, but we are still expecting a synoptic dry slot to
significantly limit QPF across all but far western North Dakota
beyond tonight. In fact, there are now only medium odds (less than
70 percent) for an event-total rainfall exceeding one inch along the
Montana border. The far west could still see some periods of heavier
rainfall on Tuesday though, moreso in the southwest where strong
westerly winds could actually be the greater concern, with some
guidance showing BL momentum transfer potential near 50 kts. Tuesday
will be cooler than today, with highs mainly in the 50s, but
possibly as low as the mid 40s in parts of the southwest.

The stacked low pressure is forecast to devolve and shift southward
on Wednesday, though the continued presence of cyclonic vorticity
keeps medium chances for lighter rain in the forecast. A drying out
and warming of temperatures should finally commence on Thursday,
with highs forecast to return to the mid and upper 60s. Global
models are projecting a clipper-like system diving down from Canada
on Friday, but ensemble analysis shows very large spread on the
evolution of the synoptic pattern heading into the weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 207 AM CDT Mon May 6 2024

A strong low pressure system will bring aviation impacts to
western and central North Dakota through the forecast period.
MVFR to IFR ceilings are forecast to build in from southwest to
northeast Monday morning, persisting through the rest of the day
and evening. Periods of showers and isolated to scattered
thunderstorms can also be expected throughout the day Monday and
into Monday night. Southeast winds will remain strong through
the forecast period, increasing to sustained speeds around 20-30
kts with gusts to 35-45 kts Monday afternoon, strongest over
central and eastern North Dakota. Low level wind shear will
impact parts of central North Dakota from KMOT to KBIS until
early Monday morning.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until midnight CDT tonight for NDZ003>005-
011>013-022-023-025-037-048-051.
Wind Advisory until midnight CDT /11 PM MDT/ tonight for
NDZ019>021-034>036-042-045>047-050.

&&

$$

DISCUSSION...Hollan
AVIATION...Hollan