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362
FXUS63 KBIS 170905
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
405 AM CDT Mon Jun 17 2024

.KEY MESSAGES...

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- Widespread showers with isolated to scattered thunderstorms
  this afternoon through Tuesday.

- Isolated to scattered severe storms possible this evening
  through tonight, with expected hazards of hail up to golf
  ball size and winds up to 60 mph. Very heavy rainfall is also
  possible with any storm.

- Below normal temperatures expected this week, especially
  Tuesday and Tuesday night.
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&&

.DISCUSSION...
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Issued at 405 AM CDT Mon Jun 17 2024

The forecast area lies under southwesterly flow this morning,
becoming increasingly so as deepening Pacific Shortwave begins
to travel over the Rockies and across the northern Plains
through the early half of this week. A surface low previously
over Colorado has been ejected into eastern Nebraska over the
last few hours, promoting a sharpening thermal gradient at the
surface that will begin to migrate northward through the mid
morning. Modest instability along this surface boundary is
promoting a widespread area of showers and thunderstorms across
southern South Dakota at this time, and the northernmost extent
of these showers has begun to tickle our southern counties. The
the lack of any real instability over the James River Valley
limits our potential for thunderstorms to maybe a few rumbles at
most this morning. Winds are generally light and variable at
this time, but will begin to strengthen and organize by the mid
morning, becoming east northeasterly. Lows are forecast from the
lower to mid 40s west, to the mid 50s southeast.

At the tip of the upper level shortwave over the rockies, a
surface low will organize in southern Wyoming and begin to
migrate eastward through the morning. An inverted surface trough
associated with this low will be pushed across the western and
north central North Dakota through the late morning and
afternoon hours today, causing widespread showers over this area
to becoming increasingly likely by the late afternoon period.
At this time, a surface trough associated with the Nebraskan low
will begin to move northwestward across the southern James
River Valley. With ample moisture filtering into the low to mid
levels ahead of this boundary, model MUCAPE values peak around
2500-2500 along with SFC-3KM Shear up to 50 knots across the
south central into the James River Valley late this evening
early into Tuesday morning. However, all this instability is
very elevated, with model MLCAPE values around 0 and SFC-1KM
Shear up to around 20 knots. With these high based storms, the
primary concern will be hail up to golf balls in size (1.75 inch
diameter), and the occasional gust up to 60 MPH . Due to the
elevated nature of this storms, the risk of tornadoes is
currently considered low. Of interest is the potential for
heavy rainfall with this system, due to the near saturation of
the low to mid levels, high PWATs exceeding the 90th percentile,
and the alignment of the inciting boundary with the overall
flow pattern that would promote training storms. As it stands,
portions of the south central have a 30 to 40% chance of
exceeding 1.0" of rainfall by Tuesday morning, which could
result in some localized flood concerns. Portions of the
northwest also have a similar, 30 to 40% chance of exceeding
1.0" of total rainfall through this period as well, though this
is for a more drawn out period of persistant stratiform
showers.

With the slow moving upper level low continuing to push across
the northern Plains, showers are anticipated to continue through
much of the day on Tuesday. While some thunderstorms will be
possible across the north through the afternoon and evening
hours as a weak cold fron begins to dig across the International
Border, the primary axis of instability will have shifted
further to our east on Tuesday and thus severe weather concerns
are low at this time. With the cooler airmass becoming situated
over the forecast area, high temperatures on Tuesday will dip
down into the mid 50s northwest to mid 70s southeast. At the
same time, high pressure will begin to develop across the Black
Hills late Tuesday afternoon and begin to push eastward across
South Dakota Tuesday night. With this setup, there is some
potential for frost development across portions the west Tuesday
morning, where the ensemble is already forecasting lows broadly
in the upper 30s.

Late Tuesday night into early Wednesday, the dominate upper
level shortwave will gradually be absorbed into a general
southwesterly flow pattern that will persist through the end of
the workweek. High temperatures through this period will
broadly be in the 70s. The occasional shortwave will travel
down this southwesterly flow, promoting chances for showers (60
to 80 percent)and thunderstorms (30%)late Thursday through late
Friday, with the best chances across the south. A slightly more
energetic shortwave wil push through the northern Plains early
Saturday through early Sunday, which may be our next best chance
to see some stronger storms develop, though confidence remains
fairly low this far out.
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&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
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Issued at 405 AM CDT Mon Jun 17 2024

VFR ceilings and visibility are expected at all terminals at
the beginning of the 06Z TAF period. Isolated to scattered
showers will begin to push into the southeast later this
morning, though these showers are not current anticipated to
impact any given terminal at this time. Winds will continue
diminish and become variable through the late morning, before
strengthening and organizing to become east northeasterly
through the morning hours, then becoming gusty through the
afternoon.

By the mid to late afternoon today, ceilings will begin to drop
while chances for showers and thunderstorms increase through the
evening and early overnight hours. By around 00Z, showers will be
present at all terminals, with periods of heavier rainfall promoting
occasional MVFR visibilities at all terminals. Thunderstorms
will move into south central North Dakota through the evening
and the end of the TAF period, within the vicinity of KBIS and
KJMS. A few strong to severe storms will be possible across the
south central North Dakota late Monday afternoon beyond the end
of the TAF period, overnight into early Tuesday morning. Hail up
to the size of golf balls and winds up to 60 MPH will be
possible. Winds will remain moderate from 10 to 15 knots and
gusts up to 25 knots at all terminals through the end of the TAF
period, generally from the east. Where thunderstorms to
develop, gusty and erratic winds are anticipated.
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&&

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

&&

$$

DISCUSSION...Adam
AVIATION...Adam