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539
FXUS63 KBIS 180832
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
332 AM CDT Wed Sep 18 2024

.KEY MESSAGES...

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- Scattered showers and thunderstorms will continue moving north
  through the area this morning. Additional showers and
  thunderstorms are possible (30-50% chance) across western and
  northern North Dakota this afternoon through tonight.

- Strong southerly winds are forecast today, with sustained
  winds up to 30 mph.

- An active pattern continues through the weekend, with low
  chances for showers and thunderstorms most days.

- A cooling trend is forecast for the end of the week, with
  highs in the 60s by the weekend.
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&&

.DISCUSSION...
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Issued at 332 AM CDT Wed Sep 18 2024

This morning, there were two surface lows analyzed across the
region, one in southwest North Dakota and one in northeast Montana,
with a stationary front connecting them. Aloft, a deep closed low
was placed over northern Wyoming, with sharp southerly flow over the
Dakotas on the east side of the low. Widespread showers and
thunderstorms developed just ahead of the upper low as midlevel
heights were falling, and on the nose of a low-level jet that was in
southern North Dakota. As of 830 UTC a relatively consistent
line of storms extends from Williston to Jamestown, with
scattered convection on either side of the main line in central
North Dakota. SPC mesoanalysis indicates the environment is
characterized by 30-40 knots of bulk shear and 1000-1500 J/kg of
MLCAPE, although MLCIN is pretty high and thus keeping storms
subsevere.

Storms will continue to lift north through the morning as the
eastern surface low and attendant front move north as well.
Precipitation chances return fairly quickly this afternoon, however,
as the western surface low becomes stacked with the upper low and
convection wraps around the southern side. Showers and thunderstorms
will likely be limited to western and northern North Dakota, with
blended PoPs mainly in the 30 to 50% range.

The main other weather concern for today is strong winds from the
influence of the stacked low. Winds will be southerly through the
day today, sustained up to 30 mph, before shifting southwest to
westerly tonight as the stacked low lifts northeast. At this point
we are expecting winds to stay below advisory criteria, although it
will likely be close in our southern counties along the South Dakota
border. Highs today will be a bit cooler, in the lower 70s to lower
80s. Lows tonight will mainly be in the 50s.

On Thursday, the upper low is progged to be moving into the southern
Canadian Prairies, keeping 20-40% chances for showers and
thunderstorms in northern North Dakota. A tight surface pressure
gradient will lead to another day of breezy winds sustained at 20 to
25 mph, and cooler air behind the system will lead to highs in the
upper 60s to mid 70s.

Temperatures will rebound just slightly on Friday as a shallow,
progressive trough moves through the region, followed closely by a
shortwave trough that ensemble guidance is showing moving east
through the southern Canadian Prairies to end the week. Model
consensus is advertising that this system will bring a cold front
and precipitation chances starting Friday night, leading to cooler
temperatures and on and off chances for showers through the weekend.
There is fairly high confidence in highs generally staying in the
60s Saturday through Monday, with little spread in NBM temperature
percentiles.

Towards the end of the extended period, ensemble guidance diverges
in its solutions, although there is some suggestion in cluster
analysis of broadly zonal flow before potentially upper ridging
building in to our west. CPC outlooks tilt towards above normal
temperatures through the end of September, with some signs of a
drier pattern emerging for the end of the month.
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&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
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Issued at 332 AM CDT Wed Sep 18 2024

IFR to LIFT stratus is in place across northern North Dakota,
impacting KXWA/KMOT. Widespread showers and thunderstorms
continue across much of the area, with the exception of
southwest North Dakota, moving north. MVFR conditions and
gusty, erratic winds are possible under any storms. Winds will
turn southerly behind the storms, with sustained winds of 20 to
30 mph through the day today. Additional showers and
thunderstorms are possible in western and northern North Dakota
tonight, with winds turning more west/southwesterly late in the
period. Conditions should return to VFR by 18Z before lower
clouds could move into western North Dakota tonight with the
precipitation chances.
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&&

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

&&

$$

DISCUSSION...Jones
AVIATION...Jones