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fxus63 kbis 161930 

Area forecast discussion
National Weather Service Bismarck ND
230 PM CDT Mon Sep 16 2019

Short term...(this evening through tuesday)
issued at 229 PM CDT Mon Sep 16 2019

Well above average temperatures are expected to continue tonight and

Currently, the apex of an upper level ridge was east of our area and
moving towards the Great Lakes while a western US trough was
established over the West Coast. This has resulted in southwest flow
aloft across the Dakotas, but a mid-level thermal ridge remains in
place over the Western Plains states. This thermal ridge was
allowing unseasonably warm and humid conditions across the region as
an east-west surface warm front over northern North Dakota continues
its northward movement, and a h925/h850 low level jet was
established over the plains states into Minnesota.

The energetic western trough continues to amplify to our west as the
ridge apex moves toward the Great Lakes. This pattern will allow
warm and humid surface conditions to continue into Tuesday.
Overnight lows tonight should remain in the 60s across our region
(average lows this time of year are in the low to mid 40s).

On Tuesday, a shortwave emanating from the western trough will lift
northeast into Wyoming/Montana and a surface low will enter the
western Dakotas Tuesday afternoon. This will diminish the mid-level
thermal ridge, but still keep unseasonably warm conditions in our
area during the day. Although we do not expect high temperatures
Tuesday to be as high as on Monday, we do expect highs Tuesday to
reach into the 80s, which is well above the average highs (around 70
for this time of year).

Long term...(tuesday night through monday)
issued at 229 PM CDT Mon Sep 16 2019

Chances of thunderstorms return to the forecast by Tuesday evening.
Then more seasonable temperatures by mid-week (highs in the 70s)
with chances of showers and thunderstorms returning Thursday
afternoon through Saturday.

As mentioned in the short term discussion, a shortwave trough ejects
from the mean longwave trough over the Pacific northwest by Tuesday
afternoon. This shortwave moves into the western Dakotas by the
evening and overnight hours. The associated surface low over the
western Dakotas Tuesday afternoon will lift northward into
Saskatchewan/Manitoba Tuesday night. A strong cold front trailing
the system will sweep east across North Dakota Tuesday night.

Look for gusty/windy westerly winds Tuesday night and Wednesday as
the cold front sweeps through the area, the low deepens over
southern Manitoba, and the pressure gradient surrounding the low

Regarding showers and thunderstorms, chances begin Tuesday
afternoon in southwestern North Dakota, then spread into the
central part of the state Tuesday night. The Storm Prediction
Center has placed the western half of North Dakota in a day 2
marginal risk for severe weather. The latest model iterations
continue to suggest that SBCAPE values of 1000 to 2000 j/kg may
overlap with 25 to 40 knot deep layer shear values. However, the
best overlap area is fairly narrow. Still, there does appear to be
some potential for a strong to severe thunderstorm somewhere
across the western half of North Dakota late Tuesday afternoon
through Tuesday night.

After the cold front sweeps through, another western US trough
deepens once more, allowing moisture to again return to the region
by the end of the week. This pattern will bring more chances of
showers and storms across the region over a more prolonged period
- Thursday night through Saturday night. This system is slated to
bring widespread rain totals of an inch or more of rain to much of
western and central North Dakota. While specifics still need to be
ironed out, strong to severe storms may be possible on Thursday
night through Friday. A cool weekend into early next week is then
expected with highs generally in the 60s and lows in the 40s.


Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1222 PM CDT Mon Sep 16 2019

VFR conditions are expected through the period with southerly to
southeasterly winds generally 5 to 15 knots. Enhanced low level wind
shear (strong southerly winds aloft) will also be possible across
the southern James River Valley through the period, potentially
affecting kjms tonight.


Bis watches/warnings/advisories...


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