Scientific Forecaster Discussion
fxus63 kbis 170550
Area forecast discussion
National Weather Service Bismarck ND
1250 am CDT Tue Sep 17 2019
issued at 1242 am CDT Tue Sep 17 2019
An area of showers and scattered thunderstorms over northeast
South Dakota will continue to track northeast early this morning
on the nose of a 50-60kt low level jet. Will throw in a slight
chance pop for Dickey County based on latest radar loop and high
res model output, which do paint some low pops there early this
morning. Otherwise the forecast remains in good shape for the
Update issued at 956 PM CDT Mon Sep 16 2019
The forecast remains on track. No changes made other than to blend
current observations and trends into the forecast.
Update issued at 618 PM CDT Mon Sep 16 2019
No major changes are needed for this update. Blended current
observations and trends into the ongoing forecast, which remains
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 06z tafs through 06z Tuesday night)
Issued at 1242 am CDT Tue Sep 17 2019
VFR conditions are expected through the forecast period. Low-
level wind shear will be present at kjms tonight, with 2 kft winds
reaching near 40 kts out of the south-southwest through 15z. Chances
for showers and thunderstorms will begin to move into southwest
North Dakota late Tuesday afternoon, and across most of western ND
Tuesday evening. Have a mention of this for kdik-kisn. More
scattered activity is expected over central North Dakota so left
out any mention of showers or thunderstorms in the vicinity for now.