884
FXUS63 KBIS 171741
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1241 PM CDT Mon Jun 17 2024

.KEY MESSAGES...

- 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.

&&

.UPDATE...
Issued at 1231 PM CDT Mon Jun 17 2024

A bit more activity north early this afternoon so increased POPs
a bit. Cloud bases rather high at around 10K Ft AGL, so didn`t
go too crazy raising chances with more sites just reporting
trace amounts of moisture.

Still on track for 2 rounds of precipitation with the arrival of
a potent mid level S/WV. First will see increasing shower and
isolated thunderstorm chances west late today into this evening.
A few could be strong given the amount of 0-6km shear, though
instability is limited. Next round will likely originate in
South Dakota, then lift north/northeast into portions of south
central and eastern ND later this evening and overnight. This
looks to be the best severe potential given the increasing
instability yet marginal shear.

UPDATE
Issued at 902 AM CDT Mon Jun 17 2024

The forecast for today remains on track. Modified POPs and sky
cover based on latest imagery and trends. Will keep precip as
showers till this afternoon when thunder chances increase with
the arrival of instability from the south.

UPDATE
Issued at 645 AM CDT Mon Jun 17 2024

Have adjusted the precipitation grids to account for the the
latest radar trends. Most of western and central North Dakota is
now covered in mid to high level clouds, with an area of weak
reflectivities developing behind the cold front pushing south
across the forecast area. Otherwise, showers have begin to push
into the south as expected. Winds remain generally light and
disorganized at this time.

&&

.DISCUSSION...
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.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1231 PM CDT Mon Jun 17 2024

VFR ceilings and visibility at all terminals early this
afternoon. A few scattered showers north, though cloud bases
remain elevated so little reaching the ground.

Ceilings will begin to drop later this afternoon into this
evening along with chances for showers and thunderstorms
increasing through the evening and early overnight hours. A few
strong to severe storms will be possible across south central
and southeastern North Dakota, with more shower activity and
VCTS elsewhere. Widespread MVFR to LIFR visibilities and
ceilings are forecast, along with some terminals occasionally
observing LIFR ceilings. Winds will remain moderate from the
east at 10 to 15 knots and gusts up to 25 knots at all terminals
through early Tuesday morning, before diminishing and turning
northerly through the end of the TAF period. Where thunderstorms
to develop, gusty and erratic winds are anticipated.

&&

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

&&

$$

UPDATE...NH
DISCUSSION...Adam
AVIATION...NH