Mercer, North Dakota Weather Forecast Discussion

496
FXUS63 KBIS 151451
AFDBIS
Area Forecast Discussion
National Weather Service Bismarck ND
951 AM CDT Mon Sep 15 2025
.KEY MESSAGES...
- Showers and isolated thunderstorms continue today, lifting
  north into Canada this evening.
- On and off low to medium chances for showers and isolated
  thunderstorms remain in the forecast through the work week.
- Seasonable temperatures are expected this week, with the
  first half being warmer than the second half.
&&
.UPDATE...
Issued at 951 AM CDT Mon Sep 15 2025
Visibility has improved, therefore the Dense Fog Advisory has
been allowed to expire on time at the top of the hour.
Otherwise, scattered showers, along with a few rumbles of
thunder, continue mainly from northwestern through south
central ND. All in all, the forecast remains on track.
UPDATE
Issued at 659 AM CDT Mon Sep 15 2025
No major forecast changes are needed with this update. Visibility is
showing signs of improvement in northwest North Dakota, but there
are still a handful of observations and webcams showing visibility
under a quarter mile. At the time of this writing, showers were
evolving as expected.
&&
.DISCUSSION...
Issued at 521 AM CDT Mon Sep 15 2025
A negatively-tilted shortwave trough resides over the western
Dakotas early this morning and is embedded in longer-wave troughing
that also features a closed low between the Cascades and Northern
Rockies and another one in northwest Saskatchewan. Broad surface low
pressure is analyzed nearly underneath the negative-tilt shortwave
from southeast Saskatchewan through western North Dakota. Bands of
rain continue along the associated 700 mb trough axis early this
morning from northwest to south central North Dakota. In the far
northwest part of the state, dense fog prevails outside of steadier
showers. A Dense Fog Advisory remains in effect until 10 AM CDT, but
could be allowed to be cancelled early if more widespread persistent
rain becomes established.
Surface low is forecast to deepen in the southwest corner of
Manitoba today as the mid and upper trough axes pivot northeastward.
High-resolution models remain in fair agreement that at least
scattered showers will lift into north central North Dakota this
afternoon. These should diminish or move off into Canada this
evening. A few thunderstorms are also possible this afternoon, but
CAPE and especially effective bulk shear are both projected to be
much lower today. A period of gusty winds cannot be ruled out as the
surface pressure gradient tightens across northern North Dakota late
this afternoon. High temperatures today are forecast around 70 to
80, coolest north and warmest south.
The upstream low approaching the Northern Rockies is forecast to
initiate convection off the higher terrain of southern Montana/
northern Wyoming this afternoon. Models favor this convection
sustaining and propagating northeastward into southwest North Dakota
late this evening as the upstream low begins broadening out and
digging back into the Great Basin, forcing a new trough with
positive tilt. CAPE and shear appear unsupportive of severe weather,
but steep low and mid level lapse rates could trigger some strong
downburst gusts. Isolated showers and an occasional thunderstorm
could linger across parts of the state on Tuesday as the upstream
low cuts itself off from the main flow but leaves weak vorticity
advection over the region. Most locations though are likely to
experience a dry and seasonably warm day on Tuesday with highs
around 75 to 80.
By Wednesday, the aforementioned northwest Saskatchewan low is
forecast to interact with the other two waves. This could result in
a chaotic synoptic pattern, but one that is generally defined by
central CONUS troughing. One possible outcome that is favored by 3
out of 4 clusters composing around 75 percent total ensemble
membership is for the two western lows to cutoff into a Fujiwhara
effect over the Northern and Central Plains Thursday and Friday.
Regardless, all ensemble systems and clusters tend to favor a slight
cool down and increased chances for rain for the second half of the
week. Southern North Dakota has higher chances for rain over this
time period compared to the north. The stagnant north central CONUS
low/trough could get pushed eastward this weekend by upstream
effects of a strong Gulf of Alaska low digging into western Canada.
Despite the inherent ensemble uncertainty and typical low
predictability of cutoff lows, clusters are in fairly good agreement
for a brief period of anticyclonic flow this weekend with strong
thermal ridging from the US Rockies through the Canadian Prairies.
This would favor a period of drier weather and a slight warmup,
moreso for western parts of the state.
&&
.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 659 AM CDT Mon Sep 15 2025
Showers with an occasional thunderstorm will continue across much of
the western half of North Dakota this morning, slowly lifting north-
northeast through the afternoon. Rain could reduce visibility as low
as IFR levels at times. Dense fog and LIFR ceilings will also
prevail throughout much of northwest and parts of north central
North Dakota until later this morning. MVFR to IFR ceilings are
otherwise expected for most areas this morning (except far southwest
North Dakota), improving to VFR from south to north through the
afternoon. Central North Dakota will see southwesterly winds
increase to around 10-15 kts Monday afternoon, with northwesterly
winds around 10 kts farther west. A period of stronger gusts cannot
be ruled out from KXWA to KMOT late this afternoon.
Lighter winds and VFR conditions are expected tonight. Another batch
of scattered showers and isolated thunderstorms could move into or
develop across southwest and south central North Dakota late this
evening through tonight.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Telken
DISCUSSION...Hollan
AVIATION...Hollan

NWS BIS Office Area Forecast Discussion