Grano, North Dakota Weather Forecast Discussion

496
FXUS63 KBIS 042041
AFDBIS
Area Forecast Discussion
National Weather Service Bismarck ND
341 PM CDT Sat Oct 4 2025
.KEY MESSAGES...
- Windy with high chances for rain, heavy at times, across
  southwest and central North Dakota tonight into Sunday, with
  medium chances for rain northwest.
- A few strong to marginally severe thunderstorms are possible
  across south central into eastern North Dakota this evening
  into tonight.
- Much cooler for the first half of next week, with highs mostly
  in the 50s and lows in the upper 20s to mid 30s.
- Medium to high chances for a freeze across much of western
  and north central North Dakota Sunday night and Monday night.
&&
.DISCUSSION...
Issued at 341 PM CDT Sat Oct 4 2025
This afternoon, a deep trough base extended into the southwest
CONUS, with a closed low and attendant shortwave lifting northeast
and approaching the Northern Plains. At the surface, a cold front
had moved through the forecast area this morning, with a secondary
front analyzed just across the International Border in southeast
Saskatchewan. An upper jet streak and multiple impulses moving
through the synoptic flow has been leading to scattered light rain
showers through the day, slowly becoming more numerous as the
afternoon goes on, although the lower atmosphere is quite slow to
saturate so some areas of reflectivity do not have any rain making
it to the surface just yet. This activity will continue through this
evening, overnight, and through Sunday morning, with widespread high
chances for rain from southwest to northeast North Dakota as the
trough base and main shortwave lift into the region.
With climatologically high PWATs, widespread rain amounts of at
least an inch are favored for this afternoon through Sunday
morning, generally from southwest to northeast North Dakota.
There is a broad corridor of elevated probabilities (30 to 50
percent) for at least 2 inches of rain from this event,
extending from Grant and Sioux Counties, through the Bismarck
area, and up to Devils Lake. Any thunderstorms could lead to
torrential rain and potentially localized flooding concerns in
urban areas.
Aside from heavy rain, we are still monitoring the potential for
isolated severe thunderstorms, mainly across the James River
Valley and eastern North Dakota. As the trough base approaches
the region, CAMs are occasionally developing some convection out
ahead of the main precipitation shield, although this has been
trending later in recent model runs as the entire system has
slowed up by a couple of hours. The 12Z HREF UH track still
focuses on eastern North Dakota in the evening before an
additional push from the south central to northeast overnight,
with strong bulk shear and marginal instability available if
storms are elevated. Still messaging 60 mph wind gusts, hail up
to the size of quarters, and heavy rain with any severe
thunderstorms. There could be a few rumbles of thunder across
southwest and most of central North Dakota, but the threat for
severe weather decreases quickly to the west, as seen by the SPC
outlook as well as NSSL and CSU machine learning output. CSU
output also paints some low tornado probabilities across the
James River Valley and east, as forecast soundings are
advertising high SRH, although hodographs don`t look
particularly convincing. Still, something to keep an eye on,
especially if we get more confident in the thunderstorm / severe
threat overall.
As the system continues pushing northeast Sunday morning, rain
chances will taper off from west to east, although a modest surface
pressure gradient and another push of cold air advection from a
secondary cold front will produce strong northerly winds
through the day. Some of the CAMs have additional showers
developing on the backside of the system Sunday afternoon and
evening, so would not be surprised if we end up increasing POPs
for this period. As previous shift noted, timing isn`t favorable
for stronger winds that would be getting close to advisory
criteria. With the winds, mostly cloudy skies, and highs mainly
in the 50s, Sunday will be quite a brisk fall day compared to
what we`ve seen lately.
A surface high behind Sunday`s cold front is progged to slide
through Sunday night into Monday morning, leading to the coldest
night of the next week. 13Z NBM probabilities show a high likelihood
of below freezing lows across the northwest and in our normal cold
corridor from Hettinger to Beulah/Hazen, with medium chances across
the rest of western North Dakota and across the north central.
Cluster analysis advertises strong agreement amongst ensemble
members in an upper ridge expanding across the region through
much of next work week, which is mirrored in NBM temperature
percentiles showing a warming trend from Monday through
Thursday. The work week starts with highs in the 50s, with the
latest deterministic NBM showing highs in the mid 60s to lower
70s on Wednesday and Thursday, about 10 degrees above average.
Chances for rain during this stretch are very low.
The synoptic pattern becomes more uncertain to end the week, with
one camp of ensemble members turning flow southwesterly late in the
weekend, while almost half of  members want to keep the upper ridge
in place through next weekend. Although spread in the 25th/75th
temperature percentiles increases, highs are still near to slightly
above average, while we start to see slowly increasing precipitation
chances associated with those ensemble members that develop a
trough over the western CONUS and subsequent southwest flow
across the Northern Plains.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 126 PM CDT Sat Oct 4 2025
A cold front passed through the area this morning, with winds
shifting to north to northwesterly through the remainder of the
forecast period. Winds will become gusty overnight tonight and
continue through the end of the TAF period, sustained around 20
knots and gusting up to 30 knots.
Rain showers are becoming more numerous across the state at the
start of the period, and will increase further this afternoon
through tonight. Expect widespread rain showers and MVFR
ceilings after 00Z, with MVFR to IFR visibilities depending on
how heavy the rain is and any fog that develops. Isolated
thunderstorms are possible across south central ND, but only
included mention at KJMS for now. Rain will be tapering off the
last few hours of the TAF period but low ceilings are expected
to persist across the south and central.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Jones
AVIATION...Jones

NWS BIS Office Area Forecast Discussion