Peterson, Iowa Weather Forecast Discussion

827
FXUS63 KFSD 271633
AFDFSD
Area Forecast Discussion
National Weather Service Sioux Falls SD
1133 AM CDT Sat Sep 27 2025
.KEY MESSAGES...
- We see a brief cooldown (but still above normal) today. Well
  above normal temperatures and periods of breezy south winds
  dominate the week ahead.
- Dry conditions prevail through much of next week, but low rain
  chances may return by the end of the week.
- Breezy afternoons and drying grasses may lead to localized
  elevated fire weather concerns, mainly west of I-29 early to
  mid next week.
&&
.DISCUSSION...
Issued at 333 AM CDT Sat Sep 27 2025
Cool front bisecting the forecast area northeast to southwest
early this morning will continue to progress southeast, exiting
northwest Iowa by daybreak or shortly after. 850mb temperatures
settle into the lower-mid teens, which is supportive of highs
in the 70s, still several degrees above late-September normal
highs. Trailing surface high will bring light winds tonight, and
with a dry air mass in place, lows dip into the lower-mid 40s
east of I-29, with lower 50s west of the James River.
The high pressure slides east Sunday, allowing southerly return
flow to become established through early next week. These winds
remain relatively light in the east Sunday in closer proximity
to the exiting surface ridge, with gusts 20 to 30 mph expected
to develop in areas west of I-29. Main challenge is how quickly
boundary layer moisture (higher surface dew points) may return
and think Sunday could still be on the drier side in the wake
of departing high pressure. Given the drying fuels and potential
impact on fire weather concerns, nudged afternoon dew points
toward the NBM 10th percentile Sunday, which yields minimum
humidity levels of 20-25% for portions of the area. The lowest
humidity is offset east of the breezier winds, so critical fire
weather conditions are not expected, but areas with locally
drier fuels may see elevated fire danger (High GFDI to perhaps
brief Very High if fuels are near-fully cured).
Early-mid next week will see the northern Plains sandwiched
between mid-upper level ridging over the Great Lakes and a
developing upper low offshore of the Pacific Northwest.
Typically a southwest flow aloft would bring concerns of more
active weather, but moisture remains very sparse above some
increase in the boundary layer and far upper levels, so rain
chances remain very low through the middle of the week. NBM has
been consistent in bringing surface dew points back into the
lower-mid 50s Monday-Wednesday. However, will have to watch
for the potential to mix drier air to the surface as the
deterministic global models (Canadian/ECMWF as well as the
typically over-mixy GFS) show good agreement in dropping
afternoon dew points into the 40s. With breezy afternoons
expected to continue (southerly gusts 20-35 mph), humidity
levels could have an impact on area fire danger as grasses
continue to slowly cure.
Western trough slowly shifts east across the northern Rockies
and into the Canadian Prairies/northern Plains by the end of
next week. Deeper moisture remains focused to our west through
north which could limit our rainfall chances until a cool front
pushes southeast late next week, but models differ on timing so
will not deviate from low NBM pops at the end of this forecast
period.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1132 AM CDT Sat Sep 27 2025
VFR conditions will continue through Sunday morning. Winds
gradually turn variable tonight, which could lead to low
probabilities of shallow river fog by daybreak.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&
$$
DISCUSSION...JH
AVIATION...Dux

NWS FSD Office Area Forecast Discussion