Treynor, Iowa Weather Forecast Discussion

418
FXUS63 KOAX 191915
AFDOAX
Area Forecast Discussion
National Weather Service Omaha/Valley NE
215 PM CDT Fri Sep 19 2025
.KEY MESSAGES...
- A cluster of showers and thunderstorms is expected to push
  into the area (50-70% chance) through the evening. Frequent
  lightning and locally heavy rainfall are the primary hazards.
- Fog is expected to develop overnight into Saturday morning,
  with patchy areas of dense fog possible.
- High temperatures are expected in the 70s to low 80s through
  the period. Periodic rain chances (15-40%) are expected into
  next week.
&&
.DISCUSSION...
Issued at 204 PM CDT Fri Sep 19 2025
Today and Tomorrow...
Water vapor imagery and objective analysis this afternoon depict a
somewhat complex mid- to upper-level pattern. Weak riding is noted
over both the Four Corners region and the southeastern CONUS, while
a 500 mb closed low pivots across eastern SD into IA/MN. An embedded
shortwave disturbance and associated speed max are rotating around
the back side of the low, pushing into central and eastern Nebraska.
This feature, along with an associated weak surface front, has
served as the focus for a cluster of thunderstorms that developed
over north-central NE earlier this morning and has since progresses
east-southeast into eastern NE. As of 2 PM, MRMS composite
reflectivity places this line of thunderstorms roughly from
Holdrege to Columbus, NE.
Afternoon high temperatures remain dependent on cloud cover and
precipitation. Areas south of I-80 will likely climb into the upper
70s, while locations farther north under the thicker cloud shield
will likely top out in the low 70s.
CAM guidance is in decent agreement on stalling the front, and
associated precipitation this evening into the overnight period
(PoPs 50-70%), near or just south of the I-80 corridor, with
the exact latitude a remaining question. Instability remains
limited (MLCAPE near 500 J/kg) and bulk shear is weak (20-25
kts), keeping the potential for strong to severe storms minimal
(below 5%). The primary concern will instead be locally heavy
rainfall where showers and storms stall and if training storms
develop. Warm cloud depths of around 3500 m and PWAT values
between 1.25" and 1.50" (near the 90th percentile of OAX mid-
September sounding climatology) suggest efficient rainfall
production in heavier cells. CAM guidance highlights a corridor
of 0.50-1.50 inches of rainfall with pockets approaching
2.50-3.00 inches, bringing some locally heavy rainfall
potential. Current flash flood guidance thresholds are
1.50-1.75" for 1 hour, 2.00- 2.25" for 3 hours, and 2.75-3.25"
for 6 hours. Current guidance keeps storms spotty enough to
avoid any widespread hydrologic concerns, though this will
continued to be monitored into the overnight period.
Another foggy morning is expected on Saturday as residual low-level
moisture and light winds near the surface set the stage for
foggy/misty conditions, with patchy areas of dense fog possible,
especially in northeast Nebraska. Showers and storms will gradually
taper off overnight (PoPs 20-40%), clearing from west to east
through Saturday morning as the low pulls to the northeast.
Behind the departing system, low- to mid-level clouds will be
slow to erode, keeping Saturday highs in the low to mid 70s.
Sunday and Beyond...
Sunday into Monday, the region will remain under predominantly zonal
flow aloft as subtle disturbances pass by. Temperatures will subtly
warm, with highs expected to reach the upper 70s to low 80s on
Sunday and widespread low 80s on Monday ahead of a cold front Monday
evening. Behind the front, highs through the remainder of the work
week will generally hold in the mid 70s, near seasonal average for
mid-September. Overnight lows are expected in the 50s.
Forecast confidence decreases with regard to precipitation timing
and location as the area remains within a split-flow regime. Long-
range guidance shows notable discrepancies in the timing and track
of individual disturbances, leading to periodic 15-40% PoPs through
the week. However, model agreement favors keeping the most
significant precipitation chances displaced to our south and east as
a closed mid-level low dips into the Ozark plateau. Confidence is
low in the potential for strong to severe storms in our area. While
pockets of instability may develop at times, weak shear will be the
limiting factor, keeping severe potential minimal. Both GEFS and
ECMWF ensemble-based machine learning guidance indicates only modest
severe probabilities, periodically peaking in the 5-10% range.
&&
.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1159 AM CDT Fri Sep 19 2025
A deck of MVFR ceilings remains in place over northeast NE,
grazing KOFK and KOMA, which is expected to gradually improve
this afternoon. A cluster of thunderstorms is pushing into
eastern NE and will continue into the evening. A few scattered
showers may approach KLNK (40% chance) this afternoon before
the heavier cluster pushes in this evening. The highest chance
(50-70%) of impacts is at KLNK this evening, with scattered
showers and storm possible over KOMA (40% chance) into the
evening. Storms will likely remain south of KOFK. Winds will
shift from northwesterly to southwesterly as the system pushes
into the area this evening.
Fog is expected to develop overnight across east-central
Nebraska. MVFR conditions are expected across all terminal, with
IFR and potentially LIFR at KOFK during the mid-morning hours.
Fog will gradually improve after 12-14Z.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&
$$
DISCUSSION...Wood
AVIATION...Wood

NWS OAX Office Area Forecast Discussion