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Lawn Hill, Iowa Weather Forecast Discussion

103
FXUS63 KDMX 031925
AFDDMX

Area Forecast Discussion National Weather Service Des Moines IA 225 PM CDT Fri Oct 3 2025

.KEY MESSAGES...

- Elevated fire weather concerns remain this weekend, particularly for field fires with windy and warm conditions both days. Any spark could cause a fire, which could spread quickly!

- Unusual early October warmth continues along with dry weather through Saturday if not much of the daytime Sunday.

- Increasing chances for scattered showers and storms into Sunday night through early Tuesday. No strong signal for severe weather.

- Cooler next week with more seasonal conditions.

&&

.DISCUSSION... Issued at 225 PM CDT Fri Oct 3 2025

It is a warm Friday afternoon across Iowa with just a few clouds in southwest and southeast Iowa. More broadly, there is little in the way of an area of substantial clouds over much of the eastern and central US as these reside beneath the now again dominate mid-level ridge and surface high pressure. GOES-East upper level water vapor imagery shows that a sharp, amplified trough has moved over the western US. This trough will move eastward and then northeastward this weekend with surface cyclogenesis over the central Rockies. With the high pressure to the east of Iowa and low pressure developing to the west, winds will increase as the pressure gradient tightens. Winds are just a bit breezy this afternoon, mainly over western Iowa, but there is a lack of stronger winds at the top of the mixed layer to tap into and mix to the surface. That won`t be the case on Saturday as winds in the low levels will be stronger, especially from Nebraska into Minnesota clipping northwest Iowa, and this raises the concern for elevated fire weather conditions in cropland. Cloud cover is expected to be at a minimum with perhaps a few high-level cirrus clouds passing over in intervals in the afternoon per latest HREF. With near full sunshine expected, deep boundary layer mixing is anticipated. Pick your model forecast soundings show this warming and drying that deepens the boundary layer up to 7000 feet or so. Thus, the stronger low level winds at the top of the mixed layer around 40 knots in western and parts of northern Iowa should be able to be mixed to the surface with surface gusts of 30 to 40 mph common with a few gusts over 40 mph in a few places. Even warming and mixing in drier air at the surface, surface dewpoints remain in the 50s with relative humidity staying largely above 30%, though a few spots may drop into the upper 20 percents. Calling around to fire weather partners yesterday and today, the consensus in our service area is that grassland fuels remain green enough to not warrant a Red Flag Warning/concerns of rapid grassland fire spread. However, cropland in many areas is dry with the cropland fire danger showing very high or extreme in central Iowa in the warm and windy conditions. With harvest in full progress, the concern is for field fires that develop and spread rapidly in these conditions and keep fire departments busy. We will continue to message this concern in our public facing forecasts and likely issue a Special Weather Statement focused on the cropland fire danger Saturday morning in conjunction with at least some of our neighboring offices.

Winds will diminish into Saturday night and relative humidity will rise ending this round of elevated fire weather conditions. Through Sunday, the upper level trough and associated surface low will lift through northern Minnesota into the southern Manitoba and Ontario provinces. With the stronger low level flow and pressure gradient moving away from the state on Sunday, winds won`t be quite as strong, but will still be quite breezy. So, another day of elevated fire weather conditions will once again be present with very high cropland fire danger. In addition, cloud cover is expected as a surface cold front - attached to the departing low - is dragged through the state. This will yield a slightly less warm day with highs in the low and middle 80s. As stronger low level QG convergence arrives and waves of theta-e advection pass over the state, scattered showers and thunderstorms should develop in the afternoon if not Sunday night in most areas with the exception being parts of northwest and north central Iowa that may miss out on much of this rainfall. Nothing has changed in the parameter space or AI/ML guidance to suggest a strong setup for severe weather given the marginal at best instability and largely out of phase shear.

Moving into early next week, conditions will be more seasonal with highs in the upper 60s or low 70s through at least midweek. The front that looked to somewhat stall south of the state is more progressive in today`s deterministic guidance. There will still be a period of scattered showers and storms in the wake of this front as QG convergence lingers and weaker waves of theta-e advection pass over Iowa Monday through early Tuesday. With the expected more progressive pattern, deterministic guidance not surprisingly has lower QPF generally between 1 and 1.5 inches. National Blend of Models probability of an inch or more of rainfall in this period focuses the highest probabilities at 20 to near 40% over the southern half of the state. Any rainfall will be welcomed by the recent stretch of dry weather that has soils showing at or below the 30th percentile in many areas.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1152 AM CDT Fri Oct 3 2025

VFR conditions will prevail through the period. Winds over western Iowa will turn a bit breezy this afternoon from the south averaging between 10 and 15 knots. Winds will not fully drop off this evening with winds increasing after midnight into the day Saturday. Winds from the south or south-southwest will be between 15 and 20 knots with gusts 25 to 35 knots by the end of the period with the strongest winds/gusts over western and northern Iowa. The peak of the wind speeds and gusts will be after 18z. Lastly overnight, have not included a period of borderline low level wind shear as it barely reaches 30 knots, but will pass along for future issuances to monitor.

&&

.DMX WATCHES/WARNINGS/ADVISORIES... None.

&&

$$

DISCUSSION...Ansorge AVIATION...Ansorge

NWS DMX Office Area Forecast Discussion

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