Marine Weather and Tide Forecast for Newton, IA

UPDATE
Issued at 345 AM CDT Mon Jul 14 2025

Isolated areas of patchy fog has developed once again in Iowa this morning, considering very light winds and clear skies, with most areas in the CWA seeing around 3-5 statute mile visibilities.
However, higher moisture content over the southeastern portion of the state has led to the formation of dense patchy fog, with the Ottumwa ASOS reporting visibilities around a quarter mile as of 3am.
HRRR and latest HRRR guidance has trended upward on dense fog covering much of southeast Iowa, which makes sense given conditions, so have decided in coordination with neighboring eastern and southern offices to issue a Dense Fog Advisory until 9am for portions of southeast Iowa. Low visibilities around or below a quarter mile are expected at times, so extra caution will be needed when traveling this morning. After sunrise, winds will increase and the inversion will fade, leading to dissipating fog and improving conditions.

Outside of the fog this morning, the forecast remains on track to remain dry today and throughout Tuesday, with temperatures generally in the upper 80s as southwest flow remains overhead. Of note is that the timing for the next chance for showers and storms per latest model guidance has slowed slightly, with most members generally keeping Iowa dry until closer to midnight into Wednesday. Increasing moisture advection into the Midwest and a gradually sinking frontal boundary draped over central Nebraska into northwest Iowa and southern Minnesota, along with the development of a 30-35 knot LLJ into western Iowa will result in the forcing necessary to develop showers and storms into the region, with a MCS looking to drop into northwest Iowa and track southeastward as it gradually weakens through Wednesday morning. Model soundings indicate elevated convection, with gusty winds looking to be the main concern given DCAPE values around 1000+J/kg, outside of favorable shear and instability into northwest Iowa, and becoming less favorable further southeast. The Marginal Risk into northwest Iowa early Wednesday per the SPC seems reasonable given that isolated severe weather may occur from this given the above setup as discussed. Following the weakening system, model guidance gets quite messy, as solutions range from mostly dry to seeing scattered lingering showers and storms until late Wednesday, when the boundary then somewhere over central/southern Iowa looks to kick off more widespread activity. This variation in solutions makes sense, as activity later on will largely depend on how the morning system evolves.
A close eye will remain on this activity, with more details expected over the next few days as more models capture this time period.

DISCUSSION
Issued at 240 PM CDT Sun Jul 13 2025

The anomalously dry air mass (PWAT of 0.71" on OAX's 00z sounding puts it in just the 10th percentile per SPC's sounding's climatology) that made a brief appearance yesterday and today disappears quickly tonight as moisture advection and typical mid-summer Iowa humidity returns to begin the week. As this begins, short-range CAMs consistently depict a decaying low-level boundary and weak convection initiating & dropping thru S MN late this evening and overnight. However, unable to sustain moisture enough to overcome the drier air mass, no solutions sustain this activity into northern sections of the CWA So for now - will keep silent precip chances across the far north. Additionally, added patchy fog mention in far southern Iowa late tonight & early Monday as clear skies combine with light winds to narrow dew point depressions to near saturation.

Flow turns zonal for Monday & southwesterly for Tuesday as the pattern buckles ahead of the next wave moving into the Pacific Northwest. Continued low-level warm-air thermal advection both days will push afternoon highs back into the upper 80s to near 90F. In the absence of any forcing the bulk of both days will remain dry. However, it'll feel noticeably muggier both days as surface dew points return back to around 70F.

By Tuesday night, the first shortwave kicks out into the region, bringing perhaps a MCS and next shot of moisture into the state late. The boundary will remain in the vicinity for Wednesday and into Thursday. This will be our best window of the week for widespread precipitation. Another week, another shot at several inches of rainfall. Deep layer shear makes a return as well during this period as right entrance of upper-level jet moves across the state. This will aid convective organization through the period. Any severe potential will be refined in the coming days as the mesoscale details can be resolved.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
Issued at 1036 PM CDT Sun Jul 13 2025

Haze remains across parts of Iowa but continues to diminish. At the same time, patchy light fog has begun to develop this evening. Have included MVFR mention at KOTM when restrictions are most likely in southeast Iowa, however expansion to other sites is possible overnight. Fog will diminish with sunrise and VFR conditions will follow for the rest of Monday.

DMX WATCHES/WARNINGS/ADVISORIES
Dense Fog Advisory until 9 AM CDT this morning for IAZ062-074- 075-084>086-094>097.