Des Moines, IA Marine Weather and Tide Forecast
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Marine Weather and Tide Forecast for Des Moines, IA

June 21, 2024 12:28 PM CDT (17:28 UTC) Change Location
Sunrise 5:38 AM   Sunset 8:53 PM
Moonrise 8:14 PM   Moonset 3:47 AM 
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7 Day Forecast for Marine Location Near Des Moines, IA
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Area Discussion for - Des Moines, IA
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FXUS63 KDMX 211151 AFDDMX

Area Forecast Discussion National Weather Service Des Moines IA 651 AM CDT Fri Jun 21 2024


Updated for the 12z Aviation Discussion

KEY MESSAGES

- Flood Watches now starting this morning for northern counties as heavy rain moves in from the west. Heaviest rain still anticipated for tonight across northern Iowa, especially nearest to the state line.

- Rainfall amounts along the front will be 3 to 5 inches with locally higher amounts at or exceeding 7 inches possible.
Flash flooding and river flooding impacts possible.

- In addition to heavy rain, severe weather will be possible this evening for the north as well as Saturday afternoon for much of the area. Both days: Damaging winds and a tornado or two possible. Hail possible, but confidence is lower.

DISCUSSION
Issued at 402 AM CDT Fri Jun 21 2024

The nocturnal LLJ has veered over into NW Iowa overnight with an MUCAPE axis near 1000 J/kg supporting an MCS entering into the state. The MCS has slowed its progression, following the Corfidi vectors and sinking to the southeast and feeding more into the instability. The cold pool from the MCS is forming training storms as the mean wind carries the new updrafts northeast. CAMs have not handled tonight's storms well and continue to initialize poorly, so here's the theory on evolution over the next few hours: seeing that the MCS is halting its southward extent, current thinking is that overall cluster will take an eastern track and turn northeast. This outcome would bring heavy rain into northern counties this morning before the H850 boundary is pushed into Minnesota. Have elected to start the Flood Watch this morning instead of tonight to capture the heavy rain potential. Can expect 1-2 inches with morning storms with some locally higher amounts, but as the storms have decreased in intensity over the last couple of hours, not expecting the 5+ inches found on personal weather stations near Sioux Falls. Through the morning and afternoon, a cold pool from the overnight convection will sink into the state today as the nocturnal jet weakens. Have kept rain chances in the north for all of today as soundings hold onto moisture in a weakly capped environment. At the very least, northern Iowa can expect to be in cloud cover today with highs held into the low 80s and perhaps even some 70s. Further south, cumulus clouds will blanket the skies by the afternoon with a non-zero chance of rain. Highs will be in the 80s.

A shortwave will approach from the west later this evening with deep layer shear values exceeding 30kts. 0-3km shear will be further enhanced by the return of the LLJ, elongating the lower portion of the hodograph. MUCAPE axis with values near 2000 J/kg will build in through the afternoon in the warm sector. Wherever the surface boundary finds itself this afternoon, all modes of severe weather are on the table for this evening. Confidence in hail is lower due to the warm clouds depths and saturated profiles. Wind threat remains as potent cold pools from rain-cooled air surge out. For tornadoes, LCLs are predictably very low with all of the present moisture and the LLJ-influenced hodographs yield favorable SRH values. The best chance for tornadoes will be immediately along the surface front, the location of which is estimated by the 5% outline.

As storms evolve more into a heavy rain threat overnight tonight, the LLJ angles across Iowa, with its front located somewhere near the IA-MN border. PWATs exceed 2 inches, warm cloud depths are over 4000m and the entirety of the profile appears saturated. Speaking to how models have handled the overall pattern for most of this week, they have consistently been too far north in QPF placement. So in turn, not confident in a solution such as the 06z HRRR that tries to trend northward. WPC Excessive Rainfall Outlooks have accounted for this well with an southern expansion beyond the main QPF output axis. Areas in the southern part of the moderate risk and in the neighboring slight risk region (or counties just south of the flood watch) should monitor for changes in the forecast as details become more refined today. 3-5 inches of rain is forecasted to fall along the H850 warm front with locally higher amounts in play. The HRRR max QPF spread speaks to the possible upper bounds of those local extremes with contours between 7 and 10 inches of QPF on the map near the state line. The atmosphere has proven itself capable of this outcome already tonight with a personal weather station south of Sioux Falls recording 9 inches of rain this morning.

The wave will remain organized and push east Saturday with its cold front draped across the state. The jet remains enhanced through the day, increasing low level SRH. Shear values exceed 30 kts and MUCAPE values will near 1500 J/kg by the afternoon. The moist profiles will once again benefit damaging wind chances and hinder hail chances. A tornado or two will be possible from the aforementioned low level shear. Confidence on storm initiation timing is low and will be better capture by high resolution guidance as less short term convection augments the near storm environment. An upper level ridge blocks the Gulf Sunday and Monday with rain chances returning by the middle of next week.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
Issued at 1201 PM CDT Fri Jun 21 2024

IFR stratus was developing across northern IA, and that should persist through at least 12z with some contributions from fog development as well. VFR conditions should return area wide later Friday morning however, with mainly dry conditions through the afternoon. Additional convection is expected to develop across northern IA Friday evening however, with sufficient confidence to mention thunder even at this lead time.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/
Issued at 644 AM CDT Fri Jun 21 2024

Fog in northeast will lift over the next 2 hours. Showers and storms to move across the north this morning, bringing with it gusty winds. Highest confidence in impacts at KMCW. Cannot rule out scatted showers and low confidence thunderstorms in the north this afternoon, so left in VCSH. More widespread rain and thunderstorms chances expected tonight with the most likely impacted site again KMCW. Have added +TSRA to reflect heaviest rain time period. Sites such as KFOD and KALO are close enough to add mentions southern extent of MVFR cigs and vsbys to be better defined in upcoming issuances.

HYDROLOGY
Issued at 326 PM CDT Thu Jun 20 2024

More of the highest QPF axis is anticipated to fall in northern Iowa counties with the highest amounts near the state line. This in turn will lead to faster initial responses from sites as more rain falls into local basins with additional water flowing in from upstream basin areas in Minnesota. The river of most concern remains the Des Moines River north of Saylorville Lake, including both its west and east fork. High confidence in at least Minor Flood Stage for ESVI4, HBTI4, EMTI4, and AGNI4. Higher stages uncertain due to QPF placement discrepancies. The East Fork will be more in play if the more southward trend in rainfall is realized. The Cedar and Winnebago rivers are also of concern as their reaches both extend into southern Minnesota.
River forecasts currently available at the time of issuance include 48 hours of rainfall and morning forecasts are also expected to include QPF beyond the usual 24 hours window due to the extended duration of the rainfall event.

DMX WATCHES/WARNINGS/ADVISORIES
Flood Watch through Saturday afternoon for IAZ004>007-015>017.




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AirportDistAgeWind ktVisSkyWeatherAirDewPtRHinHg
KDSM DES MOINES INTL,IA 3 sm34 minSSW 1110 smA Few Clouds88°F70°F55%30.12
KIKV ANKENY RGNL,IA 10 sm13 minSW 11G179 smA Few Clouds88°F72°F59%30.11
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