Mason City, Iowa 7 Day Weather Forecast
Wx Forecast - Wx Discussion - Wx Aviation
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NWS Forecast for Mason City IA
National Weather Service Forecast for:
Mason City IA
Issued by: National Weather Service Des Moines, IA |
Updated: 6:19 am CDT Jul 27, 2025 |
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Today
 Patchy Fog then Mostly Sunny
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Tonight
 Mostly Clear then Chance T-storms
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Monday
 Chance T-storms then Sunny
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Monday Night
 Slight Chance T-storms then Chance T-storms
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Tuesday
 Chance T-storms
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Tuesday Night
 Chance T-storms
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Wednesday
 Chance Showers
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Wednesday Night
 Partly Cloudy
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Thursday
 Mostly Sunny
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Hi 88 °F |
Lo 69 °F |
Hi 91 °F |
Lo 70 °F |
Hi 85 °F |
Lo 65 °F |
Hi 76 °F |
Lo 57 °F |
Hi 75 °F |
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Hazardous Weather Outlook
Heat Advisory
Today
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Patchy fog before 10am. Otherwise, mostly sunny, with a high near 88. South wind 5 to 10 mph. |
Tonight
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A 30 percent chance of showers and thunderstorms, mainly after 4am. Partly cloudy, with a low around 69. South wind around 7 mph. New rainfall amounts between a quarter and half of an inch possible. |
Monday
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A 30 percent chance of showers and thunderstorms before 7am. Sunny, with a high near 91. Heat index values as high as 106. Southeast wind around 6 mph becoming west southwest in the morning. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms. |
Monday Night
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A slight chance of showers, then a chance of showers and thunderstorms after 10pm. Increasing clouds, with a low around 70. Light and variable wind becoming northeast around 5 mph after midnight. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms. |
Tuesday
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A 40 percent chance of showers and thunderstorms. Partly sunny, with a high near 85. Northeast wind around 6 mph. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms. |
Tuesday Night
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A 40 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 65. New rainfall amounts between a quarter and half of an inch possible. |
Wednesday
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A chance of showers and thunderstorms before 1pm, then a slight chance of showers. Mostly cloudy, with a high near 76. Chance of precipitation is 30%. |
Wednesday Night
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Partly cloudy, with a low around 57. |
Thursday
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Mostly sunny, with a high near 75. |
Thursday Night
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Partly cloudy, with a low around 55. |
Friday
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Partly sunny, with a high near 74. |
Friday Night
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Mostly cloudy, with a low around 56. |
Saturday
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Mostly sunny, with a high near 75. |
Forecast from NOAA-NWS
for Mason City IA.
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Weather Forecast Discussion
918
FXUS63 KDMX 271126
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
626 AM CDT Sun Jul 27 2025
...Updated for the 12z Aviation Discussion...
.KEY MESSAGES...
- Patchy fog early this morning expected to become more
widespread through sunrise. Most dense fog anticipated in
northeast Iowa.
- Dangerous heat today and Monday. Heat indicies of 100-110+
both days. Heat may linger across southern Iowa into Tuesday.
- Storms possible across northern/northeastern Iowa late
overnight through Monday morning with another round Monday
night into Tuesday. Strong wind is the primary hazard.
- Widespread thunderstorm potential Tuesday through Wednesday.
Heavy rain is possible, along with strong to severe storms.
&&
.UPDATE...
Issued at 303 AM CDT Sun Jul 27 2025
Patchy dense fog has developed across parts of eastern Iowa this
morning. Guidance has suggested that this may become more widespread
through the morning which makes sense given current soupy high
dewpoints across the area and clearing overnight skies (something
that is more often a precursor to wintertime fog development).
Observations will be monitored closely through the morning with an
advisory at the ready should it be needed.
Dangerous heat will settle across the area this afternoon with heat
indicies 100-105+. Highest heat indicies will be across southern to
southwest Iowa. Heat continues on Monday, with more widespread 105-
110+ values possible, but there remains uncertainty there
depending on how nocturnal/Sunday morning convection plays out
(details on that in a moment). Right now most models indicate
that early convection and associated cloud cover clears out
quickly with ample time for temperature recovery through the
afternoon. However, given some of the uncertainty with just how
expansive the heat will be, and how extreme (advisory vs.
warning levels), have held off on issuing a headline. One will
be needed, and the type will be determined as we get a better
handle on convective trends.
Next up, that nocturnal system across the midwest very late tonight
and Sunday morning. An embedded shortwave is expected to drop across
the Dakotas and Minnesota late tonight, skimming across northern
Iowa through the morning (possibly very early morning) hours of
Sunday. There is more than sufficient instability available
with 2000-3000+ J/kg MLCAPE through the overnight. 0-6km shear
is also better than we`ve seen in quite some time thanks to
synoptic support, at 30-50 kts. This should help to organize
the MCS as it drops across the area and help it maintain some
severe potential through the overnight - mainly a wind threat.
While development looks likely, placement is less certain.
Models exhibit a spread of possibilities with some dropping the
system through central Iowa (NAMnest/NSSL WRF) while others
(ARW/HRRR/FV3) are several hours later and clip northern to
northeastern Iowa.
Another similar shortwave slides across northern Iowa Monday night
into Tuesday with a more robust system across the area Tuesday into
Wednesday. Further details in the full AFD below.
&&
.DISCUSSION...
Issued at 254 PM CDT Sat Jul 26 2025
Plenty of cloud cover is lingering over Iowa this afternoon as a
shortwave trough pushes eastward over top the Southeastern US ridge.
Cloud cover should continue to dissipate through this afternoon into
this evening. With the clear sky, light winds, and the sultry
airmass due to the recent rainfall, fog is expected to develop over
eastern into much of central Iowa. It is possible that the fog may
be dense over eastern into northern Iowa so will be monitoring
trends into this evening and overnight for this possibility.
As the fog dissipates Sunday morning, temperatures and
dewpoints will climb with the combination by early afternoon
creating heat index values between 100 to 110 degrees across our
forecast area. The highest heat index values will be over
western into much of central Iowa and that is where a heat
advisory has been issued (with western Iowa under an Extreme
Heat Warning).
The Southeastern US ridge is expected to expand westward and then
northwestward Sunday into early this upcoming week. During this
period, this will push the shortwave storm track farther north, but
not far enough north to negate all storm potential over Iowa. Over
time too, the shortwave track will slowly sink closer to Iowa.
In addition, high heat and humidity will set up and prevail over
much of the area with some uncertainty due to potential storm
debris cloud cover on Monday into Tuesday. Shortwaves look to
top the ridge over the Dakotas through Minnesota about every 24
hours or so, centered over the overnight hours largely. The
first storm chances comes Sunday night into early Monday as the
first shortwave moves across. Some models show a mesoscale
convective system (MCS) moving eastward and scraping our
northern counties; however, more models such as the 12z NAM,
ECMWF, and HRRR show this diving southeastward into more of Iowa
flowing around the 700mb 13C contour roughly. Looking at the
bulk of the data, this latter solution seems the probable
outcome at this point and lines up with the broadly drawn day 2
SPC marginal risk. The main severe hazard here would be wind
gusts with the mesovortex generation potential low given the
weaker 0-3km bulk shear values around or under 20 knots.
High heat and humidity may persist into Monday, but uncertainty in
what, if any, cloud cover may linger from an overnight MCS
precludes any headlines here. For example, the NAM, which is one
of the models showing the MCS diving into some portion of Iowa
Sunday night, recovers the airmass over the state such that
conditions are similar to Sunday if not a touch higher on
temperatures on Monday. Thus, additional heat headlines are
still on the table for Monday as we sort out what may or may not
occur with the MCS. Another shortwave passes north Monday night
with the global guidance showing the QPF staying largely over
Minnesota and perhaps grazing far northern Iowa. At the same
time, this shortwave will be closer to Iowa with a surface
boundary nearing the state as well from the north. The exception
to the QPF staying north is the ECMWF, which seems to be a bit
more generous with allowing storms in the hot 700mb air compared
to other models. There will be no shortage of instability, but
the higher amounts of deep layer shear will reside over
Minnesota into perhaps northern Iowa.
Tuesday will see the surface boundary moving south over the state
with widespread storm chances developing later Tuesday night into
Wednesday evening as low level theta-e pulses push over the surface
boundary. Again, while instability will not be in short supply, deep
layer shear is marginal at best. The heavy rainfall parameter space
will be more favorable with precipitable water values over 2 inches
along the boundary, weak mean flow and good moisture transport into
the boundary. So, will be monitoring the potential for heavy
rainfall in this period. With the boundary pushing well south of
the state Thursday and surface high pressure following behind
over the region, this should foster drier conditions for late in
the week.
&&
.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 626 AM CDT Sun Jul 27 2025
Dense fog has developed across eastern into central Iowa this
morning, resulting in IFR to LIFR conditions across sites
KMCW/KALO/KOTM. Improvement is expected in the next 1-2 hours
with a return to VFR conditions. Overnight thunderstorms are
possible in northeast Iowa with impacts possible at sites
KMCW/KALO. There is some uncertainty with regards to the timing
and extent, so for now have covered with a prob30 group.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 8 PM CDT this evening for
IAZ004>007-015>017-023>026-033>037-044>050-057>062-070>075-
081>086-092>097.
Dense Fog Advisory until 9 AM CDT this morning for IAZ006-007-
016-017-025>028-036>039-048>050-060>062-073>075-084>086-
095>097.
&&
$$
UPDATE...Hagenhoff
DISCUSSION...Ansorge
AVIATION...Hagenhoff
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