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Average Weather in September in Lake Marcel-Stillwater Washington, United States

In Lake Marcel-Stillwater, the month of September is characterized by falling daily high temperatures, with daily highs decreasing by 8°F, from 75°F to 66°F over the course of the month, and rarely exceeding 84°F or dropping below 58°F.

Daily low temperatures decrease by 5°F, from 57°F to 52°F, rarely falling below 45°F or exceeding 61°F.

For reference, on August 3, the hottest day of the year, temperatures in Lake Marcel-Stillwater typically range from 59°F to 78°F, while on December 23, the coldest day of the year, they range from 36°F to 44°F.

Average High and Low Temperature in September

The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on September. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Average Hourly Temperature in September

Average Hourly Temperature in September in Lake Marcel-Stillwater12 AM4 AM8 AM12 PM4 PM8 PM12 AM18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctcoldcoolcomfortablewarm
The average hourly temperature, color coded into bands: frigid < 15°F < freezing < 32°F < chilly < 45°F < cold < 55°F < cool < 65°F < comfortable < 75°F < warm < 85°F < hot < 95°F < sweltering. The shaded overlays indicate night and civil twilight.

Clouds

The month of September in Lake Marcel-Stillwater experiences rapidly increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 38% to 50%.

The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 62% of the time.

For reference, on November 29, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 78%, while on August 3, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 72%.

Cloud Cover in September

Cloud Cover in September in Lake Marcel-Stillwater0%10%20%30%40%50%60%70%80%90%100%18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctSep 138%Sep 138%Sep 3050%Sep 3050%Sep 1141%Sep 1141%Sep 2144%Sep 2144%overcastmostly cloudypartly cloudymostly clearclear
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Lake Marcel-Stillwater, the chance of a wet day over the course of September is very rapidly increasing, starting the month at 18% and ending it at 31%.

For reference, the year's highest daily chance of a wet day is 62% on November 18, and its lowest chance is 10% on August 10.

Probability of Precipitation in September

The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during September in Lake Marcel-Stillwater is rapidly increasing, starting the month at 1.8 inches, when it rarely exceeds 3.7 inches or falls below 0.2 inches, and ending the month at 3.7 inches, when it rarely exceeds 6.9 inches or falls below 0.9 inches.

Average Monthly Rainfall in September

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Sun

Over the course of September in Lake Marcel-Stillwater, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1 hour, 38 minutes, implying an average daily decrease of 3 minutes, 24 seconds, and weekly decrease of 23 minutes, 46 seconds.

The shortest day of the month is September 30, with 11 hours, 42 minutes of daylight and the longest day is September 1, with 13 hours, 21 minutes of daylight.

Hours of Daylight and Twilight in September

The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise of the month in Lake Marcel-Stillwater is 6:26 AM on September 1 and the latest sunrise is 39 minutes later at 7:05 AM on September 30.

The latest sunset is 7:47 PM on September 1 and the earliest sunset is 59 minutes earlier at 6:48 PM on September 30.

Daylight saving time is observed in Lake Marcel-Stillwater during 2017, but it neither starts nor ends during September, so the entire month is in daylight saving time.

For reference, on June 21, the longest day of the year, the Sun rises at 5:09 AM and sets 16 hours, 0 minutes later, at 9:09 PM, while on December 21, the shortest day of the year, it rises at 7:53 AM and sets 8 hours, 25 minutes later, at 4:18 PM.

Sunrise & Sunset with Twilight in September

The solar day over the course of September. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.

Humidity

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The chance that a given day will be muggy in Lake Marcel-Stillwater is essentially constant during September, remaining around 0% throughout.

For reference, on August 8, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, the least muggy day of the year, there are muggy conditions 0% of the time.

Humidity Comfort Levels in September

Humidity Comfort Levels in September in Lake Marcel-Stillwater0%10%20%30%40%50%60%70%80%90%100%18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctSep 10%Sep 10%Sep 300%Sep 300%Sep 110%Sep 110%Sep 210%Sep 210%humidhumidcomfortablecomfortabledrydry
The percentage of time spent at various humidity comfort levels, categorized by dew point: dry < 55°F < comfortable < 60°F < humid < 65°F < muggy < 70°F < oppressive < 75°F < miserable.

Wind

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Lake Marcel-Stillwater is essentially constant during September, remaining within 0.1 miles per hour of 1.7 miles per hour throughout.

For reference, on December 29, the windiest day of the year, the daily average wind speed is 2.9 miles per hour, while on August 5, the calmest day of the year, the daily average wind speed is 1.4 miles per hour.

Average Wind Speed in September

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.
The wind direction in Lake Marcel-Stillwater during September is predominantly out of the west from September 1 to September 10, the south from September 10 to September 17 and from September 26 to September 30, and the east from September 17 to September 26.

Wind Direction in September

Wind Direction in September in Lake Marcel-StillwaterWSES0%20%40%60%80%100%18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctwestsoutheastnorth
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Water Temperature

Lake Marcel-Stillwater is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average surface water temperature in Lake Marcel-Stillwater is gradually decreasing during September, falling by 2°F, from 56°F to 54°F, over the course of the month.

Average Water Temperature in September

The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy in Lake Marcel-Stillwater is rapidly decreasing during September, falling by 1.7 kWh, from 5.1 kWh to 3.4 kWh, over the course of the month.

Average Daily Incident Shortwave Solar Energy in September

The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

For the purposes of this report, the geographical coordinates of Lake Marcel-Stillwater are 47.693 deg latitude, -121.915 deg longitude, and 390 ft elevation.

The topography within 2 miles of Lake Marcel-Stillwater contains significant variations in elevation, with a maximum elevation change of 597 feet and an average elevation above sea level of 325 feet. Within 10 miles contains significant variations in elevation (3,127 feet). Within 50 miles contains large variations in elevation (10,531 feet).

The area within 2 miles of Lake Marcel-Stillwater is covered by trees (76%) and cropland (15%), within 10 miles by trees (68%) and shrubs (10%), and within 50 miles by trees (54%) and shrubs (14%).

Data Sources

This report illustrates the typical weather in Lake Marcel-Stillwater year round, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.

Temperature and Dew Point

There are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Lake Marcel-Stillwater.

For each station, the records are corrected for the elevation difference between that station and Lake Marcel-Stillwater according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.

The estimated value at Lake Marcel-Stillwater is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Lake Marcel-Stillwater and a given station.

The stations contributing to this reconstruction are: Renton Municipal Airport (50%, 32 kilometers, southwest); Snohomish County Airport (Paine Field) (43%, 36 kilometers, northwest); and Stampede Pass (7%, 63 kilometers, southeast).

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , by Jean Meeus.

All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.

Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.

Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.

Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .

Time zones for aiports and weather stations are provided by AskGeo.com .

Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.