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Adjusted Humidity Readings

We are now adding 5% when humidity readings reach 95% since that is the maximum our sensor will read. For many years Davis Instruments’ sensors have struggled to achieve 100% humidity. Unfortunately, the problem seems to worsen with time. When we placed our sensor in service last November 28th, it would reach 98%.

Also, we are adding 1% to 92% (to make 93%) , 2% to 93% (to make 95%), and 4% to 94% to reduce the jump between 91% and 100%. Tests demonstrate these adjustments closely approximate reality.

You may occasionally see other readings besides 93%, 95%, 98%, and 100% due to 5 minute averaging of humidity values.

Raw values are available on the stats page.

Here’s some more info on this problem if you’re interested:

We have a backup weather station for emergencies. It also contains a Davis VP2 station with an SHT31 sensor that is less than 2 years old. It maxes out at 96% humidity, but it also has an average +8% bias below 80% during the warm season (May – Sept). So it has a wet bias in the middle range in addition to a dry bias in the top range. Keep in mind that the maximum error for this sensor is supposed to be 3.5% according to the manufacturer.

We are not the only ones to experience these issues. Many other Davis VP2 weather station owners have reported them (in a thread approaching 1200 posts). Davis says they are “looking into it”, although that was almost 2 months ago now. Some particularly brave souls have attempted to informally wire up older (SHT11/SHT15) and/or unsupported sensors (SHT75) with varying degrees of luck. We’re not keen on performing ad hoc experiments with our primary temperature/humidity sensor. Some combination of Murphy’s Law and common sense would argue that such slapdash “solutions” will inevitably break at the worst time. Indeed our various attempts with other sensors on the test bench have not gone well. Therefore, we await a viable, proven fix preferably from Davis Instruments.

[UPDATE 9/21/18: Most of those enterprising individuals referenced above are now indicating an array of problems with the SHT75 sensor ranging from sudden failure to gross errors. It’s uncertain whether the fault lies with the sensor or the implementation. Either way, at present there appears to be no good workaround to the issues mentioned above with the SHT31.]

[UPDATE 10/23/18]: We recently swapped out our SHT31 sensor suite as part of a preventative maintenance routine. The new humidity sensor arrived with a +6% average (wet) bias below 55F, an average +4% bias above 55F and a maximum reading of 98% (after several hours in saturated air). We have corrected these deficiencies with custom programming.

When Weather Apps Fail at Weather

I wrote about this yesterday on Twitter. Given the limitations of that platform, however, I couldn’t really go deep. Let’s dive in.

Here are two screenshots taken within 60 seconds yesterday afternoon:

 

The 1st image is of a popular weather app recently redesigned for the iPhone. The 2nd image is our universal web app loaded in Safari on an iPhone.*

Continue reading “When Weather Apps Fail at Weather”

Noticed Some Changes Lately?

Last week I tweaked the color scheme to match the forecast icons. We’re keeping with the sky/water/sand theme only now just a bit brighter and more coherent.

Today, I removed the weather history icons that lived beneath the current conditions. Nobody was clicking on them. The images accounted for about 1/3rd of the data necessary to load the home page. That wasn’t a good tradeoff between useful information and bandwidth consumption. I’m always mindful that people have limited data on their mobile plans. Speed is another concern too.

I also moved the dropdown selector that was in the conditions section to the page settings (gear wheel icon in the upper right of home page). That’s where it belongs rather than cluttering up the current conditions. If you need to change the frequency of updates, it’s just one click to get there. Again, the data shows that few people adjust that setting, so why not put it where power users naturally go anyway?

One more tiny detail. I added the time zone to the conditions and forecast update times. When visitors travel, they shouldn’t have to wonder if the times listed are local time or Marquette time. The forecast will always be updated in Eastern time. The conditions will be updated according to the current time zone selected on your computer or mobile device. In Marquette, they should both show “EST” or “EDT” depending on Daylight Saving Time.

Also, I should mention that we recently changed hosts about 3 weeks ago. Regular, long-time visitors may remember some extended outages lasting hours, even days in one instance last year due to some lackluster planning by our old host, A2hosting. I picked out another Michigan hosting company, Liquid Web.  Not only do they own their data center in Lansing (rare), but their operation is prepared to withstand power & internet failures, weather events, and DDOS attacks (coordinated hacking) among other unfortunate events. That’s not to say the site will never go offline, but, hopefully, not as frequently or for as long. It’s much more expensive to host with them, but their speed and reliability so far have been phenomenal.

Well, thanks for visiting. If you enjoy the site, please tell your friends & family!

Demolish Marquette to Improve Forecasts?

Would forecasts improve if we removed all the buildings, ripped out all the concrete and moved everyone to tents situated along Lakeshore Blvd? Short answer: likely.

Too often the forecasted high temperatures for Marquette run well below the measured high temperatures, especially on sunny days when the wind isn’t blowing off the lake. This is true of all forecast agencies I’ve observed to one degree or another. It just so happens the local National Weather Service, our forecast provider, is also guilty of this trend. Continue reading “Demolish Marquette to Improve Forecasts?”

What Happened To The Forecast?

The website’s featured forecast provider, Weather Underground (WU), announced a change in policy last month. They were no longer going to allow free, limited access to their raw forecast data (API). Instead, they would begin charging hundreds per month even to those who contribute data like we do. Since this site generates no revenue, the new price tag is a nonstarter.

I’ve been exploring alternatives in hopes of continuing to offer dual forecasts. None of them have met my requirements of accuracy and affordability. Therefore, I’ve decided the National Weather Service (NWS) will be the sole forecast provider for marquetteweather.com.

In addition, the hourly forecast will not be replaced due to problems inherent in the forecasting process. Presently, the software-based weather models do not adequately represent the transient effects of the Great Lakes frequently leading to significant errors exceeding our forecast target of +/- 3 degrees. Plus, the forecasts don’t update often enough to keep pace with our weather. Routine changes in wind direction, cloud cover or precipitation can transform conditions in a matter of minutes — as most Marquetters intuitively understand.  Continue reading “What Happened To The Forecast?”

A New Stats Page is Born!

Synopsis: we are archiving the city’s climate and presenting it to the community in what we believe is an accessible and easy-to-read format.

Perhaps you’ve visited the Statistics page previously. WeatherCat, the software that grabs data from the weather station, automatically generated those numbers and even uploaded them to the website.

Well, the old saying “if it’s easy, it ain’t worth doing” proved true, unfortunately. As time went on, I kept spotting more mathematical errors. Plus, the tables were not very readable. Visitors couldn’t access daily history after 60 days. Navigating the page was difficult too.

Over a month ago I began overhauling the page. This involved taking raw data directly from the database and programming  complex mathematical formulas. Smoke may have occasionally emanated from the computer (not to mention my ears!). Continue reading “A New Stats Page is Born!”

Temperature Readings Just Improved!

Custom Davis radiation shield

There was a Problem?

So perhaps you’ve noticed lately on sunny days forecasted highs have been lower than the actual highs by several degrees. Well… it turns out that’s not entirely true.

During the deepest part of winter when the polar vortex was regularly occurring (late December into January), we were having equipment issues. Normally, we measure temperatures inside an enclosure that has a fan running on solar power during the day and batteries at night. Unfortunately, the weather destroyed the electronics that controlled the battery charging, among other casualties.

As a quick fix, we installed a passive (fan-less) shield for our sensor. Passive shelters are fine during our normally very cloudy, windy winters. Wouldn’t you know it, the sun decided to show up and, along with it, gentle breezes! That makes for beautiful winter days in Marquette. It is also a recipe for solar-induced sensor errors.

The snow acts like a mirror to the sun and the reflected radiation gets into the sensor and heats it up. How much? A rough estimate, based on before and after tests of running with and without a fan, is 3-5 degrees F. Studies have shown that, in fact, on completely calm, sunny days over a fresh blanket of snow, errors can reach up to 18 deg F! Continue reading “Temperature Readings Just Improved!”

Snow Today, Snow Tomorrow?

We measured 4.1″ out of the last system that passed through overnight and this morning. It was the light, fluffy stuff (15:1 ratio of snow to water). Almost 2.5″ fell between 7:00 and 9:30AM alone.

Looks like some more snow will fall overnight Saturday into Sunday AM. Amounts are in flux at the moment. NWS is estimating 1-2″ and Weather Underground is forecasting 3-5″.

Stay tuned! The WU forecast is updated every 20 minutes. NWS updates less frequently but we check once per hour.

Is All This Sunshine Getting You Down?

Lilac, the Marquette Weather Dog, enduring pesky prisms

How about the mornings where town is 20 or 30 degrees warmer than nearby locations?

Ice forming on the lake, partially cutting off cloud formation, seems to be helping brighten the long winter. In time, we may be joining the subzero parade once the lake gives off the last of its heat.

Looks like a very nice weekend ahead if you don’t mind slightly below normal temps.

The following weekend it may be TOO warm (near freezing). I hear the sled doggies (UP 200) like it a bit colder. Like below zero. Anyone know if that’s true?

How would you rate this winter so far?

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