Instant Weather Maps

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What sets apart from other sites, other than speed?
For the GFS: Many free sites use 0.5-degree or even 1.0-degree data, but we use the higher-resolution 0.25-degree data for all forecast hours (when referring to resolution, a lower number of degrees is better). In addition, some surface maps, including snow depth, use the full native 0.117-degree data for the short range (through forecast hour 240). The higher-resolution maps also generate much faster than the others because the files are available sooner from our data source. For the NAM: We use 12-km data as opposed to the 20-km or even 32-km data used by some other sites. We offer the full hourly NAM through hour 36, whereas other sites offer only the forecast hours divisible by 3. For the RAP: We offer the full hourly output through hour 18 at 13-km resolution (as opposed to the 20-km resolution used by most other sites). For the ECMWF: We offer every variable available in the free data set. For the GEFS: Our maps include minimum and maximum member maps, a feature not found on any other site. Our all-21-members maps display the mean alongside the members and are available for a variety of variables in the United States. For the CMC: We have by far the fastest-generating maps around, and we use 3-hourly data out to hour 240 instead of reducing the temporal resolution like many sites do.

Exactly how many maps are available on your site and app at any given time, and how many are generated every day?
As of May 11, 2015, 2,729,486 maps are generated every day, and 19,106,402 maps are available at any given time. Of these, 940,620 maps (313,540 maps per day) are available for free on this website; the rest are either only available with a subscription or are still in testing. The values quoted on the home page represent all maps currently available to the general public by any means, free or paid.

What does "06Z" mean?
Our maps present the date and time of a forecast as "YYYY-MM-DD HHZ". For instance, "2011-02-01 12Z" refers to 12:00 noon on February 1, 2011. The "Z" stands for "Zulu" and is the notation used by the U.S. government to refer to Universal Time (also known as Greenwich Mean Time). When Daylight Savings Time is NOT in effect, you can subtract 5 hours to get the time in Eastern Standard Time. When Daylight Savings Time IS in effect, you can subtract 4 hours to get the time in Eastern Daylight Time. Subtracting 1, 2, and 3 hours respectively from the result of this calculation will yield the time in Central, Mountain, and Pacific time.

What do 500mb, 2m, Sfc, etc. mean?
Sfc means surface. 2m and 10m mean 2 and 10 meters above the ground respectively. 500mb refers to the altitude where the air pressure is exactly 500 millibars.

What do "Instant", "3-hr", "Total", etc. mean?
"Instant" stands for "instantaneous" and refers to the value of a variable at a given moment. "3-hr", "6-hr", etc. refer to the value of a variable over a given time period. "Total" refers to the value of a variable over the time period from initialization (hour 0) through the given forecast hour.

What does "63h" mean?
The number before the "h" in the rightmost drop-down box is the number of hours into the future (after the initialization time, which can be seen in the leftmost drop-down box) that the forecast is valid for.

The "Status" area on the left shows that maps are available through a certain hour. Why does "Map Unavailable" show when I select a map from that hour?
Refresh the page. The Status is updated whenever the first map is generated for a given forecast hour. The final map is usually generated several seconds later. If the problem persists, make sure the map is listed in the Map List.

What are the two maps on the home page?
The two maps on the home page are the highest temperature (Fahrenheit) in the next 24 hours and the expected precipitation (inches) in the next 24 hours, both according to the latest GFS run available.

How is snowfall calculated?
Unlike most variables we offer maps for, snowfall is not explicitly included in the model output provided by the NCEP server. To get around this, uses a proprietary algorithm inspired by the Evan Kuchera method to calculate instantaneous snowfall ratios. A specially weighted average is then performed, and the result is multiplied by the precipitation over the requested time period to get the snowfall.

I was looking at some maps and the time period automatically changed. Why did this happen?
Some basic error-proofing is built into our site. When invalid input is received that is very likely to be the result of a specific human error, the site automatically corrects that error. This is usually in the form of changing the time period. For example, 6-hr CAPE makes no sense, so it is automatically changed to Instant CAPE before viewing. In the same vein, Instant Snowfall is obviously invalid, so the site assumes you meant the smallest time period possible (for short and medium range GFS forecasts, this is 3-hr). If you believe that there is an error in the site, then please contact us.

What area do the stratosphere maps cover?
Our Stratosphere maps cover the area from 30N latitude northward.

I miss the old share links. Why are they gone, and are they coming back?
We are sorry to report that due to a change in ImageShack's policies, we are unable to continue offering the automatic share link generator. However, the free Imgur Community Extension for Chrome allows you to easily upload and share our images to Imgur by right-clicking them.

Am I allowed to post maps from your site on my blog or a forum, or in a video?
You are permitted to post or otherwise disseminate maps from as long as the following remain true: 1. The maps are rehosted in some form rather than hotlinked, 2. All insignia designating the source of the map remains on the image in its original position and form (or in a still-obviously-readable form modified only by image size and format changes), 3. The image is not modified in any way such that a reasonable person would interpret the map's content in a different subjective or objective way from the original, 4. The map is posted by a human instead of a bot (this rule is in place to prohibit mirror sites and is not to be construed as prohibiting use of the Imgur browser extension or social media services to aid in posting by humans), 5. The maps are not posted in a way obviously meant to reduce traffic to (if you have to ask whether you are violating this, you almost definitely aren't), and 6. There is no rule on the specific map or its webpage overriding these policies.

What features are coming to in the future?
We hope to include more models, more variables, and more regions in the future. If you have a specific suggestion for a feature, feel free to contact us.

I have a question about the app.
Please visit the App/Subscription FAQ for details.


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Map Status

Model Run Hour
GFS 00Z 300
GFS-HR 00Z 300
NAM 00Z 084
RAP 04Z 021
ECMWF 00Z 240
GEFS 00Z 162
CMC 00Z 240

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