29. A couple of points I wanted to hit: a look at snow depth across the region, an answer to TMIP's previous question, and how Winter Weather Warnings have changed this winter.
I pulled two maps of current snow depth off Wunderground.com, one of the Contiguous US (to the right) and one of the Midwest (below).
I like the bright spot around western Lake Superior, which is more apparent in the second map.
I think it's interesting to note that the yellow and orange color depths correspond pretty neatly with NWS Duluth's county warning area. I also think that some of the depths are a little high.
Information about the maps indicates that this information comes from the Air Force each day. The information also states that snow depth is usually under-estimated in the UP of Michigan. Mustn't there be a way to correct this problem?
TMIP's question:How radar works for mountains? Only sometimes there are cores on radar maps...
I posted a blog on how lake-effect snow (and other weather phenomenon) can slip 'under the radar' (linked here). TMIP was wondering how the mountains affect the radar beams and how there are permanent voids of missing radar data.
As an example, I took this screenshot (to the right) from KMQT (NWS Marquette) today. There are several examples of these cones of silence in this radar image.
As old as the hills.
Actually, the answer lies in the hills north of Marquette's airport. From Google Maps I took this topography image (to the left) of the area north of KMQT. I drew three lines in where the three largest voids occur on KMQT's radar images.
Elevation profile along the void.
On the left is the location of KMQT and the right is a point I picked in the middle of the void.
KMQT is located at 1444 feet amsl.
At 10 nautical miles (8.7 miles) the lowest radar beam is 510 feet above the elevation of the radar dome... 1444+510 = 1954 ft.
By connecting all the dots I got this image (to the right). By looking at this profile, it's easy to see why some areas are devoid of radar echoes.
I found this graphic (to the right) from the AMS Online Journal - Volume 17, Issue 4, Augsut 2002 (linked here).
It shows the same idea - a hill or mountain blocking radar data.
This problem is encountered throughout much of the western U.S., with many mountain peaks and ranges above 5,000, not all the U.S. is covered by the same quality radar.
U.S. Radar Coverage Map.
There are several of these maps on the internet, I found this one (to the right) from the same AMS Online Journal as the previous graphic.
The darker shading, found mainly in the inter-mountain West, indicate no radar coverage below 10,000 feet above radar level. Closer to home, a close inspection of the map will reveal that northern Minnesota has an area that is not covered adequetly by base refectivity scans.
New Changes Occurred to Winter Weather Warnings and Advisories.
I'm not sure this story got any news coverage, though it was in the headlines of the NWS Offices this fall.
Certain types of Advisories and Warnings in the past have now been changed so that more winter weather will simply fall under one category -- Winter Weather Advisory or Winter Weather Warning.
Of course, some things haven't changed: Freezing Rain, Wind Chill, Blizzard, Ice Storm.
However, these will now be under one Warning: Sleet, Heavy Snow, Blowing Snow.