**UPDATE** FROST ADVISORY FOR WASHINGTON, SHEBOYGAN, FOND DU LAC, AND DODGE COUNTIES UNTIL 7AM. PATCHY FROST LIKELY AS TEMPS FALL INTO 30S.
The above image is from Sunday morning from the National Weather Service radar in Sullivan, Wisconsin. To make the image animate, touch the radar image. There was no rain in Green Lake or Dodge counties so what in the world is that weird-looking stuff on the radar screen. Here is a quick tutorial on how doppler radar works.
NEXRAD (Next Generation Radar) obtains weather information (precipitation and wind) based upon returned energy. The radar emits a burst of energy (green in the animated image). If the energy strikes an object (rain drop, snowflake, hail, bug, bird, etc), the energy is scattered in all directions (blue). Note: it’s a small fraction of the emitted energy that is scattered directly back toward the radar.
This reflected signal is then received by the radar during its listening period. Computers analyze the strength of the returned pulse, time it took to travel to the object and back, and phase, or doppler shift of the pulse. This process of emitting a signal, listening for any returned signal, then emitting the next signal, takes place very fast, up to around 1300 times each second!
NEXRAD spends the vast amount of time “listening” for returning signals it sent. When the time of all the pulses each hour are totaled (the time the radar is actually transmitting), the radar is “on” for about 7 seconds each hour. The remaining 59 minutes and 53 seconds are spent listening for any returned signals.
I want to thank the National Weather Service for the above images.
The radar does not know whether it is hitting rain, snow, hail, or birds. The radar signal is scattered and part of the signal returns to the radar. That is how we know where it is raining or snowing. The same can happen when birds are migrating. The most likely migratory bird from Green Lake and Fox Lake right now would be canada geese. These birds rest on area lakes as they move south from Canada to their wintering areas in the south. You can actually see the birds take off and then go fly in a group to the south. I have not seen this too much from Green Lake and Fox Lake, but more often from the Horicon Marsh. This is the time of year to head to the marsh to see dozens of different types of migratory birds.
As for our weather, get ready for a very quiet week. The only item of interest tonight is the cold temperatures. A frost advisory is in effect for much of the state. It does not include any counties in our viewing area, but Green Lake and Marquette counties are included. Lows in Milwaukee will be in the middle 40s, but inland temperatures will drop into the upper 30s. Remember that temperatures are officially taken at 5.5 feet above the ground so you can still get a frost even if the official temperature is above freezing. Dry weather the rest of the week with highs in the 60s on Monday and Tuesday and near 70 on Wednesday and Thursday.
Thanks for reading and enjoy the dry fall weather this week.