29. I'm a bit behind on blogs. A recap of the last two weeks: 1) The large amount of rain we received Oct 16, 17, 18, 19. 2) October has received more than two times the usual precipitation. 3) The extra rainfall has finally broken our two year drought, though we'll need more rain. 4) Fall colors have finished here in the Northwoods. 5) La Nina is beginning... what does that mean for our winter?
1) Oct 16, 17, 18, 19.
October 16th saw an unusually strong low pressure system move across the Upper-Midwest from the Central Rockies. Such a storm system occasionally comes in November, bringing winds up to 60 mph, warm temps ahead, cold temps behind, snow/rain/freezing rain/thunderstorms. This system was too early to bring the cold Canadian air down behind it, but it was able to pump up some moisture from the Gulf of Mexico that produced quite a bit of rain.
I measured 2.965" of rain over the four days of the storm. My lowest barometric pressure was 977.8 millibars (28.878 "Hg) at 4:00 on October 19th. My location is sheltered with trees and hills, so my highest wind gust was only 28 mph. Duluth/Superior however had sustained winds around 30 mph with gusts to 40.
Some numbers from the storm include:
My lowest pressure: 28.88 "Hg My total rainfall: 2.965" My highest wind gust: 29 mph
2) and 3) Wet October and drought relief.
Normal rainfall in October at the nearest ASOS weather reporting station (1905-2000) is 2.48" of rain. I have measured 6.125" here (9.7 miles) in the month of October. That is 246.9% of normal... two-and-a-half times expected!!!
According to the US Drought Monitor, the Extreme drought of northern Wisconsin is finished. This extra rainfall has helped relieve the dry soil conditions, but more rainfall in needed.
While the water tables and local lakes (esp Lk Superior) will take time to recharge, this was a good start.
4) Fall colors have finished here in the Northwoods.
Fall colors finished here by October 11th, the trees were bare. The Fall Color Report from TravelWisconsin.com show that only a few counties in the southern part of the state are at peak, the rest of us are past.
Two pics from my yard, Oct 11th.
5 ) La Nina?
Indications are pointing to a developing La Nina in the Eastern Pacific. In the image (below) the bluer waters west of South America indicate cooler-than-normal waters. This would La Nina herself.
As a refresher, El Nino would be a pool of warmer water off the shore of South America, which would be shown by redder colors.
So what does that hold for the months ahead? A lot of different people are saying different things. Let me show the offical forecast from the Climate Prediction Center and describe what has been observed in the Upper Midwest during past La Ninas.
Officially You can read more about the official winter forecast issued by the Climate Prediction Center here, but I'll recap the thoughts for the Upper-Midwest.
The first map shows Temperatures. The light 'pink' over most of Wisconsin and all of Minnesota highlights a slight chance of above-normal temperatures. Meaning that it will probably be a little warmer this winter, on average. This second map show Precipitation.'Green' indicates a chance of above-normal precipitation. Most of Wisconsin in in the 'white' category... "Equal Chances". Translation: could be more, could be less, could be right-down-the-middle, we 're not sure.
What has happened in the past?
A La Nina winter is usually a little warmer than normal. The jetstream becomes more zonal (flatter from west to east), bringing Pacific air across the northern States. This air is usually more modified and not so brutally cold, the ocean waters moderate any very cold air. However, cold Candaian air from the Arctic will make dives south occasionally. Occasionally snowstorm will draw frigid air down into the US from time-to-time.
The problem with Pacific air is that it has to come across the Rocky Mountains. By the time any moisture arrives in Minnesota and Wisconsin, a lot of it has already fallen in the mountains. Therefore, Pacific air is usually drier than air from the Gulf of Mexico. However, with warmer temperatures, the air can hold more moisture, so any winds coming up from the south will be able to bring precipitation. Historically, La Ninas are difficult to predict for precipitation, but on average, La Nina years bring 5 more inches of snowfall than normal. The map (to the left) shows typical conditions across Canada and the US during a La Nina episode. More info here.
But let me outline a problem that we may encounter. Snowfall would be expected to be normal or slightly above normal. When you add in warmer temperatures, we run the risk of having the snow on the ground melt. This has happened in the past -- it snows and melts, snows and melts, snows and melts. That actually leaves us drier in the spring due to less snowmelt, and bare ground leaves us more vulnerable to deep freezes if Arctic air invades the region.