While early autumn snowstorms aren’t uncommon in US weather history, they tend to be quick affairs that melt off quickly in a day or two. This however is a bit different in that we have a significant portion of the northern Midwest plains and northern Rockies are snow covered and it is not quickly dissipating, in fact it is increasing. Since October 10th the coverage has increased from 13.2% of the USA covered by snow.
This map below is from NOAA’s NOHRSC National Snow Analysis page.
Here is the accompanying table and discussion:
October 13, 2009
|Area Covered By Snow:||19.9%|
|Area Covered Last Month:||0.0%|
|Std. Dev.:||2.1 in|
|Snow Water Equivalent|
|Std. Dev.:||0.4 in|
By way of comparison, here is the October 13th USA snow cover for the last few years:
What is also interesting is the 6 year trend of snow depth on this date.
2003- 38.2 in
You can watch the snow cover advance in the animation they provide:
Click for animation of the last 72 hours
A series of potent systems moved across the coterminous U.S. this weekend, and they brought snow to the north and rain to the south. Late last week, heavy rain fell across the south, which continued to aggravate river flooding and keep soils most.
On Friday, up to 1 foot of snow fell at higher elevations in Wyoming, mainly due to upslope flow from a surface low which moved across the Plains. This same system produced up to 1 1/2 feet of snow to mainly Nebraska Friday and Saturday. Lighter amounts – up to 1/2 foot – fell across the southern Dakotas. On Monday, another system produced light snow across the Upper Midwest and western Great Lakes.
Much of the Western snowpack is cold and stable due due to unseasonably cold air temperatures in those areas. Along the southern edge of the snowpack – from southeastern Idaho to southern Wyoming and from southern Nebraska through southern Iowa, warm and melting conditions were present.
A deep, strong offshore system off the West Coast with potent onshore flow will cause widespread heavy rainfall across the northern two-thirds of California. Up to a foot of snow is possible in the high-elevation central Sierra Nevada, but it will be mixed with rain.
The energy of this West Coast system will shift northward and bring moderate rainfall – 1 to 2 inches – to the coastal Northwest and the Cascades on Wednesday and Thursday.
A midlevel trough will develop across the eastern U.S., and a stationary front across the South will be a focus for heavy rainfall through midweek, and this rain will shift to the Middle Atlantic states late this week.
As the West Coast system lifts northward, midlevel ridging will develop progress smartly across the West. Daily maximum temperatures are expected to be above freezing in much of the West by Friday. The ridge will move into the central U.S. by the weekend and bring seasonable temperatures to the Plains and Upper Midwest, causing snowmelt there.
h/t to WUWT reader Mike Bryant