On June 17th, this strong mid-level trough produced a large tornado outbreak across Minnesota and North Dakota, which included 4 EF4s.
A 992 mb surface low was over North Dakota as the outbreak began:
As dewpoints reached 70 as far north as Grand Forks, the dewpoints in South Dakota were in the 40s and even as low as 23 in Nebraska.
Satellite imagery shows just how quickly skies cleared behind the thunderstorms:
Both the low dewpoints and rapidly clearing skies are an indication of strong subsidence.
At 2218Z (5:18 CDT), numerous discrete supercells were moving across Minnesota and North Dakota:
This outbreak
set a record for the most tornadoes in a single day in Minnesota. More on the outbreak
here.
The next day, June 18th, the same storm system produced two separate derechos, hitting areas from Iowa to Michigan and Ohio.
The Chicago area had two damaging wind events separated by less than 6 hours:
The only major hurricane activity in the Eastern Pacific so far was in late June.
Hurricane Celia (center) reached maximum intensity on the night of June 24th with winds estimated at 140 knots, and a minimum central pressure of 926 mb. Hurricane Darby (right) was at maximum strength at the time of this image with winds at 105 knots and pressure at 960 mb.
In the Atlantic, Hurricane Alex, which had unusually low pressure for its wind speed, reached peak a strength of 85 knots and 947 mb as it made landfall in northern Mexico on June 30th. There was some question if Alex would even survive crossing the Yucatan Peninsula on June 26-27 when it was still a tropical storm. But by comparing these satellite images which were only 2 hours apart, I noticed that the only major change was that convection on the eastern half was actually intensifying.
By June 28th Alex had regained all the strength it had before crossing land:
On June 29th, Alex appeared to have entrained some dry air:
But then became filled with deep convection again just a few hours later:
Alex making landfall on June 30th:
Even though Alex quickly weakened over the mountains in Mexico, its moisture was spread over a huge area.
There was a very well defined edge to the north as the high level moisture spread into the southern United States:
The freezing line at 700 mb reached the Ohio River:
On the night of September 6th, a storm over Minnesota bottomed out at 994 mb:
Frost advisories were issued for the arrowhead of Minnesota and northern Wisconsin on the morning of September 9th, and some stations in this area dropped below freezing.
Another cold air mass on September 14th prompted frost advisories down to lower Michigan:
On September 17th freeze warnings (lighter blue) were issued for most of North Dakota, northern Minnesota, and northern Maine:
It was even cold enough for snow to accumulate in the lower elevations in central Montana.
On September 24th, a 993 mb storm prompted storm warnings (purple) over Lake Superior.
Also on the 24th, a huge Gulf of Alaska storm reached 953 mb:
On September 25th, the North Pacific jet stream had already reached 200 knots:
This morning, September 27, frost advisories went down to the county northwest of Milwaukee:
A much more extensive freeze is possible next weekend. The 850 mb freezing line is forecast by GEFS to reach the Ohio Valley by Saturday morning (12Z Oct 2).
