According to Skymet Meteorology Division in India, a strong upper-atmospheric trough is moving across the Plains and Midwest as an upper-atmospheric ridge builds in the West. This will mean very low temperatures for the northern Rockies to the southern Plains and into the Midwest, while the West Coast will bake in searing heat.
Some other unusual features in the recent weather pattern are:-
Calm Atlantic
Strong vertical wind shear has been the inhibiting factor for Hurricanes in Atlantic.This year, according to several records that date back to 1970, the period from June to August tied for the second-highest average vertical wind shear. Wind shear is important because it removes the heat and moisture from the area near the storm's center and causes displacement of the clouds. This makes it more difficult for the system to become organized and develop.
It certainly does not feel like early September in the tropical Atlantic. The weather has been active over most of the US, but the opposite is true for Atlantic hurricane season.
Tropical Atlantic has been quiet this season, and there were no named storms till the time Tropical Storm Edouard developed late on Thursday night.
There were other factors that have acted as obstacles to tropical development, including drier air than average, cooler water temperatures and higher pressure between the African coast and the Caribbean, where most Atlantic named storms form from the waves.
However, conditions could change. We have already witnessed more hurricanes than last year, including the first storm of the season, Hurricane Arthur, which impacted the East Coast.
Rain Showers due to Lake-Effect
Water temperatures are generally between 600F and 700F through the Great Lakes, with the exception of Lake Superior where temperatures are in the 40s and 50s. Colder temperatures have advanced into the region behind the strong cold front. Highs will be mainly in the 50s and 60s and lows will be in the 30s and 40s(0F) . This first taste of fall will even bring the chance for lake-enhanced rain showers later this week in parts of Great Lakes region. The cold air will remain over the warm Great Lakes this weekend and the result will be a few lake-enhanced or lake-effect rain showers.
Parching Pacific Northwest
The heat persists in much of the Pacific Northwest as a strong ridge of high pressure builds into the region again. Portland, Oregon, will see the thermometer climb to 900F this weekend. Average maximum temperatures for early to mid-September should be in the higher 70s. In fact, this could be one of the longest stretches of consecutive days with maximum at or above 900F this year. The longest so far this year has been three days.
Record highs are possible including San Diego, Los Angeles and Portland, especially on Sunday.
Late Summer Snow
South Dakota saw its earliest measurable snowfall (at least 0.1 inch) on record on September 11 with 0.9" reported (previous record was on September 13). North Platte, Nebraska also saw its earliest snow with a trace reported on September 11. Light snow was observed in Great Falls, Montana, on the night of September 16, making it the earliest snow there since 1992. More than a foot of snow had fallen in some of the higher elevations in Wyoming, causing some tree damage and power outages. Snowflakes were even seen in the Denver metro area from night of September 18 till the morning of September 19. Snow has also blanketed parts of western Canada, including Calgary, earlier this week, which led to felling of trees and causing power outages.
The first frost or even freeze of the season was seen for much of the northern Plains and Upper Midwest. Low temperatures dropped towards the freezing point deep into the Plains.
Record lows were also broken on Saturday morning including International Falls, Minnesota (250F), Kansas City, Missouri (370F) and Austin, Texas (600F).