September is when we start to transition from Summer to Winter, but this September is starting off with a bang.
Intense heat has been common across much of the West for the past few days. Temperatures well over 100 degrees were widespread during Labor Day Weekend, especially across California, with numerous records set. One location, Richmond, on the eastern side of San Francisco Bay, reached 107 degrees Monday afternoon, tying their all-time record, originally set on September 15, 1971. Several other locations set monthly records for September as well. The worst of the heat has passed, but it will remain hot on Tuesday, with highs likely topping 100 across much of interior California and the Desert Southwest, possibly setting a few more records. Temperatures should gradually cool down a little more as we get toward the middle and latter portion of the week.
Heat was also common across the Plains and Rocky Mountains over the weekend, but big changes are developing thanks to a strong cold front. Denver set a record high of 97 on Sunday, then reached 93 on Monday. On Tuesday, that 93 will get reversed, with a daytime high closer to 39 (The high for the calendar day will be the 46-degree reading at midnight). On top of that, accumulating snow is likely. Even by Denver standards, this is quite early in the year for snow. Their all-time record for earliest snow is September 3, 1961, but on average Denver doesn’t see its first flakes until October 18. This won’t be the 1st time that Denver hit 90 one day and then had measurable snow the next. On September 12, 1993, Denver recorded a high of 92 degrees, and on September 13, they had 5.4″ of snow.
While a few inches of snow are likely in Denver and onto the adjacent High Plains of eastern Colorado and western Nebraska, heavier snow is likely across the mountains on Colorado and Wyoming. Across the higher elevations, snowfall totals in excess of a foot are likely. While the snow will likely last a while in the mountains, at the “lower” elevations on the Plains, it will disappear quickly. High temperatures in Denver will be back into the 60s by Friday, and near 80 by the end of the weekend.
While the snow will get a lot of the headlines, the cold air behind the front will be making headlines of its own. The first frost and freeze of the season is likely across parts of the Dakotas, Montana, and northern Minnesota Tuesday and/or Wednesday morning, with lows in the upper 20s and 30s. The cold air will continue to push southward across the Great Plains during the day on Tuesday, with numerous record lows expected Wednesday morning as far south as the Texas Panhandle. The cold air will eventually spread eastward, but will be modified significantly before it reaches the Eastern United States.
While plenty of (frozen) precipitation is expected across the Rockies, the lack of precipitation is causing problems across the Northeast, specifically New England. Aside from a few showers with a cold front on Thursday, generally dry weather is expected across much of New England this week, and things don’t look that promising for much of next week either. This shouldn’t be a surprise, as precipitation has been generally below to well below normal across the region since the Spring. In some areas, the amount of rain has only been around 50-60% of normal since April 1. Drought conditions have developed across nearly all of New England, and for a good portion of the region, it is now considered a severe drought. What the region needs is a series of systems that can produce moderate rainfall to help alleviate the drought (too much at once won’t help that much), but prospects for that aren’t promising at this time. In fact, rainfall looks to remain below normal for much of the remainder of September.
Meanwhile, as we approach the climatological peak of hurricane season, the Atlantic is once again getting more active. Tropical Storms Paulette and Rene both developed on Monday in the central and eastern Atlantic respectively. Paulette is expected to remain a tropical storm for the next several days while remaining over open water. It is not expected to be a threat to land. Meanwhile, Tropical Storm Rene moved into the Cabo Verde Islands Monday night and early Tuesday, producing heavy rain and gusty winds. It will likely strengthen over the next couple of days, possibly becoming a hurricane later this week. Once it pulls away from the Cabo Verde Islands, it is also expected to remain over open water for much of this week, presenting no additional threat to land.
Those systems aren’t the only ones in the Atlantic that are being watched. An area of low pressure a couple of hundred miles west-southwest of Bermuda is expected to drift westward or northwestward over the next day or two. Some development of the system is possible. It may bring some rainfall into parts of the Carolinas and Southeast later this week. The other area that is being watched isn’t immediately apparent right now, as it is still over western Africa. A tropical wave is expected to emerge from the west coast of Africa later this week. Forecast models show the potential for this wave to develop rather quickly once it moves into the Atlantic. It could threaten the Cabo Verde Islands over the weekend.
The peak of hurricane season is during the middle to latter half of September. Given how active this season has been so far, there will likely be more systems developing. There are only 4 names left on this list for this season – Sally, Teddy, Vicky, and Wilfred. Once the list is exhausted, the Greek alphabet is used. This has only happened once before – in 2005. During that season, there were 28 named storms of which 15 became hurricanes.