September 8

The United States of Weather Extremes: Record Heat, Wildfires, Freak Snows Out West

The United States of Weather Extremes

2020 has been a volatile, jaw-dropping year – and disruption applies to America’s weather. In recent days I’ve witnessed things I’ve never seen before. 121F in the suburbs of Los Angeles. A 5 year drought fueling massive California wildfires, billowing smoke thousands of miles downwind. While the west bakes Denver just dropped 60 degrees in 2 days; from 100F to 30s and snow, in a meteorological blink of an eye. “Paulette” has formed in the Atlantic, the 16th storm and earliest P-name on record. And now there’s Tropical Storm Rene, the earliest R-name on record.

Massive Smoke Plume. The smoke from scores of fires raging from California to Colorado encompasses much of the southwestern USA. Remember, we are at the beginning of the traditional fire season for western states. Image credit: AerisWeather.

Crazy Extremes. The map above shows predicted daytime highs on Tuesday (NOAA NDFD data) and potential records (boxed) across the USA. Nothing like easing into autumn. Map credit:

Everything is Connected. Typhoons in the western Pacific helping to amplify weather patterns thousands of miles downwind? Happens more than you suspect.

Frequent Cool Frontal Passages. The south and west is forecast to bake for most of September, but a series of Canadian swipes will take the edge off the heat for northern tier states, if NOAA’s GFS model looking out 2 weeks is to be believed.

2020 Was Hottest Summer on Record for Dozens of US Cities. ABC News explains: “…Some of the nation’s largest cities recorded their hottest climatological summers on record this year, including destinations like Phoenix, Tucson and Sacramento, according to the National Weather Service. In Phoenix, the country’s sixth-largest city, residents saw average temperatures of about 96.7 degrees — almost 1.6 degrees above the previous summer record, the NWS said Wednesday…Meanwhile, cities like Palm Springs, Las Vegas, Vero Beach, Florida, Flagstaff, Arizona and Sarasota, Florida, saw their hottest August temperatures ever...”

August 2020 Heat: World’s Fourth Warmest on Record. Bloomberg reports: “August 2020 will go down as the fourth-warmest on record worldwide, with above average summertime heat in the U.S. and Mexico tempered slightly by below average temperatures in parts of the Southern Hemisphere. Global temperatures for the month spiked around 0.9 degrees Celsius above the historical average, according to a new report by Europe’s Copernicus Climate Change Service. That reading came in lower than the summers of 2018 and 2019, the agency said in a statement...”

Image credit: Copernicus.

Briefing: Issued Monday morning, September 7th, 2020:

Southwest Heat Concerns


Excessive Heat Warnings. We are tracking a dangerous, historic heat wave across the Southwest continuing today across the region. Yesterday, Downtown Los Angeles (111F) saw their third warmest high in recorded history with Downtown San Francisco (100F) tying for their eighth warmest day on record. Meanwhile, the warmest temperature ever recorded in Los Angeles County (121F – Woodland Hills) and San Luis Obispo County (117F – Paso Robles) occurred yesterday as well. Dangerous, record breaking heat will continue across the region today with Excessive Heat Warnings in place, though it should likely be slightly cooler than yesterday in the Los Angeles and San Francisco areas. Here’s a look at expected highs today across the region:


Extreme Fire Danger



Extreme Fire Danger Today. Meanwhile, the fire danger is ramping up quickly across the western United States. Due to a strong area of high pressure pushing south into the northern U.S. Rockies and a trough along the Pacific Coast, very strong offshore winds are expected across portions of the Pacific Northwest, in and around the Portland area, today. Widespread winds of 20-30 mph with gusts above 60 mph in higher elevations along with low humidity values and very dry fuels are leading to an Extreme Fire Danger. However, other areas of Critical Fire Danger are in place across the western United States due to very dry fuels (which the recent heat waves had contributed to), low humidity values, and gusty winds. Some of this is due to a strong cold front sinking south across northern California/southern Oregon eastward, and just due to the heating of the day in southern California.


Fire Danger Continues Tuesday. Critical fire danger will continue across several areas of the western United States Tuesday due to the continued low humidity values, gusty winds, and very dry fuels. As we head toward late Tuesday and into Wednesday, a Santa Ana wind event is expected across southern California.


Fire Weather Watches/Warnings. Due to the expected volatile fire weather conditions across the western United States, a wide area is under Fire Weather Watches and Warnings.


Ongoing Fires. Of course, we are still tracking numerous wildfires across the region – of which these expected weather conditions will not help containment. Of note are a couple of fires:

  • The Creek Fire started Friday started near the communities of Big Creek and Huntington Lake in California and has quickly grown. Over 200 people had to be rescued from the Mammoth Pool Reservoir this weekend due to this wildfire. It has burned over 73,000 acres and is 0% contained.
  • The Cameron Peak Fire started in Colorado back on August 13 and has burned over 59,000 acres with 4% of it contained. This fire has been pushing smoke into the Denver metro.

Get more information on wildfires burning out west from:

September Snowstorm



Winter Storm Warnings. Meanwhile, an area of low pressure will be dropping south into the Four Corners region as we head through today into Tuesday, bringing a dramatic blast of cold air and snow across the Rockies into the Front Range over the next couple of days. Snow will also be possible into the Black Hills of South Dakota. Ahead of this September snowstorm, Winter Weather Advisories and Winter Storm Warnings are in place, including in the following areas:

  • Casper, WY: Winter Storm Warning from 6 PM tonight through Noon Tuesday for 5-8″ of snow and wind gusts to 45 mph.
  • Cheyenne, WY: Winter Storm Warning from Midnight tonight through 6 AM Wednesday for 5-10″ of snow and wind gusts of 35-45 mph.
  • Denver, CO: Winter Weather Advisory from Midnight tonight through Noon Wednesday for 3-7″ of snow.



Snow Forecast. The heaviest snow will fall in the mountains at higher elevations where over a foot could be possible. Our forecast right now has Cheyenne picking up around 9” of snow with Denver seeing around 5” through the duration of the storm.


Denver Temperature Drop. Temperatures will quickly drop across the Denver metro as we head into the overnight hours. Highs in Denver today will top off in the low 90s, but quickly drop through the late evening hours to around 50F by 10 PM and into the 30s by early Tuesday morning with precipitation changing from rain to snow.

Atlantic Tropical Update


Paulette And Eighteen Forms. As we look at the Atlantic, we are tracking two named system out in the central and eastern Atlantic. Tropical Storm Paulette poses no threat to land over the next five days as it continues to move west-northwest to northwest. Some gradual strengthening is expected the next couple of days before it starts to weaken. We’re also tracking Tropical Depression Eighteen out near the Cabo Verde Islands. That system is expected to become a Tropical Storm later today and due to that Tropical Storm Warnings are in place for the Cabo Verde Islands. It looks to strengthen into a hurricane later this week but should curve northward. We’re also tracking an area of low pressure south of Bermuda that has a low (30%) chance of development as it continues to move westward. Meanwhile, another tropical wave will move off Africa in a few days with gradual development expected after that time (40% chance of development in the next five days).

D.J. Kayser, Meteorologist, Praedictix.

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