National Weather Service United States Department of Commerce

Cold Front Dropping South Across the Western U.S.; Watching Threat for Tornadoes and Flooding in the South

A cold front will push south across the Western U.S. into Tuesday with mountain snow and areas of gusty to high winds. An area of low pressure will form along this front on Tuesday and bring a potential for severe thunderstorms with tornadoes and excessive rainfall in the lower to mid Mississippi River Valley. To the north, heavy snow is possible in parts of the upper Midwest. Read More >

Summary of the Marshall Fire and High WInd Event on December 30, 2021

 

On December 30, 2021 the devastating Marshall Fire roared through Superior and portions of Louisville, Colorado. The fire started south of Boulder Colorado, and was fanned by intense winds along the Front Range Foothills.  Wind gusts from 70 to 100 mph occurred right at the base of the foothills, including Boulder and along Highway 93 south toward Golden.  The strong winds fanned a destructive grass fire which originated near Marshall, and then quickly spread east to Superior and Louisville.  At last count, 1,084 homes and seven commercial structures were destroyed, and 149 homes and another 30 commercial structures were damaged by the Marshall Fire.


The very strong winds developed in the mid morning hours on Thursday, the result of a mountain wave that developed as very strong westerly winds raced over the Front Range Mountains and Foothills.  The mountain wave remained nearly unchanged through the rest of the day, resulting in very persistent and extremely high winds that focused very close to the base of the foothills, along Highway 93 and points east to around Superior and at times, Lousville.  It takes just the right combination of meteorological parameters, including stability, wind shear, and wind magnitude to create a powerful and damaging windstorm like this one.  To further visualize what a mountain wave would look like, see the image below. 

This schematic represents the strong westerly winds moving down the mountain slope (in this case the Front Range Mountains and Foothills) and accelerating all the way to the base of the foothills.  From there, they spread east into the Superior and Louisville area, before suddenly weakening to the east (call the jump region).  It was interesting to note in this case, that easterly winds were observed at times immediately to the east of the "jump" area around Broomfield and Lafayette. This can also be referred to as a rotor, where winds an actual wind reversal occurs.   

 

The second recipe ingredient for this disaster was the lack of precipitation during the latter half of the year. The Front Range experienced a very wet first half of the year, with much above normal precipitation, lush and tall grass growth.  However, starting around July, a persistently dry weather pattern set up and held firm through the entire fall and early winter.  Grasses, while typically dry this time of year, were exceptionally dry as very little snow had fallen through the entire fall season. Below, are the July 1 through December 29 temperature and precipitation ranks, showing Denver being the 2nd warmest, and by far the driest in recorded history (since 1872). Boulder was ranked 2nd warmest for precipitation, while 13th dries in recorded history.  

           

Another way to look at the combination of temperatures and dryness can be visualized here, comparing this July - December period with past years.

 

 

The images below show the progression of winds and fire during the late morning and afternoon hours of December 30.  The eventual fire perimeter is outlined by light purple (upper center of the plot images), while the city of Boulder is located in the northwest corner of these images.

 

Here is the 11 am surface plot showing wind gusts in red.  Winds were gusting to 81 mph in south Boulder, while as high as 99 mph near the intersection of Highway 93 and Highway 72 (Coal Creek Canyon). 

 



The fire started approximately 11:41 am, but raced quickly eastward due to the very strong winds and extremely dry grasses.  Here's a video taken from NWS Boulder at approximately 11:55 am, showing just how fast the Marshall Fire was spreading to the east. 

 

By 12 pm, some of the strongest winds from this wind event were occurring, with a peak gust of 115 mph reported at the base of the foothills, just east of the intersection of Highway 93 and Highway 72. Here's the 12 pm surface plot - note the 85 mph gust in south Boulder, and 100 mph gust along Highway 93 (very bottom of the image below) near the top of the hour. 

 

This video below was taken shortly after noon (credit to Twiiter user @Boldmethod for research and event write-up purposes only), was taken from Boulder, looking southeast at the fire.  Here, you can visualize the flow in the mountain wave, with the downslope winds racing east toward the Davidson Mesa and Superior, before then flowing upward in the "jump" area seen in the schematic above. This view gives us a mirror-like image to the mountain wave, since we're now looking south toward the wave rather than north as in the schematic. 

 

Between 12 noon and 2 pm, the stronger winds were shifting slightly east, through all of Superior and most of Louisville. At 2 pm (plot below), a wind gust to 68 mph was recorded near Coal Creek Golf Course in Louisville, a community that would see devastation with hundreds of homes burned. The fire had already moved through much of Superior, and was spreading quickly through the Louisville area. 

 

The mountain wave was fully established through this time, and cleary visible in the smoke and cloud structure. This time lapse imagery taken from the southwest side of the Denver metro area was shared by Mike Nelson and Mario Gori, showing the fluidity of the mountain wave.  Note the reflection shown in the strongest first wave, and then the subsequent second and even third wave on the far right of the imagery. Smoke is clearly visible as gray, while clouds are also shown on the crest of the wave..  

 

 

Below is a closer view (credit to Twiiter user @Boldmethod for research and event write-up only) from the other side, this one taken from Boulder looking southeast at the Marshall Fire around 2:50 pm. US36 is in the center of this imagery. The downslope winds are crashing to the ground along Highway 93 and then racing east to Superior and Louisville, before lifting and weakening rather quickly to the east. The fire and smoke (gray and dark gray) show this wind pattern clearly, while the line of clouds shows the "jump" area with enough lift (even on this very dry day) to produce a line of clouds. 

 

The loop below, shows the radar returns from the fire (smoke and ash), being lofted far into the atmosphere and thrown east across DIA and the eastern Colorado Plains. 

 

Winds eventually calmed down through the late afternoon and evening hours, but unfortunately much of the destruction had been done. A view of the fire around 6:00 pm from the NWS Office in Boulder, to the west/northwest of the fire. 

 

And then a view of the fire from nearly the same time from the east side of the fire. This picture was taken from Broomfield.  

 

Finally, here's a look from space (22,200 miles up), with satellite showing the intense heat being released by the Marshall Fire.  This was taken around 8 pm. 

 

 

                 ...HIGHEST WIND REPORTS...

Location                     Speed     Time/Date       Lat/Lon

...Colorado...

...Adams County...
0.7 Mi S Of Northwest Pkwy   56 MPH    1235 PM 12/30   39.97N/104.99W

...Boulder County...
3 SSW Boulder                108 MPH   0225 PM 12/30   39.99N/105.27W
1 NE Crisman                 102 MPH   1120 AM 12/30   40.05N/105.35W
3 NW Marshall                90 MPH    0125 PM 12/30   39.98N/105.28W
Boulder                      75 MPH    0215 PM 12/30   40.03N/105.23W
036e03750rws1rp1 At Baseline 73 MPH    1123 AM 12/30   40.00N/105.26W
Wondervu                     72 MPH    0956 AM 12/30   39.91N/105.38W
Atoc - Univ. Colorado Campus 71 MPH    1050 AM 12/30   40.01N/105.27W
Lyons 3W                     70 MPH    1042 AM 12/30   40.22N/105.33W
Lafayette                    70 MPH    1001 AM 12/30   40.06N/105.12W
Louisville                   68 MPH    0200 PM 12/30   39.96N/105.15W
Longmont                     68 MPH    1147 AM 12/30   40.13N/105.23W
Nederland                    66 MPH    0900 AM 12/30   39.99N/105.45W
Nederland                    65 MPH    0938 AM 12/30   39.99N/105.45W
Boulder                      64 MPH    0325 PM 12/30   40.06N/105.29W
Boulder                      64 MPH    1117 AM 12/30   40.04N/105.26W
Boulder                      63 MPH    1116 AM 12/30   40.02N/105.29W
Boulder                      62 MPH    0223 PM 12/30   40.06N/105.21W
Boulder                      61 MPH    1042 AM 12/30   40.00N/105.20W
Ward                         60 MPH    0833 AM 12/30   40.10N/105.50W
Boulder                      57 MPH    0808 AM 12/30   40.03N/105.28W

...Broomfield County...
025s229 Sh7                  57 MPH    1153 AM 12/30   40.00N/104.98W

...Clear Creek County...
Corral Creek                 67 MPH    1158 AM 12/30   39.64N/105.46W
I-70 Georgetown Lake         61 MPH    1235 PM 12/30   39.73N/105.69W
I-70 Floyd Hill              60 MPH    1204 PM 12/30   39.72N/105.41W

...Douglas County...
Cheesman                     67 MPH    1223 PM 12/30   39.18N/105.27W
Carpenter Peak               56 MPH    0357 PM 12/30   39.42N/105.08W
Franktown                    56 MPH    0320 PM 12/30   39.39N/104.75W
Surrey Ridge                 55 MPH    1224 PM 12/30   39.49N/104.87W

...Elbert County...
Elizabeth                    60 MPH    0250 PM 12/30   39.35N/104.53W

...Gilpin County...
Black Hawk                   58 MPH    1253 PM 12/30   39.84N/105.47W
Dakota Hill                  58 MPH    0955 AM 12/30   39.87N/105.55W
Aspen Springs                57 MPH    1250 PM 12/30   39.83N/105.48W
Golden                       56 MPH    1131 AM 12/30   39.90N/105.40W

...Grand County...
Winter Park Eagle Wind       73 MPH    0345 AM 12/30   39.85N/105.78W
Berthoud Pass                63 MPH    0935 AM 12/30   39.80N/105.77W
Keyser Ridge                 55 MPH    0427 AM 12/30   39.89N/106.04W

...Jefferson County...
Arvada                       115 MPH   1206 PM 12/30   39.86N/105.22W
Rocky Flats Hwy 93 and 72    110 MPH   1123 AM 12/30   39.87N/105.24W
2.8 NE White Ranch Open Spac 103 MPH   0126 PM 12/30   39.85N/105.25W
2 NW Rocky Flats             98 MPH    1155 AM 12/30   39.91N/105.23W
470w014 Wadsworth            81 MPH    0348 PM 12/30   39.55N/105.08W
1.7 NE Rocky Flats (CDPHE)   78 MPH    1215 PM 12/30   39.91N/105.19W
I-70 at C470                 73 MPH    1224 PM 12/30   39.71N/105.19W
Genesee                      71 MPH    1212 PM 12/30   39.71N/105.29W
Coal Creek Canyon            69 MPH    1016 AM 12/30   39.88N/105.39W
Lakewood                     67 MPH    0346 PM 12/30   39.70N/105.15W
Golden                       66 MPH    0901 AM 12/30   39.79N/105.28W
Arvada                       62 MPH    0146 PM 12/30   39.84N/105.17W
Arvada                       62 MPH    0139 PM 12/30   39.85N/105.16W
Littleton                    56 MPH    0316 PM 12/30   39.59N/105.13W
4 SSE Rocky Flats            55 MPH    0230 PM 12/30   39.83N/105.19W

...Larimer County...
Glen Haven                   89 MPH    0827 AM 12/30   40.47N/105.45W
Livermore                    79 MPH    0846 AM 12/30   40.71N/105.41W
Lyons                        62 MPH    1156 AM 12/30   40.28N/105.31W
Virginia Dale                62 MPH    1134 AM 12/30   40.95N/105.35W
Buckeye                      60 MPH    0235 PM 12/30   40.81N/105.04W
Red Feather RAWS             58 MPH    1224 PM 12/30   40.80N/105.57W
Livermore                    57 MPH    0933 AM 12/30   40.87N/105.36W
3 WNW Loveland               56 MPH    0217 PM 12/30   40.43N/105.12W

...Summit County...
Red Cliff Pass               55 MPH    0515 AM 12/30   39.48N/106.15W

...Weld County...
Erie Muni                    59 MPH    0915 AM 12/30   40.02N/105.05W

Observations are collected from a variety of sources with varying
equipment and exposures. We thank all volunteer weather observers
for their dedication. Not all data listed are considered official.

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