High Winds across Lincoln County January 31, 2020 to February 1, 2020

As many of us know our region experienced a rather strong wind event for our region the night of January 31st that finally came to an end the morning of February 1st 2020. High winds are not very common across our region due to the presence of alternating mountain ridges and valleys and the rather stable atmosphere that typically resides across Lincoln and Sanders Counties. While our region typically sees a couple of breezy to windy events each year mainly due to either passing weather systems or strong thunderstorms the magnitude of this recent wind event definitely stands out. What makes this event more impactful for our region than most other regions is that our trees in our part of Montana are not strengthened well enough nor are they able to withstand high winds beings that our region rarely receives such winds. Many are wondering what caused these winds to blow so consistently and for so long? Below is a detailed summary of the events that likely led to this wind event.

For several days leading up to the high winds models had been showing the potential of rather strong winds for our region. Most of the time high winds for our area remain aloft across the higher elevations due to the strong stability that usually resides across our valleys which causes the winds in the higher elevations to simply ride over the top of the surface inversion and therefore they don’t surface in the valleys. The ingredients that typically produce high winds across our region are a tight southerly pressure gradient typically resulting from a strong surface low tracking across southern British Columbia or southern Alberta coupled with a strong surface high to our south, strong winds aloft at mountain top level that have a stable layer just above them to force those strong winds down into the valleys and lastly precipitation loading on the west side of the Cabinet Mountains thus coupling with the strong pressure gradient and high winds aloft which combine to produce a similar effect in our region to what typically is seen on the front range of the Rockies commonly referred to as a chinook wind. See the picture below.

Picture courtesy of islandnet.com

On Friday evening around 11:00 p.m. a 999 mb surface low was located near Edmonton, Alberta while a 1036 mb surface high was located on the northeast Utah/northwest Colorado border. The surface low deepened (or intensified) to a 993 mb surface low by 5 a.m. Saturday morning with the corresponding surface high remaining stationary at 1036 mb. That is a 43 mb pressure difference over about a 1000 mile difference as the crow flies! Air flows from areas of higher pressure to areas of lower pressure. With the surface low located to our north and the surface high to our south the winds will blow from a southerly direction which they did. The second ingredient that came together was the presence of strong winds around ridge top level in this case around 850 mb (or 5,500 feet) to the 700 mb level (or approximately 10,000 feet). Those winds were recorded on the summits of the Cabinet Mountains and other mountain ranges in our region at around 71 knots which is 82 mph with an overall average speed of around 65 knots which is 75 mph. Keep in mind that these are sustained winds and not wind gusts. So while it was windy down here in the valleys, winds were even stronger across the higher elevations. What caused these winds to be funneled down the east slopes of the Cabinet Mountains in particular is the presence of a stable layer at ridge top level. Think of the stable layer like it was a cap on top of the Cabinet Mountains. The stable layer, or cap prevents the strong winds from simply flowing across the mountains like they usually do and disperse. Because of the stable layer holding those winds down, they cannot mix higher into the atmosphere and instead are forced downward on the leeward (east side) of the mountains. As air descends it picks up speed and warms up like the chinooks. These winds were blowing basically perpendicular to the Cabinet Mountains from the west and southwest with the mountains generally running from the southeast to the northwest. The winds picked up speed as they descended down the east slopes of the Cabinets and combined with the strong southerly surface pressure gradient were easily able to break our typical inversion that sets up especially during the longer winter nights. The final ingredient that was present to produce these strong winds was the precipitation loading that took place overnight along and west of the Cabinet Mountains. This looks similar to what happens during a chinook and the results are similar. See the picture below.

Photo courtesy of Encyclopedia Britannica

Precipitation that began to fall along and west of the Cabinet Mountains on Friday night/early Saturday morning caused an even stronger pressure difference between locations such as Bull Lake and the Bull Lake River valley and the Kootenai River valley around Libby. The cooler, heavier, rain cooler air contrasted very sharply with the milder, drier air on the east side of the mountains which further exasperated the already strong winds as wind always will blow from colder locations to warmer locations. The rain cooled air created a bit of a mini surface high on the west side of the Cabinets while the warm and dry air east of the mountains created a bit of a mini surface low. The atmosphere is always trying to create an equilibrium and balance which is why we see strong winds associated with very strong surface lows including hurricanes and strong surface highs such as chinooks and Santa Ana winds in California. Colder air is heavier and denser than warmer air so that heavier, precipitation cooled air was accelerating down the east slopes of the Cabinet Mountains to replace the warmer, lighter drier air on the east side of the mountains. The combination of these 3 three ingredients all came together at the same time to produce the widespread and damaging winds across much of Lincoln County Friday night and early Saturday morning. The highest official wind speed measured at the Libby weather station occurred at 6:00 a.m. on Saturday February 1, 2020 and measured 38 mph. There were a few unofficial reports of wind gusts near 60 to 70 mph right along the base of the Cabinet Mountains around the Granite Creek area of Libby and also around the Happys Inn and Thompson Lakes region also at the base of the Cabinet Mountains. Oddly enough, while winds were still strong and gusty across neighboring Sanders County winds were not recorded as strong although downslope winds did occur off the Coeur d’Alene and Bitteroot Ranges but precipitation loading did not play as much of a factor in these locations. Also although gusty winds were reported around Troy and Bull Lake these areas also did not have the added effect of the precipitation loading as they reside on the windward or wet side of the Cabinet Mountains. What made this event also rather memorable was the fact that after several rather mild days and weeks even, the ground had begun to thaw thus making for saturated soils and trees to be more easily uprooted. These events while unusual in our region are definitely not entirely un-heard of. Odds are that many are likely to experience a similar event again in their lifetime.