Potential For All Time Record High Temperatures to be set June 27th through June 30th, 2021

The Northern Rockies of North Idaho and Northwest Montana has been exceptionally dry throughout the winter of 2020-2021 and the spring of 2021. In addition, temperatures have seen some rather dramatic ups and downs with frost occurring across valley locations as recently as the second week of June while also seeing many 90 degree days as early as late May and continuing through June. If you are a long time local or perhaps new to the area you may be wondering how dry are we. May and June historically rank in the top 5 wettest months of the year. May saw almost the entire region with record dryness and June seems to be following suite. No location across Northwest Montana or North Idaho has even received half of their normal June rainfall, which, on average is around 1.80 inches with some areas wetter and some a touch drier. I have not found any station that has seen even an inch of rainfall the entire month of June in our region. We are now about to enter a period of historic, record breaking heat that looks to last potentially up to a week. Most areas are very likely to break their all time record high temperatures ever seen in recorded history. I emphasize recorded history as we can tell from tree rings that historically there have been hotter and drier years than what we are currently in but not since weather records have been kept which is around 150 years. Take a look at the picture below.

500mb heights and 850mb temperatures from historic heatwave of August 4, 1961. Brighter blue colors are warmer temperatures. Darker purples are cooler temperatures. Numbers next to “H” and “L” are temperatures at 850mb(5000 feet) observed at 5:00 p.m. MDT/4:00 p.m. PDT on 08/04/1961.

This is a reanalysis of 500mb(18,000 feet) heights in the atmosphere along with 850mb(5000 feet) temperatures observed at 5:00 p.m. MDT/4:00 p.m. PDT on August 4, 1961. The purples are lower heights(cooler temperatures) in the atmosphere whereas the blues are higher heights(warmer temperatures) in the atmosphere. The center of the upper level high pressure area that brought the record heat was located over west central Wyoming with an astounding 601 decameter height! Another “H” located near our region just south along the Idaho/Montana border shows heights of 596 at 500mb with 850mb temperature observed of 32.3 degrees celsius(90 degrees fahrenheit)! High temperatures that day were incredible. Here are some of the observations: Bonners Ferry, ID: 98, Priest River, ID: 103, Sandpoint, ID: 100, Eureka, MT: 103, Libby, MT: 109, McGinnis Meadows, MT: 102, Thompson Falls, MT: 107, Trout Creek, MT: 110, Troy, MT: 106. McGinnis Meadows, Trout Creek and Thompson Falls all set their all time record highs that date. In addition, Spokane, WA set its all time record high that day with 108 along with Kalispell, MT which hit 105. That was a truly remarkable heat wave that actually began back on August 2, 1961 and lasted between 4 and 6 days with record highs for the dates all occurring during that stretch. How does this upcoming heat wave stand up to the one back then? Take a look at some of the pictures below.

GFS forecasted 850mb(5000 feet) temperatures for 6:00 p.m. MDT/5:00 p.m. PDT on Monday, June 28, 2021.

ECMWF model 850mb(5000 feet) temperatures for 6:00 p.m. MDT/5:00 p.m. PDT on Monday, June 28, 2021.

The top picture is a forecast from the GFS model for Monday, June 28, 2021 at 6:00 p.m. MDT/5:00 p.m. PDT 850mb(5000 feet) temperatures while the second picture is for the same time period but from the ECMWF model. The European model is slightly cooler across our region for Monday afternoon than the GFS but only by a couple of degrees. Let’s see what these 2 models show for Tuesday, June 29, 2021 for the same time as Monday.

GFS forecasted 850mb(5000 feet) temperatures for 6:00 p.m. MDT/5:00 p.m. PDT on Tuesday, June 29, 2021.

ECMWF model 850mb(5000 feet) temperatures for 6:00 p.m. MDT/5:00 p.m. PDT on Tuesday, June 29, 2021.

Again, the European model is a couple of degrees cooler at 5000 feet for our region than the GFS model. Regardless, however these forecasted high temperatures at 5000 feet are astounding! Both models have upper 80s/lower 90s for Monday and mid 90s for Tuesday at 5000 feet!! This is well above the observed readings seen back in August of 1961 by as much as 6 degrees! So what kind of high temperatures would be expected for those of us living on the valley floors with such high temperatures at 5000 feet? I will simply use Sandpoint, ID and Libby, MT as reference points for this discussion. The Euro model shows a high of 98 on Monday and 102 on Tuesday for Sandpoint, ID while the GFS shows a whopping 103 for Monday and 106 for Tuesday!!! For Libby, MT the Euro model shows a high of 93 on Monday and 96 on Tuesday while the GFS shows 97 on Monday and 99 on Tuesday. This is the raw model data so some adjustments need to be made based on local terrain. With the ridge axis directly or almost directly overhead winds will be light as can be seen with the arrows on these charts. A bit of a lake breeze coming off of Pend Orielle Lake into Sandpoint will tend to keep temperatures there a bit cooler so the Euro is likely correct in it’s forecasted temperatures for Sandpoint, keeping them right around 100. For Libby, the GFS is more accurate but taking into consideration that often both models tend to underestimate Libby temperatures a more correct reading would be for Libby to hit 105 on Monday and 108 on Tuesday. This would be at the Libby airport which is a bit higher and further south than the town of Libby itself. Typically you can add around 3 degrees to temperatures in town which would place the town of Libby at 108 for Monday and 111 for Tuesday. The main take home message here is that this upper level ridge will be centered almost directly on top of us with the core of the hottest temperatures also directly above us. This ridge also looks to be even stronger than the one back on August 4, 1961. For these reasons alone, I suspect that we will likely break all the records that were set back in August of 1961.

In any case, these temperatures are incredible and potentially very dangerous as the heat looks to last beyond Tuesday, possibly all the way up to the July 4th weekend. In addition to potentially shattering the all time record high temperatures that occurred back in August 4, 1961 the length of this heatwave looks likely to exceed that one as well with high temperatures over 100 degrees possible for much of the region for at least 5 to possibly 6 days. The only potential wild card with this heat wave will be any cloud cover and the possibility of thunderstorms. Some models are showing the atmosphere beginning to destabilize across the Washington Cascades by Monday afternoon as the ridge axis moves east and the surface thermal trough with it. In addition there are signs that a weak upper level low will get close to the Oregon coastline which would trigger showers and thunderstorms across Northeast Oregon that would send mid to high level cloudiness up our direction. Will need to watch this as we get closer. For now, get prepared for an extended, very hot and dry stretch, something that most of us will only experience once in our lifetime and not something that we are used to here in the Northern Rockies.