The focus for this week’s weather discussion lies in the tropics. Category 4 Hurricane Ida made landfall into Louisiana on Sunday, but more importantly for Colorado, the remnants of once Hurricane Nora in the Pacific will reach our neck of the woods later this week. What will this surge of tropical moisture bring to the Front Range and when do we expect the thick smoke to begin to clear out again? Read on to find out.
This week’s highlights include:
- Due westerly winds aloft will continue to pump thick smoke from California into Colorado early in the week, but improvement is expected on Wednesday
- High temperatures will be hot in the low to middle 90’s through Wednesday, generally just shy of record values
- The remnants of once Hurricane Nora in eastern Pacific will reach our area late Wednesday and linger through Thursday bringing the threat of tropical moisture-infused thunderstorms and flash flooding for the burn scars
- Much cooler temperatures are expected to end the week alongside those rain chances
DISCLAIMER: This weekly outlook forecast is created Monday morning and covers the entire upcoming week. Accuracy will decrease as the week progresses as this post is NOT updated. To receive daily updated forecasts from our team, subscribe to BoulderCAST Premium.
This seems like too much hurricane talk for a Colorado forecast?
Alook across the continental United States this Monday morning shows broad zonal flow stretching from California to New York City. Under this setup, wildfire smoke from northern California will continue to impact the Front Range early this week. At the same time, a trough approaches the Pacific Northwest and will move along the Canadian border the next few days. This generally far northern storm track will remain the case through most of the week ahead. We’ll need to look elsewhere for our weather…
There are TWO tropical systems impacting North America right now. Hurricane Ida made a devastating landfall as a strong Category 4 storm Sunday morning in Louisiana and maintained unprecedented strength as it moved inland feeding off the warm waters of the swampy Bayou. Ida has thankfully now weakened into a Tropical Storm and is located in Mississippi.
GOES-East infrared satellite animation of Hurricane Ida explosively intensifying just before landfall into Louisiana early Sunday morning.
We have landfall… pic.twitter.com/cBCOV9QSOY
— BoulderCAST Weather (@BoulderCAST) August 29, 2021
The other tropical system of note is the remnants of Hurricane Nora along the Gulf of California. Nora was absolutely massive this past Saturday evening when it still had hurricane strength. The infrared satellite animation below from Saturday puts Nora’s size into direct comparison with Ida. While much weaker, Nora was a notably larger hurricane in terms of the spread of convection.
GOES-East infrared satellite animation from Saturday afternoon showing Hurricanes Ida and Nora.
Nora was originally forecast to move almost perfectly northwestward through the warm waters of the Gulf of California during the early part of the week, maintaining strength as a weak hurricane or strong tropical storm. This is about the best track we can hope for here in Colorado, with this path giving the storm’s beneficial tropical moisture the greatest chance of eventually reaching our domain.
Forecast cone and intensity forecast issued for Nora a few days ago | AccuWeather
Unfortunately, this rare, best-case-scenario forecast cone did not verify. Nora deviated just a bit eastward and has moved over the mountainous terrain of western Mexico. The hurricane got ripped apart in short order and the National Hurricane Center has already issue its final advisory.
GOES-East infrared satellite animation from Sunday morning into Monday morning. Note Hurricanes Ida and Nora.
Nora is no more, but her remnants will still slowly migrate northward through the week and become a player for us Wednesday into Friday in the form of tropical moisture-fueled thunderstorms. The GFS forecast animation below for precipitable water anomaly shows the hefty pulse of Nora’s moisture moving northward into Arizona before getting swept across Utah and Colorado.
GFS pressure and precipitable water anomaly forecast animation spanning Monday through Thursday night.
The current timing brings the deepest moisture into western Colorado Wednesday afternoon and into the Front Range Wednesday night. This is not the most ideal conditions. Obviously we’d like to have the best moisture in-place during the daytime to maximize instability and thus storm chances. However, this timeline is not set in stone yet. Nora’s remnants have a long way to go and many mountains to pass over to get here. The system has already slowed down considerably from initial model projections. For now, expect a notable uptick in moisture beginning late Wednesday continuing through Friday.
This far out and with this much uncertainty, our best forecasting tool will be the ensembles. Every GFS ensemble member is on-board for an increase in storm activity Wednesday through Friday as the tropical moisture surges in. Wednesday could be dry for us, depending again on that tricky timing. However, Thursday looks to bring the best chance of storms to our area, followed by lessened yet continued rain chances Friday into Saturday. Flash flooding will be a concern with this much moisture moving in as precipitable water values spike close to 1.25″ around Denver on Thursday, and above 1″ Wednesday and Friday. The good news is that steering flow aloft will be 20 to 30 MPH from the southwest during the window of greatest moisture. This will curb the flooding concerns considerably, but it is still something to watch. As usual, mountain burn scars will be at the greatest risk.
As you can see above, Monday, Tuesday and much of Wednesday will be dry across the Boulder-Denver area as high pressure moves slowly from the Four Corners region eastward across Colorado. Temperatures will be toasty in the low to middle 90’s during this time. We should remain a couple degrees below existing record values (records in Boulder: 96°F Monday, 96°F Tuesday, 98°F Wednesday).
After a few bluebird days last week, we saw an increase in smoke over this past weekend as the zonal flow pattern began to assert its dominance over the nation bringing smoke directly from California to Colorado. This was the bleak view from Bear Peak in southwestern Boulder Sunday afternoon.
Bear Peak summit – 8/29/21 | BoulderCAST
This flow pattern will remain in control through early Wednesday, so the smoke and haze will stick around as well. The air quality is already not looking great as of Monday morning.
However, sometime on Wednesday our winds will shift abruptly to be from the southwest. This will bring in clearer air (and also Nora’s remnants) leading to less smoke overall. Something to look forward to, perhaps?
FireWork total smoke forecast through Wednesday evening. Monday and Tuesday will be very smoky in the Front Range, but things should start to clear up on Wednesday.
With the uptick in thick clouds and storms to end the week, temperatures will take a serious tumble. We’re forecasting highs in the upper 70’s to lower 80’s Thursday into Friday. What a great way to end the week! At this time, we’re not overly confident on how much rain we’ll actually see due to the poor, potentially overnight timing of the best moisture reaching our area. For now, we’ve added 40% storm chances to Thursday and 20% to Wednesday and Friday. If you have a little spare time this week, feel free to do your best rain dance! We’ll probably need the help…
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Forecast Specifics:
Monday: Mostly sunny with thick haze and smoke filling the skies. Highs in the lower to middle 90’s on the Plains with upper 70’s in the Foothills.
Tuesday: Morning sun with increasing late-day clouds and continued smoke. Temperatures will approach record levels in the middle 90’s on the Plains with lower 80’s in the Foothills.
Wednesday: Some sun early with increasing late-day clouds. Widely scattered showers and storms will spread from the higher terrain onto the Plains during the evening and linger through the overnight hours. Highs in the lower 90’s for the Plains with middle to upper 70’s in the Foothills.
Thursday: Much cooler and overcast with scattered showers and thunderstorms as the moisture remnants of once Hurricane Nora reach northeast Colorado. Precipitation will be possible at any time during the day and evening. Highs in the upper 70’s across the Plains with upper 60’s in the Foothills.
Friday: Mostly sunny with isolated late-day thunderstorms. Temperatures in the lower 80’s for the Plains and in the lower 70’s in the Foothills.
Mountains: Monday will be mostly dry across the state with isolated storms arriving on Tuesday. With deep tropical moisture moving in, expect scattered to widespread storms Wednesday and Thursday, then isolated storms on Friday. Moderate westerly flow will turn southwesterly through the week and eventually northwesterly by the weekend. Expect winds generally gusting 20 to 35 MPH on most of the higher, exposed peaks. Smoke will be thick Monday and Tuesday but lightens up considerably Wednesday and beyond. Check our SummitCAST page for up-to-date forecasts for more than 120 mountain destinations across Colorado, including all the 14ers.
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