Weather in Colorado will be calm but hot for the last full-week of summer. Many areas will be flirting with record heat multiple times in the coming days. Elsewhere, the Carolinas are preparing for major Hurricane Florence which is likely to make landfall later this week.
A mundane week in Colorado
We haven’t been able to completely rule out precipitation in our weekly forecast for quite some time. However, that is indeed the case this week…
On Monday, three notable large-scale features are present across the United States…
- An amplified ridge of high pressure over the East Coast
- A closed high pressure off the coast of southern California
- A trough entering the picture in the Pacific Northwest
GFS 500 mb vorticity map for Monday
Through the week, the two ridges of high pressure will merge into a “mega” ridge that will eventually stretch from Arizona to Maine by Thursday or Friday.
GFS 500 mb vorticity map for Friday
Warm and dry southwesterly flow will be in place across Colorado during this time. Really there is no moisture available at all.
GFS precipitable water forecast for Tuesday showing dry air across Colorado and in the upstream pipeline.
The massive ridge will stall the trough’s advancement through the Pacific Northwest, leading to no real weather this week for us. Abundant sunshine and the warm winds from the southwest will facilitate temperatures well above normal through the week statewide. We’re talking highs from the upper 80’s to middle 90’s for the lower elevations through at least Friday. We’ll be within a degree or two of breaking high temperature records almost every day this week in Boulder and Denver…with enough warming present to crack at least one or two in our opinion.
GFS ensemble temperature forecast through next Monday. A hot week is expected for all of Colorado.
Models diverge on temperatures a little over the weekend, resulting from what happens with the trough by then. The GFS keeps 80’s into next Monday, while the Euro brings in a slightly cooler troughy pattern to the northern Rockies.
One minor cause for concern this week are potential gusty winds. The trough in the Pacific Northwest and the building high pressure over the eastern United States will lead to a strengthening pressure gradient over the coming days, as shown below. The winds, combined with the dry airmass, may produce dangerous wildfire conditions. At this time, it appears the Front Range should be in the clear with the strongest winds impacting Utah, western Colorado and southern Wyoming. Though we wouldn’t be surprised if some of these winds work into northern Colorado later this week, especially further north towards the Fort Collins area.
GFS 700 mb wind forecast for Thursday morning. A tightening pressure gradient will lead to gusty winds for many days this week, mainly to our north and west.
Fire Weather Watches and Warnings are already posted in many locations to our west.
Current watches and warnings as of Monday morning for the southwest United States.
Active in the tropics, both east and west
The second week of September is the climatological peak of hurricane season for the Atlantic Ocean…and this week will not disappoint. There are currently three hurricanes active in the Atlantic, shown below.
As you probably know, the most critical at this time is Hurricane Florence which is on a collision course with either North or South Carolina Thursday night or early Friday, making landfall as a major hurricane.
Hurricane Florence sea-level pressure and 10-meter wind forecast for Thursday night from the HWRF model.
While the winds and storm surge will devastate the area that is unfortunate to take the direct hit, the hurricane will also be under-cutting into the large ridge we discussed earlier with very weak steering flow.
GFS ensemble 500 mb height spaghetti plots for Thursday morning.
As a result, the remnants of the storm are expected to linger across the Carolinas and Virginia for many days, with direct access to the open Atlantic Ocean for moisture influx. Huge rain totals of 20 to 30+” may be possible across these areas.
GOES-East visible satellite loop of Hurricane Florence Monday morning.
Finally, Hurricane Olivia in the central Pacific Ocean is currently on-track to make landfall in Hawaii Tuesday night or early Wednesday. The CPHC has Olivia weakening to tropical storm status by then. Minor impacts are expected, mainly from heavy rainfall on already saturated soils.
There are currently no tropical systems in-play that will have any impact, direct or indirect, on Colorado.
GFS forecast total rainfall through Saturday evening.
Forecast Specifics:
Monday: Mostly sunny with highs near 90 degrees for the Plains and in the middle 70’s in the Foothills.
Tuesday: Morning sunshine with partly sunny skies through the day. Highs near 90 degrees on the Plains and middle 70’s in the Foothills.
Wednesday: Sunny and hot. High temperatures in the low to middle 90’s across the Plains and lower 80’s in the Foothills.
Thursday: Sunny and continued hot. Expect highs in the lower 90’s for the Plains and in the upper 70’s in the Foothills.
Friday: Sunshine and hot. Look for highs in the low 90’s for the Plains with upper 70’s in the Foothills.
Weekend: The weekend will continue the trend of hot weather and sunshine for the Metro area. Saturday will probably remain in the 90’s, but model disagreements on Sunday suggest it could be slightly cooler in the 80’s, though still incredible by mid-September standards!
High Country: It will be a warm and mainly dry week for the Mountains. Expect partly cloudy skies Monday and Tuesday with a chance of isolated storms on Monday over southern Colorado. Wednesday through Sunday will see very warm conditions in the higher elevations with virtually no chances of any clouds, let alone storms. Check out our SummitCAST page for 6-day forecasts for more than 120 Colorado mountain destinations!
DISCLAIMER: This weekly outlook forecast was created Tuesday 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, subscribe to BoulderCAST Premium.
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