Denver, Colorado

The State of the Atmosphere: Monday, July 21, 2014

Posted by @brendansweather

It was a hot, but hopefully not unbearable, weekend across much of Colorado. In many respects, we all knew it had to come at some point, as this summer to-date has been fairly tame temperature-wise, and downright wet for some. The heat sticks with us through the week, though isolated to scattered afternoon storms will (like this weekend) may help knock down temperatures late in the day in some spots.

MOS guidance actually hasn’t been terrible with temperatures over the last few days. GFS has been a bit warm, NAM at times a bit cool, with highs generally leveling out somewhere in between. Both models keep us in the mid to upper 90s through the end of the week -- though we can’t entirely rule out a 100-degree reading -- with possibly a return to more climatological highs by next weekend and early next week.

There will be some moisture around through the period, which will keep storm chances in the forecast. Should see a general uptick in chances as we progress through midweek, and then again into next weekend.

Northwest fires, Colorado haze
You may have noticed the hazy conditions this weekend across Colorado. This was due to many fires burning in the northwest states where this summer’s heat has been far more relentless. NASA’s MODIS satellite captured several striking images of the fires over the last week, including this one from July 18. Several fires burning
across Oregon and Washington are visible, with dense smoke (brown-gray vs clouds) being captured over the Idaho mountains, then transported southeast.

MODIS northwest fires
Recent heat over the middle of the country has been at least brief reprieve for the northwest. Cooler than normal temperatures, or at least temperatures near average should continue through much of the week in this area, but for the pattern looks to repeat itself by the end of the week and into next.

Here are temperatures through the first 19 days of July. Denver sits at about average, the central U.S. well below normal, and it’s been baking in the northwest:

July 2014 Temperature Anomalies

June 2014 warmest on record
While temperatures have been at or below normal for a good portion of the United States this summer, as we’ve seen in the Pacific Northwest, this hasn’t been the case everywhere. In fact, according to the National Oceanic and Atmospheric Administration (NOAA), June 2014 was the hottest on record for the globe.

Below are the ocean and land temperature departures from normal for June. Notice the cool sector over the north central U.S. Expect this to look similar in the U.S. for July, with cool pool perhaps a bit further east.

June 2014 Warmest on Record

Pattern Reloads
While the next few days will remind us it is actually summer, it looks like the pattern reloads for next week, with another shot of cool air pushing into the middle of the country. This will mean a better chance for monsoonal moisture to return to the state, as well as cooler temperatures.

The question will be again how far west the cold air will make it, but expect at least a return to closer to normal temperatures as we head into the latter half of this weekend and next week.

Both the GFS and EURO ensembles have another strong trough digging into the east for next week. The GFS 00z run looked a bit stronger, and even a bit further west, which would help support cooler than normal temperatures again east of the Divide. The EURO ensemble control run looks very similar.

ECMWF 500 ensemble
And the CFSv2 continues to
insist cooler than normal temperatures across the central United States to start August. Latest runs actually look more impressive than they did last week for the first 10 days of August (degrees C).

CFSv2 temperature forecast August 2014

Enjoy the summer weather, and try and stay cool! Plenty more to come this week, so be sure to
subscribe to Weather5280 if you’re not already. We’re now less than 12 weeks away from our average first snowfall in Denver!

Flooding Rains Ease, but Here Comes the Heat

Posted by @brendansweather

Our drought-reducing progress will go on pause for a while as warmer and drier weather returns to the region. Temperatures over the next week will climb above normal levels for the state as high pressure builds in. The best precipitation chances over the next week look to be in the mountains, with very little over northeast Colorado and the Plains.

Rainfall totals
It’s been a heck of a run so far this this summer, however, and most of the monsoon season is still ahead of us. According to the latest U.S. drought monitor released Tuesday (July 15th), now 58% of the state is drought free. That’s up from 38% just three months ago.

While the worst drought in Colorado still persists across the southeast part of the state, we’ve seen some relief there as well. Take a look at the rainfall totals across the United States over the last seven days. Most notably, over southeast Colorado, New Mexico, and back into Arizona.

united states 7 day rainfall totals
While July is statistically a rainy month for Colorado, analysis run by the National Weather Service shows much of the urban corridor and southeast Colorado at 300 to 600% of normal precipitation over the last week. Some locations picked up more than 5” of rain during this period. (Though it’s worth pointing out that Denver International Airport has only recorded 0.92” of rain so far this month, and at more than halfway through the month, has only seen 30% of normal total monthly precipitation.)

rainfall as percent of normal Colorado
Temperatures remained below normal Thursday, with afternoon highs predominantly in mid-to-upper 70s the across the metro region. We’ll climb into the low 90s for Friday and Saturday, with even warmer temperatures possible by Sunday and into early next week. We’ll keep a chance for storms going for the next few days, but those chances will be much lower than they have been. Brief downpours, lightning and wind will be possible with any storms that manage to develop over the coming days.

Temperatures by early next week look to be hot. MOS guidance has highs in the upper 90s by Sunday, and staying so through at least Wednesday. We’ll stick with highs a few degrees cooler than guidance for now, but will see how the trend sets up over the next few days. In any case, the next week looks noticeably different than the last few days across the region. Here’s the culprit.

EURO 500

Models differ on just how long this area of high pressure sticks around for, but it does appear that overall the last 10 days of July will be warmer and generally drier than average. We’ll see how things progress, but given the pattern, hard to imagine we won’t see another break from the heat before too long. A quick peek at the CFSv2 shows it keeping us hot through day 15 (left), but brings cooler temperatures right back by the start of August (right).

CFSv2 Temperature Outlook

More to come on all of this. For now plan on a warmer and drier weekend, with well above normal temperatures possible by Sunday and into next week.


Update: Severe Weather Threat Today, Flash Flooding Concerns

Posted by @brendansweather

It’s shaping up to be an active 24 hours for Colorado. After seeing another round of showers and storms Monday, Tuesday evening is looking to be more even more widespread with rain and storms. We pinpointed today as our greatest severe weather threat, and that appears to hold true. The Storm Prediction Center continues with a Slight Risk for severe weather for the eastern half of Colorado for today.

severe weather outlook colorado

We should see ingredients start to come together for a few severe storms by mid to late afternoon and into Tuesday evening. A short wave approaching from the north with help enhance the severe weather threat across the region. While the severe weather threat is of concern, so too will be the flash flooding threat, especially as we head into the overnight hours and through the day Wednesday.

Main severe threat will be hail and damaging wind with any of the strongest storms that do develop. Many high resolution models keep best chance for strongest storms late in the day,
with best chances after 6pm this evening for Denver. The SPC has 2 - 5% probabilities for tornadoes across eastern Colorado today as well, which seems reasonable. This is the likelihood of a tornado within 25 miles of a given point within the included zone.

mesomap tornado outlook Denver

Flood concerns Tuesday night and Wednesday
Our attention quickly shifts from the severe threat to flash flooding threats Tuesday night and Wednesday. This type of setup is notorious for producing flash flooding across the eastern half of Colorado. While burn scar areas will be particularly prone to flash flooding, as we’ve seen over the last week, they are not the only places that should be on alert. Recent rains, in combination with slow moving downpours will keep the threat of flash flooding heightened -- even away from burn scars.

The heaviest rains rains over northeast Colorado are expected to occur this afternoon and overnight Tuesday. Flash flooding threat Wednesday will shift south a bit, with the main areas of concern generally south of I-70. A
Flash Flood Watch is in effect for the Colorado Springs area through this evening, including El Paso and Teller counties and the Rampart Range.

The WPC flash flood risk outlook for Wednesday look pretty good. The flash flood threat will include all of the Front Range foothill communities, then extend into much of southeast Colorado.

WPC flash flood outlook

Stay up to date on the latest conditions across the area with resources on our
current conditions page. We’ll be releasing our most frequent updates over the next 24 to 36 hours on our twitter account (@weather5280).

Temperatures will remain
well below normal Wednesday as well, with highs in the mid 70s for Denver, and possibly not out of the 60s for many on the eastern plains. We start to dry things out Thursday a bit, then start a warming trend heading into the week.

Storms Continue and Temperatures Tumble Midweek

Posted by @brendansweather

The start of the coming week promises to deliver more weather adventures for Colorado. As I already mentioned last week, eastern Colorado could see temperatures well below normal by the middle of the week as an upper level closed low digs in across the Great Lakes.

The greatest temperature anomalies appear to be in store for Wednesday, when temperatures could be anywhere from 10 to 30 degrees F
below normal across portions of eastern Colorado and into Kansas. Denver will be right on the line for the coldest temps relative to normal -- with a sharp east/west gradient between cooler temperatures (east) and slightly below normal (west).

The big question over the last week has been just how far west the cold pool gets. Today’s 12z ECMWF didn’t back down with this shot of cool air across eastern Colorado, and the GFS looks fairly similar -- though it keeps the core of the coldest temperatures east of where the EURO has them. With either scenario, the greatest negative temperature anomalies will be well east of Denver, but we’re liable to still see well below normal temperatures for Front Range communities as well.


ecmwf temperature anomaly united states
Responsible for this (taste of fall?) is an uncommonly strong (for this time of year) upper level low that will dip south Tuesday across the Great Lakes, ushering in chilly air for the Plains states by midweek. Highs Wednesday may not make it out of the mid 60s across portions of Western Kansas and extreme eastern Colorado, with 70s expected for highs in Denver for now.

NCEP GFS Ensemble Mean
Continued Storm Chances and Flash Flooding Concerns
Storms remain in the forecast at least through Wednesday for eastern Colorado. Storm chances Monday will be very similar to today (mostly in the 30% range), with the possibility of a storm or two becoming severe.

Precipitable Water values rise again for Tuesday, with the GFS at >1” for most of the plains by Tuesday afternoon. PWAT values stay high for Wednesday, before we gradually start to dry things out a bit to end the week. Greater available moisture, the incoming cold front, and recent rains will heighten
flash flooding potential as well for Tuesday into Wednesday as well. While recent burn scars are of greatest concerns, this type of setup can produce flood potential with just about any storm that develops. Please be wary.

PWAT values forecast Colorado

Severe Threat
As it stands, it looks like Tuesday will offer the greatest risk for severe storms, though impossible to rule out severe storms the other days as well. Tuesday will have the most ingredients in play as yet another short wave trough moves through. CAPE values are forecast to be greater than 2000, dew points in the upper 50s and low 60s, and shear.

Certainly still a lot to watch over the next 24 to 36 hours, but the SPC has issued a slight risk for severe weather Tuesday across the urban corridor and Front Range foothills. Greatest threats will be strong winds and damaging hail, but an isolated tornado cannot be ruled either.

severe weather forecast SPC colorado

We’ll keep a close eye on things and update as necessary. In short, plan for more storms to start the week (some severe) and cooler temperatures for Tuesday and Wednesday. If you’ve not subscribed to Weather5280, please do(!), and follow us on Twitter (@weather5280) for all the latest updates.

Medium range models continue to show us drying out and warming again by the end of the week and next weekend. Expect temperatures to gradually rise into the weekend, with the potential for a return of the heat by early next week. Given the pattern, it seems prudent to wait-and-see a few more days before getting too caught up on hot and dry.