Denver, Colorado

Thursday PM Update: Temperatures Back Near Normal this Weekend; Our Next Chance of Rain

Posted by @brendansweather

One week after we were discussing snow and near-record cold, summer is in full swing. Temperatures have been well above normal much of this week, and are expected to remain so through Friday. As we mentioned earlier this week in the State of the Atmosphere, the overall outlook appeared mostly warmer than how we started the month with a few ups and downs. One of those downs came Monday, another will come as we head through the weekend.

Temperatures Saturday will drop back closer to average for this time of year, with highs in the 70s across the region. 

Our next shot for precipitation looks to be during the Sunday - Tuesday timeframe. The GFS and EURO both show measurable QPF through this period to varying degrees. We’ll likely see a better chance for rain and storms at least Sunday and Monday, and possibly into Tuesday before drying out a again by midweek.

How much precipitation is yet to be determined. As of 12z today the EURO is leading with pack with pockets of >1” across northeast Colorado through Tuesday, while the Canadian has trended much drier. We’ll watch how the upper level low forecast to track across northern Utah through early next week progresses, and offer updates as needed. For now plan on a better chance for showers and storms to wrap up the weekend. Despite what some are reporting, it appears as though most of the moisture from Odile will stay south of Colorado. 

Expect temperatures next week will be cooler than this week. The CFSv2 shows a northwest/southeast split for temperature anomalies days 2-7, which would leave Denver very near average through the period.

CFSv2 7 day temperature anomaliesSource: WeatherBell

First Measurable Snowfall Prediction Contest 2014

Posted by @brendansweather

It’s already snowed once, now it’s time to predict when it will snow for real!
I’m not asleep at the wheel per se, but busy, really busy. With that, I narrowly escaped missing our annual first measurable snowfall forecast contest. Not to worry; had last week’s early season cold shot given us our first measurable snow, we would have figured out another way to challenge your forecasting skills!

The contest
This year’s first place prize will be 2 lift tickets to Arapahoe Basin ski area. Awesome! A huge thank you to A-Basin for getting involved and contributing these tickets.

Second place isn’t too shabby either, a $25 gift card to Sports Authority. Third place will be a very cool, and of course very geeky
Weather5280 t-shirt. Not sure what all those symbols mean? Basically, the perfect snowstorm for Denver. You can check out what all the symbols mean here.

The challenge is to forecast which day Denver (DIA) will receive its first
measurable snowfall of the season. This means that 0.1 inches of snow or greater must be recorded at DIA.

The contest will run of 10 days: September 17th to September 27th (weather permitting). Each contestant will be limited to one entry. We’ve included some helpful hints in creating your forecast on the
contest page, but two things to keep in mind: Denver’s average first snowfall is October 19, and we’ve been forecasting a cooler and wetter October than normal.

Contest page:
Predict Denver’s First Measurable Snowfall, 2014

Odds and ends
We’ve never asked you to jump through any hoops to enter in the contest, and the same will be true again this year. That said, please help us get the word out by sharing this contest on Twitter, Facebook, and elsewhere. We sincerely appreciate all of our readers, and we see this as a fun opportunity to get everyone excited for our fast-approaching snow season in Colorado and to say thank you for being awesome!

Good luck and happy forecasting!


Comments on the Southwest: Odile to Bring More Heavy Rain to Arizona, New Mexico

Posted by @brendansweather

A week after Phoenix saw it’s wettest day on record, the southwest is gearing up for another round of heavy rain and flooding from now Hurricane Odile, spinning into the Gulf of California. Current modeling takes the heaviest precipitation southeast of the Phoenix area, but flash flooding concerns across much of Arizona and New Mexico will be heightened for the second half of the week.

Hurricane Odile:
Odile forecast track
Forecast track of hurricane Odile (Weather5280)

Here’s the rainfall forecast from the GFS through 00z Saturday (EURO looks similar), a swath of greatest totals across southeast Arizona and western New Mexico.

GFS forecast OdileSource: WeatherBell Analytics

Is this amount of moisture for the region normal for this time of year? No, but also not unheard of when the eastern Pacific is active. We’ve discussed at several opportunities this summer our expectations for
enhanced eastern Pacific hurricane activity and sure enough, that is panning out. Take a look at the PWAT anomalies forecast for the second half of the week across the southwest, well above normal.

Odile PWAT anomalies

Southern Colorado will also try to pick up some beneficial moisture over the next week. At the present, it appears areas south of the Palmer Divide will have the greatest chance at seeing increased shower activity through the weekend -- but we’ll keep an eye on things across northern Colorado as well. For more, check out this week’s State of the Atmosphere.

The eastern Pacific stays active for the foreseeable future. Behind Odile is another disturbance with a 60% chance for formation in the next 48 hours. Today’s 12z GFS tracks it further west than Odile, but will certainly need watching as it develops.

NHC Pacific ForecastSource: NHC

The State of the Atmosphere: Sunday, September 14, 2014

Posted by @MattMakens247wx

You’ve no doubt felt this weekend’s warm-up. It would be very hard not to notice, coming from that frigid end of the week we had.

Friday and Saturday morning were both within 2-degrees of setting record lows at DIA.  The trace of snow Friday morning did not qualify as a “first snowfall” so officially Denver hasn’t had its first snow yet.

Short term Outlook:
Look at us now, back to average temperatures this weekend. Hold the presses though, we have another shot of colder air to move through tomorrow. A weaker cold front has moved into Wyoming, and will push over northern Colorado the next 24 hours or so. This one will bring only a minor dip to the temperatures, but still a noticeable one. Highs in the 60s and low 70s to start off the week.

Monday temperature forecast DenverSource: WeatherBell Analytics

This system doesn’t pack nearly as much punch as late last week’s cold blast did, and doesn’t have the moisture to work with either. Spotty storms, and some cloud cover are expected with the weak upslope flow on Monday. By Tuesday, this system will have moved out and we are back to another warm-up.

All global and climate models indicate warmer than normal temperatures for us this mid-week.  That is directly in-line with the 500mb height pattern indicating some ridging and warming temperatures. Indicated 500mb heights usually put the Front Range in the middle 80s, and luckily that’s right where ensembles keep the highs for Denver through Thursday. Good agreement is always fantastic.

GEFS Temperature Forecast

Oh, but wait. That good agreement tends to fall apart a bit later this week and the weekend.  By Friday another front will move through, relatively weak again, with a decrease in highs and improved rain chances. The disagreement between a cooler GFS, and a warmer ECM is a minor difference of 5 or so degrees. Regardless, I fall back to my 500mb heights and that does drop our highs back into the 70s for sure. This time around, though, there will be more humidity around for the trough to work with to foster rainfall.  o, rain chances appear, at least now, to be in the 30-40% range to end the workweek and start the weekend.

Long-term Outlook
These next two systems are relatively minor. However, we have our eyes set on the end of September and first two weeks of October for something more significant.

We’ve mentioned that timeframe before… two significant troughs will be moving through the region.  As depicted in the European, the 500mb pattern is anomalously shallow. That is a strong indication that these troughs will drag significantly colder air over the surface and down over Colorado. There is a slight deviation to the strength of both if you look at the CFS projections for the same events.

Source: WeatherBell Analytics

The climate model prefers a less significant cooldown. Although both situations are plausible.  Both do show that we will see colder than average temperatures in the first week of October and then again the second week. The difference is amount of cold air. I’m leaning toward the ECM based on past performance, however we can confirm that with better data as time gets closer.  We’ll keep an eye on the teleconnections to see if the AO, PNA, EPO and WPO give us indications as to the strength of the cold. We’ll have to wait though for that as those forecasts a reliable starting 14 days prior to an event.

Forecast teleconnections

In the meantime, enjoy the relatively warmer than normal pattern the rest of September (aside from some brief cooldowns along the way). This is quite a shift from the early half of the month, which has Denver 5 degrees colder than average to date.

Fall colors update
Last week we wrote about a few favorite places to view fall colors in Colorado. Here’s a collection of photos, dates, and locations to help show you the best areas of Autumn colors:

Interactive Map