Denver, Colorado

Average Daily Maximum Temperature (F) from 1979-2011 by County

Posted by @brendansweather

Last week, @MetricMaps put out this awesome animated GIF of average maximum temperatures by day for the United States. The image is a great example of how visualizing time-series can be fun, but also difficult. One of the hardest parts of creating an effective time-series visualization is that the size of the data can get large quick.

So this week I teamed up with my good friend and colleague Chris Helm (
@cwhelm) to explore a different way to built a very similar visualization.

In order to build our application we began by whipping up a little script that scraped data from
the NLDAS. After some processing of the data we were able to use D3.js to build what we think is a pretty snazzy little example of mapping long term climate data.

You can find the full version with county interaction 
here. Tell us what you think!

What the Hurricane?

Posted by @brendansweather

Animated GIF shows GFS day 9 forecast flop
The moment we had been waiting for all summer finally arrived last week. The single model run to throw the social media world into a frenzy: the day 9 ‘dream’ hurricane from the GFS.

GFS 9 day forecast Cristobal
12z GFS August 19, 2014. Source: WeatherBell Analytics

It was amazingly viral for a landfall that was never to be. It was quite possibly the best non-storm setup we had seen in years, and, it was set to make landfall in New Orleans on the 9 year anniversary of Katrina. Of course, this was ridiculous and in the hours and days that followed many came out and said as much. I’ll resist the urge to continue a rant here about media and hype around storms though -- we’ve done that already.

The problem with the frenzy that erupted last week is that models have virtually
no skill at nine days out in forecasting development, strength, and track of a system like this. At the time the system was only a tropical easterly wave east of the Caribbean islands. The amount of hype surrounding this system prompted the National Hurricane Center to remind us all to be cool:

The bottom line really is: be alert, be prepared, but also be wary of long-range projections that go beyond what the science can offer. And make the NOAA National Hurricane Center your calm, clear, and trusted source for official forecast and warning information on tropical cyclones.

Rather than call out the worst offenders here, I’ll just say this: It’s irresponsible, cut it out. Folks living along the Gulf and Atlantic coasts are understandably on edge this time of year, so offering bogus warnings to push your agenda is a really gross way to get followers, views, and clicks. And for those sharing these reports -- please pay closer attention to what sources you are using, and make some effort to find a reliable, trustworthy one.

As forecasters, we should use this type of run to help better understand the pattern, and see what models are trying to sniff out. Why we’re compelled to share images of hurricanes making landfall over a week out is baffling -- especially on Twitter where there aren’t enough characters to explain that it’s a) just a single model run, b) there is a GREAT amount of uncertainty, c) we’re “gearing this to our meteorologist friends that understand these uncertainties” (we’ve all already seen it), d) it’s not in line with its ensembles or other models like ECMWF, and d) it’s the GFS.

Since it’s naive to think we can all agree to stop sharing 10 day forecast maps from a single model… maybe we can agree to try a few things when doing so:

  • Provide context, stress uncertainty over risk.

  • Refrain from using ALL CAPS and instigating words like “WARNING” and “URGENT” (it’s not).

  • Avoid reference to other major natural disasters (i.e. Katrina landfall). That’s not context.  

  • Forecast, not model-cast.

  • (why didn’t anyone show the EURO from that day? #clicks).

So, how on-target was this pot-stirring model run on 12z Wed, August 19?
The forecast was for 12z this coming Thursday, August 28 (pictured above). By the time Thursday rolls around, now hurricane Cristobal is expected to be far out to sea in the Atlantic (though we may have another disturbance to contend with in the Gulf). So how well did it do? Wrong body of water, no U.S. landfall, and about 1300 miles from where it was forecast to end up.

GFS forecast flop
Below is an animated GIF which shows the forecast progression for 12z August 28, 2014. The initial frame shows what kicked things off last week. Projected landfall: southeast New Orleans.

The consecutive images show all 00z and 12z
model runs since then, all forecasts for the same time on August 28, 2014. The first three runs kept the system in the Gulf on the 28th, but even here we see fluctuations of several hundred miles run to run. The following several days the GFS was ushering the system far out into the Atlantic by the 28th, before again trending back west toward Florida. If nothing else, this should help demonstrate the type of confidence any single model run should be given so many days out.

Finally we see some consistency from one run to the next when a center is found by hurricane hunters on August 23. The track at this point shifts back east a little, away from Florida and the eastern United States. Fish storm.

GFS forecast GIF Cristobal

Stormy Start to Week for Eastern Colorado

Posted by @weather5280

The Storm Prediction Center has added a Slight Risk for severe weather this afternoon across northeast Colorado as strong storms are expected to develop this afternoon after we had a rather quiet day Sunday.

Today’s storm risks includes the threat for tornadoes, as well as large hail and damaging wind. The SPC puts Denver in their 2% tornado probabilities with any storms that do develop today.

Current conditions page

The best potential for strong storms should occur just east/southeast of Denver proper, though cannot rule out a strong storm developing over the city. Best ingredients for severe weather will be from just south of I-70 extending east, north to I-76. Hi-Res models continue to try and develop strong storms near Agate and Limon, CO this afternoon. Along the Palmer Divide and north/northeast will have the best chance of seeing severe weather. HRRR shows storms initiating by mid afternoon near Denver, then pushing northeast into the evening.  Flash flooding doesn’t appear to be a huge concern with fairly rapid storm motions. The caveat will be any areas that see training or repeated rounds of heavy cells.

HRRRsource: WeatherBell

We expect a few areas to get good rainfall with storms that develop today. As is typically the case, best precipitation numbers will vary greatly from one location to the next due to the scattered natured of storms, but anywhere from a few tenths of an inch to >1.5” will be possible.

We keep a good chance of storms in the forecast through Wednesday in Denver across much of the plains, with temperatures below normal. We’ll have updates here as needed to get through the next several days.

USA Pro Challenge Weather Forecast

Posted by @brendansweather

Sunday the USA Pro Cycling Challenge wraps up in Colorado with Stage 7 taking cyclists from Boulder to Denver along a 78 mile (126 kilometer) course. The weather appears as though it will mostly cooperate for the final day of this seven day event.

Storms will be a bit more numerous today across the northern Front Range a
nd eastern plains however. Storms should develop along the higher terrain to the west by early afternoon, before pushing across the plains by mid to late afternoon. Coverage and intensity will not be as great as what we say Friday, but a few storms could become strong -- with strong wind being the greatest threat.

Most HiRes models have the greatest chance for storms along and north of I-70 across eastern Colorado which seems plausible. Precipitable water values and CAPE will be greatest across northeast Colorado, with drier and more stable air south of I-70. Storm chances in Denver, as one might expect, will very hit and miss. Best chances could develop just outside the city as they did yesterday, but certainly cannot rule out a cell pushing through this afternoon. HRRR produces rainfall totals from a few tenths to nearly an inch across north central and northeast Colorado through tonight.

Saturday PWAT and PRECIP outlook Coloradosource: WeatherBell Analytics

Drier Sunday for Pro Challenge
Storm chances decrease across the plains Sunday, but there will still be a chance for a few isolated storms to develop with a good amount of moisture still around. Best storm chances for Sunday should stay west of Denver and Boulder, providing a beautiful late August day for the race.

As for temperatures… We’re expecting most locations across the Denver area and northeast Colorado to the 70s Sunday. MOS guidance for highs range from 80 to 85, but these temperatures have been overdone in recent days. I like the NAM idea for 18z Sunday, with mostly 70s along the I-25 urban corridor, and warmer temperatures across southeast Colorado.

Colorado temperature forecast map
source: WeatherBell Analytics

Cold shot for the west
We’ll continue to see chances for storms off and on over the next week, as well as below normal to well below normal temperatures across much of the west. A strong upper level trough will bring unseasonably cool temperatures well into next week for the west, and much of Colorado. You can see that strong trough digging in at the upper levels here:

With that, temperatures will be much cooler than normal, bringing a taste of fall for many from Utah and Colorado north to Montana and the Dakotas. Here is the CFSv2 temperature anomalies for the next five days across the United States.

All that cold air this time of year means... snow! Take a look at what the ECMWF is showing over the next week. Tonight we may see a few locations above 11,000 feet pick up some snow in Colorado, then again this week as things remain unsettled. Take a look at northwest Wyoming through Friday… with a few spots of blue showing in Colorado.

ECMWF snow forecast map Colorado