Denver, Colorado

Weekend Outlook & Mid-Summer-Autumn Recap

Posted by @brendansweather

Wednesday was one of those days in Colorado that nearly all conversations started with “it feels like Seattle, not Denver out there”. Topping out at 62 degrees F, Denver International Airport (DIA) set a new record-low high temperature, beating the previous record of 64 degrees F from 2009. That’s a whopping 28 degrees below average for the date, and a far cry from Seattle’s actual highs Wednesday in the upper 80s. We were also the coolest major city in the entire country.

The soggiest days of the week are now behind us, but storms remain in the forecast off and on through the next week. A few showers this morning should taper off, with about a 20% chance for storms this afternoon. Temperatures will remain below normal through the period, though will warm back into the 70s and eventually possibly the 80s by the weekend.

Platte River, Denver
South Platte running very high through Denver Wednesday

Rainfall totals
Rainfall totals, as expected, were pretty remarkable between Tuesday afternoon and Wednesday evening. DIA officially recorded 2.90 inches of rain over the two day period, with 2.96 inches recorded at
our weather station one mile south of the capitol in Denver. Coors Field received 2.86” of rain during the period. And, on July 29 (Tuesday) DIA set a new daily rainfall record when 1.80 of rain fell during the 24 hour period, beating the old record for the date of 1.44 inches set in 1989.

On average, Denver sees
2.16 inches of rain in July. As of this morning 3.85 inches of rain have been recorded at DIA this month, or 1.69 inches above average.

Here are a few other totals from across the state via the CoCoRaHS reporting network.

  • Eads, CO: 6.31”

  • Greeley, CO (3.9m WNW): 4.17”

  • Lamar, CO (10.1m N): 3.92”

  • Wellington, CO (7.5m NW): 3.88”

  • Lakewood, CO (1.7m SW): 3.35”

  • Windsor, CO (1m SSE): 3.54”

  • Golden, CO (2.0m NNW): 3.21”


This map shows the two day NWS precipitation analysis (via WeatherBell) for Colorado. Very impressive totals across eastern Colorado, especially the northern and northeast portions of the state, and again over southeast Colorado. Totals in and around Denver largely ranged from 1 to 3.5 inches (as forecast!).
 

rainfall totals NWS analysis colorado July 30, 2014
Our chance for storms in the Denver area drops quite a bit for today, but can’t rule a storm or two. Afternoon highs will be much warmer than Wednesday, but still 10 to 12 degrees below normal with temperatures expected to top out in the upper 70s this afternoon.

Storm chances will be lower yet this weekend, and temperatures will be warmer. With water-logged soil, it could take a few days to hit the 80s again. We’ll keep an eye on things as we head into next week, as overall our pattern stays pretty active with afternoon storms in the forecast almost each and every day.
 

Map: Colorado Rainfall Totals July 30, 2014

Posted by @brendansweather

Below is a map rainfall totals as of this morning from the CoCoRaHS network. These are two day totals (yesterday and today) and will be updated as more data becomes available. The greatest rainfall total so far comes from 0.5 miles east of Eads, Colorado, where 6.21 inches of rain has been recorded since yesterday afternoon. Most locations within the Denver area are reporting anywhere from 0.5 to 2.5 inches of rain so far, including 1.50" at our weather station in central Denver

Rainfall will continue off and on through the day today, heavy at times. The flash flood threat remains significant for those areas that do see heavier showers, as the ground is now very saturatated. You can find our discussion from yesterday here.

Related: U.S. Flooding Public Information Map (Esri)

We may challenge our all time coldest high temperature today, with forecast highs staying below 70 degrees for most locations in the greater Denver area. By this afternoon we could easily be running 20 to 25 degrees below normal for the date. A taste of fall!

Select marker to see station report and information.

Tuesday PM Update: Heavy Rain, Flooding Concerns Through Wednesday

Posted by @brendansweather

Radar loop Colorado

Radar Loop 2pm to 3pm

Heavy rain reached northeast Colorado early this afternoon, and has really grown in intensity over the last hour. It is expected to continue off and on through Wednesday. A Flash Flood Watch is in effect for nearly all of Colorado through Wednesday PM, including the city and county of Denver.

The overall synopsis has not changed since
our post yesterday. Heavy rain with slow moving storms will mean an increased threat for flooding over the next 24 to 36 hours. Rainfall totals for northeast and northcentral Colorado are expected to be anywhere from 0.5 to 3 inches by Wednesday night, with locally heavier amounts possible.

We have already seen several Flash Flood Warnings posted north and northwest of Fort Collins, and expect more to come over the next day or so. Please be weather aware, and heed any warnings that are issued for your area.

Complex setup for pinpoint rainfall totals
It’s proving very difficult to pinpoint exactly how much rain any single location will receive. Models have been fluctuating greatly run-to-run both with regard to timing and locations of heaviest precipitation. What is certain is that the ingredients are in place for a widespread heavy rainfall event, but expect great variation in totals when it’s all said and done.


The 12z model suite has largely continued to insist much of the heaviest precipitation from this event may occur Wednesday, especially for southern Colorado. If you happen to see less rainfall this afternoon and into this evening, you’re not out of the woods yet as the rainfall threat continues tomorrow. Here are the 12z GFS precipitation totals through Thursday morning for Colorado, the EURO looks similar.

GFS precip totals
The NAM continues to “dry-slot” much of Denver proper and the southwest suburbs, shunting the bulk of the precipitation north and east of Denver. We’ll see how it handles things, as both the GFS and EURO are a bit more impressive in the city, as well as the higher terrain to the west. As we typically do, we’ll be weighing the NAM a bit lower, especially its 18z run. (We’ve already seen more than it’s 18z run in central Denver with cell currently overhead!).


Really any way you cut it, someone’s getting a lot of rain over the next 24 to 36 hours. We’ll watch carefully and update as needed. Warnings will be posted on our Twitter feed as well.

Monday Update: Addressing Flood Potential Across Colorado

Posted by @brendansweather

The cooler air we’ve been promising for some time now has arrived, and will continue to bring temperatures well below seasonal norms through the end of the week. Wednesday looks to be the coolest day of the week with highs in the low to mid 70s for Denver, and likely a few locations in the 60s across the Plains. (Some spots could see near record-cool highs for the date.)

The focus over the coming days will not be the temperatures, however, as the threat for flooding rain will be our primary concern through midweek and beyond. Models have fluctuated in where the heaviest rainfall totals will occur through Wednesday, but there will be a few regions we will be watching very closely, and most of the state should at least see some rain.

General setup
The setup for the coming days is not atypical for this time of year in that we’ll have ample moisture to work with through the middle of this week, and quite possibly continuing off and on well into next week. Take a look at this water vapor animation of the last 24 hours across the United States. Notice the stream of “moist” air flowing into the southwest and into Colorado. Late in the frame you can see dark colors over southeast Colorado, these were the storms that brought flooding to this part of the state last night.

Water vapor loop United States

We’re expecting the water vapor loop to look very similar over the coming days. You’ll also notice the large trough digging into the upper midwest. This is responsible for the cooler-than-average temperatures being ushered into the middle of the country.

The combination of this moisture stream and a stalled front over the coming days will mean a heightened flood threat for the region. The greatest threat for heavy rain across Denver, northeast Colorado and the higher terrain west of I-25 appears to be Tuesday afternoon through Wednesday when PW values are highest. That said, ingredients are in place again today (similar to yesterday) to support some strong, slow-moving storms this afternoon -- so that’ll need to be closely watched. The greatest threat for storms today will be west of I-25 and through the Colorado high country.

Flash Flood Watch
At this time there are no flash flood watches issues for northeast Colorado and the northern Front Range. This could very well change in the coming hours, as again, Tuesday and Wednesday look potentially very wet.

A flash flood watch is in effect for most of southern Colorado, however, and will likely remain so through much of the next several days. The current watch goes through midnight tonight, and includes all of the southern I-25 corridor, including the high flood risk burn scar areas like Waldo Canyon.

Flash Flood Watch Map | Mesomap

There’s been a lot of buzz over recent days with how this setup compares to last year’s September floods. While we’re watching the flood threat very closely, it seems irresponsible to make that connection at this point. Remember, this is the time of year where it’s typical to get flooding and flash flooding in Colorado, and the atmospheric setup is not exactly the same.

Unlike during the early summer weeks, storms in late July and August are moving much slower -- which increases the flood threat. Rather than focusing on how this does and does not compare to late last summer, let’s use that as a reminder of the threat flash flooding does pose to our region, especially at higher terrain west of I-25 and over burn scar areas. Please heed all watches and warnings over the coming days.

The NAM/EURO/GFS differ on who gets the heaviest rain over the coming days, but all broad-brush most of the eastern mountains, I-25 urban corridor, and into the eastern plains with 0.5 to 3 inches of rain, with locally higher amounts. Where storms stall, or train, we could see certainly see higher totals. Today’s 12z suite of both the GFS and NAM appear to try and pull the heaviest precipitation further north than previous runs. We’ll see.


12z GFS total precipitation through Wednesday

GFS precip forecast

12z NAM total precipitation through Wednesday

NAM

SREF means (KDEN)

SREF precip means

 

We’ll keep on top of everything and offer updates as needed. Again, greatest storm chances today will likely be over higher terrain to the west, but could see a few storms push east through the afternoon and evening hours. A greater threat for heavy rainfall begins Tuesday afternoon, and will likely continue well into Wednesday, if not through the day Wednesday.

To stay ahead of the storm, subscribe to Weather5280. Also find us on Twitter (@weather5280) where we’ll have our most frequent updates over the coming days.