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.
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.
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.
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.
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.
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.
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
12z NAM total precipitation through Wednesday
SREF means (KDEN)
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.
Another cool/wet week ahead
Highs Saturday will climb into the low 90s again for most across the metro area, but should be the last time we hit the 90 degree mark for several days. Sunday's highs will be several degrees cooler, with even cooler temperatures expected by the middle of the week. We'll see another round of storms this afternoon across the Front Range and eastern Colorado, with an even better chance for storms as we head into the coming week.
Easing the drought
The first half of 2014 was slightly cooler than average for eastern Colorado, including Denver. However, the western half of the state balanced that out by being slightly warmer than average.
Precipitation was the same balanced story. Despite a lot of snow, actual moisture accumulation was slightly wetter than average for the north, meanwhile drier than average across southern Colorado.
The drought monitor is following suit:
The current drought is a vast improvement to that of last year for the same time. Remember the drought monitor takes into account not only recent precipitation, it includes surface water, longer term precipitation accumulation, temperature trends, etc. Here’s a look at where we were on July 23, 2013.
The big improvement to the drought situation in Colorado has been our consistent moisture supply this summer. As you probably have noticed, this summer has been stormier and cooler than the past few years. The stormy pattern usually takes a few weeks off in late June through late July when the monsoon kicks in. This year’s monsoon kicked in early and has been the source to all of our daily storms.
The storminess has helped keep temperatures closer to average. Remember, drought feeds heatwaves. When Colorado’s water supply is low the ground is dry and that can heat the surface air more effectively. With so much moisture in the ground this year the air temperatures have been on “par”. We’ve also noted a more northwesterly flow the past several months to keep the flow of cold fronts near the region. We had a colder push of air a couple weeks ago (remember the 70s on the 16th and 17th?) that will be a very similar pattern to what is taking shape this weekend.
The “moisture train” to continue
During the weekend the persistent ridge that brought us the 90s will be breaking down slightly with a large area of energy diving south out of Canada toward the eastern US. This will drop colder temperatures in from the north starting Sunday. Rain chances continue as monsoonal humidity collides with that colder air over the state. In fact, the upcoming week will bring valuable, additional rainfall. One model, the GFS, is bringing the country’s greatest moisture totals into our region, and especially those areas that need it most -- southern Colorado into New Mexico. Unfortunately more of the moisture won’t hit the western US for the sake of California’s drought and the Pacific Northwest wildfires over the coming week.
This moisture coincides with the forecast given here on Weather5280 with Brian’s last post on the monsoon. The climate projections indicated a wetter end to July and start to August. This is that projection verifying.
Further, the below average temperatures also forecast are on the way. The end of July and start of August will be much cooler than average. For Denver, 70s and 80s for the week versus low 90s.
As the cooler air arrives and rain chances climb we will dissect the week with a variety of posts on the system as it progresses. Subscribe to Weather5280 for email updates, and be sure to follow us on Twitter as well (@weather5280)!