SPM 08-22-2019: Flooding Over the Eastern Colorado with Post Frontal Moisture Return

Issue Date: Thursday, August 22nd, 2019
Issue Time: 10:15AM MDT

Summary:

Quite a bit of moisture in the atmosphere after the passage of a cold front early Wednesday morning. Post frontal upslope flow in this moisture rich environment, with slow steering winds, set the stage for pockets of heavy rainfall. Strongest storms popped up where there was the best break in cloud cover. Rainfall began first to the south over the eastern mountains, then to the north where it took a little longer to erode the cap. Several flood advisories were issued beginning at 1PM and ending at 10:15PM with one Flash Flood Warning issued for Denver at 6:40PM. Storms yesterday were nearly stationary with outflow boundaries and back building storms helping set off more storms over the same area. There were also two flood advisories issued for the Spring Creek and Junkins burn areas, but flooding was not reported. MetStorm indicates just over 0.5 inches and 0.25 inches fell, respectively, which are below known flash flooding rate criteria. A Severe Thunderstorm Warning was issued for the Front Range, Urban Corridor, Palmer Ridge and portions of the Northeast Plains at 4PM, so plenty of warning before the storms struck.

Denver had a whopper of a storm just after rush hour that lasted over an hour, caused intermittent power outages and flooding of low-lying intersections. Quite a bit of lightning with it, too along with 1 inch hail. The highest ALERT gage (I-25 and 6th Ave) indicated up to 1.9 inches of rainfall though this gage may have been slightly contaminated by hail as totals nearby were not this high. The highest area of rainfall looked to be near Wings Over the Rockies where gages had between 1.1 and 1.5 inches of rainfall over a fairly large area. The Cherry Creek gage briefly reach Action Stage (below). To take a look for yourself, click here and change options (top left) to 24-hour rainfall: http://alert5.udfcd.org/LDAD/gmapV3.html

Further south, over Fremont County, there was also some heavy rain where MetStorm indicates up to 1.25 inches fell. The cap never did break over the Southeast Plains, so the anticipated heavy rainfall threat never materialized over this region. Although there were totals up to 1.25 inches over Las Animas County, which was in the Low threat area. Storms also moved in over Yuma County from the panhandle, which dropped between 2 and 2.5 inches in its core. There were no official LSRs (Local Storm Reports) this morning, although flooding was confirmed by several Twitter users.


To see estimated precipitation totals over your neighborhood on Wednesday, scroll down the State Precipitation Map below.

Click Here For Map Overview

The map below shows radar-estimated, rainfall gage-adjusted Quantitative Precipitation Estimates (QPE) across Colorado. The map is updated daily during the operational season (May 1 – Sep 30) by 11AM. The following six layers are currently available: 24-hour, 48-hour and 72-hour total precipitation, as well as maximum 1-hour, 2-hour and 6-hour precipitation over the past 24 hour period (to estimate where flash flooding may have occurred). The 24-hour, 48-hour and 72-hour total precipitation contain bias corrections that are not disaggregated into the hourly estimates, so there will likely be some differences. The accumulation ending time is 7AM of the date shown in the bottom right corner. Also shown optionally are vulnerable fire burn areas (post 2012), which are updated throughout the season to include new, vulnerable burn areas. The home button in the top left corner resets the map to the original zoom.

SPM 08-21-2019: Isolated, Heavy Rain and Hail over the Northeast Plains

Issue Date: Wednesday, August 21st, 2019
Issue Time: 10:57AM MDT

Summary:

It was a very active day yesterday over the Northeast Plains with multiple reports of hail and some isolated areas of heavy rain. Strong upslope flow of moist air from Nebraska and Kansas combined with a passing shortwave around the time of peak heating to create multiple supercells over the Northeast Plains, northern Urban Corridor and eastern Palmer Ridge. Post frontal upslope flow then generated some weak thunderstorms throughout Urban Corridor, which gained strength as they moved east. Hail ranged in size from north to south across Weld County and down into Adams County from 1.75 inches to 1 inch. Heavy rainfall also increased to the east, though it was rather isolated in nature. Nearly stationary storms helped produce the high totals. Radar derived rainfall rates just below 2.5 inches in 1 hour over central Adams County and up to 2.08 inches in northern Weld County. Due to the isolated nature of the rain, surface stations did not pick up as much rain due to sparseness in location. However, a COOP station in northeast Weld County reported 1.18 inches of rain in an hour long period. Flooding was not reported as of this morning, although there was a Flash Flood Warning for central Adams County at 7:10PM last night.

Rainfall  across the foothills and Urban Corridor last night was light, with CoCoRaHS reports below 0.1 inches. There were some gusty outflow winds, which kicked up a lot of dust during the early evening hours across the metro area. A cold front also passed over the area early last night, which rapidly increased cloud cover over and produced multiple some additional areas of lighter rainfall over the far northeast corner. The cap wasn’t fully broken near the CO/NE border, so totals weren’t as high as forecast over this area.

There were a few light showers over eastern San Juan Mountains and the Northern Mountains yesterday afternoon, but surface reports indicated only trace amounts of rainfall. There were likely some gusty winds as well. Insufficient moisture prevented storm generation over the area. High temperatures reached up to 107 degrees over the Grand Valley with temperatures in the upper 80°Fs and 90°Fs throughout the high country. There were also very hot temperatures this last week over the Southeast Plains, which is uncommon for this time of year. Hopefully, we’ll get that taste of fall next week.

For a look at precipitation over your area, please visit the State Precipitation Map below.

Click Here For Map Overview

The map below shows radar-estimated, rainfall gage-adjusted Quantitative Precipitation Estimates (QPE) across Colorado. The map is updated daily during the operational season (May 1 – Sep 30) by 11AM. The following six layers are currently available: 24-hour, 48-hour and 72-hour total precipitation, as well as maximum 1-hour, 2-hour and 6-hour precipitation over the past 24 hour period (to estimate where flash flooding may have occurred). The 24-hour, 48-hour and 72-hour total precipitation contain bias corrections that are not disaggregated into the hourly estimates, so there will likely be some differences. The accumulation ending time is 7AM of the date shown in the bottom right corner. Also shown optionally are vulnerable fire burn areas (post 2012), which are updated throughout the season to include new, vulnerable burn areas. The home button in the top left corner resets the map to the original zoom.

SPM 08-20-2019: Hot Weather with a Few Severe Thunderstorms over the Eastern Plains

Issue Date: Tuesday, August 20, 2019
Issue Time: 10:50AM MDT

Summary:

Yesterday was mostly hot and dry with multiple high temperature records broken over the eastern plains. Denver International Airport broke a high temperature record of 97°F set back in 1986 with a high of 99°F yesterday. Airports in Boulder, Limon, Centennial and CSU in Fort Collins also broke their high temperature records. As far as rainfall goes, almost all of the state remained dry except for Yuma, Prowers and Baca Counties. Isolated severe thunderstorms began yesterday around the time of peak heating along the dryline. The strongest storm of the day was over Yuma County (near Vernon) where there were three reports of hail ranging in size from pennies to golf balls. Radar derived up to 1.97 inches of rain in 1 hour within the storm over Yuma County, however this total may be inflated due to hail contamination.  Flooding was not reported as of this morning.  Surface reports are sparse over these areas, however a COOP station near Holly in Prowers County reported 0.8 inches of rain over a 45 minute period around 4PM yesterday. There were no reports of rain elsewhere and relative humidity dropped into the teens and single digits throughout western Colorado once again. The area with higher surface winds (15-20 mph) and low relativity humidity wasn’t large enough or persistent enough for a Red Flag Warning to be issued.

For a look at precipitation over your area, please visit the State Precipitation Map below.

Click Here For Map Overview

The map below shows radar-estimated, rainfall gage-adjusted Quantitative Precipitation Estimates (QPE) across Colorado. The map is updated daily during the operational season (May 1 – Sep 30) by 11AM. The following six layers are currently available: 24-hour, 48-hour and 72-hour total precipitation, as well as maximum 1-hour, 2-hour and 6-hour precipitation over the past 24 hour period (to estimate where flash flooding may have occurred). The 24-hour, 48-hour and 72-hour total precipitation contain bias corrections that are not disaggregated into the hourly estimates, so there will likely be some differences. The accumulation ending time is 7AM of the date shown in the bottom right corner. Also shown optionally are vulnerable fire burn areas (post 2012), which are updated throughout the season to include new, vulnerable burn areas. The home button in the top left corner resets the map to the original zoom.

SPM 08-19-2019: Dry Weather and Seasonal Temperatures

Issue Date: Monday, August 19th, 2019
Issue Time: 10:20AM MDT

Summary:

It was bone dry statewide yesterday with a large dry air mass in place overhead. There was some morning cloud cover over the northwest quadrant of the state and dense fog reported over the Northeast Plains. The cloud cover helped keep temperatures a little cooler than to the south. High temperatures over the Southeast Plains crept up to 99°F yesterday, and relative humidity dropped into the teens and twenties. To the west of the Continental Divide relative humidity dropped into the single digits throughout the Red Flag Warning area with the high gusts measuring between 20 and 27 mph. Luckily, there were no new fires were reported over this area yesterday (as of this morning). As far as precipitation goes there was little to no measured precipitation throughout the state. Radar derived a small area up to 0.3 inches of rain in northern Lincoln County; however, no surface stations can confirm this rainfall. There was radar reflectivity over the area, but chances of measurable rainfall are low.

For a look at precipitation over your area, please visit the State Precipitation Map below.

Click Here For Map Overview

The map below shows radar-estimated, rainfall gage-adjusted Quantitative Precipitation Estimates (QPE) across Colorado. The map is updated daily during the operational season (May 1 – Sep 30) by 11AM. The following six layers are currently available: 24-hour, 48-hour and 72-hour total precipitation, as well as maximum 1-hour, 2-hour and 6-hour precipitation over the past 24 hour period (to estimate where flash flooding may have occurred). The 24-hour, 48-hour and 72-hour total precipitation contain bias corrections that are not disaggregated into the hourly estimates, so there will likely be some differences. The accumulation ending time is 7AM of the date shown in the bottom right corner. Also shown optionally are vulnerable fire burn areas (post 2012), which are updated throughout the season to include new, vulnerable burn areas. The home button in the top left corner resets the map to the original zoom.