SPM 09-25-2017: Continuing Rain for Southeast Plains and Northern Mountains

Issue Date: Monday, September 25, 2017
Issue Time: 10:30AM MDT

Summary:

The upper level low continued to sit just to our west yesterday over northern Utah and lifted to the northeast throughout the day and overnight. Most areas west of the Continental Divide were under the influence of the dry slot, so only light rainfall accumulated over the higher terrains. Further north, there was enough residual moisture to allow for another round of rain and snow in the late afternoon and evening. Counterclockwise rotation around the upper low focused the highest accumulations on the south and southwest facing slopes. Higher moisture remained east of the Continental Divide, though SW surface winds helped dry out the atmosphere a bit from the previous day. Showers were more isolated in nature except over the far Southeast Plains where multiple rounds of showers were aided by ample moisture. Multiple rounds of rain added to the already high accumulations from the previous two days.

Over the Northern Mountains and Northern Front Range, freezing levels had dropped quite a bit, so the higher elevations saw more snow that rain. A few SNOTEL stations reported totals up to 0.6 inches in the central, northern high terrains. Along the northern Front Range, totals were a bit higher. West of Fort Collins in the foothills, just under 1 inch of rain fell with totals in and around 0.5 inches for the cities of Fort Collins and Loveland.

The Pueblo radar was back up and working Sunday morning, so estimates yesterday were much more accurate than Saturday. Over the southeast corner of the state, a few rounds of precipitation yesterday and last night added up making some impressive 48-hour totals. Over the last 48-hour period, radar estimates over the eastern plains have been around 5 inches (close to a 1 in 25 year event). An Areal Flood Advisory was issued late last night for Prowers and Baca Counties as a line of thunderstorms moved over an area that had already seen 1.5 inches of rain earlier in the day. Yesterday alone, portions of Baca and Prowers Counties recorded 3-3.5 inches of rain. Fortunately, no flooding has been reported, which includes riverine flooding in and around the Arkansas River. Most stations (as seen below) are showing two distinct peaks from the rainfall on Saturday and Sunday. High running rivers, creeks and arroyos will start to recover as the system begins moving further east and the Southeast Plains dry out.

To find out how much precipitation has fallen around your area the last 24 to 72 hours, scroll down to 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 accumulation ending time is 6AM of the date shown in the bottom right corner. Also shown optionally are fire burn areas since 2012. The home button in the top left corner resets the map to the original zoom.

Note: We have identified a possible underestimation in QPE over the southwest part of the state. We are working to on this issue, and will provide an update as soon as possible.

FTB 09-25-2017: Below Average Temperatures Statewide with Rain East of the Continental Divide

Issue Date: Monday, September 25, 2017
Issue Time: 10:15 AM MDT

— Flooding is NOT expected today

Much cooler temperatures this morning with high temperatures expected to be 15-20F below normal. Overnight, some of the lower elevations over the Western Slope and San Luis Valley dipped below freezing. Still a lot of cloud cover over the eastern portion of the state, but the water vapor (wv) image below shows a decrease in the low level moisture statewide. This should give us a break from the heavy rainfall, although some rain is still expected east of the Continental Divide. Precipitable Water (PW) values at Denver and Grand Junction are 0.55 and 0.34 inches, respectively. Both have decreased a bit as the southwest flow aloft continues to advect drier air into the state. Today this southwest flow will get a bit more of a westerly component as the trough continues to move towards the northeast. Currently, the upper level low is located over Wyoming, and it is expected to pull north and reside over Montana/North Dakota by tomorrow morning.

The higher PW will also be east of Colorado today with the slow, eastward progression of the front. Another shortwave with upper level support from the jet stream is expected to move over the state. This will enhance vertical motion and help trigger showers over the eastern portion of the state. Northerly surface flow will get an easterly component this afternoon. Weak upslope flow and the associated showers are expected to be most numerous over the Front Range with more isolated showers over the Southeast Mountains. Some thunderstorms are also expected over the Northeast Plains this afternoon with the increased vertical motion. Due to decreased moisture over the western portion of the state, rainfall is only expected to be isolated and confined to the north where not as much drying has occurred. Again, expect higher elevations to see precipitation fall in the form of snow instead of rain. Tonight, showers are expected to end over the higher terrains around 11PM as subsidence behind the shortwave suppresses overnight shower and snow activity. There is no flooding expected today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Palmer Ridge, Southeast Mountains, Raton Ridge, Front Range, Urban Corridor, Northeast Plains, Southeast Plains:

Cloudy this morning with increasing showers and thunderstorms this afternoon. Heaviest accumulations in the mountains are expected to be over the Front Range. 24-hour precipitation totals up to 1 inch are possible with snow at the higher elevations. Showers and thunderstorms are also expected over the Northeast Plains this afternoon. 24-hour rain totals up to 0.8 inches are possible. Flooding is not expected today.

Primetime: 10AM to 11PM

Northwest Slope, Grand Valley, Southwest Slope, Northern Mountains, Central Mountains, San Luis Valley, San Juan Mountains:

Mostly sunny and cool with some clouds over the Northwest Slope. Dry air will limit shower activity to the north. Snow will likely fall at the higher elevations, but accumulations of both rain and snow are expected to be limited. 24-hour accumulations up to 0.25 inches are possible. Flooding is not expected today.

Primetime: 12PM to 8PM

SPM 09-24-2017: Widespread Heavy Rain and Some Snow for the Higher Elevations

Issue Date: Sunday, September 24, 2017
Issue Time: 10:35AM MDT

Summary:

Widespread showers and thunderstorms formed across the state yesterday as the trough began to slide in from the west. South and southwesterly winds aided in the return of moisture to the state, especially over the eastern plains and southern high country. This allowed for some very impressive rain rates in the early afternoon. Yesterday morning, showers and thunderstorms were already active over the eastern plains and the western portion of the state at the lower elevations. As the system began pulling to the northeast, showers and snow quickly filled in over the mountains. Over the eastern plains, showers and thunderstorms were focused along and behind the slow, eastward propagating cold front. The more convective rain quicwas just east of the Colorado border. By late evening showers over the western portion of the state ceased as drier air worked its way in from the west. Showers over the mountains ended by midnight, and rain continued through this morning over the far eastern plains along the Kansas border.

Over the western portion of the state, CoCoRaHS stations over the higher terrains recorded up to 0.6 inches of precipitation. A SNOTEL station in Grand Mesa National Forest recorded 1.8 inches. Due to the high elevation (above 10,000 feet), most of this precipitation fell as snow. There was a report of 6.3 inches of snow out of Delta County near the SNOTEL gage. Over the Southeast Mountains and southern Front Range, there were two areal flood advisories. The first was for a storm over Colorado Springs that was produced 0.5 inches of rain in 30 minutes. For the 24-hour period, a USGS gage recorded 2.04 inches at Cottonwood Creek and Woodmen Road. The Fountain Creek gage (seen below) reached action level, but it was able to avoid minor flooding. The second areal flood advisory was for the Junkins burn scar where moderate rain was reported falling. Fortunately, there was no flooding reported and creeks are expected to recover today.

Over the eastern plains, quite a bit of rain fell throughout the day and overnight. A USGS gage in Delhi, CO recorded 2.29 inches. Just over the border in Oklahoma, a USGS gage near Kenton, OK recorded 3.6 inches of rain. Radar rainfall estimates are as high as 3 inches with 1-hour rain rates of 2 inches. There was no flooding reported along the Arkansas River, but some of the smaller creeks and arroyos are running in the 90th percentile due to the widespread rainfall. These will be monitored closely as another round of heavy rainfall is likely today over the Southeast Plains and eastern Raton Ridge.

To see how much rain fell in your area, take a peek at 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 accumulation ending time is 6AM of the date shown in the bottom right corner. Also shown optionally are fire burn areas since 2012. The home button in the top left corner resets the map to the original zoom.

Note: We have identified a possible underestimation in QPE over the southwest part of the state. We are working to on this issue, and will provide an update as soon as possible.

FTB 09-24-2017: Cooler Temperatures and Continuing Rain as Upper Level Low Slowly Propagates East

Issue Date: Saturday, September 24, 2017
Issue Time: 10:20 AM MDT

LOW flood threat for the Southeast Plains, Raton Ridge, Northeast Plains

— Timing of flood threat is later than normal, and persists into the overnight hours

Heavy and widespread rainfall yesterday across the state. Much cooler temperatures in the wake of the cold front with 40s over the lower elevations and below freezing temperatures in the mountains. Heavy cloud cover over the eastern portion of the state with some convective showers still occurring over the Southeast Plains. A lot of fog was reported due to the increase in low level moisture and cooler temperatures. Currently, the western portion of the state is placed in the dry slot, so only a few clouds over the Northern Mountains. The upper trough will continue to move slowly eastward today and tonight. Colorado will continue to be under southwest flow aloft, which will draw in some drier air over western Colorado and inhibit rainfall. East of the Continental Divide, higher moisture will continue to reside, especially over the southeast corner of the state. Dew points over the plains are expected to reach 60F, so more heavy rain can be expected today and tonight.

Weaker showers are expected today over the higher terrains with snow at the higher elevations (9,500 feet). Upslope flow will continue behind the cold front with multiple upper level shortwaves enhancing lift. Expected scattered showers today and tonight. The highest accumulations are expected be in the Northern Mountains and northern Front Range. Over the southeast corner of the state, models hint at instability this afternoon with some decent shear. This could trigger a round of more convective storms capable of strong winds and small hail. Lift is expected to continue overnight, so expecting another round of showers in the moisture rich environment. High moisture paired with instability will aid in another 24-hour period of heavy rainfall accumulations. On top of accumulations yesterday, and increased runoff due to saturated soils, a Low flood threat has been issued. Threats include small stream and arroyo flooding, road flooding and field ponding.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, scroll below the map.

Flood Threat Legend

Zone-Specific Forecasts:

Palmer Ridge, Southeast Mountains, Raton Ridge, Front Range, Urban Corridor, Northeast Plains, Southeast Plains:

Cloudy this morning with increasing showers and thunderstorms over the northern, high terrains this afternoon. Some showers will move off the higher terrains into the Urban Corridor. Max 1-hr rain rates up to 0.5 inches possible. More convective rain is expected this afternoon over the Southeast Plains. Max 1-hour rain rates up to 1.5 inches are possible with isolated 24-hour rain totals up to 2.5 inches. Due to increased runoff from already saturated soils and high accumulations from yesterday, a Low flood threat has been issued. Threats include small stream and arroyo flooding, road flooding and field ponding. This is another overnight threat.

Primetime: 11AM to 7AM

Northwest Slope, Grand Valley, Southwest Slope, Northern Mountains, Central Mountains, San Luis Valley, San Juan Mountains:

Partly cloudy over the northern high country with sunshine increasing as drier air works its way in from the southwest. Some light precipitation and cloud cover is likely over the Northwest Slope as increased moisture rotates around the upper level Low. Max 1-hour rain rates up to 0.3 inches are possible over the northwest corner of the state.

Primetime: 11AM to 8PM