Issue Date: Friday, August 11, 2017
Issue Time: 10:20AM MDT

— LOW flood threat for portions of the Front Range, Urban Corridor, Palmer Ridge, Southeast Mountains, Raton Ridge

Cooler temperatures have arrived with the passage of the cold front yesterday. On visible satellite, there’s another round of dense fog along the northern Urban Corridor. This should begin to burn off with sunrise and partly cloudy skies are expected by late morning. Cloud cover and some light showers are present this morning in the southern portion of the state. This is being supported by a mid-level disturbance and should continue to move NE/E throughout the day. Unlike yesterday, there is no large-scale dynamic forcing for storms today and with these cooler temperatures and cloud cover, the far eastern plains should catch a break from the heavy PM rainfall. Precipitable Water (PW) values at Denver this morning were 0.85 inches and 0.74 inches at Grand Junction. These should increase throughout the day over the eastern portion of the state with the southerly and southeasterly flow. The flow around the high pressure, will continue to pull moisture in from AZ and NM over the SW corner of the state. Moisture will increase as dew points over AZ and NM are in the mid-50s and heating will help intensify the rainfall throughout the morning.

The wave associated with the storms over SW Colorado should begin to move to the E/NE throughout the day. Its arrival over the Southeast Mountains should enhance the daily upslope flow pattern and create widespread showers. As the storms move off the southern mountains, they will favor the higher terrains of the Raton and Palmer Ridges. Storms may produce gusty winds, small hail and heavy local rainfall. Threats over the mountains include mud flows and debris slides. Storms over urban areas may cause street and small stream flooding. Storm motion will be a bit slower than yesterday with E/SE movement, which will add to local totals. This storm motion may allow a storm to move through the Northeast Plains from the Cheyenne Ridge, but it should be late enough instability will be limited. Showers should decrease in intensity as the sun sets, but lighter showers will likely linger over the southern plains and mountains through the morning.

The Arkansas River basin has been a focus of our forecasts due to its high flow and saturated soils over the area increasing runoff. Widespread afternoon showers continue to elevate the river and only modest rainfall is needed for high runoff to cause flooding. At this time we do not expect major riverine flooding, but action levels could be met today along near La Junta and Las Animas. Stay tune to our twitter account for the latest information (@COFloodUpdates).

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:

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

Partly cloudy and cool this morning but daytime heating should burn off some of the cloud cover. Some severe storms are possible today over the adjacent SE Plains and will favor the Palmer and Raton Ridge. Max 1-hour rainfall up to 1.6 inches (east), 1 inch (west). Riverine flooding along Fountain Creek and the Arkansas River will be monitored closely with saturated soils creating high runoff. Threats include urban and small stream flooding and debris slide (mountains). A Low flood threat has been issued today.

Primetime: 1:30PM to 11PM

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

 
Partly cloudy with rainfall become more intense throughout the day over the San Juan Mountains. Max 3-6 hour rainfall totals up to 0.7 inches (north) and 1.1 inches (south). There is a no flood threat for today.

Primetime: 10AM to 9PM

Issue Date: Thursday, August 10, 2017
Issue Time: 10:40AM MDT

—MODERATE flood threat for Southeast Plains
—LOW flood threat for Urban Corridor, Front Range, Palmer Ridge, Northeast Plains and Raton Ridge
—PM update possible today

The seemingly unending string of active weather across colorful Colorado will continue once again today. As shown in the water vapor image, below, several important features will combine to produce numerous rounds of shower and storm activity today. First, a strong upper-level disturbance is noted in southern Wyoming. This will slowly move southward throughout the day. To its south, positive vorticity advection will support large-scale upward motion and enhance precipitation. Additionally, a developing jet streak will form over Colorado, further enhancing upward motion as Colorado will lie in the favorable right “exit” region of this jet streak. Second, plenty of moisture remains in eastern Colorado this morning. Surface dew point temperatures are in the 50s and 60s, which is above normal for this time of year. The moisture is not just limited to the surface but extends through a deep layer of the atmosphere, suggesting large warm layer depths and in turn, efficient warm coalescence rainfall generation within thunderstorm clouds. Finally, a surface front has entered northeast Colorado and will continue to push southwest through the day. This will be tempered by the still-strong August sun, but the front will provide a surface convergence boundary for storm formation across the Northeast Plains. The saving grace today that will limit the flood threat will be fast southeasterly steering winds above 25 mph, which will generally limit rainfall in any given location.

Overall, we expect numerous rounds of showers and thunderstorms today across eastern Colorado. Initial coverage will be over the higher terrain, though storms should have little problem surviving on the eastward trek across the Plains today. The fast steering winds suggest a Low flood threat is appropriate for most regions. However, a small region with a Moderate flood threat will exist in far southeast regions where storm complexes are expected to be the largest, and thus multiple hours of heavy rainfall are possible. Activity will continue late into the evening and into the overnight hours especially across far eastern areas. Portions of the Arkansas River, especially towards the Kansas border are included in the Moderate threat and riverine flooding is possible today.

In addition to the flood threat, severe weather will be likely especially during the mid/late afternoon. Very large hail up to 2.75 inches, along with gusty winds up to 75 mph are possible with the strongest cells.

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:

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

Scattered showers and thunderstorms developing by early afternoon. Highest coverage will be over the higher terrain as well as farther east across the Plains. Max 1-hour rainfall up to 2.4 inches (east) and 1.9 inches (west). Max 3-hour rainfall up to 3.8 inches across eastern areas. A Low flood threat has been posted for isolated flash flooding, small stream flooding, mud flows and debris slides (for higher elevations). A Moderate flood threat is in place for far southeast areas, where impacts will also include potential riverine flooding due to the elevated stream over the Arkansas River and its tributaries. Most activity will subside shortly after sunset, but isolated to scattered storms will continue, especially across eastern areas, well into the overnight hours.

Primetime: 12PM to 4AM

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

Partly cloudy early with isolated to scattered showers and thunderstorms developing by afternoon. Highest coverage will be over northwest areas (especially north of I-70). Max 1-hour rainfall up to 0.7 inches is possible. Gusty winds up to 50 mph and small hail could accompany the strongest cells. Activity will quickly subside after sunset.

Primetime: 12PM to 9PM

Issue Date: Wednesday, August 9, 2017
Issue Time: 10:40AM MDT

— LOW flood threat for the Raton Ridge

Visible satellite shows a bit of fog and low-level clouds again this morning over the northern mountains and Southeast Plains. There are a few light showers over the Northeastern Plains and Southwest Slope, but the majority of this cloud cover will burn off throughout the day with stronger daytime heating. High temperatures today continue to trend upwards, but still will be a bit below climatology. Abundant sunshine will allow some instability this afternoon, but a decrease in moisture will limit severe storm potential and rain totals further north. Shortwaves will continue to be embedded in the west/northwest flow aloft enhancing storms over the northern portion of the state today. Precipitable Water (PW) is lower than the previous few days with 0.85 inches at Denver and 0.8 inches at Grand Junction, which should limit heavy precipitation. Drier mid-levels on top of decreased surface moisture over the western slope should heavy rainfall once again. PW remains over an inch in the far eastern plains and will stay elevated throughout the day with S/SW low-level flow.

Storms will begin to fire off the higher terrain early this afternoon. Greatest instability will be further south and over the SE corner of the state. Some shear will also be present over the Southeast Plains this afternoon, which may help produce some severe thunderstorms. As far as coverage, storms will be more isolated than yesterday and favor the Raton and Palmer Ridge. While the Front Range will also initiate storms this afternoon, lower moisture should keep storm totals under the flood threat criteria. These storms will be the most likely to produce gusty winds. Further south, thunderstorms that form will produce gusty winds, large hail and quick, heavy precipitation. Saturated soils over Las Animas County warrant a Low flood threat for today with storm totals near 1.5 inches. Fast storm motion to the E/SE will also contribute to lower storm precipitation totals. Over the Western Slope, storm coverage will favor the Northern and Central Mountains with 1-hour rain rates up to 0.5 inches. Storms will quickly dissipate this evening over the mountains and by may go a bit into the evening hours over the eastern plains with lingering light showers overnight.

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:

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

Partly cloudy this morning but daytime heating should burn off most of the cloud cover. Some severe storms are possible today over the SE Plains and will initially favor the Palmer and Raton Ridge. Max 1-hour rainfall up to 1.5 inches (east), 0.9 inches (west). Riverine flooding along Fountain Creek and the Arkansas River will be monitored closely with saturated soils. A Low flood threat has been issued today.

Primetime: 1PM to 12AM

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

Mostly sunny and pleasant day with temperatures still a bit below climatology. Some cloud cover this afternoon with PM storms over the NW corner of the state. A couple embedded shortwaves will help enhance showers over the Northern and Central Mountains. 1-hour rain rates up to 0.5 inches (north) and .3 inches (south). There is a no flood threat for today.

Primetime: 1PM to 9PM

Issue Date: Tuesday, August 8, 2017
Issue Time: 10:50AM MDT

— LOW flood threat Northwest Slope, Northern Mountains, Front Range, Urban Corridor, Northeast Plains, Palmer Ridge, Southeast Mountains, Central Mountains, Southeast Plains, Raton Ridge, Grand Valley

With the broad ridge over the western US, Colorado will continue to be under westerly flow once again. Cloud cover this morning is heaviest in the eastern plains where some showers are still lingering from last night. This disturbance should exit over the Kansas border later this morning. Fog and low-level clouds are present once again with the moist atmosphere. Precipitable Water (PW) at Denver was measured at 1 inch and 1.03 inches over Grand Junction. Temperatures will be up to 10F warmer than yesterday, which should help burn off some of the cloud cover and help create more instability than yesterday. Similar to yesterday, mid-level disturbances will move through the state, which depending on timing, could help enhance the diurnal upslope pattern.

Westerly flow over western Colorado will dry out the mid-levels a bit, but PW values will be high enough for storms to form over the higher terrain favoring the north. The precipitation seems to come in a couple of waves, with the strongest precipitation over the Roan Plateau/Flat Tops and portions of the Central Mountains. A Low flood threat has been issued with storm totals as high as 1.5 inches over this region. Threats include mud flows, debris slides and flash flooding of roads and small streams over saturated soils.

Southeasterly flow over the eastern plains should help keep low-level moisture intact for storms later this afternoon with dew points over Kansas and Oklahoma in the low 60s. Storms will begin to fire over the higher terrain around 1PM and will be more scattered in nature than yesterday. While 1-hour storm totals are below flood thresholds, storm totals of 1.2 inches over saturated soils will increase the chance of mud flows and debris slides. As storms move off the mountains in to the adjacent plains, they will favor the higher terrains of the Palmer Divide and Raton Ridge. Models also have the better instability and a bit of shear over the Southeast Plains, so small hail is possible. It is also possible this afternoon that storms that form over the Cheyenne Ridge will move into the Northeast Plains later this evening. The threat over the mountains and western slope should end this evening, but a few showers may linger overnight with the support of a shortwave and low-level moisture. Over the plains, there is a threat should cease around midnight.

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:

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

Low-level clouds and rain this morning with a couple rounds of precipitation again. Storms will become more severe where sun is able to break through and create instability and with better shear, which is most likely over the Southeast Plains. Max 3-6 hour rainfall up to 2.8 inches (east), 1.2 inches (west). Riverine flooding along Fountain Creek and the Arkansas River will be monitored closely with saturated soils and widespread rainfall again, though no threat is warranted at this time. A Low flood threat has been issued today.

Primetime: 1PM to 12AM

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

A couple embedded shortwaves will create two rounds of rainfall today. 3-6 hour totals up to 1.5 inches over the Flat Tops/Roan Plateau and portions of the central mountains put it at risk for mud flows, debris slides and road flooding. 3-6 hr rain totals up to 1.2 inches possible (north) and 1 inch (south). There is a Low flood threat for today.

Primetime: 12PM to 10PM