Issue Date: Saturday, July 22, 2017
Issue Time: 10:00AM MDT

 

— MODERATE flood threat for Central Mountains, Front Range, Urban Corridor, Palmer Ridge, Southeast Mountains, Southeast Plains, Raton Ridge

—LOW flood threat for parts of Palmer Ridge, Urban Corridor, Front Range, Central Mountains, Southwest Slope, San Juan Mountains, Southeast Mountains, Southeast Plains, Raton Ridge

 

The upper-level ridge begins to rebuild north and west of Colorado today. In the water vapor imagery below, you can see some drier air over Wyoming that will mix into the northern part of the state later this morning and afternoon. Currently, there is heavy cloud cover over the mountains and eastern plains. It may take some time for this burn off, but should by early this afternoon with both the drier air and increasing sun. Partly cloudy skies should limit temperatures and instability today in the northeastern portion of the state. Currently, Precipitable Water (PW) is 0.82 inches in Denver and 0.92 in Grand Junction. Pockets of PW greater than 1 inch will be confined to the southeastern plains and SW corner of the state. There should still be enough moisture for thunderstorms over the higher terrain in the northern portion of the Front Range.

 

Upslope flow will set up once again today favoring the moisture rich areas in the south for the heavier rainfall. Storms should begin firing over the San Juan Mountains, Southeast Slope and Central Mountains by 11am with all the higher terrain storms firing just after noon. As the storms begin to move off the mountains in the late afternoon, there is a chance for an isolated shower over the Palmer Divide with more widespread thunderstorms over the adjacent Southeast Plains and Raton Ridge. Max 1-hour rain rates for the mountains could be as high as 1.3 inches. Threats include road and small stream flooding, mud flows and debris slides over the steeper terrain. A Moderate threat has been placed over portions of the SE mountains and adjacent plains due to high instability and moisture. Burn scars in the Southeast Mountains need to be monitored close with already saturated soils and high probability for rain rates greater than 0.5 inches again today. Mud flows and debris slides are possible, so campers near these burn scars and steep terrain need to watch the weather carefully. Over the adjacent plains, expect 1-hour rain rates up to 1.9 inches with 3-hour totals of 2.6 inches. Threats include road flooding, field ponding and flooding of small streams. Hail up to 1 inch and gusty winds can accompany the more severe storms.

 

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, Southwest Slope, San Juan Mountains, San Luis Valley, Southeast Mountains, Southeast Plains, Raton Ridge:

Partly cloudy becoming sunny in spots until numerous showers and thunderstorms develop shortly after 11AM. Max 1-hour rainfall up to 1.3 inches and up to 1.9 inches below 6,000 feet. 3-hr totals up to 2.6 inches are possible below 6,000 feet. Isolated flash flooding, debris slides and mud flows will be possible especially over burns scars and where soils are already saturated from multiple days of rain. There is a slight chance of severe weather with the main hazards being hail up to 1 inch and gusty winds. A Moderate flood threat has been issued.

Primetime: 1PM to 1AM

Northwest Slope, Grand Valley, Northern Mountains, Central Mountains, Northeast Plains:

High temperatures will be 5-10F cooler today with the cloud cover over the Northeast Plains this morning. Partly cloudy early then scattered to numerous showers and thunderstorms developing just after noon. Max 1-hour rain rates up to 0.8 inches. Storms should be confined to the higher terrain. Storms will start to dissipate after sundown and should be over by about 10PM.

Primetime: 12PM to 10PM

Issue Date: Friday, July 21, 2017
Issue Time: 10:30AM MDT

— MODERATE flood threat for Junkins fire scar
— MODERATE/LOW flood threat for parts of Palmer Ridge, Urban Corridor, Front Range, Northwest Slope, Grand Valley, Northern Mountains, Central Mountains, San Juan Mountains, Southwest Slope, Southeast Mountains, Northeast Plains

A persistent weather pattern continues over Colorado this morning. As shown in the water vapor image, below, the main features are a weak upper-level ridge to our southeast, along with a plume a monsoon moisture being transported northward along the NM/AZ border. A sizeable area of drier air is once again found in southeast Colorado, which will continue to limit heavy rainfall chances there. Expanding now to include more detail, there is a remnant mesoscale low pressure clearly seen on the visible satellite image in northeast AZ. At the mid-levels this feature is being supported (or is supporting!) a vorticity maximum located over the four corners. This is not expected to move much, but will likely provide enhanced moisture advection into southwest Colorado, which will in turn continue to favor heavy rainfall. Additionally, mid-level temperatures have dropped 2-4C over the past 24 hours as the upper-level high is slowly weakened by a large scale trough coming ashore in the Pacific Northwest. The sensible impact will be higher overall precipitation chances for western and central Colorado. A Low flood threat has been posted for a similar domain as yesterday. High resolution guidance is more bullish on max 1-3 hour rain rates, which looks reasonable given the mid-level cooling. Thus, a broad Moderate flood threat has been issued for the foothills of the western slope as well as the Palmer Ridge and neighboring regions. Antecedent rainfall up to 2 inches is also becoming of increasing concern (especially for debris slides) that warrants the Moderate threat.

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:

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

Partly cloudy early then scattered to numerous showers and thunderstorms developing by noon. Max 1-hour rain rates up to 1.4 inches, with max 3-hour rates up to 2.2 inches. Isolated flash flooding will be possible under the strongest cells. Mud flows and debris slides will be possible not only in areas with new heavy rainfall, but also in areas seeing multiple days of rainfall. A broad Moderate flood threat has been issued with a Low threat surrounding this region. Storms will quickly subside shortly after sunset, with some light to moderate showers possible for a few hours thereafter.

Primetime: 11:30AM to 10PM

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

Sunny early then becoming mostly cloudy with scattered to numerous showers and thunderstorms developing shortly after noon. Max 1-hour rainfall up to 2.3 inches below 6,000 feet and up to 1.8 inches above 6,000 feet. Isolated flash flooding, debris slides and mud flows will be possible. Nuisance urban flooding will be likely in the Denver metro and small stream flooding is a possibility in municipal areas with high impervious area. A Moderate flood threat has been issued south and west of Denver metro, with a Low flood threat extending north and east. There is a slight chance of severe weather with the main hazards being hail up to 1.25 inches and gusty winds.

Primetime: 12PM to 10PM

Raton Ridge, San Luis Valley, Southeast Plains:

Sunny and very warm today with isolated showers and thunderstorms possible towards the mountains. Max 1-hour rainfall up to 0.9 inches. Flooding is not expected today.

Primetime: 1PM to 9PM

Issue Date: Thursday, July 20, 2017
Issue Time: 10:45AM MDT

 

—MODERATE flood threat for portions of San Juan Mountains, Southwest Slope

—LOW flood threat for portions of Northwest Slope, Northern Mountains, Grand Valley, Central Mountains, San Juan Mountains, Southwest Slope, Front Range, Urban Corridor, Palmer Ridge, Northeast Plains

 

The upper level ridge begins to move to the east a bit today and settles over eastern Montana and Saskatchewan. Southerly surface winds over Colorado will draw some drier air into the southeastern portion of the state. Over the Northeast Plains, easterly winds will set up with the heat low and help pull in moisture from NE and KS. Precipitable Water (PW) is expected to rise to as high as 1.3 inches. The axis of moisture is marked in the water vapor image below. On the western portion of the state, PW is still over 1 inch in some places. A plume of moisture can be seen over the SW portion of the state in the water vapor imagery. PW isn’t forecasted to change much by this afternoon, so we can expected more widespread showers again today with local, heavy rainfall.

Storms will begin to fire in the mountains today around noon. The best access to moisture and lift will be over the Southwest Slope and San Juan Mountains. 3-hour storm totals could be as high as 1.6 inches with 1-hr rain rates up to 1.1 inches. Other parts of the high country will have 2-hour totals of 1.5 inches. Threats today include flash flooding, small stream flooding and road flooding, debris flows and mud slides. Burn scars should be monitored closely as a handful of storms in the Low flood threat will produce rain rates greater than 0.5 inches, which could lead to debris flows and mud slides on steeper terrain. The National Weather Service in Grand Junction has issued a Flash Flood Watch from noon until midnight for the southern and western portion of their forecast area.

The high elevation storms will drift into the southern half of the Urban Corridor later this afternoon. An isolated storms may also fire over the Palmer Divide.  Under the ridge, slow moving storms will drop local, heavy rain. 1-hour rain rates up to 1.1 are possible that could cause urban and small stream flooding and street flooding. Gusty winds and small hail are expected with storms. Outflow boundaries will likely provide lift for a couple isolated thunderstorms in the Urban Corridor and Northeast Plains. 1-hour max rain rates up to 1.8 inches are possible with the high moisture and 2-hour totals will be near 3 inches. These storms could become severe with hail up to 1 inch in diameter and wind gusts up to 60 mph. Field ponding and street and small stream flooding are expected. Storms over the mountains will begin to dissipate in coverage around 9PM and most all showers should cease by 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:

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

Sunny with highs near normal. Partly cloudy skies are likely with storms beginning to fire over the higher terrain around noon. High moisture and slow moving storms will warrant a Moderate threat today with 2-hr totals up to 1.6 inches. 1-hr max rain rates of 1.1 inch are possible over the San Juan Mountains and Southwest Slope. A Flash Flood is in effect until midnight tonight. Threats include flash flooding of small streams and road, debris flows and mud slides.

Primetime: 12PM to 11PM

Front Range, Urban Corridor, Palmer Ridge, Northeast Plains:

Sunny this morning and very hot over the Northeast Plains. Storms will begin firing over the higher terrain around noon and an isolated storm or two will move into the urban corridor by late afternoon. Max 1-hr rain rates are expected to be 1.1 inches with 3-hr totals near 3 inches. Isolated thunderstorms over the Northeast Plains are likely with initiation from an outflow boundary. Expect heavy local rain, gusty winds, 1-inch hail, field ponding and urban and small stream flooding.

Primetime: 12PM to 10PM

Southeast Mountains, Raton Ridge, San Luis Valley, Southeast Plains:

Sunny and hot for the Southeast Plains today. Drier air should limit coverage of storms and heavy rainfall potential in the higher terrain. Storms that form over the higher terrain will have max 1-hour precipitation rates of 0.5 inches. Temperatures will be in the upper 90s for the Southeast Plains. There is no flood threat.

Issue Date: Wednesday, July 19, 2017
Issue Time: 10:45AM MDT

—LOW flood threat for portions of Front Range, Urban Corridor, Palmer Ridge, San Juan Mountains, Central Mountains, Northern Mountains, Grand Valley, Northwest Slope

Moisture has returned to the Western Slope today. The Grand Junction sounding this morning showed 1.04 inches of Precipitable Water, while Denver was at 0.84 inches. The upper level ridge shifts a little to the east today and builds north throughout the day. This will allow the surface High pressure system to pull moisture into the western portion of the state with south and southeasterly winds. PW in the western portion of the state is expected to rise to 1.2 inches. These surface winds will also pull the dry air over into the southeast portion of the state confining the moisture on the eastern plains to the north. Values north will rise to 1 inch. Currently there is a band of showers over the southwest Colorado moving north that will begin to dissipate by late morning. Dense fog was reported of the Northeast Plains, but should burn off quickly with the sunrise.

Upslope flow will set up again today with the storms starting to fire over the higher terrain around 11AM. An upper level wave will help enhance lift over the western portion of the state along the border. It lifts north throughout the day and will exit over the northwestern portion of the state late this evening. Paired with high moisture, storms are expected to be slow moving and produce heavy rain; especially those forming near the upper level disturbance. Rain rates just over 1 inch 1-hour are possible with 3-hour totals up to 2 inches. Grand Junction NWS has issued a Flood Watch from 10:00AM this morning until midnight tonight. Heavy rainfall could lead to flash flooding in canyon country, over burn scars and in dry streams or creeks. Other threats include small hail, gusty winds, rock and mud slides, street flooding and small stream flooding. The return of moisture paired with upslope flow is particularly dangerous for burn scars. These will need to be monitored closely throughout the day. Storms will be confined to the higher terrains and favor the western portion of the state where there will be better lift and moisture. An isolated thunderstorm or two over the Urban Corridor and Palmer Ridge cannot be ruled out as the storms move off the mountains. These threats include gusty winds and brief heavy rainfall. Storms over the high terrain will begin to dissipate around 10PM with the exception of the Northwest Slope and Northern Mountains where storms may continue until 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:

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

Storms will continue to move north and dissipate through late morning. Partly cloudy skies are likely with storms beginning to fire over the higher terrain around 11. High moisture, an upper level disturbance and slow moving storms will warrant a low threat today. A Flash Flood is in effect until midnight tonight. Threats include mud slides, debris flows and flash flooding. 1-hr rain rates just over 1 inch and 3-hr rain rates up to 2 inches are possible. Burn scars will need to be monitored closely. There is Low flood threat for today.

Primetime: 11AM to 12AM

Front Range, Urban Corridor, Palmer Ridge, Southeast Mountains:

Sunny this morning becoming partly cloudy this afternoon as storms begin to form over the higher terrain. Max 1-hr rain rates are expected to be 1.1 inches. Storms should favor the higher terrain, but an isolate storm or two over the Urban Corridor or Palmer Divide near the mountains cannot be ruled out.

Primetime: 12PM to 10PM

Northeast Plains, Southeast Plains, Raton Ridge, San Luis Valley:

Sunny and hot today. Fog over the Northeast Plains should burn off quickly with the heating from the sun. Temperatures in the upper 90’s are expected for the eastern plains today. There is no flood threat.