Issue Date: Sunday, July 14th, 2019
Issue Time: 9:20 AM MDT

A LOW FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, CENTRAL MOUNTAINS, GRAND VALLEY, FRONT RANGE, SOUTHEAST MOUNTAINS, URBAN CORRIDOR, PALMER RIDGE, SOUTHEAST PLAINS AND NORTHEAST PLAINS.

The high-pressure ridge aloft that was a major factor in yesterday’s weather has not really budged much, although it is expected to flatten out through this forecast period. This “flattening out” will turn yesterday’s mid-level southwest flow more westerly for today, resulting in slightly quicker storm motions and allow a few more storms to reach out onto the eastern plains. The subtropical moisture from the west-southwest remains the fuel behind scattered thunderstorm activity, and there will be enough moisture available to warrant a fairly widespread low flood threat area today, with the main concerns being burn scars and urban areas.

Scattered thunderstorms will get their start over the higher terrain by 10-11 AM, with areas east of the mountains getting in on the action by 1-3 PM. Thunderstorms will move generally eastward today at 10-15 mph due to the aforementioned westerly flow aloft. All regions will see at least some rainfall today/tonight (some will get more than others), bringing a welcome relief from hot July afternoon temperatures. Thunderstorm activity will diminish after sunset, with nearly all activity ending by midnight, with a couple isolated showers expected to linger over far western Colorado into the early morning hours tomorrow. For more details on timing and rain rates, please see the zone-specific forecasts below.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, jump below the map.

Zone-Specific Forecasts

Urban Corridor, Northeast Plains, Southeast Plains, Palmer Ridge, and Raton Ridge:

Hot temperatures and scattered thunderstorms will be the name of the game today. Thunderstorms will get their start over the mountains, spreading eastward with time over the lower elevations. Most storms will produce moderate rainfall and gusty winds, but a couple stronger storms will produce locally heavy rainfall, small hail, and strong winds up to 60 mph. Street flooding in urban areas will be the main concern in the low flood threat area, with maximum rainfall rates of 1.0-1.4 inches/hour over the Urban Corridor and Palmer Ridge, 0.4-0.8 inches/hour over the Raton Ridge, and 1.0-2.0 inches/hour over the Northeast Plains and Southeast Plains.

Timing: 1 PM – 11 PM for the Urban Corridor and Palmer Ridge, 2 PM – Midnight for the Northeast Plains, and 3 PM – 1 AM for the Southeast Plains

Front Range, Southeast Mountains, Northern Mountains, Northwest Slope, Grand Valley, Central Mountains, San Luis Valley, San Juan Mountains, and Southwest Slope:

Scattered thunderstorms will be the main weather story today, beginning during the late morning hours, expanding in coverage/intensity through the afternoon and evening hours, and diminishing after sunset. Most will produce light-to-moderate rainfall and gusty winds, but a couple stronger storms will be capable of producing heavy rainfall. The maximum rain rates are as follows:

Front Range and Southeast Mountains: 0.8-1.2 inches/hour
Northern Mountains and Northwest Slope: 0.3-0.7 inches/hour
Central Mountains, Grand Valley, Southwest Slope, and San Juan Mountains: 0.7-1.1 inches/hour
San Luis Valley: 0.2-0.5 inches/hour

Timing: 10-11 AM to 9-10 PM, with a few showers lingering into the early morning hours tomorrow

Issue Date: Saturday, July 13, 2019
Issue Time: 10:15AM MDT

–A MODERATE flood threat is issued for the 416 burn area
–A LOW flood threat is issued for the Spring Creek burn area

The upper level ridge overhead is beginning to slowly break down as a trough pushes its way in off the west coast. Moisture on the backside of the high centered over Colorado has made its way into western Colorado and Utah this morning and will continue to move its way over the forecast area throughout the day. A shortwave over Utah (marked “X” below) will travel over central Colorado later today, providing lift for afternoon thunderstorms over the high country and Northeast Plains. The moisture is farther to the west than originally forecast, however there is still a Moderate to Low chance of flooding over recent burn scars that saw rainfall yesterday.

Max 1-hour rain rates are forecast to be 0.3 inches over the burn areas, but high frequency of storms over the area will allow for max 3-hour rain rates of 1 inch. Antecedent moisture from storms over the area yesterday increases the chances for flooding over the burn areas. Hot temperatures are expected again statewide with sunny skies this morning and warm air being advected in over the eastern plains from New Mexico throughout the day. Surface moisture present this morning over the eastern plains is expected to mix out throughout the day, creating a dry line (orange line below) over the far eastern edge of the area. Dry air will limit severe storm potential over the plains today. Thunderstorms are likely over the high country, Palmer Ridge, and Northeast Plains.

Riverine: As of 9:30 this morning all river gages have retreated below Action stage.  Flows may begin to increase over the weekend as rain returns.  Rivers will likely remain high and fast over much of the state so please exercise caution near river banks.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

A shortwave is forecast to move over the Central Mountains early this afternoon from Utah. Moderate to high levels of moisture and upslope flow will combine to produce thunderstorms this afternoon and into tomorrow morning. A Moderate threat is issued for the 416 Burn area, with max 3-hour rainfall rate of 1 inch and max 24-hour rainfall rate of 1.5 inches. Max 1-hour rainfall rates are not expected to be greater than 0.3 inches, however persistent storms over the area throughout the day and into tomorrow morning will create chances for flooding. A Low flood threat is issued for the Spring Creek burn area, with max 3-hour rain rates of 1 inch and max 24-hour rain rates of 1.25 inches. Other areas within the forecast area are likely to receive thunderstorms this afternoon and into tomorrow morning, with max 1-hour rain rates of 0.6 inches. Flooding is not forecast for areas outside of the burn scars.

Primetime: 1PM to 4AM

Urban Corridor, Northeast Plains, Raton Ridge, Palmer Ridge, Southeast Plains, San Luis Valley:

Surface moisture is expected to mix out over the area throughout the day as temperatures increase into the upper 90°Fs. Storms may move off of the Front Range this afternoon, but dry air underneath the storm base is likely to limit rainfall at the surface. Storm motion is forecast to be between 15 and 20 mph, but limited moisture will limit potential for heavy rainfall under the slow moving storms. Upslope flow along the Palmer Ridge will provide chances for afternoon thunderstorms over the area that will move over the Northeast Plains. Max 1-hour rainfall rate of 0.4 inches is forecast over the area.

Primetime: 3PM to 11PM

Issue Date: Friday, July 12, 2019
Issue Time: 9:40AM MDT

–Flooding is NOT expected today

It’s going to be another hot day again statewide but there will be a chance for afternoon and evening thunderstorms to cool things off. The strong upper level ridge is still present overhead but has shifted slightly to the northeast. High temperatures measured in the upper 90°Fs and up to 100°F yesterday over the eastern plains caused dewpoints to drop into the 40°Fs and low 50°Fs over the eastern plains. Midlevel moisture will continue to increase from the southwest throughout the day on the backside of the high pressure. PW at Flagstaff and Tuscon Arizona increased about 0.1 inches from yesterday’s values, measuring 0.75 and 1.23 inches respectively. This moisture, marked by the green shading below, is expected to move over our area throughout the weekend but will not be a threat for today. Weak afternoon thunderstorms are expected over most of the high country and Northeast Plains as moisture comes into the area. A cold front associated with a surface low pressure system over the Nebraska panhandle (marked “L” below) will move into the Northeast Plains this morning. The front is expected to mix out by midday but will provide a density gradient for storm formation this afternoon.

Riverine: As of 9:30AM this morning there are no NWS Flood Warnings or Flood Advisories.  Rivers statewide have seen a gradual decrease in flow due to dry conditions throughout the week.  The gage on the Rio Grande River near Alamosa remains at Action stage this morning but is forecast to retreat below Action stage midday today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Southwest Slope, San Juan Mountains, Central Mountains, Northern Mountains, Front Range, Urban Corridor, Northeast Plains, Palmer Ridge:

Afternoon thunderstorms are forecast primarily for the high elevations and Northeast Plains. Over the high country, lift of midlevel moisture over the mountainous terrain will provide a chance for afternoon and evening thunderstorms. Max 1-hr rainfall rates of 0.2 inches are forecast over the area. Storms may drift slightly off of the foothills and over the Urban Corridor, however dry air underneath the cloud base will limit accumulation to less than 0.1 inches. Over the Northeast Plains and Palmer Ridge, the passage and gradual break down of a weak cold front from the north will provide a boundary for storm formation by midafternoon. Low levels of surface moisture and weak upper level forcing will limit max 1-hr rainfall rates to 0.4 inches.

Primetime: 1PM to 9:30PM

San Luis Valley, Southeast Mountains, Southeast Plains, Northwest Slope, Grand Valley, Raton Ridge:

Dry air at the surface and weaker mountain lift will limit chances of precipitation today. Isolated storms may form over the Grand Valley, Southeast Mountains, and Northwest Slope, but max 1-hr rainfall rates will be limited to 0.2 inches. High temperatures are expected to reach 100°F over the Southeast Plains and Grand Valley again today.

Primetime: 12PM to 8PM

Issue Date: Thursday, July, 11th, 2019
Issue Time: 9:40AM MDT

–Flooding is NOT expected today

The upper level high pressure ridge remains centered over Colorado today and now covers most of the United States as the summer heatwave continues.  The clockwise rotation around the zone of high pressure (marked “H” below) will bring in moisture from the southwest, but keep the northern areas of the state mostly dry.  PW was measured at 1.12 and 0.64 inches over Tuscon and Flagstaff Arizona this morning and will move in from the south southwest throughout the day.  A shortwave embedded within the high pressure, marked by an X in the water vapor imagery below, is forecast to move over central Colorado by 2PM today.  This shortwave is expected to create a vorticity maximum over the area that will move to the southeast throughout the afternoon and into the night.  Thunderstorms are forecast over the southern half of the state, but insufficient deep moisture and weak upper level dynamic forcing will keep rainfall totals low.

Riverine: As of 9:30AM there are no NWS Flood Warnings or Flood Advisories.  The AHPS gage on the Arkansas River near La Junta retreated below action stage yesterday around noon but the gage on the Rio Grande near Alamosa remains at Action Stage.  Most rivers have seen a gradual decrease in flow this week due to dry conditions.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below.  For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Southwest Slope, San Juan Mountains, San Luis Valley, Central Mountains, Front Range, Southeast Mountains, Raton Ridge, Southeast Plains, Palmer Ridge

Midlevel moisture will increase over the region today, however low level and surface moisture remains low.  Afternoon and evening thunderstorms can be expected over the area.  A surface low is expected to form over the southern Front Range and Southeast plains by 3PM.  This feature will provide lift for storms over the Southeast Plains and Raton Ridge, with max 1-hr rainfall rates of 0.7 inches over the area.  Max 1-hr rainfall rates of 0.2 inches is forecast over the mountainous regions of the forecast area.  Flooding is not expected today, with the main threat being isolated wind gusts up to 30 mph.  High temperatures are forecast to reach 100°F over the eastern plains and low laying areas of the western slope.  Please use caution outdoors and stay hydrated.

Primetime: 1PM to 1AM

Grand Valley, Northwest Slope, Northern Mountains, Urban Corridor, Northeast Plains

The forecast area is expected to remain dry today, with chances for weak isolated thunderstorms over the higher elevations.  Storms may move into the southern Northeast Plains off of outflow boundaries from storms over the Southeast Plains.  Max 1-hr rainfall rates of 0.3 inches are possible over the Northeast plains, with max 1-hr rainfall rates of 0.1 inches over the high country.  High temperatures may reach 100°F today over the Northeast Plains and Urban Corridor, with highs in the upper 80°Fs and low 90°Fs over the valleys of the high country.  Please use caution and stay hydrated if you are outdoors.

Primetime: 7PM to 12AM