Issue Date: Saturday, September 16th, 2017
Issue Time: 8:45 AM MDT

— Flooding is NOT expected today

TThe upper-level low that has been responsible for the unsettled weather the past few days will finally get out of the area today, as the trough axis swings across the state. The current position of the axis is denoted on the water vapor image below, with drier, subsident air following behind. Ahead of the axis, more showers, and perhaps a thunderstorm or two, will kick off today, producing mainly light precipitation and gusty winds. The depth of the moisture isn’t sufficient enough to produce much more than that. A few isolated showers/weak thunderstorms will continue into the nighttime hours along/east of the Front Range as weak upslope flow and lingering moisture remain across the region.

One region to keep an eye on for an isolated, strong thunderstorm or two will be the far Southeast Plains, mainly Baca, Bent, Prowers, and far eastern Las Animas counties. Low-level convergence along the lingering cold front will provide the necessary lift and moisture, as long as the upper-level subsident air doesn’t work into the area to suppress development. Brief heavy rainfall and strong winds will result from any activity in this area. The time frame for any storms to develop in this area will be from 5 PM – Midnight. For more details, please see the zone-specific forecast discussions below.

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:

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

Isolated-to-scattered showers will continue this morning across the Urban Corridor and Northeast Plains, mainly north of I-76. During the afternoon and evening hours, a few more showers/weak thunderstorms will develop across mainly the Urban Corridor, Palmer Ridge, and Northeast Plains, with another small area of focus mentioned above for the far Southeast Plains. Maximum rain rates from showers will be in the 0.05-0.15 inches/hour, with maximum rain rates from thunderstorms in the following ranges:

Urban Corridor: 0.2-0.5 inches/hour
Northeast Plains, Southeast Plains: 0.7-1.2 inches/hour
Palmer Ridge: 0.4-0.8 inches/hour
Raton Ridge: 0.2-0.4 inches/hour

Timing: Ongoing – Midnight

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

A couple isolated showers over the high country will persist this morning, producing light rain and snow for the higher peaks. Activity will come to an end as the trough axis passes by through the afternoon hours. Maximum rain rates will be below flash flood thresholds:

Northern Mountains, Central Mountains, Northwest Slope, Grand Valley, Southwest Slope, San Juan Mountains, and San Luis Valley: 0.1-0.2 inches/hour
Front Range and Southeast Mountains: 0.25-0.5 inches/hour

Timing: Ongoing – 5 PM for locations west of the Continental Divide, Ongoing – 10 PM for areas along/east of the Continental Divide.

Issue Date: Friday, September 15, 2017
Issue Time: 10:10 AM MDT

— Flooding is NOT expected today

The system that moved through the state yesterday can currently be seen over WY in the water vapor imagery below. The SW winds associated with the dry slot of the trough will remain over the majority of the state today. This drying will give us a break from the rainfall with the exception of the Northwest Slope and portions of the Northern Mountains. Moisture will remain over this area as it wraps around the low pressure system.

Later this afternoon and evening, a cold front will move through the state and cool temperatures closer to climatology for tonight and tomorrow. The first two weeks of September have been abnormally warm with temperatures over portions of the Central Mountains reaching up to 10F above climatology. More detailed information on the temperature trends can be found in the Flood Threat Outlook. The passing cold front will initiate showers and some snow (at higher elevations) for the Northwest Slope and portions of the Northern Mountains. While the eastern portion of the state is expected to remain dry, the passage of the cold front may slightly increase low-level moisture and produce enough lift for an isolate storm. Storms will produce gusty winds and are not expected to last long in the unfavorable environment. All storms are expected to come to an end a couple hours after sundown.

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, Northeast Plains, Palmer Ridge, Southeast Mountains, Raton Ridge, Southeast Plains, Central Mountains:

Sunny throughout the day. An isolated shower or thunderstorms may be possible this evening with the passing cold front. Lack of low moisture will cause storms to produce gusty winds and be short-lived in duration. Precipitation amounts are expected to be under 0.1 inches. Flooding is not expected today.

Primetime: 4PM to 10PM

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

Partly cloudy with light showers over the northwest corner this morning as moisture wraps around the trough. Other than the Northwest Slope and Northern Mountains, showers are not expected today. Expect increasing clouds over the higher terrains this afternoon. 24-hour rainfall totals could be up to 0.8 inches (north) with some snow at higher elevations. Flooding is not expected today.

Primetime: 12PM to 11PM

Issue Date: Wednesday, September 14, 2017
Issue Time: 10:30 AM MDT

— LOW flood threat for Grand Valley, Central Mountains, Southwest Slope, San Juan Mountains

Finally some changes to the weather pattern as what’s left of Irma moves off to the NE. This will allow the persistent ridging pattern to be pushed eastward as the low pressure system off the coast of California ejects across the plains. This morning, we start with some higher clouds over the mountains and northwest corner as seen in the visible satellite image below. The approaching weather system can be seen over southwest Utah, which is expected to track NE throughout the day. Currently, PW water values at Grand Junction and Denver are at 0.72 inches. Low-level moisture is expected to increase over the western portion of the state as the disturbance moves into the area this afternoon. A slight increase in PW over the eastern portion of the state is expected later this afternoon and evening. With the arrival of the mid-level energy over western Colorado around the same time as the storms initiate over the mountains due to the daily heating pattern, shower and thunderstrom coverage is forecasted to be very widespread.

Shear profiles this afternoon are also impressive over the SW corner of the state. With moderate instability building over this same region, some isolated severe thunderstorms are possible. Threats include gusty outflow winds, brief, heavy rainfall and hail up to 1 inch in diameter. The approaching upper-level dynamics will support multiple rounds of showers and thunderstorms this afternoon, so a Low flood threat has been issued. Isolated 24-hour rainfall amounts up to 2 inches are possible. Threats include mud flows, debris slides, small stream and road flooding.

Storms are also expected to be more numerous over the Front Range and Palmer Ridge today. With stronger SW steering winds aloft and increasing moisture, storms that form over the higher terrains are expected to move into the Northeast Plains later this afternoon and evening. Low-level moisture will still be lacking, so expect strong outflow winds with these storms. Faster steering winds will also limit flooding potential, but max 1-hr rain rates up to 0.8 inches are possible further east. Tonight, rain over the western portion of the state is expected to end around midnight. A couple hours later, showers over the Northeast Plains will conclude. Some light showers over the mountains are possible through tomorrow morning.

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, Northeast Plains, Palmer Ridge, Southeast Mountains, Raton Ridge, Southeast Plains:

Sunny this morning becoming partly cloudy this afternoon. Shower and thunderstorm initiation over the mountains will be greatest over the Front Range and Palmer Ridge. These storms are expected to move over the Northeast Plains with SW steering winds aloft. Storms will likely produce gusty winds and max 1-hr rain rates up to 0.8 inches are possible further east. Flooding is not expected.

Primetime: 2PM to 2AM

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

Partly cloudy over the northwest corner this morning with increasing clouds expected throughout the afternoon. Multiple rounds of widespread showers are likely this afternoon with the approaching weather system, especially further south. Some of these storms over the southwest corner may become severe. Threats include gusty winds, brief, heavy rainfall and hail up to 1 inch in diameter. A Low flood threat has been issued for the 24-hour rainfall amounts. Over the San Juan/Central Mountains and Southwest Slope, isolated 24-hour amounts up to 2 inches are possible. Showers and thunderstorms should come to an end around midnight, but a few light showers may linger over the southern high terrains through the night.

Primetime: 12PM to 12AM

Issue Date: Wednesday, September 13, 2017
Issue Time: 10:10 AM MDT

— Flooding is NOT expected today

Today should be the last day of westerly flow under the ridge that has been persistent for the last several days. As the remnants of Irma continue move to the NE over the next 24 to 36 hours, the ridge will finally be pushed east as the west coast trough moves over the state. Currently, clear skies across the majority of the state excluding the northern Mountains. With the ridge overhead, this will help increase high temperatures over the lower elevations today. Precipitable Water (PW) at Denver and Grand Junction was measured at 0.7 inches and 0.78 inches, respectively. This is still a bit above climatology, but down from the last two days. Less moisture paired with lower dew points and drying in the mid-levels, will cause storms to be high-based and limit rainfall totals when compared to the last couple of days. Gusty winds are likely with stronger storms that form due to the inverted-V soundings.

This afternoon, some weak mid-level vorticity will make its way to the state via the west coast trough. While this will help slightly enhance the upslope flow coverage, the limited atmospheric moisture will prevent widespread rainfall in the mountains. The highest coverage of rainfall is expected to be over the southern Front Range, Palmer Ridge and Southeast Plains. The stronger W/SW steering winds aloft, will allow storms to move off the mountains and Palmer Ridge into the Southeast Plains. Dew points over the Southeast Plains are forecasted to be in the 40s and low 50s (east), so gusty winds are likely for the short duration of the storms. Activity will cease a couple hours after sundown with the decrease in instability. Flooding is not 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:

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

Sunny this morning becoming partly cloudy this afternoon. Shower and thunderstorm activity over the mountains will be greatest over the southern Front Range. Some storms are also expected to form due to convergence along the Palmer Ridge. Max 1-hr rain rates up to 0.6 inches with gusty winds possible. Flooding is not expected.

Primetime: 1PM to 10PM

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

Partly cloudy over the Northern Mountains with sunny skies elsewhere. Higher terrain will become partly cloudy this afternoon with the development of showers and thunderstorms. Highest coverage of rainfall will be in the Northern Mountains, and scattered showers are expected over the San Juans as well. 24-hour rainfall totals up to 0.3 inches (north) and 0.2 inches (south). Flooding is not expected today.

Primetime: 1PM to 10PM