Issue Date: Saturday, May 15th, 2021
Issue Time: 9:30AM MDT

— A LOW flood threat has been issued for the Palmer Ridge and portions of the Urban Corridor, Northeast Plains and Southeast Plains

On tap for today is a very similar pattern to yesterday with a few key differences. Below in the water vapor imagery, you’ll see two distinct areas of lift. The orange “X” over NV and ID is associated with the approaching cutoff low, while the “X” over Utah is the shortwave that will help spark numerous storms across the eastern mountains this afternoon. Moisture remains high to the east and low to the west. PW at Grand Junction was measured at 0.35 inches with the majority of the moisture around 500mb. This indicates that virga and cloud cover will be prevalent again this afternoon, and the scattered high-based storms that develop over the southern high terrains could again mix down some strong winds to the surface. However, measurable rainfall is not forecast.

Back to the east, moisture has been building over the last couple of days with PW at Denver going from 0.38 inches 48-hours ago to 0.64 inches this morning. To put that in perspective, that’s close to the 90^th percentile for this time of year. Fog and dew points in the upper 40Fs and 50Fs across the adjacent plains are another indication that storms that develop this afternoon and evening will be developing in a moisture-rich environment. Moderate upslope flow (east and southeast surface winds) around 10 mph will continue to hold this moisture in place throughout the day.

Expect storms to fire over the eastern mountains and ridges early this afternoon and move into the adjacent plains where they should pick up in intensity with the pooling moisture, increased CAPE and eroding cap. Slow steering flow from the west and training storms will produce a flood threat over the Palmer Ridge. Except storms to quickly form a line of convection as the move into the plains due to the high CAPE and moisture environment. More widespread severe storms will be possible today with the main threats being local heavy rainfall, hail and strong outflow winds. A Low flood threat has been issued.

With the low-level jet kicking back in tonight, some nocturnal convection may be possible over the far Southeast Plains. High moisture and slow steering winds means storms will be capable of producing heavy local rainfall. Additionally, this is the same area that received decent rainfall yesterday. Thus, the Low flood threat has been extended eastward.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

 

Zone-Specific Forecasts:

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

Once again by early afternoon, scattered storms are forecast to develop over the high terrains and elevated Ridges with more widespread activity over the Front Range. Max 1-hour rain rates up to 0.25 inches will be possible over the foothills along with small hail. As storms move into the adjacent plains and develop over the ridges, expect rainfall to intensify due to pooling moisture and higher CAPE. Over the Palmer Ridge, slow storm motion and training storms mean 1-2 hour rainfall totals around 1.50 inches will be possible along with hail. This combination of hail and heavy rainfall could cause street, low-land and local stream flooding issues. A Low flood threat has been issued. Brief strong outflow winds and severe hail will also be possible with the stronger storms that develop across the Urban Corridor this afternoon.

As storms move into higher moisture and increased instability over the plains, a line of convection is expected to form (southern Northeast Plains and Southeast Plains). These severe storms could produce winds around 60 mph, large hail (2 inches) and local heavy rainfall. Evening and overnight storms will likely continue over the eastern plains with 1-hour rain rates up to 1.75 inches. Thus, the Low flood threat has been extended east for excessive runoff, local stream flooding, road flooding and field ponding.

Primetime: 1PM to 3AM

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

A few high-based storms are possible over the San Juan and Central Mountains with an increase in cloud cover across all these regions today. Storms that develop south are forecast to produce plenty of virga, which could mix some strong winds down the surface (50 to 60mph gusts) similar to yesterday. Unfortunately, measurable rainfall is not forecast, but a few sprinkles will be possible along and near the Continental Divide. Flooding is NOT forecast.

Issue Date: Friday, May 14th, 2021
Issue Time: 9AM MDT

— Flooding is NOT expected today

The visible satellite imagery below shows dense fog over the Northeast Plains along with some mid-level cloud cover over the northwest corner of the state. As anticipated and shown by these features, PW has rebounded slightly with 0.41 inches measured at Grand Junction and 0.47 inches at Denver. Due to a very dry surface layer west of the Continental Divide, only cloud cover and not rainfall is forecast this afternoon.

A surface Low is expected to develop over the Southeast Plains this afternoon. This will help pull in higher moisture with easterly and northeastly flow on its north side and set up a dryline. Higher dew points from the dryline look to be south and east of the state, so not currently anticipating any severe storm development from this feature. Further north, weak northwest flow aloft will continue, which will move another shortwave across the northern portion of the state. With slightly higher moisture today, this shortwave will help to spark some storms off the eastern Mountains and Palmer Ridge early this afternoon. Brief, heavy rainfall and wind will be the main threat from the storms that develop west.

East and southeast steering flows will push these storms into the adjacent plains where they will likely intensify due to higher moisture content. As the storms make it into the far Southeast and Northeast Plains, increased CAPE and modest shear may help produce a couple severe thunderstorms. The main threat from these severe storms will be local, heavy rainfall, strong outflow winds and large hail. Due to the small size of the intense rain cores, flooding is not forecast.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Scattered showers are forecast to develop over the high terrains and Palmer Ridge this afternoon. As storms move into the adjacent plains, expect rainfall to intensify. Max 1-hour rain rates up to 0.25 inches (mountains) and 0.75 inches (adjacent plains) will be possible. As storms move east/southeast into higher moisture, a couple severe storms will likely develop over the Northeast and Southeast Plains. Strong outflow winds, local heavy rainfall and hail up to 1.25 inches will be possible with these storms. Additionally, max 1-hour rain rates up to 1.50 inches will be possible, but due to the small area of the intense rainfall cores, flooding is NOT forecast. Expect thunderstorms to cross the eastern border around 10PM and lingering showers over the plains to end shortly after that.

Primetime: 12:30PM to 11PM

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

Westerly and southwesterly surface winds will pick up again this afternoon over these regions. Expect wind speeds just under 20 mph with higher gusts. Paired with low relative humidity values and plenty of dry fuel, a Red Flag Warning has been issued for the lower elevations of the Southwest Slope. High temperatures will reach into the mid 70Fs to 80Fs for the valleys and upper 60Fs to low 70Fs for the mountain valleys. Measurable rainfall is not forecast, though light showers may reach the ground over the Northern Mountains along and near the Continental Divide. Flooding is NOT forecast.

Issue Date: Thursday, May 13th, 2021
Issue Time: 9:10AM MDT

— Flooding is NOT expected today

Calmer weather and warmer temperatures will continue across most of Colorado for today, as light subsidence will continue to the east of a weak upper-level ridge over the Four Corners area. With plenty of sunshine, temperatures are expected to finally push close to seasonal normal after a prolonged stretch of cool weather earlier in the week. This morning’s PW was 0.38 inches at Denver and 0.30 inches at Grand Junction, which is below the normal value for this time of year. The strong sunshine along with enough boundary layer moisture will allow for an isolated shower or weak thunderstorm in the Northeast Plains, similar to what occurred on Wednesday afternoon. However, flooding is not expected today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Northeast Plains:

Partly cloudy and warmer this afternoon with isolated showers and weak thunderstorms possible mainly along the NE border. Max 1-hour rainfall up to 0.6 inches. Gusty winds up to 50mph are possible with the strongest storms. Flooding is NOT expected today.

Primetime: Now through 6AM, with highest rainfall intensity between 1PM and 7PM

Northern Mountains, Front Range, Urban Corridor, Central Mountains, Palmer Ridge, Southeast Plains, Raton Ridge and Southeast Mountains:

Mostly sunny early then partly cloudy and warmer this afternoon. An isolated shower cannot be ruled out east of the Continental Divide. However, flooding is NOT expected today.

Grand Valley, San Juan Mountains, Southwest Slope & San Luis Valley, Northwest Slope:

Mostly sunny and warmer today with high temperatures near seasonal normal. Flooding is NOT expected today.

Issue Date: Wednesday, May 12th, 2021
Issue Time: 9:15AM MDT

— Flooding is NOT expected today

After a nearly 4-day period of cool and unsettled weather (mostly east of the Continental Divide), beautiful spring sunshine returns for nearly everyone today. The departing large-scale trough of low pressure, and its last couple of embedded shortwaves, is being replaced by a weak, transient upper-level ridge as depicted in the visible satellite image below. This will increase subsidence and limit clouds today. The increased sunshine will cause a jump in afternoon high temperatures to levels just below seasonal normal. A couple of showers this morning will dissipate quickly over the Palmer Ridge. This afternoon, weak instability will support a few showers and weak thunderstorms mainly in the Northeast Plains. Gusty winds will be possible with the strongest cells. However, flooding is not expected today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Northeast Plains:

Partly cloudy and warmer this afternoon with isolated showers and weak thunderstorms possible mainly along the NE border. Max 1-hour rainfall up to 0.4 inches. Gusty winds up to 50mph are possible with the strongest storms. Flooding is NOT expected today.

Primetime: Now through 6AM, with highest rainfall intensity between 1PM and 7PM

Northern Mountains, Front Range, Urban Corridor, Central Mountains, Palmer Ridge, Southeast Plains, Raton Ridge and Southeast Mountains:

A few showers this morning over the Palmer Ridge will dissipate and give way to partly cloudy skies this afternoon, along with much warmer temperatures. Flooding is NOT expected today.

Grand Valley, San Juan Mountains, Southwest Slope & San Luis Valley, Northwest Slope:

Mostly sunny and warmer today with high temperatures just below seasonal normal. Flooding is NOT expected today.