FTB 05-05-2021: Isolated, Gusty Storms Mainly Northeast

Issue Date: Wednesday, May 5th, 2021
Issue Time: 8:45AM MDT

— Flooding is NOT expected today

Colorado remains under the influence of a large-scale eastern US trough, with shorter wave disturbances rippling through the flow. One such disturbance brought scattered showers and a few weak thunderstorms across the state yesterday. Another such disturbance, as seen on the low-level water vapor image (orange dashed line), below, will do the same today.

This morning’s Precipitable Water (PW) at Denver and Grand Junction was just under 0.5 inches, which is very close to seasonal normal for early May. With low moisture content and cooler than normal afternoon temperatures, expect very limited atmospheric instability. Nonetheless, the atmosphere will be able to muster isolated to widely scattered showers and weak thunderstorms mainly over the northeast quadrant of the state. However, flooding is not expected today. With very strong steering winds in the upper levels of the atmosphere, any slightly stronger storms will be able to efficiently transfer that wind down to the surface. Thus, there is a chance of marginally severe wind gusts, up to 60mph, along the Kansas border.

Switching over to a check of hydrologic conditions, we note that the recent cool temperatures have kept snowmelt generally in check. The only area that currently bears watching is the northern Front Range basins: in particular, the Cache la Poudre and Big Thompson. These rivers are currently experiencing elevated flows from recent rain and snow, but are expected to recede a bit with the lack of rain over the next few days. However, given the large (and growing) snowpack in their upper basins, we will continue to watch these areas closely over the coming weeks.

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

Partly to mostly cloudy and seasonably cool with isolated to scattered showers and weak thunderstorms this afternoon and into early evening. Early snow showers possible above 7,500 feet. Maximum 1-hour rainfall up to 0.2 inches above 6,000 feet and 0.5 inches below 6,000 feet. Gusty winds up to 60 mph are possible with the stronger storms, especially towards the Kansas border. Flooding is NOT expected today.

Primetime: 11AM to 7PM

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

Mostly sunny to partly cloudy and warmer with high temperatures close to seasonal normal. Isolated rain and snow showers are possible in northern areas this morning and early afternoon. Max 1-hour rainfall up to 0.1 inches. Gusty winds are possible, mainly over higher elevations. Flooding is NOT expected today.

FTB 05-04-2021: More Sunshine & Isolated PM Storms

Issue Date: Tuesday, May 4th, 2021
Issue Time: 9:05AM MDT

— Flooding is NOT expected today

A shift in the weather pattern will take place today, which means more sunshine and warmer temperatures. The trough that brought a nice round rainfall and snow to the state the last couple of days is currently to our southeast, and more dry, northwesterly flow aloft has begun to fill in over the state. Both the Grand Junction and Denver sounding’s this morning show this much drier air mass in the mid to upper levels of the atmosphere. Nonetheless, the visible satellite image below (from 8AM this morning) still shows plenty of cloud cover and some fog, which means there will be enough residual moisture for a round of scattered storms this afternoon.

A shortwave (orange X) is expected to travel through this northwesterly flow, which will help create lift out in front of it. As this shortwave progresses through the northern and northeast portion of the state, it will help produce scattered storms across the Northern, Central and Front Range Mountains during the early afternoon. Storms will push into the adjacent plains (Urban Corridor, Palmer Ridge and Northeast Plains), but fast northwest steering flows and high cloud bases indicate rainfall accumulation will be limited. Flooding is not expected, and the main threat from the thunderstorms that develop today will be brief outflow winds and lightning.

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, Northwest Slope, Northern Mountains, Front Range, Urban Corridor, Central Mountains & Palmer Ridge:

Another round of scattered storms is expected this afternoon. Snow showers are likely over the highest elevations, but precipitation should mostly fall as rain. A couple scattered thunderstorms are not out of the question over the mountains, but heavy rainfall is not expected. Isolated max 1-hour rain rates up to 0.20 inches will be possible. Additionally, forecasting westerly and northwesterly surface winds to pick up over the high terrains as the jet moves overhead. As storms move swiftly off the mountains into the adjacent plains with southeast movement, they will likely produce a little more lightning, brief wind gusts and light to moderate rainfall. Isolated storm totals may come close to 0.30 inches. Light showers look to develop over the Palmer Ridge tonight and move into the Southeast Plains by the early morning hours with favorable lift from the jet overhead. Flooding is not forecast.

Primetime: 12:30PM to 11PM

Southeast Mountains, Southeast Plains & Raton Ridge:

Moisture and lift won’t be quite as strong over these regions today and downsloping winds will help dry out the lower levels even more. The isolated storms that are able to develop likely won’t produce much (if any) accumulation. Best chance for accumulation will be if storms can stay intact from the northwest and make it to the eastern Southeast Plains or eastern Raton Ridge. Totals up to 0.25 inches will be possible. Light showers may be possible in the early morning hours over the Southeast Plains. Flooding is not forecast.

Primetime: 3PM to 11PM

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

Broken cloud cover is forecast over the high terrains with sunny conditions for the San Luis Valley and Southwest Slope. With dew points in the teens and 20s, rainfall is not forecast for these regions. Northwesterly surface winds are forecast to pick up over the Grand Valley, San Luis Valley and San Juan Mountains with the windiest conditions over the San Juan Mountains as the jet moves in. High temperatures should be around normal for early May.

FTB 05-03-2021: Snow and Wetting Rainfall Continue for Another Day

Issue Date: Monday, May 3rd, 2021
Issue Time: 9:50AM MDT

— Flooding is NOT expected today

The surface observations from 8AM this morning show almost completely overcast conditions across the state (filled in circles) and much cooler temperatures behind yesterday’s cold front (red numbers). This is about a 20 to 30 degF drop from this weekend, so you know it must be springtime in Colorado. Precipitation continues over and near the higher terrains with the trough near the four corners region helping to produce orographic lift. The snowline has dropped slightly below the 7,000 ft contour along the Front Range, and precipitation over the mountains is falling as snow (* symbol).

Expect these conditions to continue today and expand in coverage this morning into early afternoon as the open trough moves east. Although there is plenty of moisture and lift available for widespread precipitation, limited instability means that rainfall at the lower elevations will be more wetting in nature rather than convective. This paired with snow at the high elevations means there is no flood threat issued today. The pulse-like showers and snowfall are expected to gradually come to an end by tomorrow morning.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. 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:

Northern Mountains, Front Range, Southeast Mountains, Central Mountains & San Juan Mountains:

Quite a bit of wet and heavy snow is expected this afternoon as the base of the trough, or center of energy, moves east. Generally, snowfall accumulation will be in the 6-12 inch range with local higher totals possible. The Central Mountains look to get between 0.75 and 1.50 inch of precipitation, whereas the San Juan Mountains could see the same, but will be more isolated. Over the Front Range and Southeast Mountains, isolated totals up to 1.25 inches of precipitation are possible by morning. With precipitation falling as snow, flooding is not forecast. Tune into your local NWS for the latest on winter weather advisories and warnings.

Primetime: Ongoing to 2AM

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

A dreary day is ahead for areas along and near the mountains, so expect rain across these lower elevations. As the system continues to move slowly eastward into tonight, the shortwave looks to weaken. So, generally, only about a 0.20 to 0.40 inches of rain are expected over the eastern Raton/Palmer Ridge and far southeast corner of the state, but isolated totals up to 0.75 inches are possible. Isolated totals along the Urban Corridor and areas just east of the Southeast Mountains could be slightly higher in the 0.75 to 1 inch range, but generally expect totals in the 0.25 to 0.50 inch range. Due to the gradual nature of the rainfall, flooding is not expected. However, there may be some localized, light ponding due to compounding rainfall.

Primetime: Ongoing to Midnight

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

Fairly widespread rainfall will continue today for the lower elevations of the Northwest Slope and Grand Valley. Isolated totals around 0.40 inches will be possible and totals over the higher elevations could reach 1 inch. Isolated areas of lower elevations in the Southwest Slope may see up to 0.15 inches by morning, and the higher elevations could just under 0.50 inches. Flooding is not forecast due to the gradual nature of the rainfall.

Primetime: Ongoing to 10PM

FTB 05-02-2021: Low Flood Threat Issued for the Palmer Ridge and Northeast Plains

Issue Date: Sunday, May 2nd, 2021
Issue Time: 10:15AM MDT

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

It’s going to be a true Colorado spring day with a potpourri of weather phenomenon across the state: sunshine, fire danger, rain and snow. Earlier this morning, there were some isolated light showers over the Northwest Slope and cloud cover over the eastern border associated with some energy moving through the upper-level flow. Today and into tomorrow, the trough to our west will deepen and slowly move into the four corners region. Between the lift from this strengthening system and a strong cold front returning low-level moisture, the stage will be set for widespread rainfall and snow (higher elevations) over the next couple of days.

The first round of rainfall this afternoon is expected to be more convective in nature with stronger storms forecast across the eastern half of Colorado from about Highway 50 to the northern border. The main threats from the severe storms that develop will be heavy rainfall, large hail and strong outflow winds. The largest flood threat from these storms looks to be confined to the Northeast Plains, but some heavy rainfall over the Palmer Ridge will also be possible. A Low flood threat has been issued for these regions.

Behind a strong cold front that drops south late this afternoon and evening moisture is expected to increase and upslope flow will begin to dominate the pattern. Precipitation is expected to become more stratiform in nature over the Front Range, Southeast Mountains, Urban Corridor and Palmer Ridge. Snow should initially be confined to the highest elevations but expect the snow line to drop quite a bit tonight into tomorrow morning. Additionally, as morning approaches, the precipitation should become more widespread over the mountains. Due to the more gradual nature of the rainfall, cross over from rain to snow and dry soils, no flood threat has been issued for the upslope flow component of the precipitation.

For the burn area forecast, please visit the Flood Burn Forecast tab at the top of the page.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. 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, Urban Corridor, Front Range, Southeast Mountains, Southeast Plains, Raton Ridge, & Palmer Ridge:

Expect storms to begin to pop over the Front Range by midday and move into the adjacent plains by early afternoon. Severe storms will be possible over the Northeast Plains with thunderstorms also likely along the Urban Corridor and Palmer Ridge. The main threats from today’s stronger storms will be local heavy rainfall, hail and strong outflow winds. Larger hail and stronger winds will be possible with the severe storms that form over the eastern plains. A Low flood threat has been issued for the possibility of small stream flooding, field ponding and street flooding. Max 1 to 2 hour totals up to 1.1 inches (west) and up to 2.5 inches (east) are possible.

The rainfall becomes more stratiform tonight with the post-frontal upslope flow. With the snow line dropping, precipitation over the Front Range and Southeast Mountains should turn to snow around 7-8K feet. Tune into your local NWS office for the latest on winter weather advisories and warnings. Dry soils and more gradual rainfall will limit the flood threat overnight, so the flood threat has not been extended into the higher terrains. For the burn area forecast, please visit the Flood Burn Forecast tab at the top of the page.

Primetime: Noon to 10PM

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

More precipitation is finally in the forecast. This afternoon, expect precipitation in all zones just south of I-70 to the northern border. Max 1-hour rain rates up to 0.60 inches will be possible, so at this time flooding is not forecast. Precipitation is forecast to fill in overnight and into tomorrow morning over the mountain regions after the front moves south. The snow line will drop at that time as well, so flooding is not forecast. For the burn area forecast, please visit the Flood Burn Forecast tab at the top of the page.

Over the Southwest Slope and San Luis Valley, a Red Flag Warning has been issued. Please tune into your local NWS office for the latest on fire danger.

Primetime: Noon to 9PM