Issue Date: Tuesday, June 8th, 2021
Issue Time: 10:05AM MDT

PM Update (4PM): The shortwave continues to progress to the Northeast and is currently located near the CO/UT/WY border. Lift out in front of the shortwave and southeasterly flow at the surface is producing a cumulus field over the northern Front Range, Medicine Bow and Laramie Mountains. Storms will develop along this line and move towards the northeast through this evening. An outflow boundary from the convection (south side) may push across the northern CO border later this evening. If this were to trigger any convection in the threat area below, storms could quickly become severe in the high CAPE/shear environment. In addition to large hail, strong winds and a possible tornado, storms would be located in a moisture-rich location. Dew points in the area are upper 50Fs and low 60Fs, which is extremely elevated. This would help storms that develop to produce very heavy rainfall with max 1-hour rain rates up to 2.25 inches for an hour or more. Flash flood threats would include road/small stream flooding as well as field ponding. While heavy precipitation chances are still on the lower end, this scenario warrants an upgrade to a Low flood threat. This is an overnight threat. 

— Flooding is NOT expected today

Not much change in the large-scale weather pattern today, but there are some subtle differences. Today, the shortwave that was off the coast of California will start to become absorbed into the high amplitude trough/ridge pattern (see yesterday’s FTO for more details). This mid-level lift (orange “X”) is linked to a very dry air mass (note the cloud-free conditions), and PW at Grand Junction has already dropped to 0.27 inches. The shortwave will help tighten the pressure gradient as it moves to the northeast, which in turn will increase the surface winds over western Colorado. This will produce elevated fire danger with the very low relative humidity values, so a Red Flag Warning has been issued. The drier air mass has also worked its way into the mountains and immediate adjacent, eastern plains (central and south), which will reduce the precipitation chances close to zero this afternoon.

Better moisture is located near the northern border (cloud cover in central Wyoming) and over the far eastern plains (green dashed line). That means isolated storms, producing mostly virga and wind, could pop over the northern Front Range this afternoon. Best chance for measurable rainfall from a meaningful storm will be over the Northeast Plains. This would occur if the shortwave or outflow boundaries can provide enough lift to break the cap over this region later this evening. Slow steering flow and a moisture-rich environment would mean that the storms would be capable of producing heavy rainfall. However, it looks like a strong enough cap is intact, and that the chances for this happening are low. If this scenario for evening storms becomes increasingly more likely, a PM update will be issued. For now, flooding is NOT expected.

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:

Higher moisture exists over the eastern plains; however, there is a pretty strong cap in place. If the cap is broken over the Northeast Plains, with aid of the shortwave or an outflow boundary, heavy rainfall would occur. Max 1-hour rain rates up to 2 inches would be possible along with hail and strong outflow winds. At this time, this scenario is not looking likely enough to issue a threat, but if chances for this solution increase, a PM update will be issued. Overnight/early morning rainfall may also be possible over the northeast corner as convection rotates in from the panhandle of Nebraska. Totals between 0.50 and 0.75 inches would be most likely, but there’s low confidence in this occurring.

There may also be an isolated stray storm that forms over the Southeast Plains that pops along a convergence line. Drier air is in place, but max 1-hour rain rates up 1 inch would be possible. Flooding is NOT forecast.

Primetime: 1PM to 11PM

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

Hot and dry today with highs reaching into the low to mid-90Fs for the lower elevations. The Pueblo area could reach slightly above the 95F mark, and 80Fs are forecast for the mountain valleys. Measurable rainfall is most likely over the northern Front Range, but the more likely scenario is virga , sprinkles and wind. Totals will remain under 0.10 inches.

Primetime: 3PM to 10PM

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

A Red Flag Warning has been issued through 9PM this evening. South winds in the 10-15 mph range are forecast, and gust could reach between 30 and 40 mph. Relative humidity in the single digits means high fire danger, so use caution with any activities that could cause a spark. Rainfall is not forecast and highs should be slightly cooler than yesterday.

Issue Date: Monday, June 7th, 2021
Issue Time: 9:00AM MDT

— Flooding is NOT expected today

Colorado continues to be sandwiched between two systems today. The Low to our east, is helping to produce more northernly flow over eastern Colorado. The trough over the Pacific Northwest and a cut off low off the California coast are aiding in more southwesterly flow aloft over western Colorado. Across central Colorado, the transition flow between the two systems is more westerly. With the ridge continuing to strengthen, expect another day with hot temperatures. The water vapor imagery below also shows some residual moisture over the area, more so east than west.

PW at Denver this morning was measured at 0.56 inches and over Grand Junction was measured at 0.50 inches. This indicates that the higher moisture accompanying yesterday’s front over eastern Colorado has already begun to mix out with the westerly flow. With southwest and westerly flow aloft forecast to continue today, the drier air mass marked below should be advected across the state (west to east), which will continue to decrease the available moisture. Decreasing this moisture should cause a downtick in storm coverage and intensity over the mountains that develop from the upslope flow. Additional scattered storm development is likely over the eastern, elevated ridges by mid-afternoon with southwesterly flow at the surface. These storms, and the storms that meander off the Front Range this evening, are expected produce lower rainfall totals in their storm cores when compared to yesterday. If stronger storms develop, the main threat will be strong outflow winds, lightning and only brief, heavy rainfall in the small storm cores. Therefore, flooding is NOT forecast 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:

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

It rapidly has transitioned from spring to summer. Today’s high temperatures will reach into the upper 80Fs and low 90Fs across the I-25 corridor. Mid 90Fs are forecast across portions the eastern plains. Over the mountains, valleys will reach into the low 80Fs.

As for rainfall, isolated (south) to scattered (north) storms will develop over the mountains this afternoon. With the dry air mixing in from the west, rain rates will be lower with some storms only producing virga. Isolated max 1-hour rain rates up to 0.25 inches (north) and 0.15 inches (south) will be possible. Storms that develop over the ridges will produce slightly higher rain rates, up to 0.45 inches per hour. If outflow boundaries can help break the cap and initiate some storms over the eastern border, max 1-hour rain rates up to 1.25 inches will be possible. The main threat from the stronger storms that develop will be brief, heavy rainfall, strong outflow winds and lightning. Small hail may also be possible. Flooding is NOT forecast.

Primetime: 1PM to 11PM

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

With the ridge continuing to strengthen and southwest flow pulling in a drier air mass, it’s going to be hot and dry day ahead. High temperatures over the valleys and NW/SW Slope will reach into the mid-90Fs. Over the mountain valleys, highs will be in the low to mid-80Fs. Isolated storms will be possible along and near the Continental Divide. However, storms will likely produce more cool outflow winds than measurable rainfall. Totals should remain around or just below 0.10 inches. Flooding is not forecast.

Primetime: 1PM to 8:30PM

Issue Date: Sunday, June 6, 2021
Issue Time: 10:05AM MDT

— A LOW flood threat has been posted for the Palmer Ridge

Colorado’s weather has quickly transitioned from spring-time to summer-time dynamics. In short, this implies that more subtle features in the flow can account for the presence of heavy rainfall, but also the lack of it. This was seen on Saturday afternoon in the higher terrain east of the Continental Divide, where a couple of thunderstorms resulted in a quick 1 inch per hour or more of rainfall. This morning’s visible satellite image, below, shows a few differences from yesterday’s setup. First of all, PW is higher both at Denver (0.55 in. yesterday, 0.67 in. today) and Grand Junction (0.62 in. yesterday, 0.71 in. today). West of the Continental Divide, moisture will drop sharply this afternoon as yesterday’s lack of steering winds are replaced by 30mph drier, westerly flow. However, winds turn sharply in a southward direction right along the Continental Divide today implying areas along and east of it will experience another day or rather weak steering flow (albeit a little stronger than yesterday). Additionally, there is a more discernable forcing feature, both aloft and at the surface, currently noted over far northern Colorado and into Wyoming. At the surface, there is a pronounced wind shift from SW to N in far southeast Wyoming. This will move into Colorado later this afternoon and evening, providing a little more focus for storm activity.

Overall, we expect a few rounds of thunderstorm activity later this morning and into the afternoon. An initial round of activity is expected early in the afternoon, followed by a more organized round of storms in the late afternoon and early evening as (i) early storm complexes merge, and (ii) as the forcing feature moves across Colorado. The majority of storms will be conventional summer-time pop-up storms with short-term heavy rainfall but not much of a flood threat. However, along the Palmer Ridge, the pattern of light northerly winds aloft along with easterly boundary layer flow suggests the potential for training of storm cells, which will raise the rainfall intensity enough to warrant a Low flood threat for this region. Hail and gusty winds will also be possible with the strongest storms 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:

Palmer Ridge:

Partly cloudy and continued hot with scattered to numerous showers and thunderstorms developing later this morning and continuing into the early evening hours. Max 1-hour rainfall up to 1.3 inches possible, with max 3-hour rainfall up to 2.0 inches. A Low flood threat has been posted for this region for isolated flash flooding, debris slides and mud flows. Hail and gusty winds could also accompany the strongest storms today.

Primetime: 12PM through 9PM

Front Range, Urban Corridor, Northeast Plains, Southeast Plains, Raton Ridge, Central Mountains, Northern Mountains, San Juan Mountains, Southeast Mountains:

Continued hot with isolated to scattered showers and thunderstorms this afternoon and into early evening. Max 1-hour rainfall up to 1.4 inches (far east below 5,000 feet) and 0.8 inches (west, above 5,000 feet). Hail and gusty winds are possible with the strongest cells but flooding is NOT expected today.

Primetime: 12PM through 8PM

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

Continued hot and drier today but an isolated shower or storm is possible especially in the higher elevations. Max 1-hour rainfall up to 0.3 inches. A drier atmosphere along with gusty winds has resulted in a Red Flag Warning for parts of the region.

Primetime: 2PM through 7PM

Issue Date: Saturday, June 5th, 2021
Issue Time: 9:05AM MDT

— Flooding is NOT expected today

There’s a split in the weather pattern over the state today, which can be seen below in the water vapor imagery by an increase in moisture west (blue/white shades) and dry conditions across the lower elevations east (orange/yellow shades). As some mid-level energy rotates around the High (orange “X”), it will bring a slight increase in PW values west. More importantly, it looks like this increase in moisture will be in the surface layer. That will translate into more widespread storms and higher efficiency of rainfall when compared to the last couple of days.

Expect numerous storms to fire by early afternoon over the mountains and elevated plateaus as the shortwave moves overhead and combines with the diurnal flow. For the most part, rainfall cores should be small in area and will likely pulse in intensity. Storms that form over the mountains east of the Continental Divide are expected to slowly drift eastward with the disturbance. However, as they move off the mountains and into the adjacent plains this evening, they will encounter that aforementioned dry air mass. Thus, storms should rapidly dissipate and pose more of a wind than rainfall threat.

Overall for rainfall today, there’s still a decent spread in the temperature and dew point over the mountains and west. So brief, heavy rainfall may be possible in the storm cores, but only moderate rainfall totals are forecast. Once again, the main threat from the stronger storms that develop should be gusty outflow winds; although, dangerous lighting and small hail are also possible. 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:

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

Numerous scattered storms will develop by midday over the mountains regions as the shortwave increases lift and moisture over the area. Storms will be small in area size this afternoon/evening and are expected to pulse in intensity. Brief, heavy rainfall in the cores will be possible with isolated max 1-hour rain rates up to 0.60 inches. The majority of storms will produce between 0.25 and 0.40 inches of rainfall. Strong outflow winds, lightning and hail will be the main threat from the stronger storms that develop. These outflow boundaries may help trigger additional convection. Storms should start to come to an end a couple hours after sundown with all activity ending by midnight. Flooding is NOT forecast.

Primetime: 11:30AM to Midnight

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

It’s going to be another hot day ahead with temperatures similar to yesterday (mid to upper 90Fs). It might not be quite as hot over some areas if a cool outflow boundary can knock a couple degrees off late this afternoon. Storm development over the mountain and ridges will be more widespread this afternoon and some rainfall may occur 1) if storms push off the mountains into the valleys and 2) if outflow boundaries collide to trigger additional convection. The main threat from those storms will be wind and lightning. Totals should remain around 0.10 inches, so flooding is NOT forecast.

Primetime: 11:30AM to 10PM

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

Summer temperatures return with 90F+ forecast across the I-25 corridor and eastern plains. Mountain valleys should reach into the upper 70Fs and may perhaps cross the 80F marker. The cut off low will reinforce the dry air over these regions. So, as storms move off the mountains this evening, expect them to dissipate quickly and produce gusty outflow winds. Plenty of virga means totals will remain under 0.05 inches except over the Palmer Ridge where isolated totals may reach up to 0.15 inches.