FTB 05-19-2022: The Hot, Dry Wind Before The Snowstorm

Issue Date: Thursday, May 19th, 2022
Issue Time: 9:45AM MDT

— Flooding is NOT expected today
— Widespread Red Flag Warnings in effect for most of Colorado

A common saying goes “If you do not like the weather [insert location here], just wait a few minutes”. On a day like today, this saying will be right on point for all of Colorado. As shown in the visible satellite image, below, a strong cold front is currently draped across the Northern Rockies. It will quickly move southward today and enter Colorado early this evening. Behind it, substantial moisture and vigorous dynamics will couple with our unique terrain to provide a powerful May snowstorm for most of the higher terrain and adjacent foothills. However, before we get there, with dry, downsloping winds increasing in strength today, afternoon high temperatures will hit their highest mark of the season for many locations east of the Continental Divide. Now add into the mix very low humidity values, and you guessed it: Red Flag Warnings are widespread today for all but northwest Colorado.

Precipitation will begin as rain below about 11,000 feet today but quickly change to snow. Snow levels will drop all the way to about 6,000 feet by morning. By tomorrow morning, up to 2.25 inches of liquid equivalent is expected over the Northern Mountains! Flooding is NOT expected today.

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:

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

Increasing clouds and warm today with temperatures 5-12F above normal. Windy conditions will develop by afternoon ahead of the strong incoming cold front, and Red Flag Warnings are in effect for parts of the region. Rain and snow will quickly develop shortly after sunset. Max 1-hour rainfall up to 0.4 inches possible very early in the event before the transition to snow occurs. By tomorrow, up to 2.25 inches of liquid equivalent is expected over the Northern Mountains. However, flooding is NOT expected today.

A few streams in the Northern Mountains (especially the Elk River) are running high. Flows are expected to drop quickly tonight as snowmelt pauses for a few days.

Primetime: 6PM continuing into tomorrow morning

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

Partly cloudy with very warm temperatures today, running 10-20F above normal. Windy conditions will develop this afternoon and Red Flag Warnings are in effect. Late in the evening, rain and snow will develop over northern areas and spread south quickly during the overnight hours. Max 1-hour rainfall up to 0.4 inches is possible. Up to 1.4 inches of liquid equivalent is possible over the higher terrain by morning. However, flooding is NOT expected today.

Primetime: 9PM continuing into tomorrow morning

FTB 05-18-2022: Severe Storms and Minor Flooding Possible Over Southeast Colorado

Issue Date: Wednesday, May 18th, 2022
Issue Time: 10AM MDT

LOW flood threat has been issued for the Southeast Plains

The best moisture and dynamics for storm development will move into southeast Colorado today, and a few severe storms will be possible over the far Southeast Plains late this afternoon and evening. Storms are forecast to develop with upslope flow and a little mid-level energy (orange “X”) over the southern Front Range, Palmer Ridge and Southeast Mountains by early afternoon. As they move off these elevated regions, an incoming trough over the Pacific Northwest will help steering flows gain a bit more of a northerly component. So, expect storms to move ESE at a moderate rate and initially only produce lighter rainfall, wind and a little lightning.

As far as moisture, after the passage of yesterday’s cold front, PW has bounced back to 0.59 and 0.61 inches at Denver and Grand Junction, respectively. At Dodge City, PW was measured just under an inch at 0.92 inches, so a nice gradient, as one would expect, as you move east. There also seems to a weak surface High circulation developing over the eastern border, that will help to produce dry, westerly winds on its north side, and moist, easterly and southeasterly winds on its south side. This should keep dew points in the low 50Fs over the far corner (green dashed line), and may help pull in slightly higher moisture, especially as the diurnal flow kicks in.

As the storms move into this deeper moisture, upscale growth is anticipated, and there is a greater threat for severe thunderstorms to develop. Strong winds will be possible as this occurs along with severe hail and local heavy rainfall. Although the flood threat is on the lower end today, minor road flooding and field ponding will be possible as the storms roll through the far Southeast Plains this evening. Therefore, a LOW flood threat has been issued.

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

Storms will kick off over the southern Front Range, Palmer Ridge, Southeast Mountains and to a lesser extent the Raton Ridge by early afternoon. As storms move into the adjacent plains, they should encounter more moisture, which is when upscale growth is anticipated. Large dew point depressions back to the west mean more of a wind than rain threat, and this wind threat will grow as storms move to the southeast. Severe storms will be likely over the far corner with hail up 1 inch in diameter and gusts up to 65 mph possible, if the storms begin to bow. Max 1-hour rain rates up to 1.75 inches are forecast for the Southeast Plains, which could cause local flooding issues such a minor road flooding and field ponding, so a LOW flood threat has been issued. Over the mountains, isolated totals up to 0.15 inches and over the adjacent plains, max 1-hour rain rates up to 0.50 inches will be possible. So, flooding is not anticipated for these regions.

Primetime: 1PM to 8PM (west); 5PM to 10:30 PM (east)

Northeast Plains, San Luis Valley, Central Mountains, Northern Mountains, Northwest Slope, Southwest Slope, Grand Valley, San Juan Mountains & Urban Corridor:

Isolated storms may develop over the eastern San Juan Mountains and southern Central Mountains with isolated totals up to 0.40 inches (south) and 0.10 (north) possible. Elsewhere, it should remain dry today with 80Fs for the lower elevations and upper 60Fs to low 70Fs for the mountain valleys. Flooding is NOT expected.

Primetime: 1PM to 8PM

FTB 05-17-2022: Scattered Storms, Some Severe, Mainly For Northeast Colorado

Issue Date: Tuesday, May 17th, 2022
Issue Time: 10AM MDT

— Flooding is NOT expected today
— One fire burn area is under an elevated threat today. Click here for more details.

As shown in the water vapor image below, an elongated plume of moisture is clearly noted over the northern Rockies this morning. This is associated with a modest jet streak that is poised to enter Colorado today. As seen in observed and modeled atmospheric soundings, the moisture we are seeing in the water vapor image is all in the mid and upper levels of the atmosphere, while the lower levels continue to be dry. Morning PW at Denver was 0.41 inches (close to seasonal average) and 0.28 inches at Grand Junction. However, a close look at observations this morning shows the presence of a bit more boundary layer moisture over northeast CO, southeast WY and western NE.

If the boundary layer moisture persists, which it may over localized pockets of our Northeast Plains, we could see instability of perhaps 1,400 J/kg. On the other hand, a look at the shear profile of the atmosphere does not show a structure conducive of heavy rainfall, but instead more supportive of severe weather. More specifically, the shear in the lower to mid-levels is quite weak, with storm motions of only 17-22 mph expected. But with the approaching jet, shear will increase dramatically in the upper levels, with flow above 500mb exceeding 50mph. This kind of shear favors “low-top” storms, which tend to be less effective at generating sustained heavy rainfall. Overall, we expect an increase in storm coverage for northern Colorado, with brief heavy rainfall possible mainly over the Northeast Plains. However, the more notable threat today will be for large hail and especially damaging winds. Thus, 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:

Mostly sunny early then becoming partly to mostly cloudy with scattered showers and storms developing by early afternoon. Highest coverage over northern areas by the WY/NE border. Max 1-hour rainfall up to 1.4 inches possible, along with large hail and damaging wind. Some nuisance field ponding is possible, but flooding is NOT expected today.

Primetime: 3PM to 10PM

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

Mostly sunny early then becoming partly cloudy with scattered showers and a few storms expected during the afternoon and evening. Max 1-hour rainfall up to 0.8 inches possible along with large hail and damaging wind. Flooding is NOT expected today.

Primetime: Noon to 8PM 

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

Mostly sunny and hot this afternoon, but winds will generally stay down. An isolated shower or storm, accompanied by some brief gusty winds, cannot be ruled out but max 1-hour rainfall of only 0.3 inches expected. Thus, flooding is NOT expected today.

Primetime: 2PM to 8PM

FTB 05-16-2022: Return of Isolated Storms

Issue Date: Monday, May 16th, 2022
Issue Time: 9:15AM MDT  

Flooding is NOT expected today

There’s finally some rainfall to forecast today due to a disturbance that has worked its way in from the west under the ridge (orange “X”). This feature will move east today, along with the axis of the ridge, and help to initiate scattered storms over the mountains by early afternoon. These storms are forecast to work their way into the adjacent plains with westerly steering flow aloft late this afternoon into the evening hours. There’s a nice plume of moisture over southeast Colorado shown in the water vapor imagery below (green dotted line), and SSW surface flow is anticipated to turn more southerly throughout the day with a developing surface Low. That means not much moisture advection back to the west, but higher dew points should remain intact over eastern Colorado that could cause some stronger thunderstorms to develop. 

PW at Denver and Grand Junction remains about the same as yesterday, 0.36 and 0.35 inches, respectively. The Grand Junction sounding showed this moisture aloft, so it will be too dry to generate storms across the lower elevations. Over the mountains and immediate adjacent plains, expect high-based storms to develop similar to yesterday. A slight increase in dynamics with the mid-level energy should help generate more coverage, although it will still be pretty spotty with only light accumulation forecast. As the storms move east and encounter the weak dryline over the far eastern plains, a couple of severe storms are possible with strong outflow winds and severe hail being the main threats. As for the flood threat, the lack of deeper surface moisture means that the storms will have high bases and likely become outflow driven, which should limit their heavy rainfall potential. Nonetheless, moderate rain rates and much needed rainfall are anticipated under these isolated storm cores. Since storms are not likely to meet flood threat criteria as they quickly move eastward, NO flood threat has been issued.

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, Northeast Plains & Southeast Plains:

Expect the highest coverage and strongest storms over these forecast zones today. Over the Palmer Ridge, better moisture will be over the far eastern portion of the forecast zone. As mentioned above, slightly less moisture north than south and west than east. Isolated max 1-hour rain rates up to 1.10 inches (east) and 0.40 inches (west) are possible. Storms will likely produce strong outflow winds today and severe hail may be possible for storms that can make it to the eastern border before instability drops off. Flooding is NOT anticipated at this time.

Primetime: 3PM to 10PM

Front Range, Southeast Mountains, Central Mountains, Northern Mountains & Urban Corridor:

Isolated to scattered, high-based storms are anticipated to develop by early afternoon today favoring the Front Range and areas near and along the Continental Divide (north). A very dry surface layer will increase the wind threat with only limited rainfall forecast. Max 1-hour rain rates up to 0.15 inches are possible with most storms producing under 0.05 inches of accumulation. Flooding is NOT forecast.

Primetime: 1:30PM to 8PM

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

Too dry for any rainfall today, but an isolated weak storm may be possible over the San Juan Mountains near the Continental Divide. High temperatures will climb into the mid to upper 80Fs across the lower elevations. A Red Flag Warning has been issued from 12PM to 8PM this evening for the SLV, eastern San Juan and La Garita Mountains as well as portions of the Raton Ridge. Dry southwest winds in the 15 to 25 mph range and gusts up to 35 mph are forecast with relative humidity dropping into the low teens.