Issue Date: Thursday, May 21, 2020
Issue Time: 11AM MDT

— A LOW flood threat has been issued for the Southeast Plains
—Afternoon update possible today

As shown in this morning’s water vapor image below, a large-scale trough is continuing to move eastward across Colorado. Significant drying has occurred over the last 24 hours. For example, this morning’s Precipitable Water (PW) from the Denver and Grand Junction radiosonde balloons is 0.28 inches and 0.24 inches. However, deeper moisture is not very far away, with PW above 1 inch just across the border into Nebraska and Kansas. With very cold upper-level temperatures today, it will not take much heating and surface moisture to initiate isolated storm activity across the Palmer Ridge during the early afternoon. This activity will be benign, with perhaps some light showers possible along with gusty downdraft winds.

Of more concern is storm activity expected to develop along the aforementioned moisture boundary across the Southeast Plains. Although most of the activity will remain in Kansas, there is enough confidence that a mesoscale-to-synoptic outflow boundary from the Kansas convection will propagate into Colorado, carrying with it significant instability (CAPEs > 2000 J/Kg). With relative weak storm-scale steering wind, there is the potential for prolonged redevelopment of activity over the same areas. Thus, a Low flood threat has been issued for eastern parts of the Southeast Plains. Activity could persist well into the overnight hours, supporting the threat of isolated street and field flooding along with flooding of smaller creeks and streams. Favorable shear profile forecasts support large hail in earlier storms, up to 2 inches in diameter.

Although more uncertain, it is possible that the moist outflow boundary will make it as far west as the Wet Mountains west of Pueblo during the overnight hours. This would be unusual from a climatological perspective, but high-resolution guidance suggests that if this were to occur, heavy rainfall, capable of flooding, would be possible. Thus, an afternoon update is possible today to address this risk.

Elsewhere, significant cooling will occur today, which will somewhat reduce the threat of wildfire initiation and spread.

 

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:

Northern Mountains, Front Range, Urban Corridor, Northeast Plains, Southeast Plains, Grand Valley, Northwest Slope, Southwest Slope, San Juan Mountains, Central Mountains, Southeast Mountains:

Mostly sunny, much cooler and drier today with temperatures up to 15F cooler than Wednesday. Isolated thunderstorms are possible over the Front Range and Urban Corridor in the afternoon. However, only very light rainfall is expected along with gusty winds. Flooding is not expected.

Palmer Ridge, Raton Ridge, Southeast Plains:

Mostly sunny early then scattered thunderstorms developing over far southeast areas. Max 1-hour rainfall up to 2.25 inches, with max 3-hour rainfall up to 3 inches possible. A Low flood threat has been issued for parts of the Southeast Plains for isolated street and field flooding. Large hail may accompany the earlier storms. Primetime is 5PM to 3AM.

An afternoon update may be possible to address possible overnight storm concern in areas farther west.

Issue Date: Wednesday, May 20th, 2020
Issue Time: 9:30AM MDT

— A LOW flood threat has been issued for the Northeast Plains

The low pressure system starts to migrate to the northeast today, which will place the jet stream over western and central Colorado. With increasing surface winds and dry south and southwest flow, fire danger will expand across the state. Today, the Red Flag Warning will also include the Central Mountains, southern Front Range, Southeast Mountains, Raton Ridge and western Southeast Plains. Be sure to tune into your local NWS office for more information.

With the dry air intact over western and central Colorado, not expecting any rainfall activity today. The exception will be over the eastern plains where a nice dry line sets up as the moisture mixes out from west to east with help from a lee trough. This will set the stage for some severe thunderstorms later this afternoon and evening with the main threats being large hail and strong winds. Although, a brief/weak tornado can’t be ruled out over the northeast corner of the state.

Storm coverage looks spotty along the dry line, so anticipating fewer storms over the Southeast Plains. If storms are able to sustain themselves, localized heavy rainfall will be possible. Due to better dynamics near the Wyoming/Nebraska border and a nearly stationary storm line forming, there is higher confidence for localized flooding along the southern end of this MCS. Thus, a Low flood threat has been issued. A cold front drops through overnight, which will help knock down high temperatures tomorrow another 5-7F.

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:

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

Looks to remain dry over these regions this afternoon with the exception of the Northeast and possibly the Southeast Plains. If storms on the southern end of the MCS drop into the state, expect 2-3 hours of continuous rainfall, which could produce totals just over 2 inches this evening. A Low flood threat has been issued for this reason with the main threats being road and low-lying area flooding. Lower confidence in storms over the Southeast Plains, but if they do form and are able to sustain themselves, they will produce strong outflow winds, large hail and localized flooding. There will be a PM update if confidence in storm formation increases by noon. Fire danger is critical for the southern Urban Corridor, Front Range and western Palmer Ridge, so be sure tune into your local NWS office for the latest.

Primetime: 4PM to 10PM

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

Today is the peak of fire danger for the week as the jet moves overhead, dry air is in place and warm temperatures will help drop humidity values into the low teens to single digits over a large area. A Red Flag Warning has been issued from 10AM to 9PM for the majority of these regions. Surface winds will again be in the 15 to 25 mph range with gusts up to 50 mph possible. Use caution with any activity that can cause a spark and avoid burning. Be sure to tune into your local NWS office for the latest.

 

Issue Date: Tuesday, May 19th, 2020
Issue Time: 8:40AM MDT

— Flooding is NOT expected today

Hot temperatures and critical fire weather will once again be the main weather stories, and western and far eastern Colorado will likely see a slight uptick in highs when compared to Monday. The low pressure and associated jet start to move slightly westward and northward throughout the day, which will once again cause critical fire weather over western and southern Colorado. As these higher wind speeds mix down to the surface and dry continues to be entrained from the southwest (PW was only 0.25 inches in Grand Junction), relative humidity values are forecast to drop into the low teens.

There is a nice, albeit weak, axis of subtropical moisture marked with the green dashed line below. As this feature moves eastward, it will be met by more humid, southeast surface winds over the adjacent eastern plains thanks to a developing lee trough. Together, this moisture will allow some showers and weak thunderstorms to pop up over the mountains with a few stronger storms possible over the plains. Quick storm motion to the NNE and overall limited atmospheric moisture will keep the flood threat away, although the stronger storms over the plains will likely produce impressive winds gusts and small hail.

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, Northern Mountains, San Juan Mountains, Central Mountains, Southeast Mountains, Urban Corridor, Palmer Ridge, Raton Ridge, Northeast Plains & Southeast Plains:

The ribbon of moisture from the Gulf of Mexico will help spark scattered afternoon thunderstorms over the mountains and adjacent plains. Storms over the mountains will likely produce some gusty winds due to the high bases and dry air aloft. Expecting the best accumulations along and near the Continental Divide with max 1-hour rain rates up to 0.30 inches possible.

Over the adjacent eastern plains, storms will favor the southern Palmer/Raton Ridge and western portions of the Northeast/Southeast Plains for accumulations. Isolated 1 to 2-hour rain totals up to 0.75 inches will be possible with max 1-hour rain rates around 0.50 inches. A couple severe storms are possible over the western portion of the eastern plains with the main threats being strong winds and hail up to 1-inch in diameter. The far eastern plains should remain capped, so we won’t be able to tap into that moisture today. Light rainfall may linger over the Northeast Plains into the early hours of the morning. Flooding is not forecast.

Primetime: 1PM to 3AM

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

Critical and enhanced fire weather returns today (and again tomorrow) with a Red Flag Warning issued from 11AM to Midnight for the majority of these regions. With the jet moving over the area, southwest surface winds are expected to increase. Generally, winds will be in the 20 to 30 mph range with gusts up to 50 mph possible. Relative humidity values are forecast to drop into the low teens, so please use caution with any activity that can cause a spark. Be sure to tune into your local NWS office for the latest.

Issue Date: Monday, May 18th, 2020
Issue Time: 8:30AM MDT

— Flooding is NOT expected today

It’s going to feel like a hot summer day with high temperatures generally 15F above normal! This is due to the strong, amplified ridging pattern in place. This pattern will continue to pull in an arid air mass from the southwest, which will keep Colorado rain free this afternoon and help increase fire danger. A weak disturbance is marked with the orange “X” below, and it is helping provide some morning cloud cover. Most of this moisture will mix out as the feature moves eastward throughout the morning, and behind the feature, the dry air will fill in. There may be enough residual moisture left for a high-based rain shower or two over the eastern Raton Ridge. However, don’t expect more than a light sprinkle.

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, Northern Mountains, Northwest Slope, Urban Corridor, Palmer Ridge, Northeast Plains, Southeast Plains, & Raton Ridge:

What little moisture remains over eastern Colorado will likely mix out and dry air will continue to move northwestward. Other than an outside sprinkle over the Raton Ridge later this afternoon, rainfall is not forecast. Expecting highs to reach the mid to upper 80Fs over the eastern plains and Urban Corridor. Lower 80Fs are forecast for the Northwest Slope, and highs over the mountain valleys will reach into the 70Fs.

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

High fire danger for these regions this afternoon with a Red Flag Warning issued from 11AM to Midnight. Increasing southwest surface winds are forecast as the gradient to the west tightens and the low moves slightly eastward. This will produce winds in the 15 to 25 mph range with gusts up to 40 mph possible. Additionally, relative humidity values will drop into the single digits. Tune into your local NWS office for more information.