Issue Date: 5/26/2018
Issue Time: 7:30 AM

NO FLOOD THREAT IS FORECAST TODAY.

Memorial Day Weekend is being kicked off by hot and dry conditions statewide, as high pressure ridging aloft continues its hold on Colorado. The ridge axis is sliding eastward, however, and this will allow the southwesterly flow aloft to pull just a bit of the mid- & upper-level moisture from across Arizona and New Mexico into western Colorado. This moisture will be enough to kick off a couple afternoon/evening thunderstorms, aided by upslope flow and hot temperatures, but it won’t be enough to really create any wetting rains. Instead, dry thunderstorms, characterized by cloud-to-ground lightning, gusty winds, and little (if any) rainfall, are expected across the High Country, coinciding with low surface relative humidities (5-15%) and dry fuels thanks to worsening drought conditions. This is a dangerous cocktail for fire ignition and subsequent rapid fire growth, and extreme care must be taken for all regions west of I-25. Even if you aren’t included in the Red Flag Warning officially, the fire danger is still elevated.

For areas east of the mountains, hot and dry conditions will be widespread, with temperatures taking aim at record highs across the Urban Corridor and Northeast Plains. The record high for the date in Denver is 95°F, to give you an idea as to the magnitude of heat expected. High-based cumulus clouds will be about all the atmosphere can muster, with a few streaks of virga being present beneath the cloud bases. An isolated dry thunderstorm near the Cheyenne Ridge cannot be ruled out, but will most likely occur on the Wyoming side of the border.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, jump below the map.

Zone-Specific Forecasts

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

Hot and dry will be the name of the weather game today, with high temperatures reaching near-record levels across the Urban Corridor and Northeast Plains. High-based cumulus clouds will be the best Mother Nature can do with the only moisture existing 5km above the surface. An isolated, dry thunderstorm near the Cheyenne Ridge during the evening hours cannot be ruled out; if one does occur, it will produce gusty winds and lightning, and little (if any) rainfall. Some low clouds will be present during the morning hours tomorrow across the far eastern plains thanks to a surge of moisture from the Great Plains readying the atmosphere for thunderstorms tomorrow.

Timing: 6 PM – Midnight

Front Range, Northwest Slope, Northern Mountains, Central Mountains, Grand Valley, Southwest Slope, San Juan Mountains, Southeast Mountains, San Luis Valley:

Hot and dry, with a few isolated dry thunderstorms expected during the afternoon/evening. Little, if any, rainfall will occur. Fire danger is high across the area, so please use caution if you have any plans that could involve a spark of any kind (i.e., grilling). Red Flag Warnings have been issued across much of the area; be sure to check with your local NWS office for more information.

Timing: 3 PM – Midnight

Issue Date: Friday, May 25, 2018
Issue Time: 08:30AM MDT

— Flooding is NOT expected today

— Elevated Fire Danger for Colorado through Saturday night

It’s going to be dry and hot to kick off Memorial Day weekend across Colorado. The visible image below shows clear skies this morning thanks to the building ridge to our east. Temperatures are expected to reach 85-90F in the low elevations and valleys today with highs in the mountains reaching the mid to upper 60s. Soundings at Denver and Grand Junction this morning confirm dry air throughout the atmosphere. So other than a few cumulus this afternoon over the mountains and elevated ridges, it should be a severe clear day across the state. There is a small outside chance for an isolated thunderstorm over the Palmer Divide/eastern Plain intersect, but rain totals will be under 0.1 inches. These storms are expected to provide more shade from the heat than rainfall.

The main weather concern going into this weekend is elevated fire danger. Low relative humidity values and increasing winds through Saturday night will place most of the state under a Red Flag Warning. Outdoor enthusiasts, please use extra caution this weekend with any activities that may start a fire.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Very hot temperatures today with the building ridge. Some afternoon cumulus will pop up over the mountains and elevated ridges, but rain is not expected. Skies should clear overnight. There is increased fire danger through Saturday night, and a Red Flag Watch has been issued for this time period. Please use extra caution when burning this weekend.

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

Expect a few broken clouds over the higher terrains this afternoon, but clear and hot conditions at the lower elevations. Red Flag Warnings have already been issued through Saturday night as breezy conditions and low relative humidity create critical fire danger.

 

Issue Date: 5/24/2018
Issue Time: 10:15AM

NO FLOOD THREAT IS FORECAST TODAY.

A large ridge of high pressure has been developing off to our west and will continue to build into Colorado as the day progresses. The water vapor image below shows that the low that passed just north of Colorado yesterday is now over Montana/North Dakota, and subsequent dry air and high pressure is replacing it in in its wake. With limited atmospheric moisture, this spells mostly clear and quiet conditions for the vast majority of Colorado throughout the day and evening.

There will not be enough moisture or instability present in the atmosphere to kick off thunderstorms along the western slopes or mountains. For areas to the east of the Urban Corridor, however, potential energy at the surface and middle levels of the atmosphere, aided by still relatively moist air left over from the last round of showers and thunderstorms, may kick off a few spotty showers with the occasional thunderclap as the afternoon and evening commence. Thunderstorm activity should be limited in its strength and organization, however, as the above-mentioned dry and stable air moving in from the west will counteract any major storm development. No flood threat is anticipated for today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts

Grand Valley, Southwest Slope, San Juan Mountains, Southeast Mountains, Raton Ridge, Northwest Slope, Northern Mountains, Central Mountains, San Luis Valley, Front Range, Urban Corridor:

Mostly sunny and seasonally warm conditions are anticipated for the day in these areas. Cumulus clouds will likely build during the afternoon, especially for the Front Range and Urban Corridor, with plenty of virga streaks but not much in terms of appreciable rainfall. If you’re along the Urban Corridor, as the sun sets, look for intermittent flashes of lightning far off to your east.

Southeast Plains, Northeast Plains, Palmer Ridge:

In the afternoon, continuing into the early evening, scattered thunderstorms are expected to develop, mainly near and along the Palmer Ridge. The storms will then move east, crossing into Kansas and Nebraska overnight. Below the strongest storms, local rainfall rates up to about 1 inch per  hour with small hail may occur, resulting in some ponding of low-lying roads and fields, but no major flooding is expected. More isolated storms may form throughout the Northeast and Southeast Plains as well, near the preferred terrain of the Cheyenne Ridge and Raton Ridge, but precipitation totals will be negligible.

For the Palmer Ridge:
Rainfall rates: < 0.25” per hour, but up to 1.25 inches/hour is possible in isolated, stronger thunderstorms
Primetime: 3PM to 10pm

For the Northeast and Southeast Plains:
Rainfall rates: 0.1-0.3 inches/hour
Primetime: 3pm to 9pm

Issue Date: 5/23/2018
Issue Time: 7:45 AM

NO FLOOD THREAT IS FORECAST TODAY.

NOTE: THE ANNUAL FLUSH OF CHERRY CREEK WILL OCCUR TODAY. 1300 CFS WILL BE RELEASED FROM CHERRY CREEK DAM, POTENTIALLY CAUSING BIKE PATH AND STREAM CROSSING CLOSURES ALONG THE CHERRY CREEK TRAIL.

The upper-level low that was centered over the Great Basin yesterday has weakened and is lifting off to the northeast, as denoted by the red “L” in the water vapor image below. As it does so, it will place Colorado under drier, southwesterly flow aloft (orange arrow), which will suppress thunderstorm development across much of the Colorado High Country. The exception to this rule will be a few isolated thunderstorms north of I-70, thanks being nearer the broad upper-level support provided by the decaying upper-level low and a weak shortwave expected to pass overhead during the afternoon hours.

East of the mountains, isolated afternoon/evening thunderstorms are expected thanks to the presence of convergence along a surface low-pressure trough/dryline. The drier, southwesterly flow aloft will mix down into the low-levels and scour out the moisture, much like across western Colorado, but thanks to low-level easterly flow east of the dryline, some moisture will be able to hang on. Due to the expected surface wind fields, the best opportunity for isolated thunderstorms will be east of a line from Cheyenne-Fort Collins-Boulder-Castle Rock-Limon-La Junta-Trinidad. For more specifics on rain rates and timing, please see the zone-specific forecast discussions below.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, jump below the map.

Zone-Specific Forecasts

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

Isolated-to-widely scattered thunderstorms are expected to rumble during the afternoon/evening hours, breaking up the otherwise mostly sunny, dry, and warm day across the area. A few storms will be on the strong-to-severe side, producing hail, strong winds, and periods of moderate-to-heavy rainfall. Due to the risk of small hail, be on the lookout for street/field ponding where hail accumulates and clogs drainage. Maximum rain fall rates will be as follows:

Front Range: 0.2-0.4 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 0.4-0.8 inches/hour
Northeast Plains and Southeast Plains: 1.0-1.35 inches/hour

Timing for Front Range: 11 AM – 7 PM
Timing for Urban Corridor and Palmer Ridge: Noon – 8 PM
Timing for Northeast Plains, Southeast Plains, and Raton Ridge: 1 PM – 11 PM

Northwest Slope and Northern Mountains:

Isolated-to-widely scattered showers/thunderstorms are expected to begin during the late morning hours, continuing into the late evening hours. The higher terrain has the best chance at any wetting rainfall, while lower valleys will feel the gusty winds and notice a sprinkle or two with plenty of virga to go around. Rainfall rates will generally remain low, with maximum rates of 0.2-0.4 inches/hour.

Timing: 10 AM – 8 PM

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

A warming and drying trend begins as drier, southwesterly flow aloft invades the region. Cumulus clouds will bubble over the higher terrain in the afternoon/evening warmth, resulting in streaks of virga and perhaps a sprinkle or two over the higher terrain of the Central Mountains and Grand Valley. Otherwise, dry conditions will prevail.