STP 06-25-2017: Isolated Showers/Thunderstorms Rumbled Across Eastern Colorado

Issue Date: Sunday, June 25th, 2017
Issue Time: 10:10 AM MDT

Summary:

Once again, the Continental Divide was a barrier that kept low-level moisture from eastern Colorado from moving into western Colorado, separating the two sides into different weather “regimes.” Along and east of the Continental Divide, isolated showers/thunderstorms rumbled. Moisture was too shallow to produce heavy rain and subsequent flooding issues, so the wetting rain is a welcome event. The best rainfall occurred overnight/this morning across the eastern plains, as the low-level jet provided the additional boost for better storms. On the flip side of the coin, west of the Divide resembled a typical hot and dry summer day.

No flooding occurred yesterday. Please see the STP map below for a look at precipitation totals from the last 24 hours.


Storm Total Precip Legend

FTB 06-25-2017: Upslope Flow Continues Across Eastern Colorado

Issue Date: Sunday, June 25th, 2017
Issue Time: 9:20 AM MDT

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHEAST MOUNTAINS, FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, RATON RIDGE, AND SOUTHEAST PLAINS.

There isn’t *much* change from yesterday’s forecast in the general sense, as northwest flow aloft continues across the state, while low-level easterly flow holds moisture into eastern Colorado. Drilling down to the details, however, shows a slightly weaker cap in place around 700-600 mb. This will allow for a few more storms to fire (compared to yesterday), along and east of the Continental Divide. The greatest storm coverage will occur across the southern Front Range/Urban Corridor, Southeast Mountains, Raton Ridge, and Southeast Plains, where the best moisture resides and is in closest proximity to a mid-level shortwave expected to rotate across New Mexico. A low-end, low flood threat has been issued due to the chance for isolated strong-to-severe storms capable of producing brief periods of heavy rainfall. More isolated activity will occur across the northern Front Range, Urban Corridor, Palmer Ridge, Northeast Plains, and eastern portions of the Northern Mountains and Central Mountains.

Elsewhere across western Colorado, today’s forecast is nearly identical to yesterday’s forecast. Most areas will be basking in sunshine, with only a few cumulus clouds developing over the higher terrain as the afternoon heats up. The San Juan Mountains and San Luis Valley will have a few isolated showers/thunderstorms develop during the afternoon and evening hours, moving southeast with time into New Mexico. Moisture is fairly limited in these regions, so no flood threat is warranted.

Flood Threat Legend

Zone-Specific Forecasts:

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

Isolated-to-scattered showers/thunderstorms are expected today, with the greatest relative storm coverage over the southern Front Range/Urban Corridor, Southeast Mountains, Raton Ridge, and Southeast Plains. In general, storms will not produce rain rates capable of flash flooding, but a couple of isolated strong-to-severe storms will be capable of producing periods of heavy rain. Thus, a low flood threat has been issued. Maximum rain rates are as follows:

Front Range: 0.6-1.2 inches/hour
Urban Corridor, Palmer Ridge, and Northeast Plains: 1.0-1.5 inches/hour
Southeast Mountains: 1.0-1.25 inches/hour
Raton Ridge and Southeast Plains: 1.5-2.0 inches/hour

Timing: 1 PM – 11 PM, with a few lingering showers/storms into the morning hours

Northern Mountains, Central Mountains, San Juan Mountains, and San Luis Valley:

Isolated showers/storms are expected over eastern portions of the Northern Mountains and Central Mountains (Continental Divide), as well as over the San Juan Mountains and San Luis Valley. Western portions of the Northern Mountains and Central Mountains are expected to remain dry. Maximum rain rates are as follows:

Northern Mountains and Central Mountains: 0.3-0.5 inches/hour
San Juan Mountains: 0.3-0.6 inches/hour
San Luis Valley: 0.4-0.8 inches/hour

Timing: 1 PM – 10 PM

Southwest Slope, Northwest Slope, and Grand Valley:

Plenty of sunshine and warm temperatures will bring a pleasant end to the weekend. A few fair-weather cumulus clouds will develop over the higher terrain during the afternoon/evening hours, resulting in nothing more than shade from the sun.

STP 06-24-2017: Hot Out West, Cooler/Wetter to the East

Issue Date: Saturday, June 24th, 2017
Issue Time: 10:10 AM MDT

Summary:

The Continental Divide separated the dry air from the western US and the shallow, moist layer of air from the Great Plains, resulting in two separate weather regimes yesterday. Dry conditions west of the Divide made for a nice, albeit hot end to the work week, while upslope, easterly flow brought widespread cloud cover and cooler temperatures to areas east of the Divide. A few showers/thunderstorms rumbled, as daytime heating played on the moisture, but no flooding was experienced as rain rates remained well below flash flood thresholds. According to CoCoRaHS observers, the big “winners” in yesterday’s rainfall sweepstakes were:

Pueblo County: 0.27 inches
Adams and Jefferson County: 0.26 inches
Boulder County: 0.25 inches
Las Animas County: 0.22 inches

No flooding occurred yesterday. Please see the STP map below for a look at precipitation totals from the last 24 hours.

Storm Total Precip Legend

FTB 06-24-2017: Continental Divide Separates Two Weather Regimes

Issue Date: Saturday, June 24th, 2017
Issue Time: 9:20 AM MDT

NO FLOOD THREAT IS FORECAST TODAY.

Easterly, upslope flow east of the mountains has kept the low-levels fairly saturated east of the Continental Divide, resulting in widespread cloud cover this morning for those areas. As the day wears on, clouds will begin to mix out and daytime heating will play on this moisture, producing isolated showers/thunderstorms along and east of the Continental Divide. Any activity is expected to remain garden-variety, producing gusty winds (up to 40 mph) and periods of light-to-moderate rainfall. Moisture isn’t deep enough to warrant any flood threat considerations, but any heavy rain over poorly-drained areas may result in brief street/field ponding. The majority of the showers/thunderstorms that develop will do so over the Front Range, Southeast Mountains, and Palmer Ridge, moving east-southeastward with time over adjacent regions.

West of the Continental Divide, however, dry air is running the show resulting in nothing but sunshine. A few afternoon clouds will develop over the higher terrain, but mostly sunny skies will prevail. The one exception to the rule will be over the San Juan Mountains, where an isolated shower/weak thunderstorm or two is expected during the afternoon/evening hours, resulting in gusty winds, lightning, and light rainfall.

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:

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

Clouds will mix out a bit as the day wears on, resulting in partly sunny skies by this afternoon. Isolated showers/thunderstorms are expected to develop over the higher terrain of the Front Range and Southeast Mountains, as well as the preferred terrain of the Palmer Ridge. With time, the showers/storms will move east-southeastward over the adjacent regions. Maximum rain rates are as follows:

Front Range and Southeast Mountains: 0.3-0.7 inches/hour
Palmer Ridge, Raton Ridge, and Urban Corridor: 0.4-0.8 inches/hour
Northeast Plains and Southeast Plains: 0.6-1.2 inches/hour

Timing: 1 PM – 11 PM, with a few lingering showers/storms over the eastern plains and Raton Ridge into the early morning hours

Northern Mountains, Central Mountains, San Juan Mountains, and San Luis Valley:

A couple isolated showers/weak thunderstorms are expected over the higher terrain, eventually moving over the lower elevations to the south/southeast. The main impacts from any activity will be gusty winds, brief periods of light-to-moderate rainfall, and lightning. Maximum rain rates (0.3-0.6 inches/hour) will remain below flash flood thresholds, so no flood threat is warranted.

Timing: Noon – 11 PM

Southwest Slope, Northwest Slope, and Grand Valley:

Mostly sunny and dry conditions will be the name of the weather game today for these regions as high pressure and very little moisture remain settled over the area. A few cumulus clouds over the higher terrain will be about all Mother Nature can muster today.