Issue Date: Monday May 14, 2018
Issue Time: 10:05AM MDT

— Flooding is NOT expected today

The low pressure system that has dominated Colorado’s weather pattern the last few days remains intact over Nevada. This disturbance will provide some upper-level support for thunderstorms in the form of minor shortwaves this afternoon. Southwest flow will continue, which will have various weather affects statewide. Over western Colorado, dry air will continue to be entrained from Arizona and New Mexico as indicated in the water vapor imagery below. The sounding at Grand Junction this morning indicates very little mid-level moisture, which will continue to mix out throughout the day. Thus (west), the isolated storms will be restricted to the Northern Mountains and Northwest Slope this afternoon with very limited rainfall.

East of the Continental Divide, cooler and moist air remains after the passage of the frontal boundary. Upslope flow is expected to form this afternoon, favoring development of thunderstorms over the Front Range and Palmer Ridge. To the north, storms are expected to be more of a garden variety as they move into the Urban Corridor and Northeast Plains. Further south, more isolated, severe storms are expected to develop due to stronger daytime heating over the Palmer Ridge. The main threats will be large hail and gusty winds. Upslope flow continues into the evening and overnight creating more widespread but lighter showers over the eastern Southeast Plains and Raton Ridge. Flooding is not expected today.

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, Raton Ridge, Southeast Mountains:

Cloudy this morning with clearing expected this afternoon. Less clearing to the north will cause more garden variety showers with 1 hour rain rates up to 0.8 inches/hour. Further south, isolated, stronger thunderstorms will develop over the Palmer Ridge. Large hail up to nickel size can be expected under the core of the storms along with gusty winds. Max 1 hour rain rates up to 1 inch are possible. Scatter storms will persist overnight, but rainfall totals are expected to be under 0.5 inches. Minus some minor field ponding with the stronger, afternoon thunderstorms, flooding is not expected.

Primetime: 1PM to 7AM

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

Warm and dry again today with a few broken clouds over the higher terrains. The Northern Mountains have the best chance for rainfall this afternoon, but storms will produce more gusty winds than rainfall. Rainfall totals are expected to be under 0.1 inches. Thus, flooding is not expected today.

Primetime: 12PM to 9PM

Issue Date: 5/13/2018
Issue Time: 10:15 AM

— LOW flood threat for the Front Range, Urban Corridor, and Northeast Plains today.

The upper-level low pressure system that has been responsible for rain and thunderstorms across the state over the last few days continues to spin in place over Idaho, Utah, and Nevada. This has kept dry southwesterly flow aloft over much of Colorado, resulting in largely dry conditions in the high country with instability over the plains. For those in the northeastern portion of the state, this morning has looked like a rerun of yesterday, with easterly upslope winds near the surface resulting in fog, low stratus clouds, and drizzle/light rain for the Urban Corridor and eastern plains. As indicated on the image below, low-level moisture has extended further south today, over the Palmer Divide and into the southeastern portion of the state.

As the sun angle increases throughout the day, expect much of this fog and low-level cloud cover to burn off. Instability will increase as the surface heats, particularly along the northern Front Range and northern plains, enabling the development of scattered thunderstorms this evening. The Storm Prediction Center has indicated that there is potential for some stronger and better-developed thunderstorms to pose a brief severe weather risk along the northern Front Range and Urban Corridor, with hail, strong winds, and a brief tornado all possible. Later in the evening and after sunset, storms are expected to persist, transitioning into more of a flood threat as they grow into clusters that may produce several bouts of brief heavy rainfall over the same areas.

Today’s Flood Threat Map

There is a LOW flood threat over the northeastern corner of the state today. 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.

 

Front Range, Urban Corridor, Northeast Plains, Palmer Ridge:

The drizzle, low cloud, and fog this morning will gradually lift and thin throughout the day, and there may be a few hours of sunshine around mid-day. Clouds will build back in as thunderstorms initiate this afternoon, with rain scattered at first and becoming more widespread through the evening. Rain could linger into the early morning hours of Monday. Rainfall rates this evening will widely be in the 0.25-0.50” per hour range, but may briefly approach 1.00” per hour. Moderate to heavy rain rates may persist for a few hours, leading to an isolated nuisance flooding and road ponding threat.

Primetime: 4PM to 4AM Monday

Northwest Slope, Northern Mountains, Central Mountains:

Partly cloudy with a chance of some showers building in later in the day and overnight, transitioning to snow above 11,000 feet this evening. Rainfall rates should be low, mainly in the 0.05-0.15” per hour range.

Primetime: 12PM to 9PM

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

Low-level cloudiness on the Southeast Plains this morning will quickly erode from the southwest, leaving much of the southern half of the state sunny and dry. Expect a few fair-weather cumulus to develop over the mountains during the afternoon, and clouds may build back from the northeast over the plains tonight.

Issue Date: 5/12/2018
Issue Time: 8:03 AM

NO FLOOD THREAT IS FORECAST TODAY.

This morning started out with a mixture of fog, clouds, and pockets of drizzle east of the mountains, thanks to low-level, moist, upslope flow. Meanwhile, scattered mid-/high-clouds streamed over the High Country, associated with the upper-level low positioned over the Great Basin. The fog will scour out as the morning turns to the afternoon, but expect mostly cloudy skies to hang around north of the cool front across the Urban Corridor from Castle Rock northward, the Front Range foothills north of Highway 285, the northern half of the Palmer Ridge, the Northeast Plains, and far northeastern portions of the Southeast Plains. The air north of the cool front will be marked by plenty of moisture and cooler temperatures than yesterday, with a few isolated showers/thunderstorms expected during the late afternoon/evening hours. I have denoted the boundary of low-level moisture in green on the visible satellite image below. To the south of the cool front, breezy, warm, and mostly sunny will be the name of the game, with critical fire danger remaining in place.

For the High Country, it will be a windy and warm, with southwesterly flow ushering in dry air, increasing the fire danger. The exception to this rule will be the Front Range, where an isolated shower/weak thunderstorm or two cannot be ruled out during the late afternoon and evening hours, thanks to the moist, upslope flow from the east.

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, Palmer Ridge, and Northeast Plains:

A couple isolated showers/weak thunderstorms are expected later this afternoon and into the evening hours, as the peak of daytime warmth works with a weak upper-level disturbance. Due to the relative coolness of the low-level air, and the warm, dry southwest flow aloft, it’s going to be difficult for storms to strengthen, keeping rainfall rates low. Generally speaking, rainfall rates will be in the 0.1-0.25 inches/hour range, with maximum rain rates under thunderstorms in the 0.3-0.6 inches/hour range.

Timing: 3 PM – 10 PM, with a shower or two possible into the early morning hours across the Urban Corridor and Northeast Plains

Northern Mountains, Northwest Slope, Central Mountains, Southeast Mountains, San Juan Mountains, Southwest Slope, Grand Valley, San Luis Valley, Raton Ridge, and Southeast Plains:

Warm, mostly sunny, and dry will be the name of the weather game across these regions, with breezy conditions elevating fire danger. Be sure to check with your local NWS office for more information regarding any Red Flag Warnings. The exception to the mostly sunny rule will be across far northeastern portions of the Southeast Plains, where low-level moisture will be in place behind a quasi-stalled surface boundary, leading to mostly cloudy skies. A stray shower/pocket of drizzle in the early morning hours tomorrow near the CO/KS border cannot be ruled out as the surface boundary pushes southward and upslope flow continues.

Issue Date: 5/11/2018
Issue Time: 8:40 AM

NO FLOOD THREAT IS FORECAST TODAY.

A dichotomy of weather conditions will exist today, with warm/dry conditions for the southern half of the state, and isolated-to-widely scattered showers/thunderstorms for the northern half of the state, where the better moisture/upper-level support will coincide. The upper-level support will be provided by a jet streak (orange hatched area on the water vapor image below) that will round the base of the upper-level trough, and position itself favorably to provide some broad-scale support for showers/thunderstorms over the northern half of Colorado. Better moisture than the last few days exists across the Northeast Plains, Urban Corridor, northern Palmer Ridge, and Front Range regions thanks to easterly low-level flow. This will help storms produce more rainfall than previous days, but still not enough to warrant a flood threat as deeper moisture is still lacking. For the High Country north of I-70 (and not including the Front Range), moisture is still lacking and will limit the coverage and rainfall potential of any activity in the area.

For the High Country south of I-70 and the Southeast Plains, Raton Ridge, and San Luis Valley regions, warm and dry is the name of the game. Dry, southwest flow aloft and a tightening pressure gradient will mean windy conditions and increased fire danger – in fact, Red Flag Warnings have been issued for much of the area. Check with your local National Weather Service office for more details.

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, Palmer Ridge, and Northeast Plains:

Warm and dry for most, with isolated-to-scattered showers/thunderstorms expected this afternoon and evening, with one or two rumbling into the early morning hours across the far Northeast Plains. Relatively moist easterly low-level flow underneath southwest flow aloft will create an environment capable of producing a few strong-to-severe thunderstorms, with the main threats being large hail, strong winds, and lightning, with brief periods of moderate rainfall. Generally speaking, rain rates will remain in the 0.15-0.25 inches/hour range, with maximum rain rates of 0.4-0.8 inches/hour possible near the CO/WY border where upper-level support will be best.

Timing: 3 PM – Midnight, with a couple of isolated showers/storms lingering until 2-3 AM over the Northeast Plains

Northern Mountains and Northwest Slope:

Isolated-to-scattered showers/weak thunderstorms are expected this afternoon and evening, providing breaks from the otherwise dry and warm conditions. Due to dry, low-level conditions, expect plenty of virga and gusty winds from shower/thunderstorm activity, with very little in the way of rainfall. Maximum rain rates will be in the 0.05-0.15 inches/hour range. Cloud cover will keep high temperatures a bit below yesterday’s readings.

Timing: 11 AM – 6 AM

Central Mountains, Southeast Mountains, San Juan Mountains, Southwest Slope, Grand Valley, San Luis Valley, Raton Ridge, and Southeast Plains:

Warm, dry, and breezy will be the weather theme today, as tightening pressure gradients and dry, southwest flow aloft combine to produce critical fire weather conditions. As the surface boundary moves southward overnight across the Southeast Plains, an isolated stray shower is possible over northeast portions of the Southeast Plains. Any activity will produce gusty winds and virga, with little-to-no rainfall expected.