FTB 05-12-2018: Mainly Dry with a Few Isolated Showers/Thunderstorms

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.

Flood Threat Legend

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.

FTB 05-11-2018: Fire Danger in the South, Showers/Thunderstorms to the North

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.

Flood Threat Legend

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.

FTB 05-10-2018: More Heat and Dry Weather for Colorado

Issue Date: 5/10/2018
Issue Time: 10:00 AM

NO FLOOD THREAT IS FORECAST TODAY.

The ridge of high pressure that has parched Colorado over the last few days will continue its slow crawl towards the east, leaving the state once again dry and with above-average temperatures. For today, expect temperatures near or even a bit warmer than they were yesterday. With very little cloud cover across Colorado as the sun rises, and a lack of moisture for clouds to build on, temperatures will be able to increase more steadily compared to yesterday, when there was at least a weak upper level disturbance that was able to keep a good portion of the state with some amount of cloud cover midday to offer respite from the heat. By the afternoon on the Front Range to the eastern plains, there may be enough instability and moisture to work with in the upper levels of the atmosphere to kick off a few stray thunderstorms, but again, with the dry and hot surface conditions there will likely be very little in the way of measurable rainfall. One notable exception is the far northeast part of the state, where some storms could dump a fair amount of rainfall over a short time period. To get substantial rainfall today, you’d need to travel north to Wyoming or Nebraska, where converging winds and better moisture look primed for an afternoon and evening of high thunderstorm activity. An hourly forecast model run by NOAA, known as the High Resolution Rapid Refresh (HRRR) model, is shown below. The image shown is merely an estimate of radar reflectivity for this evening around peak thunderstorm time. Here we see that Colorado, for better or for worse, might be just missing out on the more widespread thunderstorm activity, with only an isolated storm or two expected for the far eastern plains. No flood threat is forecast 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, jump below the map.

Zone-Specific ForecastsFlood Threat Legend

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

Arid, summery conditions for today across the entire eastern portions of the state. Much like yesterday, anticipate hot weather and increasing clouds in the afternoon, with the possibility of a few isolated thunderstorms late in the afternoon and into the evening. Don’t expect much in the way of substantial precipitation, however, with gusty winds and lightning being the main sources of hazardous weather. The exception to this is the far eastern and northeastern areas of Colorado, especially in Logan, Sedgwick, and Philips counties, where tonight dew point temperatures might be up into the lower 50’s on top of ambient temperatures in the upper 60’s/lower 70’s at night. This means that with stronger storms a non-negligible amount of rainfall might occur over about a half hour to an hour time span. Under these heavier showers, hourly rainfall rates of 1 to 1.25 inches are possible. While fairly substantial, no flooding is forecast.

Timing for isolated thunderstorms: 3 PM – Midnight
Timing for heavier thunderstorms across the far Northeast Plains: 6 PM – Midnight

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

Seasonably warm weather will continue to dominate over the mountains and the western slopes today. The majority of this forecast area will enjoy very comfortable weather, with fair weather cumulus and breezy wind in the afternoon hours, and in the high country perhaps a quick shower before the sun begins to set. The only area that has a good chance for precipitation today is up in the northwest, mostly in Moffat County. Here, some showers and storms might begin brewing late in the afternoon and may survive into the evening hours. The lack of good storm dynamics, however, will make it difficult for anything more than a quarter of an inch of rainfall per hour to be observed. The timing of the storms here is from 5pm to Midnight.

FTB 05-09-2018: Weak Disturbance Passing Overhead

Issue Date: 5/9/2018
Issue Time: 9:45 AM

NO FLOOD THREAT IS FORECAST TODAY.

The high-pressure ridge that was in control yesterday will remain in control today, but there’s a new player in today’s forecast. A weak, upper-level disturbance, and associated moisture, (highlighted in the water vapor image below) will push into the state from the west, kicking of isolated showers/thunderstorms as it traverses Colorado. These storms will produce little in the way of rainfall, as low-level moisture continues to lack across much of the state. The exception to this will be across the eastern Plains, along and east of a line from Hereford-to-Brush-to-Kim, where dewpoints in the upper-30s/low-40s will hang on long enough to allow for brief shots of wetting rain underneath isolated thunderstorms. For more details on timing and rain rates, 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.

Flood Threat Legend

Zone-Specific Forecasts

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

Warm and dry conditions will be the name of the game for most locations today, with only a few isolated thunderstorms rumbling during the afternoon/evening. Low-level moisture continues to lack across the area, so rainfall rates will be limited. The best chance for wetting rains will be east of a line from Hereford-to-Brush-to-Kim where dewpoints in the mid-30s/low-40s will hang on. Generally speaking, the main threat from storms will be gusty winds and lightning, with plenty of virga and only brief periods of rainfall. Maximum rain rates will be 0.05-0.15 inches/hour over the Urban Corridor, Palmer Ridge, and Raton Ridge, with maximum rain rates over the Northeast and Southeast Plains of 0.25-0.5 inches/hour.

Timing: 2 PM – Midnight

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

Increasing clouds and warm temperatures will be the main weather story today, as upper-level moisture streams over the area. A couple isolated, high-based showers and thunderstorms will develop during the afternoon/evening over the higher terrain as the disturbance passes overhead. The main impacts will be plenty of virga, gusty winds, and some lightning, but very little rainfall. Expect nothing more than a sprinkle or two, with the best rain rates that any thunderstorm can produce being 0.05-0.1 inches/hour.

Timing: 11 AM – 10 PM