Issue Date: 7/28/2015
Issue Time: 9:47 AM

A LOW FLOOD THREAT IS FORECAST FOR THE EVENING/OVERNIGHT PERIOD ACROSS PORTIONS OF THE RATON RIDGE, SOUTHEAST MOUNTAINS, AND SOUTHEAST PLAINS.

Much of today will be marked by mostly sunny and stable conditions thanks to a few main players:

1. Upper-level low tracking across south-central Canada (red “L”)
2. Upper-level high anchored over the south-central US (blue “H”)
3. A weak, cool front that passed through this morning

The upper-level low and high will promote the continued advection of dry air into Colorado, thanks to west-southwesterly flow aloft, and the weak cool front has brought drier and cooler conditions to the lower levels. Altogether, these main players will lead to a stable and dry start to the afternoon for most locations across the state.

As the day wears on, isolated, weak thunderstorms will develop this afternoon over the higher terrain; mainly the San Juan Mountains, Central Mountains, Front Range south of I-70, and Southeast Mountains. The main impacts from these storms will be gusty winds and light rain – there simply will not be much moisture to aid precipitation processes. One or two weak storms will move over adjacent locations of the Urban Corridor (south of I-70), Southeast Plains, and Raton Ridge, but will struggle to produce good rainfall.

The main event will come during the evening and overnight hours, as a weak disturbance will rotate across New Mexico and into southeastern Colorado, leading to scattered showers and thunderstorms capable of producing heavy rain. Moisture will hold on best for these southeastern locations throughout the day as upslope flow reinforces surface moisture, and the plume of modest subtropical moisture continues overhead (green arrow). Please note the timing of the flood threat in the map/zone-specific 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 north of I-70, Urban Corridor North of I-70, Northeast Plains, Grand Valley, Northern Mountains, Northwest Slope, and Southwest Slope:

Mostly sunny and warm, with temperatures a few degrees cooler than yesterday. A few fair weather clouds will develop, but no precipitation is expected.

Front Range south of I-70, Urban Corridor south of I-70, Palmer Ridge, Southeast Plains, Southeast Mountains, and Raton Ridge:

Isolated weak thunderstorms over the higher terrain and adjacent lower elevations are expected to develop after noon, and continue through the late afternoon/evening hours. The main event, as described above, will begin later in the evening as a disturbance moves across southeastern Colorado. The flood threat will start around 8 PM, and continue into the early morning hours. Maximum rain rates will break down as follows:

Front Range/Urban Corridor south of I-70 and Palmer Ridge: 0.4-0.8 inches/hour
Southeast Mountains: 0.7-1.0 inches/hour
Raton Ridge: 1.2-1.8 inches/hour
Southeast Plains: 1.5-2.5 inches/hour

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

A few isolated, weak thunderstorms are expected over the higher terrain later this afternoon and into the evening hours. A couple of lingering showers will continue into the early morning tomorrow. Rain rates will be low, less than 0.2 inches/hour.

Issue Date: July 27th, 2015
Issue Time: 10:15AM

— Flooding is NOT expected today
— Elevated Fire Threat for Northern Mountains and Northwest Slope

Today’s water vapor image, below, shows a large disturbance located over the Pacific Northwest, stretching southward into Nevada. Late last week, it appeared that as this disturbance crossed Colorado, it may have subtropical moisture support and pose a heavy rainfall threat. However, the subtropical connection did not materialize and heavy rainfall is not expected as the disturbance races by our state. Despite morning precipitable water values in the 0.8 – 1.1 inch range, there is very dry air just to the west. As this propagates eastward, it will put a cap on rainfall intensities. There are two additional limiting factors to rainfall today. First, the disturbance is moving very rapidly, meaning that storm motion is expected to be in the 25-40 mph range. Second, the surface low pressure noted over Wyoming this morning will induce downsloping flow east of the Divide. Climatologically speaking, downsloping flow is extremely unfavorable for heavy rainfall east of the Divide.

For today, we expect mostly sunny skies this morning to quickly give way to scattered thunderstorm activity by early afternoon. Coverage will be highest in the Central Mountains. Storms will race to the northeast across the Plains as the afternoon transitions into evening. Storm activity will quickly diminish around sunset. While rainfall amounts will be limited today, gusty winds, up to 60mph, will accompany many storms.

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

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

Sunny early with a few cumulus clouds developing by early afternoon. Scattered high-elevation storms will develop over the higher terrain and spread eastward. Max 1-hr rainfall will be 0.5 inches over the higher terrain to 0.9 inches over the far northeast. Wind gusts up to 65 mph will be possible with stronger storms. Flooding is not expected today.

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

Sunny to partly cloudy early with scattered afternoon storms possible across the higher elevations. Highest coverage is expected to be in the Central Mountains. Due to fast storm motions, max 1-hour rain rates will be 0.5 inches. Thunderstorms will be capable of wind gusts up to 55 mph. Across the Northern Mountains and Northwest Slope, the combination of very dry air coming in from the west and a sustained period of gusty winds of 40-50 mph will lead to a fire weather danger this afternoon. Please stay tuned to local news sources for specific information. Flooding is not expected today.

Issue Date: 7/26/2015
Issue Time: 9:44 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHEAST PLAINS, PALMER RIDGE, AND SOUTHEAST PLAINS.

The water vapor image below is a bit messier than previous days, but the same major players remain; an upper-level ridge across the central US with upper-level troughs flanking either side. One feature that hasn’t been present across Colorado the last few days is a mid-level disturbance, and one is forecast to move across the state today (marked by the black dashed line). This disturbance will be accompanied by a slight increase in mid-level moisture, mainly for southern and eastern regions. The disturbance and accompanying moisture will lead to more thunderstorms, overall, today and tonight.

If one was to draw a line approximately from the Pawnee National Grassland -> Granby -> Glenwood Springs -> Grand Junction, the best chances for thunderstorms will be to the south and east where the better moisture resides. An isolated, high-based thunderstorm or two cannot be ruled out north and west of that line, but in that environment the biggest threats will be gusty winds and lightning, with very little rain.

The biggest threat for heavy rain today will be across the Palmer Ridge, Southeast Plains, and Northeast Plains regions, where the better surface moisture will be; surface dewpoints will likely remain in the 50s this afternoon. Near the mountains, i.e. the Urban Corridor and western extents of the Southeast Plains, drier air will mix down to the surface through the afternoon, creating more of an inverted-V environment; this means that the main threat will be gusty winds and lightning, with brief periods of moderate rainfall. Specifics such as rain rates and timing will be given in 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

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

Scattered showers and thunderstorms are expected this afternoon and evening. A few will become strong-to-severe across the Palmer Ridge, Southeast Plains, and Northeast Plains regions. The main threat with strong-to-severe storms will be strong winds (gusts >50 mph) and large hail. Brief periods of heavy rainfall are also likely with those storms, see rain rates below.

Urban Corridor: 0.5-1.0 inches/hour
Raton Ridge and western extents of the Southeast Plains: 0.6-1.1 inches/hour
Palmer Ridge, Southeast Plains, and Northeast Plains: 1.5-2.5 inches/hour

Timing: Noon – 9 PM, with a few showers/thunderstorms lingering over the Raton Ridge and Southeast Plains until just after midnight.

Northwest Slope and Northern Mountains:

Mostly sunny and warm, with an isolated shower/weak thunderstorm over the highest terrain of the Northern Mountains possible. Gusty winds and lightning will be the impacts from any thunderstorm activity, and very little rain. Max rain rates will be less than 0.25 inches/hour.

Timing: Noon – 7 PM

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

Isolated-to-scattered showers and thunderstorms, favoring the higher terrain. The best relative chances will be across the San Juan Mountains, Central Mountains, and Southeast Mountains. Maximum rain rates will be 0.25-0.5 inches/hour for all regions except the Front Range, where rain rates could push 0.4-0.8 inches/hour. Storm motions at 20 mph ENE will limit potential flood threats.

Timing: 11 AM – 8 PM, with a few showers lingering over southern areas until the early morning hours.

Issue Date: 7/25/2015
Issue Time: 9:30 AM

NO FLOOD THREAT IS FORECAST.

The same general upper-air pattern remains across the continental US, generally characterized by a high pressure ridge across the central US, flanked by a trough on either coast. The upper-level high pressure is expected to stay centered over Texas today; this is a bit further east than yesterday, thanks to the upper-level low pushing onshore over the Pacific Northwest. This will force drier air into the state today as flow becomes more westerly, but decent mid-level moisture will hang to the south and east of a line bisecting the state from southwest to northeast.

For High Country areas underneath the drier air, i.e., the Northwest Slope, Northern Mountains, Grand Valley, and Southwest Slope, sunny skies and hot temperatures will be the main story today, with fair weather clouds breaking up the sunshine. A bit better moisture will hang out over the Central Mountains and Front Range, so a couple isolated showers/weak thunderstorms cannot be ruled out, especially across southern portions.

Isolated-to-scattered coverage of thunderstorms is expected over the higher terrain of other western Colorado regions (San Juan Mountains, San Luis Valley, and Southeast Mountains). With precipitable water values running below average for this time of year, rain rates will not be particularly impressive, and the biggest impacts will be gusty outflow winds and dangerous lightning.

For eastern Colorado, mostly sunny skies and hot temperatures will be the name of the game for most. Near the interface with the higher terrain, a few isolated showers/weak thunderstorms will move overhead off the mountains for southern portions of the Urban Corridor and western portions of the Southeast Plains. The best chance for thunderstorms today will be along the CO/NM and CO/KS borders, where a surface boundaries will enhance thunderstorm development a bit. With relatively dry air still in place below cloud bases, the main threats will be strong winds and large hail. Brief moderate rainfall will attend the strongest storms near the CO/KS border across the Southeast Plains and southeastern portions of the Northeast Plains, but dry air and storm motions will limit the impacts to minor street/field ponding.

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

Mostly sunny and hot will be the main story, with a few isolated-to-scattered showers and thunderstorms breaking the heat near the mountains south of I-70, and near the CO/KS and CO/NM borders (as described above). Temperatures will be a degree or two cooler than yesterday, so not really a noticeable change. Max rain rates break down like this:

Urban Corridor and Palmer Ridge: 0.25-0.5 inches/hour
Northeast Plains: 0.8-1.2 inches/hour
Raton Ridge: 0.9-1.3 inches/hour
Southeast Plains: 1.0-1.8 inches/hour

Timing: Noon – 9 PM, with a few isolated showers/thunderstorms lingering until midnight before crossing into Kansas.

Northwest Slope, Northern Mountains, Southwest Slope and Grand Valley:

Hot and dry, with a few fair weather clouds breaking up the otherwise sunny sky. Today would be a great Saturday to get outside and enjoy the summer. Remember to drink plenty of water and take breaks from the sun, when necessary.

Front Range, Central Mountains, Southeast Mountains, San Luis Valley, and San Juan Mountains:

Isolated storms for the Front Range and Central Mountains, becoming more scattered to the south. Main impacts will be gusty winds and lightning, with only light rainfall expected. Rain rates will be 0.2-0.4 inches/hour.

Timing: 11 AM – 9 PM