Issue Date: 8/5/2015
Issue Time: 8:45 AM

NO FLOOD THREAT IS FORECAST FOR TODAY.

Another mainly dry and seasonably hot day is in store for Colorado today, as upper-level ridging remains in control. The ridge will flatten a bit this afternoon as an upper-level low works across the northwest US, but overall, the flow will remain west-southwesterly aloft. This flow pattern will allow for a plume of modest mid-/high-level moisture to enter the state from the west, but fairly dry low-levels will limit the impact of the increase in moisture aloft. All in all, isolated-to-widely scattered showers/thunderstorms across the higher terrain will be possible, mainly along the Continental Divide and Front Range. The main impacts from this activity will be light rain and gusty outflow winds, as well as lightning. A couple of isolated thunderstorms will move off of the higher terrain and over the Urban Corridor, and western portions of the Northeast Plains/Southeast Plains/Raton Ridge/Palmer Ridge. Not expecting much more than brief light rain and gusty winds from such activity.

The only concern for isolated stronger thunderstorms this afternoon/evening will be near the CO/KS border, where a bit more moisture/instability will be present along and east of a weak surface boundary. If the low-level moisture can hang around sufficiently, and surface convergence can be enough, an isolated thunderstorm or two will develop; but if the moisture mixes out or surface convergence is too weak, thunderstorm chances will diminish rapidly. Brief bouts with heavy rain will attend these potential storms, as well as strong winds and small hail. No flash flooding is expected, as rain rates will be too low with the expected storm motions (15-20 mph) to cause issues.

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, Raton Ridge, Palmer Ridge, and Southeast Plains:

Mostly sunny and hot for most, with high temperatures near seasonal average. A couple of isolated thunderstorms are possible, as described above. Maximum rain rates along and near the higher terrain will be 0.2-0.4 inches/hour, and 0.9-1.3 inches/hour near the CO/KS border.

Timing: 2 PM – 10 PM

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

Mostly sunny and hot for most areas today, with isolated-to-widely scattered thunderstorms developing over the higher terrain. The best relative chances for thunderstorms are across the Northern Mountains, Central Mountains, Front Range, and Southeast Mountains regions, with lower chances elsewhere. Maximum rain rates will be 0.15-0.3 inches/hour.

A Red Flag Warning has been issued for portions of Moffat, Rio Blanco, Garfield, and Mesa Counties, so be sure to check in with the local National Weather Service Office for more details.

Timing: Noon – 9 PM

Issue Date: 8/4/2015
Issue Time: 10:05AM

— Flooding is NOT expected today.

After a very busy weather day yesterday, Colorado now sits in the wake of yesterday’s disturbance. The net result is two-fold: first, substantial drying of the atmospheric column statewide, and second, general subsidence as is typical after a disturbance passage. The time series of precipitable water (PW) values, shown below, illustrates just how much drying has occurred in the last 24 hours. For example, yesterday morning, Grand Junction had a PW of 1.35 inches, but today it is only 0.8 and falling.

For today, we expect a mostly sunny and seasonally hot day across the state. Gusty winds have been observed in the higher elevations (especially north of I-70) this morning and these may continue through mid-afternoon before the pressure gradient eases. An isolated afternoon thunderstorm cannot be completely ruled out in the Northeast Plains but rainfall amounts will stay below 0.5 inches.

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

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

Mostly sunny to partly cloudy skies and seasonally hot today with highs between 90-95F in the lowest elevations and 60s in the highest elevations. Gusty winds, up to 50 mph will be possible through mid-afternoon above 10,000 feet. Winds should subside by early evening as the disturbance causing the strong pressure gradient moves eastward. Flooding is not expected today.

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

Mostly sunny with a few spotty clouds and seasonably hot today with high temperatures in the low to mid 90s in the lowest elevations of the Arkansas River valley to the 60s in the highest terrain of the Front Range. Gusty winds, up to 65 mph, will be likely over the highest terrain of the Front Range through mid-afternoon. A stray shower or weak thunderstorm may graze the far northeast corner of the Northeast Plains but rain rates will be below 0.5 inches. Thus, flooding is not expected today.

 

Issue Date: 8/3/2015
Issue Time: 10:30AM

— MODERATE flood threat for Central Mountains, Northern Mountains, Raton Ridge and Southeast Plains
— LOW flood threat for Northwest Slope, Grand Valley, Southeast Mountains and Palmer Ridge

This morning’s weather map is crowded with many players, as shown by the water vapor image below. The most notable feature is the strong disturbance stretching from Colorado west-northwest into Oregon. This was responsible for yesterday’s thundershower activity over our state, and it is slowly moving northeastward today. This feature is also helping to maintain a rather thick cloud deck across central and northern Colorado this morning. It will once again support storm activity across our state today. Meanwhile, in the lower levels, a surface circulation is noted over southwest Wyoming. The main impact of this will be to induce a deep easterly flow east of the Divide through late evening today. It is in fact already doing so: this morning’s atmospheric sounding from Denver has an easterly wind component extending from the surface all the way up through about 17,000 feet. The wind speed in that layer ranges between 17 and 25 knots; these values are noteworthy. Such deep easterly, and thus upslope flow is an important variable in the equation for heavy rainfall in Colorado. Finally, checking this morning’s moisture levels: precipitable water ranged from 0.9 to 1.2 inches. Some subtle drying is seen entering in from the southwest. Surface dewpoint temperatures are very high: mid 50s to mid 60s. Clearly, there is a heavy rainfall threat today. Let’s figure out when and where.

We anticipate two different regions to see a heavy rainfall threat today: in the northwest and in the southeast. In the northwest, proximity to the surface disturbance, combined with precipitable water values near 1 inch will provide necessary ingredients for a Low/Moderate flood threat. In the southeast, instability will be greater, but coverage will be more scattered. Nonetheless, with the advection of precipitable water values as high as 1.6 inches, a Low/Moderate flood threat will be warranted.

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

Northwest Slope, Northern Mountains, Central Mountains, Grand Valley:

Mostly cloudy early with scattered showers turning into thunderstorms by early afternoon. Max 1-hr rain rates up to 1.2 inches will be possible. Higher elevation regions, including the Park and Gore Ranges as well as the Flat Tops, could see 3-hr rainfall amounts up to 1.8 inches. A Moderate flood threat is posted for the higher terrain, with a Low flood threat elsewhere. Activity will quickly subside around sunset.

Primetime: 12PM to 8PM

Palmer Ridge, Southeast Mountains, Raton Ridge, Southeast Plains:

Partly cloudy early, with scattered thunderstorms forming by mid afternoon. Max 1-hr rain rates up to 2.4 inches will be possible (highest amounts to the southeast). There is also a good possibility that individual storms will merge into a storm complex. This will add the threat of strong winds, up to 65 mph. Storm activity will generally subside in the late evening, but the flooding threat will exist all the way through 1AM in the far southeast.

Primetime: 2PM to 9PM near the mountains, 3PM to 1AM in the far southeast

Northeast Plains, Front Range, Urban Corridor:

Partly to mostly cloudy with isolated to widely scattered thunderstorms possible in the afternoon. Due to limited instability, maximum 1-hr rain rates are expected to be around 0.7 inches. Thus, no flooding is anticipated. However, stronger storms could provide for gusty winds, up to 50 mph.

Southwest Slope, San Juans, San Luis Valley:

Partly sunny with isolated thunderstorms possible from early afternoon to through sunset. Due to drying behind the disturbance passage, max 1-hr rain rates will be 0.3 inches. No flooding is expected.

Issue Date: 8/2/2015
Issue Time: 9:50 AM

A HIGH FLOOD THREAT HAS BEEN ISSUED FOR THE WEST FORK COMPLEX AND LITTLE SAND BURN SCARS AND ADJACENT AREAS.

A MODERATE FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE SAN JUAN MOUNTAINS, SOUTHWEST SLOPE, GRAND VALLEY, AND NORTHWEST SLOPE REGIONS.

A LOW FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE SAN LUIS VALLEY, GRAND VALLEY, NORTHWEST SLOPE, NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, FRONT RANGE, URBAN CORRIDOR, SOUTHEAST MOUNTAINS, RATON RIDGE, PALMER RIDGE, SOUTHEAST PLAINS, AND NORTHEAST PLAINS.

Current observations show the elongated upper-level ridge stretching from the Pacific NW into the south-central US, with a circulation center over southeast NM/western TX. The position of the circulation continues to stream subtropical moisture into Colorado, and precipitable water values continue to run above above average for most locations across the state. The best moisture resides west of the Continental Divide, brought in bulk by the mid-/upper-level disturbance rotating across Utah and western CO at this time (circled in black on water vapor image below). Widespread showers are currently ongoing across southwest Colorado, in association with the mid-/upper-level disturbance.

The disturbance will provide the dynamics necessary for scattered-to-widespread showers and thunderstorms across the mountains, with the best coverage across the San Juan Mountains, Southwest Slope, and Grand Valley mountain locations. Locally heavy rainfall will be present with the stronger thunderstorms, and persistent heavy showers with slow storm motions, has heightened flash flood concerns. The burn scars of the West Fork Complex and Little Sand should be watched closely today.

For eastern Colorado, isolated-to-scattered thunderstorms are expected for areas near the interface with the mountains and along the Raton Ridge. Comparable to yesterday, a surface trough is oriented northeast-to-southwest across the Northeast Plains and Palmer Ridge; isolated thunderstorms are expected to develop along this trough, and will be capable of producing strong winds (gusting to 60-65 mph), large hail (> 1 inch), and locally heavy 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, jump below the map.

Zone-Specific Forecasts

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

Isolated-to-scattered showers and thunderstorms are expected across the areas highlighted by the low flood threat, with a couple of isolated storms expected elsewhere along the Urban Corridor, Northeast Plains near the Cheyenne Ridge, and western portions of the Southeast Plains (namely eastern Pueblo and Las Animas counties). Maximum rain rates are as follows:

Urban Corridor, Palmer Ridge, Northeast Plains and Southeast Plains: 0.8-1.2 inches/hour.
Raton Ridge: 1.0-1.4 inches/hour

Timing: Noon – 10 PM, with a lingering shower/weak thunderstorm possible until the early morning.

Northern Mountains, Front Range, and Central Mountains:

Isolated-to-scattered showers and thunderstorms, with coverage increasing from north to south. Locally heavy rainfall will be possible, and this is accounted for in the low flood threat areas. Maximum rain rates will be 0.8-1.2 inches/hour. Slow-moving storms will be a concern.

Timing: 11 AM – 10 PM, with a few lingering showers over the higher terrain into the early morning hours.

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

Scattered-to-widespread showers and thunderstorms are expected, with the best coverage across the San Juan Mountains, Southwest Slope, and Grand Valley regions. Fairly slow-moving storms, abundant low-level moisture, and the presence of mid-/upper-level disturbance has heightened flash flood concerns today for locations west of the Continental Divide. Maximum rain rates are as follows:

Southeast Mountains: 0.8-1.2 inches/hour
San Luis Valley, Southwest Slope, Grand Valley, and San Juan Mountains: 1.2-2.0 inches/hour
Northwest Slope: 0.8-1.2 inches/hour

Timing: Current – 10 PM will be primetime, with scattered showers and thunderstorms continuing into tomorrow morning. The heavy rain threat will continue into the overnight hours with the presence of the disturbance.