STP 08-28-2016: Isolated-to-Scattered Showers/Storms Dotted the State

Issue Date: Sunday, August 28th, 2016
Issue Time: 9:00 AM MDT

Summary:

The best coverage of showers/storms occurred over the High Country and Western Slope, particularly across the Southwest Slope and San Juan Mountains regions. East of the Divide, activity was mainly isolated, with one or two stronger storms mixed in across the Southeast Plains. Rain rates remained below thresholds, and no flash flooding was reported.

According to CoCoRaHS observers and NRCS Stations, these were the rainfall “winners” from the past 24 hours (as of 7:00 AM MDT):

Cheyenne County: 0.50 inches
Baca County: 0.50 inches
Pueblo County: 0.45 inches
La Plata County: 0.43 inches
Ouray County: 0.43 inches

For a closer look at rainfall totals in your area, please see the STP map below for a look at 24-hour precipitation totals.

20160828_STPImage
Storm Total Precip Legend

FTB 08-27-2016: Best Coverage of Storms Over the High Country/Western Slope

Issue Date: 8/27/2016
Issue Time: 9:25 AM

A LOW FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE SAN JUAN MOUNTAINS, SOUTHWEST SLOPE, AND GRAND VALLEY.

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

A few degrees of warming aloft will bring slightly warmer afternoon high temperatures across the state, along with a bit of capping to the environment. For the Northeast Plains to the north of I-70, this will act to suppress any shower/thunderstorm chances, keeping the area mostly sunny and warm. Further south, and west over the High Country/Western Slope, isolated-to-scattered showers/storms will overcome the slight warming aloft, owing largely to orographic effects and the passage of a weak, upper-level disturbance. The main impacts from any storm activity today will be gusty winds and lightning, with light-to-moderate rainfall.

IPW_20160827

With that being said, IPW values (shown above) continue to run about average at Grand Junction (green line), dipping to slightly below average at Boulder (blue line) and Schriever AFB (pink line). There’s enough moisture for some concern over locally heavy rainfall, especially with interacting outflow boundaries that locally enhance moisture content. Steeper terrain and burn scars will be the main focal points for today’s low flood threat areas, as well as urban areas with large amounts of impervious surfaces. For more information on timing and rain rates, please see the 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.
20160827_LFT

Flood Threat Legend

Zone-Specific Forecasts

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

Isolated-to-widely scattered showers/thunderstorms are expected, mainly along and south of I-70. The best coverage will occur over the Front Range and Southeast Mountains, where orographic effects will play a role in development. Spill over from High Country activity will be the main source of showers/storms over the Urban Corridor, Palmer Ridge, and western portions of the Southeast Plains. Over the far Southeast Plains, a few strong thunderstorms will develop this afternoon/evening, producing strong winds, periods of moderate-to-heavy rainfall, and small hail. Maximum rain rates are as follows:

Urban Corridor and Palmer Ridge: 0.8-1.4 inches/hour
Front Range, Southeast Mountains, and Raton Ridge: 0.6-1.0 inches/hour
Northeast Plains and Southeast Plains: 1.5-2.0 inches/hour

Timing: Noon – Midnight, with a couple showers/weak thunderstorms lingering into the early morning hours

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

A fairly active day is expected, with scattered showers and thunderstorms likely across much of the region. With IPW values around average, widespread heavy precipitation is not expected; rather, the main threats will be gusty winds, lightning, and light-to-moderate rainfall. Locally enhanced moisture from outflow boundaries will provide the opportunity for locally heavy rainfall, and this is taken into consideration with the low flood threat issuance. The best coverage will occur across the higher terrain of the Grand Valley, Southwest Slope, San Juan Mountains, and Southeast Mountains regions. As far as rainfall rates are concerned, most will be 0.25-0.5 inches/hour, with maximum rates of 0.6-1.0 inches/hour.

Timing: 11 AM – 9 PM, with a few lingering showers/weak storms over higher terrain into the early morning hours

STP 08-27-2016: More Activity West of the Divide, A Couple Stronger Thunderstorms East

Issue Date: Friday, May 1st, 2015
Issue Time: 9:00 AM MDT

Summary:

Another upper-level shortwave passed overhead yesterday afternoon/evening, kicking off scattered showers/storms across the Western Slope and High Country. Daytime heating early in the day undoubtedly helped provide the necessary fuel, and a few thunderstorms produced locally moderate-to-heavy rainfall. Storm motions helped mitigate the flood threat, however, and no flash flooding was reported. To the east of the Divide, extensive cloud cover left over from early morning showers/storms limited heating, thus limiting instability, and the environment could only muster a couple isolated showers/storms.

According to CoCoRaHS observers and NRCS Stations, these were the rainfall “winners” from the past 24 hours (as of 7:00 AM MDT):

Pueblo County: 1.65 inches
Yuma County: 0.71 inches
Morgan County: 0.54 inches
Montrose County, Grand County: 0.40 inches
Weld County: 0.33 inches
San Juan County, Broomfield County: 0.30 inches

No flash flooding was reported. For a closer look at rainfall totals in your area, please see the STP map below for a look at 24-hour precipitation totals.

20160827_STPImage
Storm Total Precip Legend

FTB 08-26-2016: Locally Heavy Rainfall Remains a Threat

Issue Date: 8/26/2016
Issue Time: 9:25 AM

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

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

A LOW FLOOD THREAT IS ALSO FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE AND SAN JUAN MOUNTAINS.

A somewhat tricky forecast is in the cards today/tonight, thanks to the potential for a few stronger thunderstorms to mix in with otherwise garden variety activity. Currently, a weak shortwave aloft is tracking east-northeastward across Colorado, producing extensive cloud cover across eastern and southern Colorado, along with a few scattered showers/thunderstorms (mainly across the Northeast Plains). Expect these showers/weak thunderstorms to wind down later this morning. As far as moisture is concerned, the IPW chart below shows mainly average moisture for the 3 usual reporting stations (Boulder, Grand Junction, and Schriever AFB); enough for a few locally heavy rainfall reports, but not enough for widespread heavy rain.

IPW_20160826

Today’s main event, so to speak, will begin early this afternoon as daytime heating and orographic effects help kick off scattered showers/storms across the High Country and Western Slope. These storms will generally move eastward with time, pushing over the lower elevations of eastern Colorado by early-to-mid afternoon. Wind shear and moisture will be sufficient for a few strong-to-marginally severe storms across eastern Colorado, but cloud cover will be a limiting factor. Where clouds can break earliest, allowing the most daytime heating, will be where the strongest storms can occur. Further west, the concern for locally heavy rainfall is mainly limited to the San Juan Mountains and Southwest Slope regions, thus the issuance of the low flood threat area. For more information 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.
20160826_LFT

Flood Threat Legend

Zone-Specific Forecasts

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

Scattered showers/thunderstorms are expected, with a couple strong-to-marginally severe storms mixed in with the garden variety majority. The main threats from stronger storms will be small hail, strong winds, lightning, and locally heavy rainfall. Maximum rain rates are as follows:

Urban Corridor and Palmer Ridge: 0.8-1.2 inches/hour
Northeast Plains and Southeast Plains: 2.0-2.5 inches/hour
Raton Ridge: 1.0-1.4 inches/hour

Timing: Noon – 10 PM, with a few showers/storms continuing until around midnight

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

Scattered showers/thunderstorms are expected during this period, mainly over the higher terrain. Storm motions will help carry a few showers/storms over lower valleys. Most activity will be produce gusty winds and light-to-moderate rainfall, but a bit better moisture/instability over the San Juan Mountains, Southwest Slope, Front Range, and Southeast Mountains will bring the potential for locally heavy rainfall to those regions. Maximum rain rates are as follows:

Southwest Slope, San Juan Mountains, Front Range, and Southeast Mountains: 0.8-1.2 inches/hour
Northwest Slope, Northern Mountains, Grand Valley, and Central Mountains: 0.4-0.8 inches/hour
San Luis Valley: 0.3-0.6 inches/hour

Timing: 11 AM – 9 PM, with a few lingering showers/weak thunderstorms over the higher terrain until midnight