FTB 05-26-2016: Unsettled Weather, Flood Threat Returns

Issue Date: 5/26/2016
Issue Time: 10:30 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, SOUTHEAST PLAINS AND NORTHEAST PLAINS REGIONS.

A LOW FLOOD THREAT ENCOMPASSES THE MODERATE FLOOD THREAT, AND INCLUDES PORTIONS OF THE NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, SOUTHEAST MOUNTAINS, RATON RIDGE, AND SOUTHEAST PLAINS.

Current analysis of the atmosphere shows the upper-level low centered over northern Arizona, and a surface low centered over the OK/TX panhandles. A surface boundary extends from the surface low center back across the Southeast Plains, and then northward along the Front Range. South of the boundary, the air is a bit drier with dewpoints in the 20s and 30s. To the north of the boundary, dewpoints are in the 40s and 50s.

The upper-level low will move east-northeastward throughout the day today, reaching southeast Colorado by tonight. The surface low will continue to transport moisture into eastern Colorado from the central US plains. This moist, upslope flow, combined with upper-level support and steep lapse rates, will support strong-to-severe thunderstorms today/tonight over portions of the Northern Mountains, Central Mountains, Front Range, Northeast Plains, Southeast Plains, Palmer Ridge, and Raton Ridge regions.

WV_20160526

To the west, scattered showers and thunderstorms are expected as broad-scale support spreads overhead. The higher elevations will be favored for thunderstorm activity, but a few will drift over lower valleys. Low-level moisture will be a bit on the low side, so showers/thunderstorms will remain high-based; rain rates will be tempered. Gusty winds, lightning, and small hail will be the main threats from stronger storms (relatively speaking). The highest peaks will likely see a couple inches of snow, while most areas receive rainfall.

For more information regarding timing, rain rates, and impacts, 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.
FTB_20160526Flood Threat Legend

 

Zone-Specific Forecasts

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

Scattered thunderstorms are expected today for all areas. Some of the thunderstorms will become strong-to-severe, with the main threats being large hail, lightning, and a couple tornadoes. Moderate-to-heavy rainfall is also expected, thus the issuance of the low-to-moderate flood threat. The threat will continue into the nighttime hours for all regions, but especially over the Palmer Ridge, Urban Corridor, and western portions of the Southeast Plains regions due to north-northeasterly low-level flow favoring persistent showers/thunderstorms in those locations. Maximum rain rates will be 1.5-2.2 inches/hour across all regions. Overall, the flood threat will peak this afternoon and evening, but will remain in effect throughout the period. Scattered showers/thunderstorms will continue overnight and into tomorrow morning.

Timing: 11 AM – 11 AM Friday

Northern Mountains, Central Mountains, Front Range, and Southeast Mountains:

Scattered showers and thunderstorms are expected. A couple will become strong-to-severe, with the main threats being hail, lightning, and damaging winds. Moderate-to-heavy rain will also attend stronger storms, with maximum rain rates varying:

Northern Mountains and Central Mountains: 0.8-1.4 inches/hour
Front Range and Southeast Mountans: 1.2-1.8 inches/hour

The Waldo Canyon Burn Scar will need to be monitored closely today/tonight.

Scattered showers and thunderstorms will continue through the overnight hours and into tomorrow morning, mainly across the Front Range and Southeast Mountains.

Timing: 11 AM – 11 AM Friday

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

Scattered showers and thunderstorms expected throughout the day and into the nighttime hours. Coverage will peak during the late afternoon/early evening, and most storms will have ended by Midnight. A few isolated showers over the higher terrain will linger into tomorrow morning. Maximum rain rates will be 0.4-0.7 inches/hour. The highest elevations will receive a couple inches of snow.

Timing: 11 AM – Midnight, with a few lingering into the morning

STP 05-26-2016: Mostly Sunny and Dry for Most, Isolated Thunderstorms Rumbled

Issue Date: Thursday, May 26th, 2016
Issue Time: 9:00 AM MDT

Summary:

A shortwave ridge suppressed the atmosphere yesterday, keeping Colorado mainly dry with plenty of sunshine. A few isolated showers dotted the higher terrain of western Colorado; showers were most numerous overnight with the approach of the upper-level low. Further to the east, isolated thunderstorms rumbled across the Northeast Plains and northern sections of the Front Range and Urban Corridor. A couple isolated thunderstorms sparked overnight as a cool front moved in from the north and deeper moisture was reintroduced. The stage is set for an unsettled day today.

No flash flooding occurred yesterday. For a look at 24-hour precipitation, please see the STP map below.

STP_20160526

FTB 05-25-2016: Drier and Warmer Overall, Isolated Thunderstorms Remain

Issue Date: 5/25/2016
Issue Time: 9:55 AM

NO FLOOD THREAT IS FORECAST.

A shortwave ridge (depicted in the water vapor image below) will move overhead today, which will bring subsidence aloft. The ridge will be largely responsible for the drying/warming trend across the state through this period. There will be a few exceptions, and we will get to that below. Generally speaking, though, today will be a very pleasant day across Colorado. Overnight, changes start knocking on the doorstep and set the stage for unsettled weather on Thursday.

There will be a couple isolated showers/weak thunderstorms over the Northwest Slope, Northern Mountains, and Front Range regions today, owing to a nearby 700-mb trough axis and associated moisture oriented SW to NE across the intermountain west. Further south, orographic effects may be able to produce one or two isolated showers/weak thunderstorms over the higher terrain of the San Juan Mountains, but those probabilities are low. Overall, high country regions other than the Northwest Slope, Northern Mountains, and Front Range will remain mostly sunny and dry, with gusty winds. Overnight and during the early morning hours tomorrow, as the ridge moves out of the area and the upper-level low draws nearer, a few isolated showers/weak thunderstorms will develop over the higher terrain.

WV_20160525

For the lower elevations of eastern Colorado, today will feature mostly sunny conditions with high temperatures ranging from the mid/upper 70s to upper 80s (in the far Southeast Plains). With surface dewpoints hanging on in the 40s and 50s this morning, a couple isolated thunderstorms will develop this afternoon/evening across the Urban Corridor, Palmer Ridge, and Northeast Plains. Overnight, a cool front will begin to push southward across the Northeast Plains, bringing an isolated thunderstorm or two.

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

Mostly sunny with high temperatures a few degrees warmer than yesterday. A couple isolated thunderstorms will develop this afternoon and evening as a result of daytime heating working on remaining surface moisture. The regions with the best chance of seeing isolated thunderstorms, relatively speaking, will be the Palmer Ridge and Northeast Plains. The Southeast Plains and Raton Ridge will remain dry. Maximum rain rates are as follows:

Urban Corridor: 0.15-0.25 inches/hour
Northeast Plains and Palmer Ridge: 0.3-0.5 inches/hour
Southeast Plains and Raton Ridge: N/A

Overnight and into the early morning hours tomorrow, a cool front will move southward through northeast Colorado, kicking up a couple isolated showers/weak thunderstorms. Rain rates in these storms will generally be 0.3-0.6 inches/hour.

Northern Mountains, Northwest Slope, and Front Range:

Isolated showers/weak thunderstorms are expected this afternoon and evening, producing mainly light rain, gusty winds, and occasional lightning. A few isolated showers/storms will develop during the overnight/early morning hours over the higher terrain in response to the approaching upper-level low. Maximum rain rates will be 0.15-0.25 inches/hour.

Timing: 11 AM – 8 PM

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

The main weather story today will be the mostly sunny skies and occasionally breezy conditions. One or two isolated showers/weak thunderstorms are possible over the higher terrain of the San Juan Mountains this afternoon, but those probabilities are very low. A couple isolated showers/weak thunderstorms will develop over the higher terrain during the early morning hours tomorrow in response to the approaching upper-level low, setting the stage for tomorrow’s unsettled weather.

STP 05-25-2016: Strong-to-Severe Thunderstorms Rumbled Across Northeast Colorado

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

Summary:

An upper-level disturbance helped kick off an afternoon of isolated-to-scattered showers/thunderstorms across northern Colorado, mainly east of the Continental Divide. The presence of increasing moisture at the surface, instability, and favorable wind shear led to the development of severe strong-to-severe thunderstorms across the Urban Corridor and Northeast Plains regions. Moderate-to-heavy rain fell from thunderstorms, in addition to a plethora of severe weather impacts. A few of the more significant severe storm reports include:

1.75 inch hail: S of Akron (Washington County), 6 miles SSE of Denver (Denver County)

1.5 inch hail: 1 mile W of Platner (Washington County), SE of Akron (Washington County), 2 miles NE of Denver (Denver County), 2 miles ESE of Denver (Denver County)

Tornado: Akron (Washington County), S of Akron (Washington County), 10 miles NW of Last Chance (Adams County)

Elsewhere, during the evening and overnight hours, isolated showers developed over the higher terrain of northwestern Colorado. These showers produced mainly light rain and gusty winds.

Rainfall winners, according to CoCoRaHS (reports as of 7:00 AM MDT):

Yuma County: 0.82 inches
Phillips County: 0.79 inches
Sedgwick County: 0.74 inches
Adams County: 0.56 inches
Weld County: 0.45 inches

No flash flooding occurred yesterday. For a look at 24-hour precipitation, please see the STP map below. It is important to note that hail contamination will be present in the STP map, so rainfall totals are likely lower than what is shown in most locations.

20160525_STPImage
Storm Total Precip Legend