FTB 06-20-2018: High Pressure Takes Over

Issue Date: 6/20/2018
Issue Time: 8:10 AM

NO FLOOD THREAT IS FORECAST TODAY.

After a sufficiently active weather day yesterday, today will be marked by the return of high pressure and drier air. In the water vapor image below I have denoted the location of the mid-level high pressure center, along with its axis (blue dashes). The high pressure will shift eastward today, placing drier and cooler northwest flow over the state, resulting in mostly sunny skies and high temperatures that are reminiscent of spring time. A few isolated, brief, showers/weak thunderstorms will rumble across eastern Colorado during the afternoon/evening as daytime heating and residual moisture will have just enough “oomph” to trigger their development. Gusty winds and light rainfall will be the main threats from any such activity. For western Colorado, where it will be less about northwest flow and more about the ridge axis moving overhead, plenty of sunshine and near-average high temperatures are the name of the game 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.

Flood Threat Legend

Zone-Specific Forecasts

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

Mostly sunny skies and pleasant high temperatures are the weather story today, with only a few, brief, isolated showers/weak thunderstorms breaking up the otherwise beautiful day. Gusty winds and light rainfall will be all the atmosphere can muster, and no flood threat is warranted. Rain rates will generally be 0.05-0.15 inches/hour, with maximum rain rates as follows:
Front Range, Urban Corridor, Southeast Mountains: 0.2-0.4 inches/hour
Northeast Plains, Palmer Ridge, Southeast Plains, and Raton Ridge: 0.5-0.7 inches/hour

Timing: Noon – 10 PM

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

Mostly sunny skies and seasonal temperatures will mark this FTB period as high pressure builds overhead. Fair weather cumulus clouds will bubble over the higher terrain, and a weak shower or two cannot be ruled out over the Northern Mountains and Central Mountains, but that will be all the atmosphere can produce today.

Maximum rain rates from any showers that develop over the Northern Mountains and Central Mountains will be 0.05-0.15 inches/hour, with more virga and gusty winds than rain being the general rule.

Timing: Noon – 9 PM

FTB 06-19-2018: Severe Weather and Heavy Rain Threat Continues for Eastern Colorado

Issue Date: Tuesday, June 19, 2018
Issue Time: 10:20AM MDT

— A MODERATE flood threat has been issued for portions of the Northeast Plains, Palmer Ridge and Southeast Plains

— A LOW flood threat has been issued for the Urban Corridor, Front Range, Northeast Plains, Palmer Ridge and Southeast Plains

The visible satellite imagery below shows some lingering high clouds from the overnight, heavy rainfall. While it may take a bit to burn off this cloud cover, breaks in the clouds indicate this is a likely scenario (at least over some areas). Breaks in clouds over Weld and Morgan County should be monitored closely because where the sun can shine through, instability can build for another round of severe thunderstorms this evening. Models indicate a boundary from the north setting off storms over the Urban Corridor tonight in the high moisture environment. If these or any other storms track over the area that received heavy rainfall yesterday, increased runoff and flooding is likely due to saturated soils. The loaded gun sounding at Denver this morning shows quite a cap, but upper level atmospheric support this afternoon should help break it. With freezing levels at 8957 feet and a humped hodograph, there will be a large hail threat and possibly a tornado for the severe thunderstorms that form this afternoon and evening.

High moisture remains over eastern Colorado again today. Dew points are forecast to be in the 50-60F range, which means the heavy rainfall threat returns. Expecting storms to fire off the southern Front Range, Southeast Mountains and Palmer Ridge later this afternoon. Storm motion today will be to the east/southeast, and models indicate that the discrete severe thunderstorms that fire further south this afternoon will eventually form a MCS over the far Southeast Plains by the early evening. A second wave of storms is expected to form later tonight as a boundary slides down from the north, which could also create some late night thunderstorms over the Urban Corridor. This second wave of storms will continue the flood threat over the Southeast Plains/Palmer Ridge overnight. A Low and Moderate flood threat have been issued due to the likelihood of road and small stream flooding, arroyo flooding and field ponding.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Flood Threat Legend

 

Zone-Specific Forecasts:

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

Severe weather and heavy rainfall threat return once again to eastern Colorado. Expected severe thunderstorms today to produce large hail (up to 2.25 inch), gusty winds and possibly a tornado. High dew points will promote efficient rain rates as well. Should storms form over the northern Urban Corridor this afternoon, rain rates up to 1.25 inches/hour will be possible. If these storms track over Weld and Morgan Counties, expect some flash flooding due to saturated soils from heavy, overnight rain. Further south, over the Palmer Ridge and Southeast Plains, max 1-hr rain rates up to 2 inches/hour will be possible. Overnight rainfall over the eastern plains is expected and local totals by tomorrow morning could exceed 3 inches near the CO/KS border. For the storms that form over the Southeast Mountains, max 1-hr rain rates will be much lower (0.25 inches/hour) due to moisture being scoured east. A Moderate and Low flood threat have been issued for street flooding, field ponding and local stream flooding.

Primetime: 2PM – 5AM

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

Dry air continues to be entrained over the area from the southwest, which means there is no chance for rainfall again today. The strong winds yesterday associated with the passing trough have ended, which will drop the Red Flag Warning. Expect a few clouds over the Northern Mountains and Northwest Slope this afternoon, but should be clear elsewhere. High temperatures will continue to be on the increase, but highs today will be average for this time of year.

FTB 06-18-2018: Heavy Rain and Severe Weather for Northeast Colorado

Issue Date: Monday, June 18, 2018
Issue Time: 09:55AM MDT

— A LOW flood threat has been issued for portions of the Northeast Plains, Urban Corridor and Front Range

The water vapor imagery below shows that most of the moisture associated with Bud has moved through the state and is replaced by dry southwest flow. The burn scars over the San Juan Mountains, along with much of western Colorado is now under the influence of the dry slot, which should put an end of the heavy rainfall chances. The sounding at Grand Junction this morning shows PW values have dropped to 0.58 inches. Today and tomorrow the upper low over Idaho will continue its slow eastward migration. Today, the jet streak will move over the northwest corner of Colorado and mix down strong winds to the surface. Wind gust this afternoon are expected to be in the 30-40mph range, which with dry air, returns critical fire weather. A Red Flag Warning has been issued through 8PM tonight for the lower elevations of this region.

In eastern Colorado, a surface cyclone is expected to develop over the eastern plains, which will help create severe weather for the Northeast Plains this afternoon. Threats include large hail, strong winds and the possibility of some isolated tornadoes. For the Southeastern Plains, the dry southwesterly flow will limit moisture for afternoon showers and thunderstorms. However, some dew points in the 30Fs near the Palmer Ridge may allow for a few scattered storms. With decent storm motion and direction in this area paired with lower dew points, heavy rainfall is not forecast.

Over the Northeast Plains, southeasterly to eastern flow will return low level moisture with dew points reaching the mid 50sF (west) and 60s (east). Storms are expected to fire over the Palmer Ridge and Front Range this afternoon. As they move east into the high dew points heavy local rainfall is likely. Later this evening a southwest to northeast band of showers sets up overnight near the I-76 corridor. With high low level moisture, local heavy rainfall is likely. A Low flood threat has been posted for this afternoon into early tomorrow morning. Threats include street and small stream flooding over the Urban Corridor and field ponding/street flooding near low roads over the eastern plains.

Today’s Flood Threat Map
For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Flood Threat Legend

 

Zone-Specific Forecasts:

Palmer Ridge, Front Range, Urban Corridor, Northeast Plains:

High moisture returns to the Urban Corridor and Northeast Plains today. Initial set of thunderstorms this afternoon will have access to favorable severe weather parameters and high moisture. Threats include large hail, gusty winds, an isolated tornado and heavy rainfall. Max 1-hr rain rates up to 1.7 inches/hour are possible. Overnight a band of showers sets up near the I-76 corridor, which will allow for high rainfall accumulations. Max 1-hour rain rates up to 1.25 inches/hour are possible with local totals up to 2.25 inches by tomorrow morning. A Low flood threat has been issued for street flooding, field ponding and local stream flooding.

Primetime: 2PM – 5AM

Southeast Plains, Raton Ridge, Southeast Mountains:

Dry air will limit precipitation chances this afternoon. Expect isolated high clouds with limited rainfall over this area. An isolated storm may be possible over the Southeast Plain, but max 1-hour rain rates will be under flood thresholds. Over the Southeast Mountains, 1-hour rain rates up to 0.25 inches/hour are possible.

Primetime: 1PM –8PM

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

Southwest flow will pull in dry air to the area. Paired with increasing wind speeds over northwestern Colorado, a Red Flag Warning is in effect through this evening for the lower elevations. Clear skies are expected over the region with temperatures closer to average for this time of year. There is no flood threat today.

 

FTB 06-17-2018: Main Flood Threat Show Shifts East

Issue Date: 6/17/2018
Issue Time: 9:30 AM

A MODERATE FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE FRONT RANGE, URBAN CORRIDOR, NORTHEAST PLAINS, AND PALMER RIDGE.

A MODERATE FLOOD THREAT HAS BEEN ISSUED FOR THE 416 FIRE AND BURRO FIRE AREAS.

A LOW FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, NORTHEAST PLAINS, AND SOUTHEAST PLAINS.

Remnants of Bud will continue to overlay the state today, with the best mid-level moisture shifted to the east as compared to the previous FTB period. Drier air is currently working its way in from eastern Utah, which will eventually eliminate the flood threat for the 416 Fire and Burro Fire during the evening hours. The main features to focus on for today’s main show, however, is the surface low and associated cool frontal boundary across eastern Colorado. I have denoted the location of these features, as of 8:16 AM MDT, in the surface map below. The surface convergence and wind shear along the frontal boundary, coinciding with the passage of the mid-/upper-level low this afternoon, will provide the trigger for scattered-to-widespread showers and thunderstorms today/tonight along, and to the north of, the frontal boundary.

The front isn’t expected to move much, perhaps sag southward a few miles, so the threat of training thunderstorms riding the boundary (northeast storm motions on a southwest-to-northeast oriented boundary) is the culprit behind today’s moderate flood threat. Plenty of moisture is in place for heavy rainfall, with precipitable water values ranging from 1.0 to 1.4 inches expected across the threat area.

Burro Fire and 416 Fire burn areas:

Flash flooding, debris, and rocks were reported across Highway 550 just north of Durango this morning. With the threat of rainfall still in the forecast through the afternoon hours, the moderate flood threat has been issued. The threat today is less than yesterday due to drier air moving in from the west, but with the rain that has already fallen, it will take even less today to produce more 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.

Flood Threat Legend

Zone-Specific Forecasts

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

Along and north of the frontal boundary, scattered-to-widespread showers and thunderstorms are expected. With precipitable water values exceeding 1 inch, and ranging up to 1.4 inches near the CO/KS/NE border, rainfall production will be very efficient. The threat of training showers/thunderstorms producing periods of heavy rainfall is the culprit behind the moderate flood threat. To the south of the frontal boundary, a lack of focusing mechanism for shower/thunderstorm development will keep activity for isolated and sporadic. Maximum rain rates are as follows:

Northern Mountains, Central Mountains, and Front Range: 0.8-1.2 inches/hour
Urban Corridor and Palmer Ridge: 1.0-1.3 inches/hour
Northeast Plains: 1.5-2.0 inches/hour
Southeast Plains: 0.8-1.4 inches/hour
Raton Ridge and Southeast Mountains: 0.2-0.4 inches/hour

Threats: Flash flooding, street/field ponding (especially in poorly drained areas/intersections), low-lying area flooding along streams/creeks, mud flows/debris slides from impacted burn scars in steep terrain.

Timing: Noon – Midnight for the mountains, with a few showers/weak storms lingering into the early morning hours. Noon – 1 AM for all other areas, with a few storms over the Urban Corridor and Northeast Plains until 5 AM.

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

Isolated-to-scattered showers are expected today, with a few weak thunderstorms mixed in during the afternoon hours. Drier air is beginning to make its way in from Utah, so activity will end from west-to-east during the late afternoon and into the evening hours. Generally speaking, rainfall rates will be 0.1-0.3 inches/hour, with maximum rain rates as follows:

Northwest Slope and Grand Valley: 0.4-0.8 inches/hour
Southwest Slope and San Juan Mountains: 0.3-0.6 inches/hour
San Luis Valley: 0.2-0.4 inches/hour

Timing: Ongoing – 11 PM, with activity diminishing from west to east beginning around 5 PM.