Issue Date: 6/23/2018
Issue Time: 8:40 AM

A LOW FLOOD THREAT IS ISSUED FOR PORTIONS OF THE URBAN CORRIDOR, PALMER RIDGE, NORTHEAST PLAINS AND SOUTHEAST PLAINS FROM 3 PM – 11 AM TOMORROW.

The main focus of this FTB period’s forecast is an upper-level low, currently situated over Northeastern Idaho/western Montana, that will dig southeastward through today and tonight, becoming centered over western Wyoming around midnight tonight. This movement will place a jet streak (black-hatched area in water vapor image below) in a favorable position to produce lift and trigger thunderstorms over Colorado later today and continuing into tomorrow. At the surface, a cold front will pass through the state tonight and early tomorrow, with increasing moisture behind the front and east of the mountains. This will set the stage for the low flood threat that has been issued, as deeper moisture coincides with the broad-scale lift brought on by the upper-low and jet streak.

Prior to this period’s “main event” described above, a few isolated showers and thunderstorms are expected this afternoon/evening thanks to daytime heating and residual moisture. Activity west of I-25 will produce more gusty winds than rain, as low-level moisture will be a bit too low for anything more. For areas east of I-25, isolated thunderstorms will have access to better moisture and better wind profiles, so a couple strong-to-severe storms cannot be ruled out. These storms will be capable of periods of heavy rainfall, strong winds, and small hail. Relatively quick eastward storm motions will mitigate heavy rainfall residence time over an area, so street/field ponding in poorly drained areas will be only concern with heavy rainfall during this time frame.

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

A few isolated thunderstorms expected this afternoon/evening (3 PM – 7 PM) triggered by daytime heating. Later this evening and into tomorrow morning (6 PM – 11 AM), the influence of an upper-level low, jet streak, and moisture return behind a surface cold front will allow for the development of scattered showers and thunderstorms, mainly north of a line from Kit Carson to Colorado Springs. The bulk of the thunderstorm activity is expected north of Highway 36. Maximum rain rates are as follows:

Urban Corridor: 0.5-1.0 inches/hour
Northeast Plains and Southeast Plains: 1.4-2.0 inches/hour
Raton Ridge: 0.5-0.8 inches/hour
Front Range: 0.25-0.5 inches/hour
Southeast Mountains: 0.05-0.15 inches/hour

The main threats will be street/field ponding in poorly drained areas, flooding of low-lying areas and intersections, and small stream/creek flooding.

Timing: 3 PM – 11 AM

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

Mostly sunny, breezy, and hot for most areas today, with Red Flag Warnings in effect across much of the region until 9 PM tonight. A few isolated showers/weak storms are expected over the higher elevations of the Northwest Slope, Northern Mountains, and northern portions of the Central Mountains later this afternoon (thanks to daytime heating), with a few continuing into the overnight hours thanks to the upper-level low and jet streak. Moisture remains too low for any flood threat, and more wind than rain is expected from any activity. Maximum rain rates will be 0.05-0.15 inches/hour.

Timing: 3 PM – Midnight

Issue Date: Friday, June 22, 2018
Issue Time: 9:30AM MDT

— A LOW flood threat has been issued for the Northeast Plains, Southeast Plains and eastern Palmer Ridge

Taking a look at the low level water vapor imagery below, the first upper trough described in yesterday’s FTO can be seen over the MT/WY border. The upper jet associated with this feature is producing strong westerly flow over Colorado and helping produce the shortwave (disturbance) marked in the image below. This is currently generating high cloud cover and some very light showers over the northwest corner of the state. This trough will continue to move eastward across the state today and help produce severe weather over the eastern plains. Threats include very large hail, strong winds and local, heavy rainfall. To the west, a tightening gradient and weak front will increase surface winds. The lack of low level moisture (Grand Junction PW at 0.52 inches) will produce critical fire weather; thus, a Red Flag Warning has been issued through this evening.

Over eastern Colorado, the shortwave trough will help promote more widespread showers and thunderstorm development over the Front Range and Southeast Mountains this afternoon. However, with dry upper levels and downsloping winds, these storms will produce more gusty winds than measureable rainfall. As the disturbance arrives to the plains during peak heating, favorable severe weather parameters will have set up. A lee cyclone will have helped pull in high low level moisture with easterly flow increasing CAPE values, decent shear will have developed thanks to westerly flow aloft and a nice SW to NE convergence boundary will provide lift for the severe thunderstorms. Hodographs indicate a low tornado threat, and instead the atmosphere is expected to produce a line of convection capable of generating strong winds and very large hail. Although storm motion will be fairly quick to the E/SE, with dew points in the upper 50Fs to 60Fs, heavy, local rainfall is possible. A Low flood threat has been issued for 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.

 

Zone-Specific Forecasts:

Northeast Plains, Southeast Plains, Palmer Ridge:

Expecting severe thunderstorms this afternoon with very large hail and strong winds. With high dew points, a quick 1.75 inches in an hour is possible closer to the KS/CO border and over the northeast corner of the state. Storms will move quickly to the E/SE and exit the region by 9PM this evening, but there may be some showers that wander into the plains through midnight. A Low flood threat has been issued for road flooding, small stream flooding and field ponding for the line of convection this afternoon.

Primetime: 12PM to 9PM

Front Range, Urban Corridor, Southeast Mountains, Raton Ridge:

Expecting increased shower and thunderstorm coverage over the mountains this afternoon with the passing shortwave. Storms will likely produce gusty winds as there will not be much moisture available for measureable rainfall. Max 1-hr rain rates up to 0.15 inches/hour north and 0.25 inches/hour south. Over the adjacent plains max 1-hour rain rates up to 0.6 inches/hour are possible. There is a chance for some lingering showers over the adjacent plains through midnight.

Primetime: 11AM to 9PM

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

As the upper wave continues eastward throughout the day, the cloud cover should decrease over the northwest corner of the state. Expect a few high clouds over the higher terrains this afternoon. Surface winds will also increase with the passing trough and create another day of critical fire weather. Rainfall is not likely outside of light showers this morning over the Northern and Central Mountains.

Issue Date: 6/21/2018
Issue Time: 8:15 AM

NO FLOOD THREAT IS FORECAST TODAY.

The ridge of high pressure that dominated the forecast yesterday is being flattened today by the approach and passage of a mid-level shortwave (denoted by the purple line in the water vapor image below). This will result in the development of a few more isolated-to-widely thunderstorms this afternoon/evening, mainly along/east of the Continental Divide. Westerly flow aloft will work against the potential for heavy rainfall today in two ways: 1) it will keep better moisture further east over the plains, and 2) storms will move quickly towards the east, reducing the residence time of any periods of rainfall over a particular location.

West of the Continental Divide, a couple of high-based, isolated showers/weak thunderstorms cannot be ruled out over the Northwest Slope, Northern Mountains, and northern portions of the Central Mountains, where the close(r) proximity to the mid-level disturbance will provide enough lift for the development of said activity. Moisture will remain on the lower end of the scale, so any showers/storms will produce more wind and virga than rainfall. Other than that, western Colorado will remain dry and mostly sunny.

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

Isolated-to-widely scattered thunderstorms are expected this afternoon/evening, first developing over the mountains, then progressing eastward over the lower elevations with time. The strongest storms will occur over northern portions of the Urban Corridor, Palmer Ridge, and Northeast Plains, where low-level moisture will be best (dewpoints in the 50s). A brief period of heavy rainfall in these locations may result in localized street/field ponding, but storm motions will be too quick to necessitate the issuance of any flash flood threat. Maximum rain rates are as follows:

Front Range: 0.25-0.5 inches/hour
Urban Corridor, Northeast Plains, and Palmer Ridge: 0.8-1.2 inches/hour
Southeast Plains: 0.6-1.0 inches/hour
Raton Ridge: 0.3-0.5 inches/hour

Timing: 3 PM – 10 PM, with the any lingering activity diminishing/exiting the state by Midnight

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

Mostly sunny and dry will be the weather story for the vast majority of the area, with only a couple isolated showers/weak thunderstorms expected over higher terrain north of I-70. This includes the Northwest Slope, Northern Mountains, and northern portions of the Central Mountains. Very little rainfall is expected from any activity, as moisture remains on the lower end of the scale. Gusty winds, virga, and lightning will be the most likely outcome. Maximum rain rates will be 0.05-0.10 inches/hour.

Timing: 2 PM – 9 PM

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.

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