Issue Date: Wednesday, June 1st, 2016
Issue Time: 10:35AM MDT

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

It is June 1^st, official summer by the astronomical calendar, and it certainly shows on this morning’s weather map. Unlike the nice, organized disturbances of winter and spring, this morning’s water vapor image, below, shows many features all dueling to impact the day’s weather.

The most notable feature is the cut-off low centered over southeast Arizona that has been crawling eastward for about the last 5 days. It is far removed from our state to have a limited factor, but a factor nonetheless. Associated with it is a weak disturbance, noted most easily in the mid-level vorticity field. This feature will help spark off thunderstorms mostly east of the Divide today. An inspection of this morning’s atmospheric soundings shows a very deep layer of moisture extending from the surface to about 13,000 feet at Denver. Precipitable water values remain near or slightly above seasonal normal, ranging from 0.7 to 0.9 inches east of the Divide. Finally, just like last night, it appears that a nocturnal low-level jet will again provide instability for late evening thunderstorms over the Urban Corridor and Northeast Plains. In all, a wide-covering Low flood threat is in order 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, scroll below the map.

Zone-Specific Forecasts:

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

Partly sunny early with scattered showers and thunderstorms developing by early afternoon and lasting into the early evening with a secondary wave of storms possible in the early overnight hours. Maximum 1 hour rainfall rates up to 1.7 inches are possible, leading to isolated field and roadway flooding. Mud slides and debris flows are possible in steeper terrain. A Low flood threat has been posted for parts of the region.

Primetime: 1pm to 1am

Southeast Plains, Southeast Mountains, Raton Ridge, San Juan Mountains, San Luis Valley:

Partly sunny early with scattered showers and thunderstorms developing by noon and lasting into the early evening. Maximum 1 hour rainfall rates up to 1.7 inches are possible, leading to isolated field and roadway flooding. Mud slides and debris flows are possible in steeper terrain. A Low flood threat has been posted for parts of the region.

Primetime: 1pm to 8pm

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

Mostly sunny early then partly cloudy skies. An isolated showers and perhaps a weak thunderstorm is possible over the higher terrain, with dry conditions elsewhere. Max hourly rain rates up to 0.2 inches. Flooding is not expected today.

Issue Date: Tuesday, May 31st, 2016
Issue Time: 10:40AM MDT

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

This morning’s water vapor image, below, shows many players across the Rocky Mountain states and the central US. Of particular important is the surface low-pressure system located over North Dakota. This is associated with an attendant trough that extends southward into central Colorado. Also associated with this low is a moist cool front that has entered Colorado from the northeast. Meanwhile, a cut-off low continues to drift along in southern Arizona. This feature looks like it is less and less likely to impact our state.

With the above features in mind, we considered the following factors for assessing today’s flood threat:

• Moisture levels continue to be fairly limited for heavy rainfall with Precipitable Water (PW) values running close to seasonal normal in the 0.5 – 0.7 inch range east of the Divide and lower to the west; PW is expected to stay steady or increase, especially in the Southeast Plains as a weak low-pressure circulation may develop over Southeast Colorado later today. PW’s may reach 1.0-1.2 inches from about La Junta southeastward.
• The cool front has increased moisture content, but also brought in a stable layer above the surface. Thus, instability will be focused immediately south of the cool front boundary. Roughly along and south of the Palmer Ridge.
• Dynamics are neutral to slightly favorable for heavy rainfall. The presence of the trough will provide weak positive vorticity advection east of the Divide. However, most of the fuel for heavy rainfall will likely be provided by solar heating.
• Storm steering winds will be 25mph+ today and storm training is not expected. It will likely be a “one-and-done” type day with heavy rainfall potential. The only exception is in the far southeast portion of the state where a nocturnal low-level jet may continue to fuel storm activity after sunset.
• Dry air entrainment is expected over southern parts of the Raton Ridge which will likely limit rainfall rates.

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, scroll below the map.

Zone-Specific Forecasts:

Front Range, Urban Corridor, Northeast Plains, Palmer Ridge, Southeast Plains, Southeast Mountains, Raton Ridge:
Partly sunny early with scattered to widespread showers and thunderstorms developing by early afternoon and lasting into the late evening and early overnight hours in the far southeast. Maximum 1 hour rainfall rates are shown below:

Front Range/Urban Corridor/Northeast Plains: 1.3 inches per hour
Palmer Ridge/Southeast Plains/Southeast Mountains/Raton Ridge: 1.9 inches per hour

Primetime: 1pm to 8pm in northern sections and 1pm to midnight in the Southeast Plains

A Low flood threat has been issued for isolated field and roadway flooding. Mud flows and debris slides are possible over steeper terrain, including fire scar areas.

Central Mountains, Northern Mountains, San Juan Mountains, San Luis Valley, Grand Valley, Northwest Slope, Southwest Slope:
Mostly sunny early then turning partly cloudy. An isolated showers and perhaps a weak thunderstorm is possible over the higher terrain, with dry conditions elsewhere. Max hourly rain rates up to 0.2 inches. Gusty winds up to 50 mph will be possible under the thunderstorm updrafts. Flooding is not expected today.

Issue Date: Monday, May 30, 2016
Issue Time: 10:20AM MDT

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

This morning’s weather map is a bit busier than past days. As the water vapor image below shows, yesterday’s transient ridge is a thing of the past. Today, it is replaced by an elongated, but broken trough stretching from the Canadian border south-southwest into the Baja of California. A closer inspection reveals this trough is actually comprised of two different centers of action: a main one from about Utah northward and a secondary one in the form of a weak cut-off low in southwest Arizona. Several days ago, it appeared these two features would move as one and could provide for a widespread rain across CO. This is no longer the case. Instead, the northern feature will propagate rather swiftly eastward, while the southern feature will more-or-less lose touch with steering winds and may not move much.

The northern feature is the main player today. It will trek eastward accompanied by a surface low centered over western South Dakota and a weak cold front stretching into Colorado’s Northeast Plains. With precipitable water values between 0.8 and 1.0 inch expected in the region by this afternoon,this will be the focal point for a few stronger thunderstorms capable of heavy rainfall, hail up to 1.5 inches and perhaps a tornado along the Kansas border. A Low flood threat has been issued for eastern areas.

For everyone else, expect a similar day to Sunday with isolated to scattered showers and thunderstorms from early afternoon into the evening hours. Just like yesterday, the bigger impact of this action will be gusty winds as a dry lower-atmosphere will help evaporate most of the rainfall before it reaches the ground.

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, scroll below the map.

Zone-Specific Forecasts:

Northeast Plains, Southeast Plains, Palmer Divide:

Mostly sunny early with scattered thunderstorms developing by early afternoon and lasting into the early evening hours. A few of the strongest storms will be capable of produce heavy, short-term rainfall, hail up to 1.5 inches and wind gusts up to 60mph. An isolated tornado is also possible. Max 1 hour rainfall rates up to 1.7 inches will lead to isolated field and road flooding. A Low flood threat has been posted.

Primetime: 1pm to 8pm

Front Range, Urban Corridor, Raton Ridge:

Sunny early with isolated to scattered showers and a weak thunderstorm developing by early afternoon and lasting into the early evening hours. Hourly rainfall rates up to 0.4 inches are possible, along with gusty winds up to 45 mph. Flooding is not expected.

Primetime: 12pm to 7pm

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

Mostly sunny early then turning partly cloudy. Isolated showers and perhaps a weak thunderstorm are possible mainly over the higher terrain. Max hourly rain rates up to 0.25 inches. Gusty winds up to 50 mph will be possible under the thunderstorm updrafts. Flooding is not expected today.

Issue Date: Sunday, May 29th, 2016
Issue Time: 9:55AM MDT

— Flooding is NOT expected today.

Today’s pattern will be a continuation of yesterday, with a temporary transient ridge setting up overhead as shown in the water vapor image below. The mid-levels of the atmosphere have warmed several degrees Celsius in the last 24-hours and additional height rise are expected. This points to subsidence above the boundary layer and should act to limit rainfall amounts. However, with ample sunshine and enough low-level moisture, expect lots of cumulus clouds to pop up and some of those to lead to scattered showers and thunderstorms. Highest coverage will be east of the Divide, and especially in the Northeast Plains. But with precipitable water values at or below their seasonal normal, rainfall is expected to remain in check. Flooding is not expected today.

The next weather player is also seen on the water vapor image. This cut-off low, currently over southern California, is expected to propagate east and will impact Colorado’s weather on Memorial Day (Monday) and into Tuesday. An increase in shower and thunderstorm activity is expected each day.

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, scroll below the map.
Zone-Specific Forecasts:

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

Mostly sunny early with isolated to scattered showers, and weak thunderstorms developing by early afternoon and lasting into the early evening hours. Storms will form in the higher terrain and move slowly eastward through the day. Flooding is not expected today. Max hourly rain rates:

0.6 inches in the Palmer Divide, Front Range, Urban Corridor and Raton Ridge

1.2 inches in the Northeast Plains and Southeast Plains

Primetime: 12pm to 8pm

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

Mostly sunny early then turning partly cloudy. Scattered showers and perhaps a thunderstorm are possible mainly over the higher terrain. Max hourly rain rates up to 0.25 inches. Flooding is not expected today.