Issue Date: 6/18/2015
Issue Time: 10:13 AM

A LOW FLOOD THREAT IS FORECAST FOR THE FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, NORTHEAST PLAINS, AND SOUTHEAST PLAINS.

LOW-TO-MODERATE FLOOD THREATS CONTINUE FOR PORTIONS OF THE CACHE LA POUDRE, SOUTH PLATTE, AND ARKANSAS RIVERS.

High-pressure ridging continues to build over the southwestern US, leading to another day of increasing sunshine and decreasing showers/thunderstorms. Drier, warm air aloft continues to work across Colorado from the west, and will limit thunderstorm coverage through this forecast period. Areas along and west of the Continental Divide will be much drier today, with thunderstorms staying confined to the higher terrain of the Central Mountains and San Juan Mountains. East of the Continental Divide is a bit of a different story…

Working against the mid-/upper-level dry air is shallow, low-level moisture across eastern Colorado, currently being reinforced by an outflow boundary from the Mesoscale Convective System (MCS) over NE/KS (circled in blue on water vapor image below). This reinforcement of moisture is working in concert with a lee-side trough that has developed across the eastern plains, backing in moisture and the low-level clouds that currently sit across the Front Range and Urban Corridor. Even so, this moisture is shallow enough that as the day progresses it will mix out somewhat, lowering dewpoints into the 40s across the Front Range and Urban Corridor; this will reduce potential rain rates of isolated thunderstorms in these regions as compared to previous days. Moisture will be more successful at hanging on near the CO/KS border, so maximum rain rates from thunderstorms will still be quite high across the Northeastern Plains, Southeastern Plains, and eastern extents of the Palmer Ridge. With all of that being said, however, today will be warmer and drier overall across Eastern Colorado. Without any real upper-level support, and the warmer air aloft moving across the state, only isolated thunderstorms are expected, with a few growing into a small line of storms across far eastern Colorado later this evening.

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 and Urban Corridor:

Mostly sunny and hot, with highs in the upper 80s/low 90s for lower elevations and in the 70s for higher elevations. Isolated showers and thunderstorms will interrupt the pleasant weather this afternoon and evening, resulting in mainly gusty winds and brief moderate-to-heavy rain. Maximum rain rates will be in the 0.6-1.2 inches/hour range, leading to a low flood threat due mainly to antecedent conditions.

Timing: 2 PM – 8 PM, with another round of isolated storms possible between 10 PM and 2 AM as outflow from thunderstorms on the plains backs into the foothills.

Palmer Ridge, Southeast Plains, and Northeast Plains:

Mostly sunny and hot, with highs in the upper 80s and 90s. Isolated thunderstorms are expected this afternoon and evening, with a few continuing until midnight. A few storms will be severe, with the main threats being large hail, damaging winds, and an isolated tornado. Heavy rainfall will also be attendant, as max rain rates will be 2.0-2.6 inches/hour.

Timing: 2 PM – Midnight

Raton Ridge and Southeast Mountains:

Mostly sunny and hot; high temperatures will be some of the highest so far this year. Isolated showers and thunderstorms are expected this afternoon, resulting in mainly gusty winds and lightning. Maximum rain rates will be 0.4-0.7 inches/hour.

Timing: 1 PM – 8 PM

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

Mostly sunny and hot, with highs in the 80s for the valleys and into the upper 40s and 50s in the mountains. Very isolated thunderstorms will develop this afternoon over the Central Mountains and San Juan Mountains, but otherwise, not much break in the summertime heat today. Locally gusty winds, lightning, and light rain will be the main threats from any activity today.

Timing: Noon – 8 PM

Issue Date: 6/17/2015
Issue Time: 10:16 AM

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

LOW-TO-MODERATE FLOOD THREATS CONTINUE FOR PORTIONS OF THE CACHE LA POUDRE, SOUTH PLATTE, AND ARKANSAS RIVERS.

Finally, the atmosphere is beginning to dry out as weak, upper-level ridging builds across Colorado and the Southwest US. This will have an impact on overall storm coverage as the downturn that began yesterday continues today. That is not to say that it will be all sunshine; there will be isolated showers and thunderstorms this afternoon/evening that develop over the higher terrain and move east-southeastward. Those storms that move/develop over the Urban Corridor, Palmer Ridge, and the Northeast/Southeast Plains will have access to sufficient moisture and instability to produce locally heavy rainfall. With the moisture and instability available, a few storms will become strong-to-severe, capable of producing large hail (greater than 1 inch), strong winds (gusts up to 60 mph), and an isolated tornado.

For areas to the west, ridging aloft and drier air will limit thunderstorm potential, relegating most of the activity to the higher terrain of the Continental Divide and San Juan Mountains. Heavy rainfall is not a concern over these areas, as rain rates will generally be in the 0.2-0.4 inches/hour range, with lighter rates expected out of weaker showers.

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

Isolated showers and thunderstorms are expected this afternoon and evening, and a couple will become strong-to-severe. Locally heavy rainfall is still a concern for the Urban Corridor, Palmer Ridge, Northeast Plains, and Southeast Plains regions where the best moisture and instability will reside.

Maximum rain rates vary, so check out the following breakdown:

Front Range, Southeast Mountains, and Raton Ridge: 0.5-0.9 inches/hour
Urban Corridor, Palmer Ridge, Northeast Plains, and Southeast Plains: 1.4-2.0 inches/hour

Timing: 1 PM – 11 PM, with a few showers and thunderstorms continuing over the Palmer Ridge and plains regions until Midnight – 1 AM before diminishing/exiting the state.

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

Warmer and drier, especially for the lower elevations of the Grand Valley, San Luis Valley, Northwest Slope, and Southwest Slope regions. Isolated showers and weak thunderstorms will mainly stay confined over the higher terrain of the Northern Mountains, Central Mountains, and San Juan Mountains where orographic effects can work against the upper-level ridging. Storms will drift east-southeast with time, so a few lower elevations will likely see a few raindrops downstream of the aforementioned mountains.

Timing: Noon – 8 PM

Issue Date: 6/16/2015
Issue Time: 10:50 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE URBAN CORRIDOR, PALMER RIDGE, AND NORTHEAST PLAINS. A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, NORTHEAST PLAINS, SOUTHEAST MOUNTAINS, RATON RIDGE, SOUTHEAST PLAINS, SAN JUAN MOUNTAINS, CENTRAL MOUNTAINS, AND NORTHERN MOUNTAINS.

For today, storm coverage takes a slight downturn as the mid- and upper-levels of the atmosphere become drier/weakly subsident from west-to-east with time. This is due to the passing shortwave, noted on the visible satellite image below. Associated with this shortwave is a weak lobe of vorticity which will drag south across Colorado, firing off scattered storms across the higher terrain, which will then move eastward with time. Additionally, ahead of the shortwave, scattered strong-to-severe thunderstorms are expected across northeastern Colorado as daytime heating combines with ample low-level moisture. The Palmer Divide will provide support for a few isolated strong-to-severe storms across the southern Urban Corridor and Palmer Ridge regions, as well.

While storm coverage will take an overall downturn today, do not let that lull you to sleep with respect to heavy rainfall and potential flooding issues. Heavy rain will still be a threat, especially in the moderate flood threat areas outlined below. With saturated soils and streams already running high/out of their banks, any additional rainfall will cause flood-prone areas to react quickly. As always, we urge everyone to stay away from high-flowing streams/rivers because saturated banks are unstable and can give way, throwing you into the swift current. Please see the zone-specific forecast discussions below for more details regarding timing and rain 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, jump below the map.

Zone-Specific Forecasts

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

Scattered showers and thunderstorms expected this afternoon and evening as the shortwave translates from west-to-east. Maximum rain rates will vary across these regions, so see below for a breakdown:

Northeast Plains: 2.0-2.5 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 1.2-1.8 inches/hour
Southeast Plains: 0.7-1.2 inches/hour
Southeast Mountains and Front Range: 0.6-1.1 inches/hour

Timing: 11 AM – 10 PM, with a few showers/thunderstorms continuing over the Northeast Plains until around midnight.

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

Scattered showers and thunderstorms, mainly over the higher terrain as upper-levels become weakly subsident this afternoon and orographic effects become the main focus. The San Juan Mountains will feature the greatest coverage of storms overall, and also feature the relative highest rain rates.

Most storms will produce rain rates of 0.25-0.4 inches/hour, with the San Juan Mountains holding the chance for maximum rain rates in the 0.8-1.1 inches/hour range.

Timing: 11 AM – 9 PM, with a few showers lingering after midnight across the highest terrain.

Issue Date: 6/15/2015
Issue Time: 10:45 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE FRONT RANGE, URBAN CORRIDOR, AND PALMER RIDGE. A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHEAST PLAINS, SOUTHEAST PLAINS, RATON RIDGE, NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, SOUTHEAST MOUNTAINS, AND SAN JUAN MOUNTAINS.

Today has started off pleasant across much of the state, with only the northeast quadrant of the state experiencing expansive cloud cover thanks to a passing cool front. The cool front will continue to drop south across Eastern Colorado today, leaving moist, upslope flow in its wake. This cool front will contribute much of the ingredients responsible for today’s moderate flood threat area, and will be assisted by a mid-level disturbance moving across Colorado from the west this afternoon/evening. During the afternoon and early evening hours, daytime heating will contribute to an increase in instability which will support a few strong-to-severe storms capable of producing large hail (up to 1.75 inches in diameter) and damaging winds (gusts up to 55-70 mph).

Rain production will be efficient within today’s storms as precipitable water values climb to near, or just above an inch, along and east of the Front Range/Southeast Mountains. With streams and rivers already running high thanks to snowmelt and saturated soils due to the active weather pattern we have been immersed in, the moderate flood threat is warranted as any additional rainfall will cause flood-prone areas to react quickly. Showers and thunderstorms will diminish between sunset and midnight, with a few overnight showers and thunderstorms possible over the higher terrain of Northern Colorado.

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 Plains, Southeast Mountains, and Raton Ridge:

Scattered showers and thunderstorms will first develop over the mountains late this morning as the mid-level disturbance moves in from the west, pushing/developing to the east with time. Maximum rain rates will be 1.2-2.0 inches/hour over the Front Range, Urban Corridor, and Southeast Plains; near 1.5-2.5 inches/hour over the Northeast Plains and Palmer Ridge; 1.0-1.5 inches/hour over the Raton Ridge and Southeast Mountains.

Timing: 11 AM – Midnight, with a few showers and thunderstorms continuing after midnight, mainly over northern portions of the Front Range, Urban Corridor, and Northeast Plains.

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

Scattered showers and thunderstorms, beginning late this morning and continuing through the evening and into the nighttime hours. A few showers and weak thunderstorms will continue into the overnight hours, mainly across the Northern and Central Mountains. Rain rates will typically be 0.25-0.5 inches/hour, with the stronger storms producing 0.7-1.0 inches/hour.

Timing: 11 AM – Midnight, with a few showers continuing into the early morning hours over the Northern and Central Mountains.