Issue Date: Thursday, June 8th, 2017
Issue Time: 8:40AM MDT

— Flooding is NOT expected today
— Multi-day period of elevated fire danger begins today for western Colorado

Much drier air is on its way into Colorado, as can be seen by the GOES-16 “Low-level water vapor” imagery shown below. While this morning’s Denver sounding still showed 0.71 inches of Precipitable Water, farther west Flagstaff had a reading of 0.14 inches and Salt Lake City with 0.20 inches. This air will make it to western Colorado by late afternoon, removing all chances for rainfall. Farther east on the other side of the Continental Divide, some drying will take place, but the diurnal lee-side trough will cause light easterly low-level flow that will continue to transport (or at least maintain) elevated moisture levels across the region. Thus, in the Northeast and Southeast Plains, isolated to scattered thunderstorms will be seen once again. However, with lower available moisture and faster steering winds, we expect localized pockets of heavy rainfall but without a flood threat.

Severe weather will be possible towards the Kansas/Nebraska border with large hail up to 1.5 inches being the main impact.

Across the western part of the state, a multi-day period of elevated fire danger will begin later this afternoon. Stay tuned to local National Weather Service products for more detailed information.

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.

Issue Date: Wednesday, June 7th, 2017
Issue Time: 10:25AM MDT

— MODERATE flood threat for parts of Urban Corridor and Northeast Plains
— LOW flood threat for Front Range, Palmer Ridge, Southeast Mountains, Raton Ridge and Southeast Plains

This morning’s water vapor imagery, below, continues to show Colorado positioned under a ridge axis that extends to the southwest. Although by itself this pattern is not particularly conducive to heavy rainfall, it becomes significantly more so when ample moisture is available. Such has been the case over the past 72 hours with precipitable water (PW) values exceeding 0.7 inches east of the Continental Divide. This morning’s surface analysis shows that surface dew point temperatures are now approaching 60 F across parts of northeast Colorado. Meanwhile, PWs range from 0.7 to just under 1 inch and are expected to gradually increase through the afternoon as moist easterly flow is advected upslope in the lowest 3-5K feet of the atmosphere. Another feature noted on water vapor imagery is the presence of a weak disturbance centered over the CO/WY border. This will move southeastward and sustain higher mid-level shear (surface-500mb exceeding 30 kts) than has been observed in the past few days, which is more conducive for maintaining an updraft and thus, heavy rainfall. Acting against the heavy rainfall threat is the large-scale subsidence from the ridge, which will continue to limit heavy rainfall coverage.

In all, we expect a similar evolution in today’s weather as the past 2-3 days. Higher elevation storms will develop east of the Continental Divide shortly before noon, then expand south and east into the Plains. A broad Low flood threat has been issued for most of eastern Colorado for the risk of isolated flash flooding. However, a Moderate threat has been posted for parts of northeast Colorado due to the region of higher shear that will support longer-lived storms and potentially storm training. Hail up to 1.75 inches is possible with these strongest cells.

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.

Issue Date: Tuesday, June 6th, 2017
Issue Time: 10:45AM MDT

— MODERATE flood threat for parts of Urban Corridor, Front Range, Palmer Ridge and Southeast Plains. Flooding threat to persist into the late evening hours.
— LOW flood threat for parts of the Northeast Plains, Raton Ridge, Southeast Mountains

— Afternoon update may be required today

A tale of two atmospheres continues today, with a moist atmosphere residing east of the Continental Divide while a dry, hot atmosphere is found to the west (see morning precipitable water analysis by RAP model, below). Not surprisingly, this provides insight into today’s heavy rainfall chances. With a center of high pressure continuing to provide a return flow of moist air to eastern areas, expect a similar evolution today as was observed on Monday. A slight difference will be the entrance of a cool front into northeast Colorado that will likely lower or eliminate storm chances by bringing in a more stable airmass. Farther south and west, At least one round of showers and thunderstorms will develop over the higher terrain east of the Continental Divide, and then spread south and eastward with the steering winds. Moisture content will be even higher than on Monday, with precipitable water values approaching or exceeding 0.9 inch even in the foothills. With sufficient instability in place due to the strong June sunshine (CAPE exceeding 1,500 J/kg), expect scattered to numerous storms to produce heavy rainfall and also be capable of producing isolated flash flooding. A Low flood threat has been posted for most of eastern Colorado. However, a Moderate flood threat is in place for some areas where multiple rounds of storms could pose a higher flooding threat. Hail up to 1.25 inches could accompany the strongest storms.

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

Mostly clear this morning then partly to mostly cloudy with scattered showers and thunderstorms developing shortly before noon. Storms will form over the higher terrain first, then move into lower elevations. Highest coverage will initially be in the foothills, then farther east, especially over the Palmer Ridge. Max 1-hour rainfall up to 1.1 inches for most locations, but up to 2.4 inches for parts of the Palmer Ridge where the highest instability and best upslope flow will be. Max 6-hour rainfall up to 3.6 inches is possible due to multiple storms passing through a given locale. A Moderate flood threat has been posted for the Palmer Ridge, with a Low flood threat has been posted for other parts of the region. The flood threat will persist into the late evening hours for the Front Range as upslope unstable flow could spark off additional thunderstorms.

Primetime: 11:30AM to midnight

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

Sunny this morning then becoming partly cloudy with isolated showers and a weak thunderstorms developing by early afternoon over the higher elevations. Max 1-hour rainfall up to 0.5 inches. Flooding is not expected today.

Primetime: 11:30AM to 7PM

Issue Date: Monday, June 5th, 2017
Issue Time: 9:48AM MDT

— LOW flood threat for parts of Urban Corridor and Northeast Plains

Colorado is positioned underneath a weak ridge centered over northwest Mexico, with an axis extending northward through the Canadian border. It is a tale of two atmospheres today. To the west of the Continental Divide, precipitable water (PW) values are in the 0.4 – 0.6 inch range, and only isolated showers and a weak storm are expected. Instead, hot weather will continue to be the story. To the east, morning PW values are in the 0.7 to 0.9 inch range and are expected to slowly increase as moist easterly flow is established with the afternoon development of a lee-side trough. Instability up to 1,800 J/kg will develop this afternoon in the foothills and western parts of the plains. In addition, very steep lapse rates up to 8C/km were noted across east-central Colorado, supportive of deep moist convection. Scattered storms are likely east of the Continental Divide, generally being limited to within 100-150 miles of the foothills. In terms of heavy rainfall potential, storms will be slow moving, with expected SSE motions of 15-20 mph. But acting against heavy rainfall will be weak shear, implying mostly “pulse” storms that will not be able to last long over any given locale. In all, a Low flood threat is warranted for parts of northeast Colorado for this afternoon and evening for isolated flash flooding. Hail up to 1.5 inches is possible with the strongest storms. Elsewhere in eastern Colorado expect a few heavy downpours, but not enough rain to warrant a flood threat.

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.