FTB 06-06-2018: Weak Cold Front Will Bring Chance of Storms for Some

Issue Date: Wednesday, June 6, 2018
Issue Time: 09:45AM MDT

— Flooding is NOT expected today.

Much of the state was subjected to its hottest day of the year so far yesterday, with temperatures in the low country soaring well into the 90°Fs. While most locations are expected to remain above seasonal average temperatures today, a weak cold front is edging its way into the northeastern corner of the state as of this morning (see graphic below), bringing slightly cooler and significantly moister air. In addition to surface conditions becoming more favorable for thunderstorms today, some upper-level support for convection in the form of a weak, subtle shortwave (dashed red line in figure) is anticipated today. While not particularly robust, the shortwave is expected to cross the mountains and into the eastern plains just after midday and into the early afternoon today, providing extra lift at an ideal time for generating afternoon and evening storms.

The cold front is expected to continue sagging south throughout the day, but will likely not make it further south than the Palmer Ridge before washing out. The bulk of the thunderstorm activity is expected along and north of this boundary, where the passing shortwave will have the most surface moisture to work with and winds will be an upslope northeasterly. Storms may even produce some severe weather along and northeast of a line from the CO/WY/NE border region down to the southeast corner of the state (including towns like Springfield and Lamar). All threats are possible, with hail and wind being the most likely forms of severe weather. Storms that do form are expected to grow upscale into a large cluster before exiting the state into Kansas and Nebraska later this evening. Rainfall may be briefly heavy, but winds aloft should keep the storms moving off to the east or northeast at a decent clip, limiting the threat of sustained heavy rain. No flooding is expected today.

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:

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

Partly cloudy and warm to begin the day, with clouds increasing as the shortwave approaches this afternoon. Storms will begin to fire over the Front Range and the eastern plains by early afternoon, with some severe weather possible over eastern portions of the area. The heaviest rain will be from the Palmer Ridge to the northeast, with rain rates of around 1 inch/hour possible under the strongest storms. With the scattered nature of the rainfall, totals will vary widely, but total accumulations of up to 2” are not out of the question in isolated locations.

Primetime: 1PM to Midnight

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

Partly cloudy with continuing warm conditions for most today, with just a small chance of a brief, isolated shower or thunderstorm near some of the high mountain peaks today.

FTB 06-05-2018: Heat in Full Force Today Leading in to Afternoon Thunderstorms

Issue Date: Tuesday, June 5, 2018
Issue Time: 10:25 AM MDT

— Flooding is NOT expected today

South to southwesterly winds near the surface today will make for another unseasonably hot afternoon for much of Colorado. This is due to a large upper air ridge that is sitting almost directly above Colorado this morning – the crest of this ridge situated almost exactly in the middle of the state. West of the continental divide, despite seeing some weekend rainfall, will be too dry to see any weather other than increasing clouds throughout the day. While dry weather has persisted east of the divide as well, this part of the state will see a boost in its chance for thunderstorms due to small disturbance at the crest of the ridge. This kink may help generate enough atmospheric lift to trigger thunderstorm development this afternoon and evening.

With the combination of the hot surface air rising and a modest increase in relative humidity values in the middle layers of the atmosphere, there is an appreciable chance for thunderstorms from the Front Range and Urban Corridor east to the plains. Mid-level moisture will not be enough to churn out significant thunderstorms, however, and rainfall rates will generally be confined to about 0.1 to 0.25 inches per hour. No flood threat is forecast today.

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:

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

Temperatures well into the 90s are forecast for today, with initially sunny conditions leading to increasing cloud cover as the day progresses. By around 5pm, towering thunderstorms are anticipated to begin forming over the area, especially over the Palmer Ridge. Rainfall will likely start as virga, but as the lower atmosphere continues to moisten as thunderstorms pass overhead the rain will likely be able to make it all the way to the surface. Rainfall rates are forecast to generally be between 0.1 to 0.25 inches per hour, but underneath the strongest thunderstorms brief periods of up to 0.5 inches per hour are possible. No flood threat is forecast today.

Primetime: 5 PM to 12 AM

Northern Mountains, Central Mountains, Front Range, and Urban Corridor:

For today, expect unseasonably hot conditions accompanied by a south/southwest wind. As the afternoon progresses, cumulus clouds will build with some managing to develop into thunderstorms. Given how dry the atmosphere is near the surface, rain showers will likely only be noticeable as wispy virga from the ground. Should the showers be persistent, however, a few areas may see measurable rainfall late in the afternoon and into the evening. Hourly rainfall rates are not expected to exceed 0.25 inches, and no flood threat is forecast.

Primetime: 3 PM to 10 PM

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

Plenty of sunshine today with fair weather cumulus clouds forming in the afternoon. Southerly winds will bring in hot and dry air throughout the region, and while no substantial fire danger exists today, use caution with open flames or flammable substances outdoors. No appreciable rainfall is expected.

FTB 06-04-2018: Drying Pattern Set in Motion as Ridge Begins to Build

Issue Date: Monday, June 4, 2018
Issue Time: 08:40AM MDT

— Flooding is NOT expected today

The disturbance that brought rainfall to the southern portion of the state yesterday is marked in the visible image below (red). This will continue to move to the east throughout the day, and in its wake, a ridge of high pressure will begin to build north of Colorado. This will create more westerly flow aloft, which will pull in dry air from the southwest. Thus, the drying pattern for the week has begun. Today showers will be more isolated in nature and high temperatures are expected to climb back into the 90s over the lower elevations.

East of the Continental Divide, storms will initiate over the higher terrains of the Cheyenne Ridge and Palmer Ridge later this afternoon. Some low-level moisture is able to hold on over the Northeast Plains with more south/southeasterly flow. With storm motion to the southeast, the storms coming off the Cheyenne Ridge may be able to drop a quick 0.5 inches of rainfall over the far Northeast Plains. However, an inversion at 700mb may put a kibosh on all convection. Over the Southeast Plains, dew point values will be in the upper 30s, so expect storms that form over the Palmer Ridge to produce gusty winds and total rainfall amounts under 0.2 inches. Lastly, west of the Continental Divide, there is a little residual moisture over the San Juan Mountains. This will help spark some very isolated scattered showers and thunderstorms later this afternoon over the higher terrain. Rainfall amounts under the storm cores are expected to be under 0.1 inches and strong gusts are likely. Flooding is not expected today.

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:

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

A couple scattered showers and thunderstorms will be possible over the Northeast Plains and Southeast Plains. If they are able to break the cap, better moisture to the north will allow max 1-hour rain rates up to 0.5 inches. Further south, dew points in the mid to upper 30s will keep rainfall totals under 0.2 inches. Expected gusty winds under all storms that form today. Storms should quickly dissipate with increased stability after sundown. Flooding is not expected today.

Primetime: 3PM – 9PM

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

Residual moisture over the San Juan Mountains will allow some isolated showers and thunderstorms to fire over the higher terrains this afternoon. Storm totals are expected to be under 0.1 inches and gusts up to 45mph are possible. Elsewhere, expect clear skies and high temperatures in the lower elevations to reach 90F. There is no flood threat today.

Primetime: 3PM – 8:30PM

FTB 06-03-2018: Compact Upper Wave to Deliver Rain to Drought-Stricken Southern CO

Issue Date: 6/3/2018
Issue Time: 10:15 AM


Following several days of largely dry and hot weather across Colorado, a compact and fast-moving but potent upper-level low is currently approaching the state from the southwest. The low has begun to draw plentiful moisture northward into the southern half of the state, as evidenced by this morning’s GOES-16 water vapor imagery (see figure below). As the low moves rapidly east-northeastward, this envelope of moisture will expand, allowing for widespread showers and some thunderstorms across most of the southern half of the state. In addition, the moisture may creep far enough northward to produce some scattered thunderstorms across northeastern portions of the state. At this time, chances of receiving notable precipitation outside the mountains appear remote.

With the abundance of moisture expected, there is some risk of brief heavy rainfall across portions of the state, particularly across the southwest. However, with the dry conditions and very low snowpack that have prevailed there of late, excessive runoff is not anticipated to be an issue. Instead, the moisture will provide welcome relief for many. As the low continues to track off to the east-northeast, the precipitation threat will diminish from southwest to northeast. Precipitation will come to an end before sunset across the southwest corner, whereas rain in the central portion of the state may linger for several more hours. There is no flood threat 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

Grand Valley, Southwest Slope, San Juan Mountains, Central Mountains, Southeast Mountains, Northern Mountains, Front Range:

Mostly cloudy conditions with a few showers along the state’s southern border are already present this morning, with both clouds and precipitation expected to increase in coverage through early- to mid-afternoon. Generally, precipitation intensities should be in the 0.05” to 0.20” per hour range, but isolated spots may briefly approach 0.5” per hour. The highest rainfall totals may reach around 1.0-1.5” and will be over elevated terrain on the west/southwest facing slopes.

Primetime: 10AM to 9PM

Northwest Slope, San Luis Valley:

 Just isolated light rain is expected for the state’s two high arid regions, with precipitation largely confined to the higher terrain on the fringes of these regions. Rain that occurs will be light, with rainfall rates less than 0.1” per hour and daily rainfall totals of less than 0.25”. Cloud cover will likely be present for much of the day, keeping temperatures down.

Primetime: now through 9PM

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

Widely scattered thunderstorms are possible but unlikely today for most of the area east of the mountains, with locations nearest the mountains (i.e., farther west) the most likely to experience any measurable precipitation. Rainfall rates will be light, as dry surface air will evaporate much of what falls. Nonetheless, 1-hour rain rates up to 0.25” per hour are possible.

Primetime: 3PM to 9PM