FTB 09-09-2018: More Sunshine and Fewer Showers/Thunderstorms

Issue Date: 9/9/2018
Issue Time: 6:45 AM

NO FLOOD THREAT IS FORECAST TODAY.

Plenty of sunshine is on tap today, with high temperatures ticking up a few degrees higher than yesterday. Drier air will be filtering in from the west, but enough mid-level moisture will hang on for a few isolated high-based showers and thunderstorms during the afternoon and evening hours. A quick look at the infrared imagery below shows the current cloud cover over, much of it over the high country and south of I-70, denoting where the best mid-level moisture currently resides.

The majority of activity will occur over the High Country south of I-70 in response to remaining moisture and the presence of a weak disturbance, and a few isolated, high-based showers/thunderstorms will drift over the adjacent lower elevations of eastern Colorado. The main impacts of any activity will be gusty winds and light rainfall, with brief periods of moderate rainfall underneath any thunderstorm activity over the Southeast Plains and Raton Ridge. For more information on rain rates and timing, please see the zone-specific forecast discussions below.

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

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

The main weather story today will be the plentiful sunshine and warmer temperatures, with only a couple isolated, high-based showers/thunderstorms breaking up the otherwise quiet day during the afternoon and evening hours. Most of the activity will occur west of I-25, employing the help of nearby terrain. Rain rates will be tempered by dry air beneath the cloud bases; generally speaking, rain rates will be less than 0.15 inches/hour, with maximum rain rates of 0.2-0.5 inches/hour underneath thunderstorms over the Southeast Plains and Raton Ridge.

Timing: 1 PM – 9 PM, with an isolated shower or two lingering until 10-11 PM

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

Dry conditions and mostly sunny skies will be the main weather story for most today, with a few isolated-to-scattered showers/thunderstorms dotting the area during the afternoon/evening. The bulk of the activity will occur south of I-70 where the better moisture (relatively speaking) will be positioned. Rain rates will generally be less than 0.15 inches/hour, with maximum rain rates of 0.2-0.3 inches/hour.

Timing: Noon – 9 PM

FTB 09-08-2018: Main Course of Sunshine, Side Dish of Showers

Issue Date: 9/8/2018
Issue Time: 6:35 AM

NO FLOOD THREAT IS FORECAST TODAY.

The upper-level trough that had been meandering across the region the past couple of days has finally moved on, shifting over the central Great Plains. Behind the recent upper-level trough, and ahead of the next trough, a plume of moisture has begun to push into western Colorado, which will spread east through the day. This next wave of moisture will provide enough fuel for a few isolated-to-widely scattered showers/thunderstorms over the High Country, and a couple isolated showers/storms over adjacent lower elevations.

The best coverage, relatively speaking, will be north of I-70, where the influence of a passing disturbance will provide some support. Overall, there is no threat of flash flooding as the best moisture is confined to the mid-levels (with drier air near the surface) and there will be very little instability with which to work. Thus, gusty winds and light rain will be the main impacts. For more information on rain rates and timing, please see the zone-specific forecast discussions below.

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

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

Plenty of sunshine and warmer temperatures are the main weather story for today, providing a nice kickoff to the weekend. During the afternoon/evening hours, a few clouds will bubble, especially over areas near the mountains. A couple of showers, and perhaps a thunderstorm or two will dot the area, mainly north of I-70 thanks to the presence of the passing disturbance. Gusty winds and light rainfall will be the main impacts from any activity, so no flood threat is the call today. Rainfall rates will generally be less than 0.15 inches/hour, with maximum rates of 0.2-0.4 inches/hour.

Timing: 3 PM – 11 PM, with an isolated shower/thunderstorm or two lingering into the early morning hours over the Northeast Plains in association with the passing disturbance.

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

The day will begin with plenty of sunshine, with clouds increasing over the higher terrain during the afternoon and evening hours in response to the increase in mid-level moisture. A few isolated-to-scattered showers will dot the region, with the best coverage, relatively speaking, over the higher terrain of the Northwest Slope, Northern Mountains, Front Range, and Central Mountains. Rain rates will generally be less than 0.1 inches/hour, with maximum rates of 0.2-0.3 inches/hour.

Timing: 2 PM – 10 PM for areas south of I-70, 1 PM – 1 AM for areas along and north of I-70. A few lingering showers will continue into the early morning hours over the higher terrain of the Northern Mountains, Northwest Slope, Grand Valley, and Central Mountains.

FTB 09-07-2018: Upper-Level Trough Begins its Migration East

Issue Date: Friday, September 7th, 2018
Issue Time: 08:35AM MDT

— Flooding is NOT expected today

Finally expecting some movement with the upper-level trough. Throughout today and early tomorrow the trough will migrate eastwards across Colorado. Behind the trough, drier, stable air will start to work its way into the state as seen with the clearer skies over western CO and Utah. This morning there is some dense fog over the eastern plains and northern Urban Corridor with added cloud cover over the Southeast Plains. Expecting the fog to last until about 9AM this morning. Cloud cover will also begin to burn off with the sunrise, but between the two, cooler high temperatures and minimal instability is forecast over eastern Colorado today. A few breaks in the clouds near the Palmer Ridge is likely as drier air moves in from the east. This may allow for some instability to build for a few showers and weaker storms this afternoon.

A bit more instability will be able to build over San Juan Mountains, Front Range and Southeast Mountains and mix with some minimal low-level moisture for some isolated afternoon showers. The 12Z sounding at Denver shows quite the dry layer at 700mb, so the threat for heavy rainfall will decrease when compared to the last couple of days. This is especially true as the drier air will start to move into the area today. This also means storms will be much more isolated in nature. Also forecasting stronger steering winds (20mph from the north), so this will keep the storms moving and prevent too much rainfall over one area. Over the Southeast Mountains, moisture will be slower to mix out behind the trough, so the higher rainfall amounts are expected in this area along the CO/NM border. Over western Colorado, PW values have already dropped to 0.66 inches at Grand Junction. This shows the trough has passed through and a drier, more stable air mass is beginning to establish itself. A little better moisture remains over the San Juan Mountains, so some isolated storms will likely form this afternoon. With the drier air mass and decent steering winds, flooding is not likely today even over recent burn areas.

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:

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

Moisture will start to decrease this afternoon as the trough passes through and a more stable, dry air mass moves into these regions. So not expecting any heavy rainfall today. There is a possibility for some breaks in cloud cover that would allow some instability to build over the Palmer Ridge this afternoon. Low-level convergence may initiate some showers and weak storms over this area. Max 1-hr rain rates up to 0.6 inches are possible. More isolated storms are possible over the Front Range and Southeast Mountains/Raton Ridge. With north to south movement, not expecting storms to track into the adjacent plains. Max 1-hr rain rates up to 0.2 inches (north) and 0.6 inches (south) are possible. Flooding is not expected today.

Primetime: 2PM – 9PM

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

The trough has passed through, which will allow a more stable and dry air mass to fill in behind it. Moisture will be slower to mix out over the San Juan Mountains, so expecting some rainfall, and the highest totals, to be over the southern-most, east-west oriented ridges today. Cloud cover will still increase over the Central and Northern Mountains this afternoon, though measureable rainfall is not likely. Gusty outflow winds are also possible. Swift steering winds and drier air should keep rainfall rates below the flood threat criteria for Friday.

Primetime: 1PM – 8PM

FTB 09-06-2018: Heavy Rainfall Potential Continues for the Front Range and Southeast Mountains

Issue Date: Thursday, September 6th, 2018
Issue Time: 09:30AM MDT

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

— A MODERATE flood threat has been issued for the Spring Creek, Hayden Pass and Junkins burn areas

Upper-level clouds are blanketing the majority of the state with some light rain and fog mixed in to start the morning. Mostly clear skies over the Southwest Slope with some breaks in the cloud cover over western Colorado as some drier air has been entrained from the west. Should be a similar pattern to yesterday with a few minor differences. Current temperatures are in the 50Fs over the lower elevations with upper 30Fs to mid-40Fs over the higher terrains. Warmer temperatures over CO/UT border as the front stalled out before it reached this area.

PW this morning was measured at 0.82 inches and 0.85 inches at Denver and Grand Junction, respectively. So not much change in low-level moisture though the water vapor imagery shows some pockets of drier air have moved into western CO. This should cause storms today to be a bit more isolated when compared to yesterday. Also, expecting some gusty outflow winds with storms today (Central/Northern Mountains) as well as there is quite a bit of spread between the temperature and dew points. The greatest coverage will likely be over the San Juan Mountains with more patchy coverage and lower rainfall intensities over the Central and Northern Mountains.

To the east, rinse and repeat pattern of yesterday. Storm motion may look to increase a little, which will mean storms are less likely to produce as much rain as yesterday. However, 15 mph steering winds to the SE will still allow another day of some heavy rainfall. The SW to NE oriented upper-level jet and shortwave marked over the NW corner of the state will help support storms as they move off the mountains. So, storm coverage will likely increase over the adjacent plains this afternoon when compared to yesterday. Storms will decrease north to south this evening starting around sundown with some storms likely over the Raton Ridge/Southeast Plains intersect through midnight.

Burn scars over the SE Mountains will be susceptible to flooding again today, so storms that track near these areas should be monitored closely this afternoon. There is high confidence storms today will have rain rates greater than 0.5 inches/hour, so a Moderate threat has been issued for the Southeast Mountain burn areas. A Low flood threat has been issued  for eastern CO again today as heavy rainfall is expected once again and decent rainfall over the mountains yesterday will likely increase runoff this afternoon.

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.

Flood Threat Legend

 

Zone-Specific Forecasts:

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

Rinse and repeat pattern of yesterday with some more action in the adjacent plains this afternoon into tonight. Instability along the Urban Corridor is not expected to be as high today, so not expecting as much hail as yesterday. However, a quick 0.5 inches in a half hour could cause some minor flooding issues in low-lying roads. Over the mountains, small hail and snow above 13,000 feet will be possible. A Low flood threat has been issued as moisture and slow steering winds combine to create pockets of heavy rainfall this afternoon. Saturated soils from yesterday will also increase runoff. A Moderate threat has been issued for the Spring Creek, Hayden Pass and Junkins burn areas. A Low threat for Weston Pass should suffice. If a storm tracks over a burn area, mud flows, debris slides and local stream flooding are possible. 1-hr rain rates up to 1 inch are possible over the higher terrains with max 1-hr rain rates up to 1.2 inches over the Front Range/Urban Corridor intersect.

Primetime: 1PM – 12AM

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

Some pockets of drier air have been entrained from the west, so storm coverage will be more isolated this afternoon when compared to yesterday. Low-level moisture will still allow some decent rain to reach the surface with the most action over the San Juan Mountains. Gusty winds will be possible with the stronger storms to the north. Max 1-hr rain rates up to 0.75 inches (south) and 0.5 inches (north) are possible. Storms should end a couple of hours after the sun sets.

Primetime: 12PM – 10PM