Issue Date: Friday, September 18th, 2020
Issue Time: 8:45AM MDT

— Flooding is NOT expected today

Finally, a little bit of change to talk about in regard to the weather pattern. The 500mb ridge and associated High have started to be pushed south with the incoming trough off the west coast (red arrow). The center of upper Low will start to move onshore and into the Pacific Northwest throughout the day, and upper level lift (orange “X”) out in front of the trough will bring increasing cloud cover to the state from west to east beginning later this afternoon. The Salt Lake City sounding is showing most of the moisture in the mid and upper atmosphere and measuring PW at 0.36 inches. This translates to no rainfall for the state with this first wave of energy, especially with the large dew point depression.

As the trough approaches and the pressure gradient tightens, surface winds are anticipated to increase over the northwest corner of the state. Additionally, a lee surface Low is expected to develop to our north, which will increase south and southwesterly winds over eastern Colorado this afternoon. This may cause some elevated fire conditions, particularly over the Northwest Slope.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Expect an increase in southwest and westerly winds over the northwest corner of the state this afternoon. Winds are expected to be in the 12 to 18 mph range with gusts up to 25 mph possible. With relative humidity values dropping into the single digits, elevated fire weather is anticipated. Afternoon temperatures are expected to be similar to yesterday, so still 4F to 8F above average for this time of year. As the Low approaches, upper level cloud cover will increase this afternoon into this evening, but no rainfall is anticipated. Not much change in the near surface or upper level smoke levels when compared to yesterday.

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

The lee cyclone to our north will produce south and southwesterly winds across the eastern plains this afternoon in the 10 to 15 mph range. Slightly higher winds are forecast over the Southeast Plains with gusts up to 25 mph possible. Similar story to yesterday in regard to the high temperatures. Still well above normal for this time of year, especially over the Northeast Plains (~10F above normal). Expect increasing upper level cloud cover late this afternoon and into the overnight hours, which will help a bit with the heat and may keep overnight lows slightly higher. No rainfall is forecast due to the dry surface layer, but virga storms could produce some brief wind. The HRRR smoke model is showing a decrease in near surface smoke by this afternoon, but not much change in the upper level smoke. Please, follow your local NWS office for the latest on Air Quality Alerts issued for your area.

Issue Date: Thursday, September 17th, 2020
Issue Time: 09:35AM MDT

— Flooding is NOT expected today

Just like a broken record, today will mainly be a repeat of the previous days this week as it will mainly stay dry across the state. Colorado remains on the east side a high pressure ridge with weak west/northwest steering flow (see image below). The only chance for seeing some light measurable rainfall will be due to diurnal mountain slope flows initiating clouds and maybe a couple light showers over the higher terrains. The southern mountains once again have the highest chances of seeing a few high-elevation raindrops. However, it looks like some increased cloud-cover is expected for the Front Range, but no rainfall is expected. Moisture remains limited across the state as the Grand Junction and Denver soundings only contain 0.34 and 0.42 inches of precipitable water, respectively. Most of this moisture seems to be in the lower half of the atmosphere (boundary layer) according to soundings, but surface dew points are only in the 20Fs and 30Fs across the mountain regions and in the 40Fs across the plains. Dry air and a strong inversion at the top of the boundary layer will make it difficult for storms to fire across the state. The water vapor satellite image below shows some drier air, and likely stronger inversion, is situated over eastern Colorado this morning (see image below). Temperatures will be warmer today for the plains regions, pushing slightly above average into the mid 80Fs for most locations. No flooding is expected today.

Unfortunately, smoke and haze will remain in the air across Colorado today. The highest concentrations of smoke will be over the eastern plains regions, where an Air Quality Alert remains in place today. Check out your local NWS office for more information. There will likely continue to be some local smoke being produced from the Middle Fork, Williams Fork, and Cameron Peak wildfires in the state as the dry and warm weather will favor more active fire activity. However, winds are not expected to be strong today, so fire activity should be limited.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Warmer temperatures (80Fs) and continued smoke will impact the area today. An elongated surface low pressure region will extend from southwest to northeast over the northern half of the plains regions, which will set up a convergence boundary over the Palmer Ridge and Northeast Plains regions today. This could be the focus for a few clouds to form, but a strong cap will likely keep storms from developing. Additionally, daytime heating will mix out some of the higher 40Fs dew points, so moisture will be limited. No flooding is expected today.

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

Daytime heating will allow up-mountain flow today and some clouds and a few showers to form near mountaintops and ridgelines. The southern San Juan Mountains have the highest (although still low) chances of seeing measurable rainfall from a light shower, but total accumulations should stay below 0.1 inches and confined to the higher elevation locations due to plenty of sub-cloud evaporation. The Front Range should see an increase in fair weather clouds, but rainfall is not expected. Any showers that form today could create some wind gusts up to 30 mph due to plenty of sub-cloud evaporation, but these winds are not likely over the active wildfires in the state. No flooding is expected.

Issue Date: Wednesday, September 16th, 2020
Issue Time: 09:35AM MDT

— Flooding is NOT expected today

It will once again be dry and warm today across Colorado, with even less likelihood of any mountain clouds being able to generate measurable precipitation. Diurnal heating will still allow some mountaintop clouds to develop over the high terrains, especially the San Juan Mountains, but that should be about it. A shallow cold front has worked its way into the Northeast Plains of Colorado, but this front is not bringing much moisture with it as dew points are in the 40Fs behind it. This will not be enough moisture to allow precipitation over the plains locations today, but it should keep high temperatures a few degrees cooler over the Northeast Plains compared to yesterday. High temperatures will still be a few degrees above average across Colorado today. No flooding is expected.

Unfortunately, the smoke concentration is on the rise as more smoke moves into Colorado from the north. The true-color satellite image below shows this smoke is circulating from the US West Coast directly into northern Colorado due to our location on the eastern side of the High pressure clockwise flow. This infiltration of smoke is lowering air quality this morning into the Moderate to Unhealth for Sensitive Groups range, and it will likely continue to affect air quality today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Smoke will create hazy conditions, but there should be plenty of sunshine. A passing weak cold front will increase surface dew points a few notches today, with 30Fs along western portions of the plains regions and increasing to near 50F along the eastern border. However, this limited moisture will not allow any precipitation to fall today. The cold front will keep daytime high temperatures down a few degrees compared to yesterday, with highs in the low 80Fs over northern regions and mid 80Fs over southern regions. The cold front is currently generating winds up to 40 mph over the Palmer Ridge and up to 30 mph over the Northeast Plains. These winds should decrease over the course of the day. No flooding is expected today.

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

There will be plenty of sunshine and more smoky haze, especially over the southwestern part of Colorado where a hole in wildfire smoke kept skies fairly clean (see the SPM). Temperatures will again climb above normal for lower elevation locations, with upper 80Fs expected in the Grand Valley, low to mid 80Fs along the Southwest and Northwest Slope, and mid 70Fs for the San Luis Valley. Some afternoon fair weather clouds will build over the high elevation mountaintops and ridges, but there is less chance of seeing measurable precipitation from these clouds today compared to yesterday. No flooding is expected.

Issue Date: Tuesday, September 15th, 2020
Issue Time: 8:50AM MDT

— Flooding is NOT expected today

Below is the visible satellite imagery and Hurricane Sally pops out over the Gulf of Mexico. Sally should be making landfall by early this afternoon, and will bring with her life-threatening storm surge and major flooding. Over Colorado, the ridge is holding steady and building to the northwest a bit. This is pulling in smoke from fires across the western US (gray hue), and the HRRR smoke continues to show an increase in near surface smoke along and just south of the northern border today. PW was measured at 0.38 and 0.45 inches at Grand Junction and Denver, respectively. So, it’s quite dry, which can also be seen by the 50F dew point line both south and east of the state (dashed green). Further drying of the atmosphere is expected today, so other than some cloud cover building over the mountains this afternoon with residual mid-level moisture, it should be another clear and warm day. Flooding is not forecast.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Cloud cover is forecast again this afternoon over the mountains, and it looks to be better in coverage further south over the climatologically favored San Juan Mountains. A few sprinkles may be possible, but the more likely scenario is just cloud cover like we saw on Sunday with the very dry surface layer. Brief gusty winds may also be possible under the virga showers. High temperatures will continue to be 4 to 10F above normal with 80Fs for the valleys and 70Fs for the mountain valleys. Expect an increase in smoke over the Northwest Slope and northern Mountains from the ongoing fires.

Palmer Ridge, Raton Ridge, Southeast Mountains, Front Range, San Luis Valley, Urban Corridor, Northeast Plains, & Southeast Plains:

Afternoon temperatures will be similar to yesterday, and a few degrees uptick over the southeast corner is possible. So high temperatures remain well above average for mid-September. Some scattered cloud cover is expected again this afternoon over the mountains and Palmer Ridge, but rainfall is not forecast. Also expecting an increase in near surface smoke from the western US fires, which could lower air quality some by later in the day. This will mostly be across the northern border and south, and especially affect the Front Range and Urban Corridor.