Issue Date: Thursday, July 16th, 2020
Issue Time: 10:30AM MDT

— A LOW flood threat has been issued for parts of the Front Range, Palmer Ridge, Southeast Mountains, Raton Ridge, Southeast Plains and San Juan Mountains
— A LOW flood threat has been issued for the 416 burn scar

This morning’s visible satellite image, below, reminds us that monsoon season is here, even if its start has been modest. Within the clockwise flow around a strengthening upper-level ridge over Texas is an embedded rather strong but small-scale shortwave. Its southerly origin is a common feature of monsoon dynamics. It is already causing mainly mid and high clouds with some light showers over the Four Corners region. It is anticipated to slowly move across the southeast quadrant of Colorado today, causing scattered to numerous shower and thunderstorm activity for the third day in a row. Flood threat aside, no complaints for a region that has been plagued by a worsening drought.

Taking a closer look at heavy rainfall parameters, a PW of 0.59 inches was measured at Denver this morning, which is below normal for this time of year. The Grand Junction radiosonde launch was not successful, but we estimate a PW of about 0.5 inches there, also below seasonal normal. However, the PW at North Platte, Nebraska (1.21 inches), Dodge City, Kansas (1.35 inches), and Albuquerque, New Mexico (1.00 inch) were all at or above seasonal normal. This implies that a strong moisture gradient exists to our south and east. Most notable is the value from Albuquerque, since that is where today’s air mass will be coming from. Importantly, it appears model initialization is underestimating the moisture content in northern New Mexico today, with model estimate PW of about 0.85-0.90 inches at Albuquerque, about 15% below the observed value.

A look at our high-resolution guidance today shows underwhelming maximum 1-hour rainfall intensity (see below). Keeping in mind guidance is almost always biased high across the San Juan Mountains, it appears that guidance is underestimating rain intensity east of the Continental Divide. This is likely because of the propensity to mix out low-level moisture too quickly at this point in the summer. Accounting for this, we are issuing a Low flood threat for a large portion of southeast Colorado, but also including the eastern part of the San Juan mountains today. The 416 burn scar is also under a Low threat, because of the potential for multiple bursts of short-term heavy rainfall that will elevate the threat for mud flows.

East of the Continental Divide, large hail will also be possible with the strongest storms along with a slight chance of tornadoes.

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:

San Juan Mountains, San Luis Valley, Southeast Mountains, Palmer Ridge, Southeast Plains, Raton Ridge:

Increasing clouds with scattered to numerous showers and thunderstorms likely by noon. First over the higher terrain, then spreading eastward by mid-afternoon. Max 1-hour rainfall up to 2.2 inches out east and 1.4 inches in the higher terrain, except up to 1.1 inches in the San Juan Mountains. We expect several rounds of storms today, lasting later than normal into the evening due to the upper-level dynamical support. A Low flood threat has been issued by isolated flash flooding, street and field flooding, as well as mud flows and debris slides over steeper terrain. The 416 burn scar is also included in this Low threat. Large hail will be possible with the strongest cells, especially in eastern areas below about 6,500 feet.

The Fountain Creek basin will need to be watched carefully this afternoon, as it has received several days of heavy rainfall, causing saturated soils. While we do not expect it to enter flood stage today, it may come close.

Primetime (San Juan Mountains): 11AM-11PM
Primetime (east of Continental Divide): 2PM-3AM

Grand Valley, Central Mountains, Front Range, Urban Corridor:

Becoming partly cloudy with isolated to scattered showers and thunderstorms possible this afternoon. Much warmer than Wednesday, with highs near seasonal normal today. Max 30-minute rainfall up to 0.7 inches (east of Continental Divide) and 0.5 inches (west of Continental Divide), but flooding is not expected today. Gusty winds will be possible with the strongest storms.

Primetime: 12PM-9PM

Northwest Slope, Northern Mountains:

Mainly sunny with a few clouds possible later today. Isolated storms will be possible, mainly above 8,000 feet. Max 1-hour rainfall up to 0.4 inches. Gusty winds up to 40mph will be possible with the strongest storms. Flooding is not expected today.

Issue Date: Wednesday, July 15th, 2020
Issue Time: 9:30AM MDT 

— A LOW flood threat has been issued for the southern Urban Corridor, Palmer Ridge, Southeast Plains and Raton Ridge
— A LOW flood threat has also been issued for the Spring Creek burn area

A large MCS can be seen to our east in the image below (orange “X” over KS/MO), which originated from the cluster of storms over the Southeast Plains yesterday. Today, the high will start to strengthen over Texas and push the 5880m height contour northward, so Colorado will be under moderate west/southwest flow aloft. This morning, there is quite a bit of fog over the eastern Plains, Palmer Ridge, and portions of the Urban Corridor. This should start to break up over the next couple of hours with a little daytime heating. The fog indicates that there is still plenty of low-level moisture still over eastern Colorado, and the sounding at Denver measured PW at 0.69 inches (note that the balloon popped at about 9km). Slightly higher PW values are present over southeast Colorado, and easterly flow at the surface this afternoon will keep surface moisture in place for another round of scattered afternoon storms. Looks like a cap across northern Colorado will keep rainfall chances low, so the storm activity this afternoon will generally along and south of I-70.

With the high to the southeast, mid-level energy and moisture from New Mexico (orange “X”) should move north across the southern border. Therefore, storms are also expected to return to the San Juan and Central Mountains this afternoon, and rainfall chances also increase for the San Luis Valley with more westerly steering flow. Due to higher moisture in the area, rain rates up to 0.5 inches will be possible over the Southeast Mountains. Therefore, a Low flood threat has been issued for the Spring Creek burn area. As the storms move off the mountains, rain rate efficiencies are predicted to increase due to an uptick in low-level moisture and better dynamics. So expect growing coverage of thunderstorms with a few becoming severe, and storms steering more to the southeast over the plains. A Low flood threat has been issued for urban flooding, road flooding, and flooding of low-lying areas.

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:

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

A Low flood threat has been issued for the adjacent eastern plains this afternoon, and a few severe thunderstorms will be likely. Max 1-hour rain rates up to 1.9 inches will be possible in the threat area, so urban flooding, road flooding, and small stream flooding will be possible. There should be plenty of time for Fountain Creek to recover from the storms yesterday, but always a good idea to keep an eye on this one during heavy rainfall events. Severe thunderstorms that form will be capable of producing severe hail and strong outflow winds. Be sure to follow NWS Pueblo for the latest on storm warnings. Rainfall should start to come to an end just after midnight. High temperatures will drop off a bit behind the cold front, but rise 5-10F over the northern Urban Corridor and portions of the Palmer Ridge.

Primetime: 1:30PM to 12AM

San Juan Mountains, Central Mountains, Front Range, San Luis Valley, & Southeast Mountains:

Best chance for thunderstorms and rainfall today will be south of I-70. Max 1-hour rain rates just over 0.50 inches will be possible with totals decreasing over the San Luis Valley. Isolated totals (along the edges of the valley) up to 0.25 inches will be possible by tomorrow with more general totals in the 0.10 to 0.15 range. Storms will again be capable of producing gusty outflow winds and dangerous lightning if hiking.

Primetime: 12:30PM to 1AM

Northern Mountains, Northwest Slope, Grand Valley, Southwest Slope, & Northeast Plains:

These areas should remain dry today with high temperatures increasing over the Northern Mountains and Northeast Plains (5-10F). Other regions high temperatures will be about the same as yesterday, which is still above average for this time of year. Widespread fire danger will decrease today due to an increase in moisture and lighter surface winds. However, spotty fire weather conditions may still occur over the Northwest Slope this afternoon.

Issue Date: Tuesday, July 14th, 2020
Issue Time: 9:30AM MDT

— A MODERATE flood threat has been issued for the Southeast Plains
— A LOW flood threat has been issued for the Palmer Ridge and portions of the Urban Corridor, Northeast Plains,  and eastern Raton Ridge

Not much change in the overall synoptic set up from yesterday. The trough will continue to pass to our north and the high will be pushed south, so Colorado will remain under westerly flow aloft. Taking a look at the water vapor imagery below, there are some subtle changes with the details. First, the jet will sit just north of the border. This will help produce faster, westerly surface winds over western Colorado and the mountains. PW will continue to drop off over western Colorado as a drier air mass is entrained, and with relative humidity values falling between 10 and 15%, critical fire weather is anticipated. A Red Flag Warning has been issued for the region in red below. Mid-level energy will continue to move across the western border, so weak storms are forecast again across the western high terrains. Overall, rainfall totals and coverage are expected to decrease, and strong outflow winds (50 mph) should be anticipated once again.

Back to the east, a cold front has started to drop south over the plains. This will help return low level moisture, which can be seen by the increase in cloud cover on its north side. Additionally, there will finally be a break in the hot temperatures over the northeast quadrant of the state, and afternoon highs are expected to drop off ~15F! The front will continue to drop south through tonight, and very high dew points will fill in over the eastern plains (60F). With plenty of lift from shortwaves moving through the flow overnight and concentrated lift along the front, a Moderate and Low flood threat have been issued. While the northeast corner of the state is expected to remain capped today, the Low threat has been extended back west to pick up any overnight convection firing over the Cheyenne Ridge due to extra dynamics in the area.

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:

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

A Moderate flood threat has been issued for the Southeast Plains as the cold front drops south overnight through the area. Storm totals just over 2.5 inches are possible, which would cause local stream flooding, road flooding, and flooding of low-lying areas. Additionally, severe thunderstorms are expected to develop over the plains, and these storms will be capable of producing 60 mph gusts and large, damaging hail. In the Low threat area (east), max 1-hour rain rates up to 1.50 will be possible with totals just over an inch forecast over the Palmer Ridge. Storm motion will be more easterly this afternoon and overnight, and the flood threat is expected to end just after midnight.

Primetime: 1PM to 1AM

San Juan Mountains, Central Mountains, Northern Mountains, Front Range, & Southeast Mountains:

It has started to dry out west of the Continental Divide, but there will still be some moisture left for some high-based, convection over the high mountain peaks with shortwaves moving through the flow. Expect coverage of storms to decrease when compared to yesterday as well. The main threat from the stronger storms that form will be again be outflow winds (50 mph gusts), and max 1-hour rain rates will decrease to 0.25 inches (north/central) and 0.15 inches (south).

Over the eastern mountains, coverage of storm coverage will be greatest along the Divide (north), northern Southeast Mountains, and Front Range/Palmer Ridge intersect. Max 1-hour up to 0.50 inches (north foothills) and 0.15 inches (south) are forecast. Flooding is not expected, and light showers may linger over the Central Mountains through 11PM.

Primetime: 12:30PM to 11PM

Northwest Slope, Grand Valley, Southwest Slope, & San Luis Valley:

Critical fire weather is forecast for these western regions with spotty critical fire weather anticipated for the San Luis Valley. Westerly winds will pick up to 10 to 15 mph by noon with gusts up to 30 mph. Relative humidity will drop off to 10 to 15%, so conditions will be favorable for the rapid ignition, growth and spread of fires. NWS Grand Junction has issued a Red Flag Warning, and please use caution with open flames. Rainfall is not forecast, and high temperatures should reach the mid to upper 90Fs over the lower elevations with high 80Fs for the San Luis Valley.

Issue Date: Monday, July 13th, 2020
Issue Time: 9:40AM MDT

— Flooding is NOT expected today

Flow aloft is expected to become more zonal today as the trough passes to our north and squashes the ridge. Between the High and the trough, there will still be plenty of mid-level lift moving across the state, and some upper air dynamics creating a little lift across portions of the northern border. As far as moisture, PW values should be high enough for another round of storms statewide. Currently, there are some ongoing showers over the Central Mountains with some reflectivity also over Moffat and Montezuma/La Plata Counties. Moisture at the surface is still fairly shallow, so the westerly flow will likely mix out this out quickly over western Colorado, the mountains, and I-25 corridor. This, along with not much instability being able to build with the ongoing showers, means storms today will generally only produce light rain rates and gusty outflow winds. However, coverage of storms over the mountains is forecast to increase, especially the Central and San Juan Mountains.

Higher surface moisture will again reside over the far eastern plains, but the surface low’s location should only allow dew points in the mid-50Fs and low 60Fs to maintain themselves along the border and east of the state. Also, storms will arrive the plains a little sooner than normal due to the first shortwave arriving earlier than typical, so this will limit the amount of instability that can build further north. Between these two factors, the severe threat will be over a smaller area (border counties) and generally, only moderate rainfall is forecast. Over the Southeast Plains, there is a chance that a severe thunderstorm will be able to generate rain rates just over 1.50 inches/hour; however, the areal coverage is expected to be small enough that no flood threat will be issued. If this flood threat area increases by early afternoon, a PM update will be issued.

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:

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

Moisture isn’t quite as high at the surface as it was yesterday, which means the westerly flow will more quickly mix it out from west to east. As storms move off the mountains, higher rain rates are anticipated over the Palmer Ridge. Additional storm formation should occur over the Palmer Ridge as the first shortwave moves off the mountains by noon. Max 1-hour rain rates up to 0.50 inches will be possible with lower rain rates for the I-25 corridor (0.25 to 0.40 inch range).

Further east over the plains, some severe thunderstorms will be possible again along the border. The best chance for a severe storm or two will be over the Southeast Plains due to a slight delay in arrival of a second shortwave. Severe thunderstorms that form this afternoon will be capable of producing 60 mph wind gusts, 2.25 inch diameter hail, and local, heavy rainfall. For the most part, max 1-hour rain rates should remain around 1 inch, but a stronger storm may be able to produce rain rates just over 1.50 inches. However, decent storm motion to the southeast and higher dew points over Kansas will mean the area of intense rainfall would be small enough that flooding is not expected. There could be some light showers over the eastern plains overnight, but the more likely scenario is just increased cloud cover.

Primetime: 12PM to 10PM

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

Storm coverage is expected to pick up today with extra mid-level energy moving through the flow, which will also help increase moisture slightly. Max 1-hour rain rates up to 0.25 inches over the Central, San Juan, and Northern mountains will be possible with slightly lower rates over the valleys/elevated plateaus forecast. Over the Front Range and Southeast Mountains, coverage will decrease slightly with max 1-hour rain rates up to 0.25 inches possible. Again, the main threat from storms will be outflow winds with gusts up to 50 mph possible under the stronger storms. Mid-level energy will likely keep weak showers going over the Central Mountains overnight. Flooding is not forecast.

Primetime: Ongoing to 4AM