FTB 09-30-2019: High Fire Danger Continues with Cooler Temperatures Expected by Morning

Issue Date: Monday, September 30th, 2019
Issue Time: 9:20AM MDT

— Flooding is NOT expected today

NOTE: This is the last scheduled Flood Threat Bulletin of the 2019 season. It has been a pleasure to serve you! The next Flood Threat Bulletin season begins on May 1, 2020.

Same pattern is in place over the US with a tight surface gradient creating strong, dry southwest flow over the majority of the state again today. Thinking this gradient will slightly weaken throughout the day, but fast winds and low relative humidity will create Red Flag Warning conditions again for the majority of the state. Conditions will be favorable for the rapid ignition, growth and spread of fires, so open burning is strongly discouraged. PW at Denver was measured at 0.40 inches with very dry air above 600 mb. Grand Junction’s sounding was similar, but slightly higher due to some mid-level moisture. This moisture paired with the jet overhead is helping produce some cloud cover and light rainfall over the northwest corner this morning. As the jet streak moves out later this morning and dry air above and below this mid-level layer mixes out the remaining moisture, showers should begin to diminish. Not expecting rainfall this afternoon with the dry air mass in place over the state.

At the surface, a low develops this afternoon over eastern Colorado, which may help pull in slightly higher moisture over the far southeast corner by making winds a little more southerly. If this moisture (marked by the green arrow below) can push slightly northward, overnight rainfall will be possible for Baca/southern Prowers Counties. Guidance is showing the heaviest rainfall to the south and east, but if higher PW values continues to move north tomorrow morning, some heavier rainfall will be possible on Tuesday morning. Overnight, a strong cold front starts to drop through the state, which looks to return some low-level moisture to the northeast quadrant of the state. Therefore, behind the front, some light showers and cloud cover are possible with fog to start Tuesday morning. The cooler, more fall-like temperatures will be a great way to round out the end of the heavy rainfall forecast season. As anticipated, flooding is not 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:

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

Red Flag Warning is in place for the following regions minus the northern portions of the Urban Corridor, Front Range and Northeast Plains where moisture is little higher. Still expecting Elevated Fire conditions over those regions. Southwest winds in the 15 to 25 mph range with gusts up to 40 mph are expected from noon to 7PM with relative humidity values in the teens. Rainfall is not forecast this afternoon with the dry air mass overhead, and temperatures should warm quite a bit when compared to yesterday. Overnight and early morning light rain may be possible behind the passage of a strong front over the northeast quadrant of the state. Max 1-hour rain rates will remain below 0.10 inches with the best chance for accumulation over the northeast corner or northern Front Range.

Additional rainfall may be possible over Baca and southern Prowers Counties tonight if the moisture boundary shifts far enough north. If this occurs, totals up to 0.90 inches will be possible by morning (7AM), so flooding is not forecast at this time. Assuming this moisture continues to push northward tomorrow morning, some heavier rainfall may be possible from Tuesday morning (7AM) into the early afternoon (1PM). Since the FTB season is over and this is a lower end threat at best, not thinking there will be a special bulletin FTB issued at this time.

Primetime: 10PM to 7AM

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

High fire danger continues for these regions as well, although the slight increase in moisture over the Northwest Slope (from movement in the west coast low) should keep relative humidity values high enough that no Red Flag Warning will need to be issued for that region today. Ongoing showers from early this morning may produce isolated totals up to 0.30 inches. A Red Flag Warning has been issued for the Grand Valley, northern Southwest Slope and Central Mountains where southwest surface winds in the 15 to 25 mph range and gusts up to 35 mph can be expected from noon to 9PM this evening in a low relative humidity environment. High temperatures will be a couple degrees warmer than yesterday, minus the Northwest Slope and Northern Mountains due to the increase in cloud cover.

Primetime: Ongoing to 11AM

FTB 09-29-2019: Wind is the Main Weather Story Today

Issue Date: 9/29/2019
Issue Time: 7:35 AM

NO FLOOD THREAT IS FORECAST TODAY.

The upper-level pattern has changed little since yesterday, but additional strengthening of both the low pressure over the western US and the high pressure over the southeastern US will bring an increase in winds over yesterday’s gusts. These winds will contribute to well above-average temperatures and critical fire weather conditions across much of the eastern half of Colorado. Red Flag Warnings have been issued for portions of the Northern Mountains, Central Mountains, and Front Range; nearly all of the Urban Corridor, Northeast Plains, Southeast Plains, and Raton Ridge; and all of the San Luis Valley, Southeast Mountains, and Palmer Ridge. Please check with your local National Weather Service office for more information.

West of the Continental Divide, a bit more moisture will be present, and a few scattered showers/garden-variety thunderstorms are expected, mainly over the higher terrain, with the best coverage over the Northwest Slope. Wind gusts of 20-35 mph are expected in the lower mountain valleys, with gusts as high as 60-70 mph at the highest peaks, and temperature will be near (or just above) average for this time of year.

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

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

Gusty and dry conditions will be the main impacts today, resulting in dangerous fire weather conditions for the area. Wind gusts up to 35-45 mph over the plains, and up to 50-60 mph over higher terrain are expected. Red Flag Warnings have been issued, please check with your local National Weather Service office for more information. There is a small chance (less than 10%) of an isolated thunderstorm across the far Southeast Plains, but most likely this activity will remain just outside of the state border.

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

Gusty winds will be the most noticeable impact today, as well as a bit of increased cloud cover thanks to a bit more moisture being transported into the state by the upper-level low. With the moisture, a few scattered, high-based showers and garden-variety thunderstorms are expected throughout the afternoon and into the nighttime, with one or two continuing into the early morning. Generally speaking, rain rates will be less than 0.1 inches/hour, with maximum rates less than 0.2 inches/hour. Wind gusts will be 20-35 mph in the lower mountains valleys, and up to 60-70 mph at the highest peaks.

FTB 09-28-2019: Windy and Mainly Dry

Issue Date: 9/28/2019
Issue Time: 7:16 AM

NO FLOOD THREAT IS FORECAST TODAY.

If you take a look at the upper-air analysis below, you will notice the main features for today’s forecast. The upper-level low, marked by the red “L,” is in the process of deepening along the west coast, and in response, strong, southwesterly flow aloft (maroon arrows) has settled in across the Central and Northern Rockies. This strong, southwesterly flow will serve two purposes today: 1) it will allow for the development of a couple isolated, high-based showers over the High Country, and 2) it will lead to very gusty winds over the High Country.

East of the mountains, a strengthening surface low over eastern Wyoming will bring gusty, southerly winds to the area. The breezy conditions will allow temperatures to warm to pleasant levels, with highs in the 70s/80s for most of eastern Colorado, with a few locations remaining in the mid-to-upper 60s over the Palmer Ridge and in the far Northeast Plains where a bit of cloud cover this morning will hinder full daytime heating.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, jump below the map.

Flood Threat Legend

Zone-Specific Forecasts

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

Breezy conditions will be the most noticeable impact today, with wind gusts up to 35-45 mph in the Front Range and Southeast Mountains and 25-35 mph over the lower elevations. An isolated shower over the Front Range is possible during the afternoon/evening, but little-to-no rainfall is expected.

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

Gusty winds will be the main weather story today, with wind gusts of 25-40 mph over the Southwest Slope and San Juan Mountains, 35-45 mph in the San Luis Valley, and 40-55 mph over the Northern Mountains, Northwest Slope, Grand Valley, and Central Mountains regions. Gusts up to 60 mph will be possible at the highest peaks north of I-70. A few isolated, high-based showers will develop during the afternoon/evening hours, with one or two continuing into the early morning. Little-to-no rainfall is expected.

FTB 09-27-2019: The Next Trough Begins to Dig South and Returns Rainfall Chances to Northern Colorado

Issue Date: Friday, September 27th, 2019
Issue Time: 9:25AM MDT

— Flooding is NOT expected today

Taking a look at the water vapor imagery below there are a couple of things happening today. First the cut off low, which is now an open wave, finally starts to move eastward and will be located over southern New Mexico by tonight. It’s a little bit too far south to push much mid-level energy or extra PW into the state, but it should help enhance storm coverage over the eastern San Juan Mountains this afternoon by providing a slight increase in moisture. Westerly flow aloft will scour out most of the moisture over the San Luis Valley, Southeast Mountains and adjacent eastern plains, but a weak shower or two be possible over the mountains with the main threat being wind due to the large spread in temperature and dew point.

To our north, the next trough starts to dig south over the west coast, which will push a shortwave into the state, which is currently over the Utah/Idaho border (orange “X” with arrow). As the next trough has been digging south, there has been a slight increase in moisture (that will continue) over the northern portion of the state. Denver measured 0.64 inches in this morning’s sounding, which is up 0.10 inches from this time yesterday. The shortwave is expected to help spark more widespread coverage of showers and weak thunderstorms over the Front Range and Northern Mountains this afternoon. The jet also began to move into northern Colorado this morning, so this will similarly help fuel storms this afternoon and will likely support weak showers over the high terrains near the Divide tonight. With fast westerly steering flows aloft, expecting the storms to push into the adjacent plains by late this afternoon. With low dew points (upper 30°Fs to 40°Fs), despite a cold front that pushed through overnight, gusty outflow winds will be the main threat from storms today with only moderate to light rainfall forecast. Flooding is not expected from storms today due to the fast storm motion and lack of low level moisture.

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, Palmer Ridge, Northern Mountains, Northeast Plains:

Fast storm motion and lack of low level moisture will keep storms at moderate to light rainfall accumulations with scattered coverage. Storms will fire a little later this afternoon, so they are expected to spread into the adjacent plains around 4PM. Max 1-hour rain rates up to 0.4 inches are possible with 24-hour totals up to 0.5 inches possible along the northern Continental Divide and northern Weld County. Most storms will produce rain rates at or below 0.25 inches favoring the Palmer Ridge and southern Cheyenne Ridge over the adjacent plains. A few lingering showers will be possible over the high terrains this evening, but flooding is not forecast. The main threats from today’s storms will be gusty outflow winds with the jet overhead. This is especially true over the Northern Mountains and Front Range where gusts could reach 40-45 mph.

Primetime: 3PM to 4AM

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

Storms today will be confined to the high terrains, although the increased cloud cover at the lower elevations may produce some light sprinkles for western Colorado. Slight increase in moisture over the eastern San Juan Mountains and north Central Mountains from the open wave and approaching trough. Max 1-hour rain rates up to 0.5 inches (south) and 0.3 inches (north) will be possible favoring the western facing slopes. Westerly wind will scour out most of the moisture east of the Divide, so only a few showers will be possible over the Southeast Mountains, again favoring the west facing slopes. Flooding is not forecast for storms today, and all activity should end a few hours after sundown.

Primetime: 2:30PM to 11PM