FTB 10-02-2018: Flood Threat Bulletin Special Edition as Remnants of Hurricane Rosa Move into Western Colorado

Issue Date: Tuesday, October 2nd, 2018
Issue Time: 09:55AM MDT

NOTE: This is a special edition of the Flood Threat Bulletin. At this time, we do not foresee a threat needing to be issued after today. However, if a flood threat appears additional Bulletins will be produced as warranted.

— A MODERATE flood threat has been issued for the flood threat has been issued for the Bull Draw, Plateau, Burro and 416 burn scar areas

— A LOW flood threat has been issued for the Southwest Slope, San Juan Mountains, Central Mountains, Grand Valley, Northern Mountains and Northwest Slope

The main axis of subtropical moisture associated with the remnants of Hurricane Rosa will make its way into southwest Colorado and move NNE throughout the day. This will bring widespread showers and thunderstorms to western Colorado as well as over the higher terrains through tomorrow morning. While the threat for rainfall is widespread today, the largest totals will be confined to higher terrains over the Grand Valley, Central Mountains, Southwest Slope and San Juan Mountains. The snow line is expected to be somewhere between 12,000 and 13,000 feet, so only the highest peaks will have a dusting of snow by tomorrow morning. As anticipated, Precipitable Water (PW) has increased drastically over Grand Junction, and PW was measured at 0.98 inches in the 12Z sounding. This surpasses the daily record, but the October record of 1.05 inches remains (for now).

This morning, the first wave of showers has made its way over the Southwest Slope and San Juan Mountains associated with the shortwave marked in the water vapor imagery below. This feature and associated stratiform rain will continue to move to the NNE throughout the morning into this evening. Expecting showers to become lighter and less widespread as they move into the Northern Mountains and Northwest Slope. None the less, 24-hour totals just under 1 inch will be possible over the Northern Mountains. A second wave of showers is expected to move into the southwest corner of the state this afternoon associated with the second shortwave marked in the water vapor imagery below. Widespread stratiform rainfall is forecast with some embedded convection (limited instability) through early tomorrow morning. Some light, isolated showers will likely continue over the Central and San Juan Mountains into Wednesday. Normally, stratiform rain and steering winds around 20 knots would keep the flood threat low. However, the multiple rounds of storms in a high moisture environment and convection embedded in the showers will warrant flood threat today. Recent burn scars will be especially susceptible to flash flooding, mud flows and debris slides. A Low flood threat has been issued for western Colorado with a Moderate Flood threat for the Plateau, Bull Draw, Burro and 416 burn scars.

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:

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

Multiple rounds of showers with embedded convection this afternoon are expected over these regions with the highest totals favoring the southern high terrains and their southwest facing slopes. However, 24-hour totals just under 1 inch are possible over the Northern Mountains as well with max 1-hr rain rates up to 0.5 inches. The more stratiform nature of the showers to the north should bring some relief to fire crews in the area and limit the overall flood threat. 24-hour totals up to 2.25 inches will be possible over the San Juan Mountains with max 1-hr rain rates up to 0.7 inches due to embedded convection. These rain rates and totals will put the region and recent burn scars at risk for local flash flooding, debris slides and mudflows. A Low and Moderate flood threat has been issued.

Primetime: 10AM to 3AM

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

While not at the main center of action today, some isolated afternoon showers will be possible over the higher terrains this afternoon as moisture moves into the area from Rosa. A couple of these storms may wander into the adjacent plains, but storms are expected to be high-based with limited rainfall totals. Storms this afternoon will also be capable of producing brief, gusty winds. Max 1-hr rain rates up to 0.25 inches will be possible with 24-hour totals up to 0.6 inches over the Southeast Mountains.

Primetime: 12PM to 12AM

 

FTB 09-30-2018: Final FTB of the 2018 Season

Issue Date: 9/30/2018
Issue Time: 7:10 AM

NO FLOOD THREAT IS FORECAST TODAY.

NOTE: This is the final scheduled Flood Threat Bulletin of the 2018 season. However, additional Bulletins may be necessary next week to cover the potential heavy rainfall threat over western Colorado. If a flood threat appears, we will be doing special Flood Threat Bulletin(s) as warranted.

A weak cool front pushed southward overnight across eastern Colorado, bringing cooler temperatures and a slight increase in low-level moisture. Ultimately, this has resulted in low clouds, fog, and a couple pockets of light drizzle across the eastern plains this morning. The clouds will attempt to hang on as long as possible today, clearing from west to east as the day wears on. This means highs in the upper 60s and 70s for the Urban Corridor, low-to-mid-80s across western portions of the Southeast Plains, with temperatures struggling to get out of the 50s near the eastern border north of Highway 50, and mid-60s south of Highway 50.

For the High Country, the shallow cool air and moisture from the east won’t have an impact, and instead another day of mostly sunny skies and warm temperatures are in store. As the day wears on, scattered high- and mid-level clouds will stream across the area, thanks to a pocket of moisture associated with an upper-level shortwave from the Great Basin and outflow from Hurricane Rosa. A couple isolated, high-based showers, and perhaps a weak thunderstorm or two, will develop over the higher terrain in association with these moisture streams, producing mainly light rainfall and gusty winds. Moisture is too shallow for anything more. For more details on timing and rain rates, please see the zone-specific 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:

Cool and cloudy for most to start the day, with the low-level clouds and fog mixing out from west to east. A wide range of temperatures are expected, with eastern portions of the Northeast Plains and Southeast Plains (north of Highway 50) struggling to get out of the 50s, the Urban Corridor expected to be in the 60s and 70s, and western portions of the Southeast Plains reaching into the mid-to-upper 80s. Pockets of light drizzle are expected during the morning and early afternoon hours, mainly over the Northeast Plains, but very little accumulation will result.

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

Mostly sunny and warm will be the main weather story today, with a slight uptick in moisture and downtick in winds lessening (somewhat) the fire danger as compared to yesterday. Pockets of mid- and high-level moisture will stream over the High Country, resulting in an increase in clouds as the day wears on, with a couple isolated, high-based showers (and a weak thunderstorm or two) expected from the late afternoon and into tomorrow. Moisture is shallow and high-based, so not much rainfall is expected; the main impacts will be gusty winds and light rainfall. Maximum rain rates will remain below 0.15 inches/hour.

Timing: 5 PM – 11 AM

FTB 09-29-2018: Big Temperature Swing for Eastern Colorado, Fire Danger Returns

Issue Date: 9/29/2018
Issue Time: 7:11 AM

NO FLOOD THREAT IS FORECAST TODAY.

Yesterday’s cold front has come and gone, and the shallow cold air left behind across eastern Colorado will be eroded quickly by warm air currently hanging out around 7000 feet (for a visual representation of just how shallow the cold air is, check out the atmospheric sounding below: 38°F at the surface, ~70°F approx.1000 feet above). This will cause a wild swing in high temperatures, with today’s highs being 25-35°F higher than yesterday’s. This warm air is also relatively dry, and as it mixes down to the lower elevations, it will bring with it elevated fire danger due to the gusty, west/southwest winds associated with it. Scattered high clouds will hang around for much of the day over the Urban Corridor and western portions of the Southeast Plains, Northeast Plains, and Palmer Ridge, but the rest of the area should be mostly sunny.

Image via: Storm Prediction Center (spc.noaa.gov)

For the High Country, the day has started mostly clear and will remain mostly sunny throughout the day, with a few passing high clouds associated with a bit of high-level moisture. High temperatures will be above average, and combined with dry fuels and low relative humidities, fire danger is the main concern with today’s weather conditions. Red Flag Warnings have been posted for much of the High Country; please check with your local National Weather Service office for more information.

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:

Warm and dry, with high temperatures 25-35°F warmer than yesterday’s highs. Breezy conditions and low relative humidities will bring elevated fire concerns to the area, with a Red Flag Warning issued for portions of the Urban Corridor and Palmer Ridge. Please check with your local National Weather Service office for more information.

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

Warm and dry is the name of the weather game today, with gusty west/southwest winds combining with low relative humidities to elevate fire danger across the area. Red Flag Warnings have been issued for much of the High Country; please check with your local National Weather Service office for more specifics.

FTB 09-28-2018: Cold Front Passage brings Drizzle and Light Showers to Eastern Colorado

Issue Date: Friday, September 28th, 2018
Issue Time: 09:05AM MDT

— Flooding is NOT expected today

The aforementioned cold front from yesterday’s FTB and FTO has made its way through eastern Colorado this morning. This is brining quite the cool temperatures to the eastern plains with current temperatures in the upper 30Fs to mid 40Fs. Behind the front, there are some low-level clouds and fog as seen in the visible satellite imagery below. Light showers are also being reported over the Southeast Plains. Flow aloft will also turn more westerly today as the trough continues to migrate east and the upper-level high moves over NM/AZ. This should help entrain a drier air mass from the west. The front is rather shallow, so expecting clouds to dissipate west to east as deep mixing occurs in the boundary layer with the drier air aloft this afternoon. Moisture is a bit deeper over the Colorado/Kansas/Nebraska border, so forecasting skies to remain overcast. Light showers will be possible throughout the day but not expecting 24-hour totals to exceed 0.15 inches. Due to the shallow nature of the cold front, only the eastern plains and lower elevations of the eastern high terrains will have afternoon high temperatures affected. This means sunny skies and warm temperatures for the mountains and western Colorado. Tonight, expecting cloud cover to increase as a shortwave moves clockwise around the 500mb high into western Colorado. This should help keep low temperatures a few degrees higher than the last few nights across the state. As you may have predicted, 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:

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

Cooler high temperatures today thanks to the passage of a cold front. Highs today over the plains will be in the mid-50Fs with temperatures warming into the low 60Fs over the adjacent plains. The mountains will remain mostly unaffected by the cold front minus the foothills. Cloud cover is expected to decrease west to east this afternoon, although overcast skies will remain over the far eastern plains. With limited low-level moisture and instability, light showers and drizzle will be possible west of 104deg as well as over the northern Front Range/Cheyenne Ridge intersect. Totals for the 24-hour period are expected to remain under 0.15 inches, so flooding is not expected today.

Primetime: 9AM to 10PM

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

The shallow cold front should leave these regions unaffected today with highs reaching the mid 80Fs over the lower elevations. With westerly flow aloft, dry air entrainment will keep skies mostly clear, so plenty of sunshine to go around. This evening a shortwave will rotate around the 500mb high, so cloud cover will increase from west to east. This will keep low temperatures warmer than the last couple of days as radiative cooling will decrease.