FTB 08-18-2019: Rain Free Day & Critical Fire Weather for Northwest Colorado

Issue Date: Sunday, August 18th, 2019
Issue Time: 9AM MDT

— Flooding is NOT expected today

Quiet weather day in store as the ridge begins to build back to the north and produces subsidence (sinking motion) over the state. There is currently some cloud cover over the northwest corner, which is marked below. This should begin to break up as morning heating occurs and the low level moisture mixes out by noon. There is a much drier air mass in place over the state with PW measured at 0.57 inches and 0.55 inches in Denver and Grand Junction, respectively. Not expecting any rainfall today, but there will be some broken cloud cover over the higher terrains and western Colorado border this afternoon. Clouds look to increase overnight for the Southeast Mountains and eastern Plains, so it will be a cooler start to Monday morning. Flooding is not forecast.

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

Cloud cover over the northeast corner of the state is forecast to mix out by noon with high temperatures slightly cooler over the area this afternoon. Further south, temperatures will look similar to yesterday. Best chance for afternoon shade from the sun will be near the Palmer Ridge and southern Front Range. Forecasting overcast skies tomorrow morning for the Southeast Plains, Raton Ridge and Southeast Mountains. Rain is not forecast.

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

Critical fire weather continues for another day with a Red Flag Warning issued over the northwest corner of the state. Surface winds will decrease a bit when compared to yesterday, but southwest winds in the 10 to 20 mph range (and gusts up to 35 mph) will mix with low humidity, which will allow flames to spread quickly. So, please use caution with any open flames. A few clouds are forecast over the western border and high terrains this afternoon, but rain is not forecast. High temperatures will be similar to yesterday with possibly a 2-3°F increase.

FTB 08-17-2019: Red Flag Warning for Western Colorado Continues

Issue Date: Saturday, August 17th, 2019
Issue Time: 8:25AM MDT

— Flooding is NOT expected today

The ridge pattern has completely broken down and flow has become zonal statewide as the base of the trough passes over the state. The strong westerly flow will mix out all the of moisture from west to east beginning this morning, and the best moisture this afternoon will be east of the green dashed line below. A shortwave, marked with the orange “X”, is forecast to move east with the zonal flow throughout the day. This will help spark widespread afternoon storms over the Front Range and then adjacent plains this afternoon as the westerly flow pushes them off the higher terrain. Since the best moisture will be east, storms are expected to be high-based and produce little rainfall with brief, gusty winds. Best accumulations will be over the border counties where dew points will be in the 40°Fs. Flooding is not forecast.

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

Not expecting a lot of rainfall today from storms as they will be high-based. They will provide some nice shade from the sun over the northeast quadrant of the state. Gusty winds will be possible along with some weak thunderstorms. Max 1-hour rain rates west of Washington County should remain below 0.1 inches with max 1-hour rain rates increasing to 0.6 inches over the border counties.

Primetime: 1PM to 9PM

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

Critical fire weather continues today with the Red Flag Warning now extending into the San Luis Valley. High surface winds are mixing to the surface due to the jet stream sitting over the northern border as the base of the trough passes. Winds are forecast to be from the southwest at 15 to 25 mph with gusts up to 45 mph possible. A few clouds will be possible over the northern border as shortwaves move through the area, but other than a couple of rain drops, rain is not forecast. Please use caution with open flames.

FTB 08-16-2019: Another Round of Isolated, Severe Thunderstorms and Heavy Rain for the Northeast Plains

Issue Date: Friday, August 16th, 2019
Issue Time: 10:45AM MDT

A LOW flood threat has been issued for the Northeast Plains

The threat of isolated, severe thunderstorms will return to the Northeast Plains once again today with multiple dynamic features in place to aid in severe thunderstorm development. Early morning fog and low level cloud cover can be seen visible satellite imagery below over the northeast quadrant of the state thanks to an outflow boundary from the MCS over Nebraska. This shows the moisture return to the area and will help contribute to instability later this afternoon. A low pressure system over the southeast corner of the state will also advect in low level moisture to the eastern plains throughout the day with southeasterly flow.  The jet streak that has been perched over the northern border is forecast to move slightly east throughout the day, putting the Northeast Plains in a favorable position for extra lift.

An embedded shortwave that will pass over the CO/WY border during peak heating this afternoon, which will help break the cap and contribute to more widespread coverage of thunderstorms this afternoon. Additionally, lee troughing is expected to create a surface low and vorticity maximum over the eastern plains, which will also help aid thunderstorm development over the southern Urban Corridor and Palmer Ridge intersect. Storms are forecast to initiate along the stationary front (red dashed line below) early this afternoon. PW over the eastern plains will increase to ~1.1 inches over the far northeast corner, with surface dew points over the area remaining in the 60°Fs throughout the day. Although storm motion will be to the east around 20 mph, storms have been maximizing rainfall rates in this moisture rich environment the last few days. Additional storms may pop from outflow boundaries, which would increase rainfall accumulations over localized areas. Thus, a Low threat has been issued for field ponding, road flash flooding and local stream/creek flash flooding. The wind profile in this morning’s Denver sounding indicate severe storms that form over the Low threat area will again produce damaging winds and very large hail. Hail size may again reach sizes close to tennis balls.

Mid-level moisture advection can be seen by the cloud cover over Utah this morning. Westerly flow of this moisture over the western border into the higher elevations will provide some cloud coverage, but fast steering flows and insufficient moisture at other layers of the atmosphere should keep accumulations to under 0.1 inches again. The best chance for this measurable rain is over the eastern San Juan Mountains. As forecast in the FTO, dew points over the west measured in the 30°F’s this morning (green contours below), but are forecast to decrease by 10°F-20°F throughout the morning. Thus, a Red Flag Warning is in place with high winds mixing down to the surface from the jet over the northern border. Please use caution with open flames.

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, scroll below the map.

Flood Threat Legend

Zone-Specific Forecasts:

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

Storms are forecast to begin early this afternoon over the high terrains favoring the Palmer Ridge and Cheyenne Ridge for development. Brief isolated showers are also possible over the Front Range and Southeast Mountains this afternoon, but only trace amounts of rain are expected. The primary threat over the high country and surrounding plains will be brief, gusty winds from storms in the vicinity.

Max 1-hour rain rates up to 0.5 inches will be possible as storms begin traveling east of the I-25 corridor. As they move east at 20 mph, the environment will promote severe thunderstorm development (Northeast Plains). Max 1-hour rainfall rates up to 1.75 inches will be possible within the storm cores due to dew points in the 60°Fs. The primary threats for today include heavy rainfall, damaging winds (> 60 mph) and large hail. Heavy rainfall from Tuesday and Wednesday over southern Yuma, Kit Carson and Cheyenne Counties may cause a little more runoff, but rain rates further south should be closer to 1.15 inches and storms are forecast to be fairly isolated, so flooding issues should be avoided.

Primetime: 2PM to 11PM

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

A slight increase in mid-level moisture from the southwest will provide a chance for isolated, weak showers again this afternoon over the eastern San Juan Mountains. Max 1-hour rain rates will remain below 0.1 inches again, so flooding is not expected. Storms may produce some gusty outflow winds. Upper level steering flows increase from 20 mph over the San Juan Mountains to 45 mph over the Northern Mountains. These fast steering flows will increase the fire threat, so a Red Flag Warning has been issued. Please follow NWS Pueblo for the latest on this threat.

Primetime: 1PM to 8PM

FTB 08-15-2019: Break from Heavy Rainfall and Severe Thunderstorms

Issue Date: Thursday, August 15th, 2019
Issue Time: 8:35AM MDT

— Flooding is NOT expected today

There’s a break in severe thunderstorms and heavy rainfall forecast for Thursday as northwest flow ushers in a dry air mass. This dry air can be seen by the cloud free skies over Utah and Wyoming in the visible satellite imagery below. PW values have dropped off both east and west of the Continental Divide as forecast in the FTO. This morning’s sounding measured Denver’s PW at 0.59 inches and Grand Junction’s PW at 0.51 inches, which is well below average for this time of year. Most of the remaining low level moisture east of the Divide will mix out from west to east throughout the day. While there will be some higher moisture and CAPE values along the Colorado border, it doesn’t look like there will be any disturbances to help break the cap. Also forecasting the dense fog over the Northeast Plains to dissipate with a little more morning heating.

As far as storm potential today, a couple high-based, isolated, weak storms are forecast with residual moisture under the ridge over the eastern San Juan Mountains. Some heftier cloud cover will also occur over the Northwest Slope by late this afternoon, but only a drop or two of rainfall is forecast. There is a 20-30% chance for an isolated storm or two over the far Southeast Plains along the CO/KS border, but rainfall totals should remain below 0.20 inches. Flooding is not forecast.

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:

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

Best chance for storms today will be over the eastern San Juan Mountains. Without much changing in the way of forcing and moisture from yesterday, thinking totals for rainfall will be under 0.10 inches. Additional cloud cover will move into the Northwest Slope later this afternoon, which should provide some relief from the heat. High temperatures over the lower valleys will be in the upper 90°Fs with low 90Fs over the mid-level elevations. Flooding is not forecast.

Primetime: 2PM to 8PM

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

Another day with seasonable high temperatures. The northeast corner of the state might be a little bit cooler than the Southeast Plains, but 90°Fs are forecast across all lower elevations. Storms that form over the Southeast Plains will produce under 0.20 inches, so flooding is not forecast. There is an MCS that forms over the NE panhandle tonight, so this may cause another round of fog tomorrow morning over the northeast corner of the state.

Primetime: 3PM to 9PM