FTB 09-26-2019: Late Afternoon and Evening Scattered Storms Return to the Western Mountains

Issue Date: Thursday, September 26th, 2019
Issue Time: 9:20AM MDT

— Flooding is NOT expected today

The cut off low that has been sitting over southern CA/AZ becomes an open wave today as the next trough starts to dig south over the Pacific Northwest. This will release some mid-level energy and push slightly higher PW values northward. So forecasting isolated to scattered showers to return to the Central and San Juan Mountains later this afternoon and evening. Over Grand Junction, PW increases 0.3 inches to put it around 0.7 inches by late this afternoon. While this moisture return will allow for light accumulation (high-based storms), back building storms could help slightly increase totals. The high-based storms are also expected to produce some gusty outflow winds. Rainfall may continue overnight in the Central Mountains and along the Continental Divide as a cold front starts to drop south. Additionally, Critical Fire weather returns to the Northwest Slope and Northern Mountains this afternoon as moisture won’t reach that far north. The increase in winds is due to the tightening gradient from the approaching trough. Southwest surface winds in the 20 to 30 mph range with gusts between 40 and 50 mph can be expected. A Red Flag Warning has been issued from noon to 8PM tonight.

There is a slight moisture return for eastern Colorado as well, so this may allow a weak shower or two to form over the southern Front Range/Palmer Ridge this afternoon. Rather than wetting rainfall, the more likely scenario is just an increase in cloud cover due to the lack of moisture and fast storm motion to the east. Elevated fire danger is expected over the northern Front Range, which includes the foothills and mountain valleys. Flooding is not forecast for Thursday.

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:

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

Best chance for rainfall accumulation will be over the higher terrains of the San Juan and Central Mountains favoring the southwest facing slopes. Storms will likely produce gusty outflow winds as well. Max 1-hour rain rates up to 0.5 inches will be possible over the San Juan Mountains with max 1-hour rates decreasing to 0.25 inches over the Central Mountains. Very isolated storm totals up to 0.7 inches will be possible over the San Juans with up to 0.5 inches possible over the Central Mountains. Due to the later nature of the rainfall (decrease in instability = gradual rainfall), flooding is not forecast.

Primetime: 4PM to 11PM

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

Best chance for an isolated afternoon storms will be over the Front Range and Palmer Ridge. With fast westerly steering flows, and only minimal increases in low level moisture, max storm totals should remain under 0.1 inches. Virga may allow for some brief, gusty outflow winds. Strong surface winds can be expected over the Northern Front Range with gusts up to 50 mph possible with the tightening pressure gradient. Flooding is not forecast.

Primetime: 4PM to 9PM

FTB 09-25-2019: Warm and Dry Statewide

Issue Date: Wednesday, September 25th, 2019
Issue Time: 9:05AM MDT

— Flooding is NOT expected today

Not much change in the forecast when compared to yesterday. Colorado remains sandwiched between the same two weather systems, which will keep the dry air overhead another day. Visible satellite was showing a little fog over eastern Prowers/Baca Counties earlier this morning, but it has likely mixed out by now. Another rainless day is forecast with temperatures slightly cooler than yesterday, but still above average for late September. There will likely be an increase in cloud cover this afternoon, and a weak cold front is forecast to move through the eastern plains overnight as a trough moves eastward to our north. This may bring some morning cloud cover and light rainfall/mist to the eastern plains tomorrow morning. Be sure to get out and enjoy the nice weather as rain will return to the forecast as the cut off low begins to lift north and east tomorrow.

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:

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

High temperatures will be similar to yesterday an increase in cloud cover expected again this afternoon. Dew points in the mid to upper 20°Fs and 30°Fs means it is too dry for any rainfall this afternoon. Surface winds will be weak, so there is no fire danger. Some stronger winds (15-20 mph) may be possible over the Northern Mountains, so there may be some patches of enhanced fire weather with the dry vegetation. Flooding is not forecast.

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

Another rain free day with temperatures slightly cooler than yesterday thanks to a weak cold front that moved south earlier this morning. Not expecting post frontal rainfall from upslope flow due to the dry air overhead, but an increase in cloud cover will be likely. Some stronger surface winds may also be possible over the northern Front Range with the jet moving through northeast Colorado today. Overnight, another cold front moves through the eastern plains, so morning cloud cover may be possible with some light rainfall/mist over the eastern plains.

FTB 09-24-2019: Slight Increase in Temperatures and Another Dry Day Ahead

Issue Date: Tuesday, September 24th, 2019
Issue Time: 9:10AM MDT

— Flooding is NOT expected today

Marked in the visible satellite imagery below is mid-level energy (orange “X”), which is helping produce some cloud cover over the eastern plains and southern Urban Corridor. Not much moisture in the low levels, so this is mostly mid-level cloud cover. This should begin to burn off throughout the morning and move eastward with the upper flow. The yellow arrows below are showing the upper level steering flow direction (various strengths) with the state between two systems. There is one system to the north with the jet moving towards Colorado’s northern border throughout the day. This will drop a very weak cold front though the plains, which will translate to a change in direction of the surface winds to more northerly. Then there is the cut off low to our southwest, which is marked below. The southwest flow from AZ/NM around this low will likely pull in high cloud cover again to the southern tier of the state, which will start west and then move east. A dry air mass, especially at the lower levels, remains over the state with the best moisture for afternoon storms east of the green line below and to our southwest. This translates to another rain-free day with temperatures also rising a 5°F to 10°F. 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:

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

Expecting afternoon and early evening cloud cover once again with mid-level energy rotating around the cut off low. This will be similar to yesterday with mid to high level clouds. It’s also a bit drier in the low levels, so not thinking there will be any rainfall. Temperatures will rise a few degrees this afternoon when compared to yesterday. Clearing skies will allow low temperatures to drop off tonight, but freezing temperatures are only expected for the highest terrains.

Front Range, Urban Corridor, Palmer Ridge, Northeast Plains, Central Mountains, Northern Mountains, Northwest Slope, Grand Valley:

Rainfall is not forecast for these areas due to the dry air mass overhead, upper level temperature inversions (capped) and subsidence in the right exit region of the jet streak (northeast corner). Temperatures will increase 5°F to 10°F when compared to yesterday despite northerly surface winds. Overnight lows will drop into the 50°Fs (lower elevations) with mid-30°Fs for most of the mountains regions.

FTB 09-23-2019: Cool Morning to Start Fall with Mostly Dry Conditions Forecast

Issue Date: Monday, September 23rd, 2019
Issue Time: 9:10AM MDT

— Flooding is NOT expected today

Fall officially began early this morning, and cooler morning temperatures certainly made it feel more seasonable. Lows dipped into the 30°Fs over the northwest corner (lower elevations) and San Luis Valley again with Denver bottoming out at 48°F. Highs should rebound quite a bit today with a building ridge and drier air mass overhead. There’s some morning cloud cover over the state associated with some energy moving through the southwest flow aloft. Expect this cloud cover to continue on and off today with only clear skies forecast for the far southeast corner. The upper low over Nevada will dig south throughout the day and be cut off from the main flow by early tomorrow morning. This feature is forecast to sit south and west of the state, which should keep a drier air mass in place for the majority of the state. Thus, rainfall is not anticipated for the northern 2/3 of the state.

Over the southern 1/3 of the state, moisture associated with the mid-level energy below (orange “X”) is forecast to move in, so some isolated showers and weak thunderstorms will be possible over the southern Southwest Slope and San Juan Mountains this afternoon. This vorticity max will move eastward this evening, so storms are expected to spread into the San Luis Valley and maybe even the Southeast Mountains by morning. With instability dwindling after sundown, rain rates will really start to drop off, so the accumulating rainfall might not make it all the way east. A light dusting of snow may also be possible for the highest elevations of the eastern San Juan Mountains.

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:

San Juan Mountains, Southeast Mountains, Southwest Slope, San Luis Valley:

Best chance for rain this afternoon and evening will be over southern tiers of these regions. Highest totals are forecast for the eastern San Juan Mountains and eastern Southwest Slope due to a bit more instability and moisture available during the afternoon. Max 1-hour rain rates up to 0.2 inches will be possible with most totals below this threshold. Some light showers may also occur over the San Luis Valley as this feature moves east, but totals should remain under 0.1 inches with more mist and cloud cover than measurable rainfall. Can’t rule out a light dusting of snow over the highest elevations of the San Juan Mountains later tonight, but large accumulations are not expected. Low temperatures should also be warmer, so freezing temperatures should be avoided in the San Luis Valley.

Primetime: 2PM to 4AM

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

Highs this afternoon will rebound into the 80°Fs with some upper 80°Fs over the Southeast Plains where skies remain clear. The drier air mass overhead and inversions in the upper atmosphere will prevent accumulating rainfall, though on and off cloud cover can be expected with the shortwave. The 50°F dew point line in the visible satellite imagery above is to the east of the area, which is usually a good marker for rainfall chances. Should be a beautiful day with calm winds except over the far Southeast Plains where some breezy southerly surface winds are expected (15 to 20 mph).

Central Mountains, Northern Mountains, Northwest Slope, Grand Valley:

These areas should remain rain-free as well with dry air in place and a building ridge. Highs will barely reach 80°F over Grand Junction with 70°Fs forecast for the other valleys. Still a little warm for this time of year, but appreciated after the late hot streak. Lows should be about 5°F warmer than last night, so not thinking any Freeze Watches will need to be issued for the lower elevations.