FTB 09-19-2018: Widespread Rainfall Returns to the Forecast

Issue Date: Wednesday, September 19th, 2018
Issue Time: 09:50AM MDT

— Flooding is NOT expected today

Changes to the weather are finally on their way, which should bring a more fall-like feel to the state after today. The 500mb high has shifted to the east and the trough to our west will start to move into the Great Basin. This pattern has pulled up a plume of subtropical moisture northward (see water vapor imagery below), which will work its way into western Colorado throughout the day. The plume of moisture will then transition east throughout the day and into tomorrow with the axis of the trough. The shortwave marked in the image below will help promote widespread shower and thunderstorm activity this afternoon and evening as it moves eastward. Also noted on the water vapor imagery below is a weak cold front over the Northeast Plains. This feature will sag southward throughout the day and increase low-level moisture a bit behind it. This should bring higher rainfall totals to northeastern Colorado. The main cold front (further north) will begin to drop south through the state this evening. This will help promote showers and thunderstorms overnight for the eastern plains and bring a cool, cloudy start to Thursday morning.

Precipitable Water (PW) values at Grand Junction are currently at 0.51 inches, so forecasting an increase as the plume moves north with the highest PW values expected over the southwest corner of the state. This means showers and thunderstorms will begin as high-based storms later this morning with more wetting rains starting this afternoon. Storms will be oriented southwest to northeast aligned with the positive tilt of the trough. This means more widespread rainfall over the southwest corner with storms confined to the higher terrains as you move north. As the trough begins to move east today, the upper-level jet will position itself over the northwest corner of the state, which should keep the moisture to the south and east of the Northwest Slope. Low relative humidity values with surface winds in the 20-25 mph range will produce critical fire weather. A Red Flag warning is in place through this evening with gusts up to 40 mph possible over the Northwest Slope.

Low-level moisture is also forecast to return over eastern Colorado as the shortwave travels eastward. This moisture should be confined to the Southeast Mountains, Front Range, Urban Corridor, Palmer Ridge and Northeast Plains. Similar to western Colorado, storms will be oriented southwest to northeast with steering winds moving storms along around 15 knots to the northeast, which should keep storms from dropping too much rainfall over one area. First expecting storms to fire over the mountains and then push into the adjacent plains in the evening hours. Storms will then spread into the eastern plains overnight. Models aren’t showing much instability this afternoon likely due to cloud cover increasing throughout the day in front of the trough. This will be another factor that will help keep rainfall intensities below flood threat criteria. Still, 500-900 J/kg of CAPE (measure of instability) should be enough for some decent showers and thunderstorms over the Urban Corridor and Northeast Plains. Storms over the eastern plains tonight are not expected to be severe or meet flood threat criteria, but should instead bring some beneficial rainfall. Localized totals near 1.3 inches are possible by Thursday morning. Flooding is not expected for Wednesday, though rainfall will be widespread.

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:

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

Plume of subtropical moisture associated with the eastward movement of the trough will return showers and thunderstorms to the forecast. Storms will begin as high-based over the southwest corner and spread northward throughout the day with northeast movement. Intensity of rainfall is also forecast to increase this afternoon with storms further north confined to the mountains. Max 1-hr rain rates up to 0.5 inches (south) and 0.3 inches (north) are possible with the Central Mountains recording up to 0.75 inches by morning. Localized 2-3 hour totals just under 1 inch will be possible over the eastern San Juan Mountains. Flooding is not expected.

Primetime: 11AM to 2AM

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

Expecting high clouds to increase throughout the day as the shortwave makes it way eastward. This should limit instability, and in return, keep rainfall rates below flood threat criteria. The passage of weak cold front over the Northeast Plains will leave low-level moisture the highest over this area, therefore rainfall totals should be highest here as well. Surface winds should push some of that moisture west this afternoon, which will allow for some heavier rainfall over the Urban Corridor. Storms are expected to be rather widespread over the eastern mountains this afternoon and even the San Luis Valley is expected to get some rainfall. Max 1-hr rain rates up to 0.5 inches are possible over the higher terrains. In the adjacent plains, max 1-hr rain rates up to 0.8 inches are possible due to the increase in low-level moisture. Shower activity is expected to continue overnight as the storms push into the eastern plains and the cold front drops south. Totals up to 1.3 inches will be possible by the morning over the Northeast Plains.

Primetime: 3PM to 11AM

 

 

FTB 09-18-2018: Last Day of Hot and Dry Weather

Issue Date: Tuesday, September 18th, 2018
Issue Time: 08:20AM MDT

— Flooding is NOT expected today

Just a few mid-level clouds over the Northeast Plains to start the morning, otherwise nothing but clear skies. The severe clear skies to our southwest are an indication that mid-level cloud cover this afternoon will be less today. Not seeing any signs of a shortwave in the water vapor imagery, which has brought the increased moisture the last two days. Soundings confirm this theory showing a drier layer between 500 and 600mb. With Precipitable Water (PW) values at Grand Junction and Denver near 0.6 inches, it will be another day without measurable rainfall though some high-based clouds may produce a few sprinkles over the mountains. The southwest winds aloft will continue for one more day, which will continue to promote hot afternoon temperatures. Highs over the lower elevations will reach the mid 90Fs with close to 100F over the far eastern plains. The higher elevations should expect temperatures in the mid 70Fs. As mentioned in yesterday’s FTO, an upper-level jet will move into the northwest corner of the state as the trough transitions east. This will bring some breezy conditions this afternoon with surface winds in the 15-25 mph range over the Northwest Slope, Grand Valley, Central Mountains and Northern Mountains. Gusts up to 35 mph are possible. While a Red Flag Warning has not been issued, enhanced fire weather is expected through this evening. 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:

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

The hot temperatures continue for another day. Not expecting too much cloud cover this afternoon as mid and upper-level moisture is lacking. Still could get some scattered clouds over the San Juan Mountains though with a couple sprinkles near the Divide. The jet begins its move eastward this afternoon, which will place it over the northwest corner of the state. While a Red Flag Warning has not been issued, dry fuels, gusts to 35 mph and surface winds in the 15 to 25 mph range will produced enhanced fire weather through this evening. As always, please use caution with any outdoor activities capable of producing a spark.

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

Another hot and dry forecast for Tuesday. Highs over the lower elevations will be close to record values with extreme September heat (near 100F) again over the far eastern plains. Not expecting as much cloud cover this afternoon though some scattered clouds are possible over the southern Front Range/Palmer Ridge intersect and Southeast Mountains. A few of the storms near and along the Continental Divide may produce a sprinkle or two and some brief winds, but measurable rainfall is not anticipated. Models hint at downsloping winds off the eastern mountains today, which may produce some windy conditions in the foothills and immediate adjacent plains. This will keep fire danger elevated, so continue to exercise caution.

FTB 09-17-2018: September Heat Wave Continues with the Persistent Ridge Pattern

Issue Date: Monday, September 17th, 2018
Issue Time: 08:50AM MDT

— Flooding is NOT expected today

The September heat wave continues for another day as the persistent ridging pattern keeps it hold over Colorado. This means southwesterly winds aloft will remain and entrain dry, warm air from the desert southwest. Marked in the water vapor imagery below is some weak mid-level energy that is carrying a bit of moisture. Currently, this is producing some cloud cover of the northwest corner of the state. This mid-level moisture is expected to help increase cloud cover over the northern half of the state, especially over the higher terrains this afternoon. There is a slight chance for some light rainfall over the Northern Mountains today, though totals will stay under 0.05 inches. Precipitable Water (PW) values at Grand Junction have increased to 0.73 inches, with the majority of the moisture located between 600 and 500mb. This increase in moisture should keep western and north-central Colorado from reaching Red Flag Warning criteria; however, surface winds in the 15-25mph range will created enhanced fire weather through this evening. To the east, PW was measured at 0.53 inches at Denver this morning. This means we can expect cloud cover this afternoon similar to yesterday, which should help knock the edge off the 90F+ temperatures in the immediate adjacent plains. The temperature/dew point spread will remain quite large, so some brief winds may be likely as the clouds evaporate in the low-moisture environment. Over the far eastern plains, some scattered cloud cover is possible, but mostly clear skies are expected. As anticipated, 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:

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

Plentiful sunshine today with some cloud cover expected this afternoon. Increased surface winds are expected again today over western and north-central Colorado. Though Red Flag Warning criteria is not expected to be met, 15-25 mph winds should keep enhanced fire weather conditions. A couple high-based showers are possible over the Northern Mountains this afternoon, but totals should remain under 0.05 inches. These storms could also produce some brief winds. Please continue to use caution with any outdoor activities capable of producing a spark.

Urban Corridor, Palmer Ridge, Northeast Plains, Southeast Plains, Raton Ridge, San Luis Valley:

The dry and warm streak continues to start the work week. Expecting above average temperatures again today to flirt with the records. Some brief winds are possible over the adjacent plains/Front Range intersect this afternoon. Also, forecasting some cloud cover to the west, which should help take the edge off the heat later this afternoon. Fire danger will remain elevated with the dry fuels and low relative humidity values, so continue to exercise caution.

FTB 09-16-2018: The Heat is On (Again)

Issue Date: 9/16/2018
Issue Time: 6:20 AM

NO FLOOD THREAT IS FORECAST TODAY.

The upper-level ridge that has dominated the forecast for the past few days will continue to do so today, resulting to another day of above-average to near-record warmth across Colorado. After a clear start to the day statewide, a few cumulus clouds will bubble over the High Country in association with a subtle stream of mid-level moisture from the west/southwest. A few of these clouds will develop into high-based showers over the higher terrain during the afternoon and evening hours, but due to abundant dry air in the lower-levels of the atmosphere, gusty winds and streaks of virga will be all they can muster. Perhaps a sprinkle or two is possible at the tops of mountains in the Northwest Slope and Grand Valley regions, but even so, it will not be enough to even wet the ground. Overnight, temperatures will remain on the mild side as skies clear for the start of the work week.

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:

Hot and dry will be the name of the weather game, with very few clouds (if any) in the sky. High temperatures will push to near-record levels. Gusty winds over the Urban Corridor and western portions of the Northeast Plains and Raton Ridge are likely late this afternoon and evening, as high-based showers produce gusty winds over the Front Range. Leftover clouds from this High Country shower activity will shift over the same regions, providing a bit of late-day shade and nothing more. Fire danger will be elevated, so please use caution with any outdoor activities.

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

Mostly sunny skies and above-average warmth is on tap again today, with breezy southwest winds keeping fire danger elevated. A stream of mid-level moisture from the west/southwest will allow for the development of isolated, high-based showers over the higher terrain during the afternoon and evening hours. Due to very dry air below cloud bases, showers will produce virga, gusty winds, and shade, but no rainfall will be able to reach the surface, except perhaps a sprinkle or two at the top of the mountains. Once again, due to the dry conditions, fire danger will be elevated. Please use caution with any outdoor activities.

Timing: 2 PM – 11 PM