FTB 09-21-2018: Morning Upslope Showers for the Southeast Mountains and Raton Ridge

Issue Date: Friday, September 21st, 2018
Issue Time: 08:55AM MDT

 — Flooding is NOT expected today

Taking a look at the visible satellite imagery below, there are some moderate showers and cloud cover over the Southeast Mountains and Raton Ridge this morning. These upslope showers fired earlier this morning after the passage of a secondary cold front. Isolated showers are expected through noontime before drier air works its way in from the west. There is also some low cloud cover over the northern Urban Corridor, but this will quickly burn off with the morning heating. Temperatures overnight dropped very low with efficient radial cooling due to mostly clear skies. Highs this morning over the plains were in the 40Fs with low 30Fs over the Northwest Slope. This likely means that some of the mountain valleys dropped into the 20Fs. Expecting similar lows tonight even though high temperatures today will be slightly above normal. Perfect timing for these large diurnal temperature swings since fall officially begins tomorrow.

Today the ridge in the image below will begin to slide east as the 500mb high works its way to the NM/AZ border. This means higher heights will build over the state, which will bring calmer weather. The 500mb high will set the stage for WSW winds aloft, and with the 500mb high moving east, moisture should remain to our south and east as well. The WSW winds will entrain a dry air mass from Utah and Arizona, both of which are cloud free at this moment. So outside of morning showers over the Raton Ridge and Southeast Mountains, not expecting measureable rainfall this afternoon. There will be enough moisture for some high clouds and an isolated high-based showers or two near the Continental Divide this afternoon. These storms will likely produce sprinkles and brief winds though minor accumulations are possible. 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, Southeast Plains, Raton Ridge, Front Range, Southeast Mountains:

Some moderate upslope showers are present over the Southeast Mountains and Raton Ridge. These showers fired early this morning in the wake of a secondary cold front. Expecting these storms to last until noontime with max totals up to 0.25 inches. WSW flow will begin to entrain a drier air mass this afternoon, and with rising heights, not expecting much rainfall this afternoon. The dry air should also begin to break up the clouds over the Southeast Mountains and adjacent plains throughout the day. More afternoon cloud cover will be likely over the higher terrains near the Continental Divide, and an isolated high-based shower or two is possible. Though these storms may produce brief rain, not expecting totals over 0.1 inches.

Primetime: 9AM to 8PM

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

Drier air continues to be entrained from the WNW as the ridge builds over the area today. Without the jet influencing surface winds today, we should get a brief break in fire weather. Surface wind speeds today should remain around 5mph, though there is a fire weather watch for the Northwest Slope on Saturday and Sunday. This afternoon increased cloud cover is likely over the southern high terrains near the Continental Divide, so there may be an isolated shower or two. Totals up to 0.1 inches are possible. Morning temperatures were quite low, but expecting high temperatures to reach the mid-70Fs at the lower elevations and 60Fs over the mountains. Grand Valley high temperatures are forecast to reach the mid-80Fs.

 

FTB 09-20-2018: Showers and Thunderstorms Continue over Eastern Colorado as the Trough Travels East

Issue Date: Thursday, September 20th, 2018
Issue Time: 09:20AM MDT

— Flooding is NOT expected today

Finally some fall weather to start the day as we near the end of September. Overnight and morning showers are producing lots of cloud cover over the mountains and eastern Colorado. There were even reports of snow over 11,000 feet last night. Temperatures have dropped to more seasonal values in the wake of the cold front, which is very much welcomed after the last heat wave. The main axis of the trough (and moisture) will continue to move eastward today, which means the line of showers will travel eastward as well. That should bring some stronger showers and thunderstorms to the southeast corner of the state and eastern Raton Ridge early this afternoon. Light showers and weaker thunderstorms will be possible over the eastern plains north of Prowers County. A bit of moisture is also able to hold on over the far northeast corner of the state. A surface low in the area is expected to produce a line of convergence on its northeast side, so some isolated thunderstorms will be possible near the NE/CO border.

Behind the trough, much drier air will work its way into the state with WNW flow aloft as evidenced by clear skies over the Utah/Colorado border. Dew points are forecast to quickly drop off starting this morning, so expecting clouds to clear west to east as the dry air mass moves eastward. The clearing skies will also allow temperatures to the west to begin to increase, so it should be a beautiful afternoon and evening. The entrainment of the dry air will limit rainfall chances over the higher terrains this afternoon though a couple isolated high-based showers possible. Storms that do initiate will likely form along the southern Continental Divide, but totals will remain under 0.1 inches. The Southeast Mountains will get a bit more rainfall today as the moisture plume is still over this region. These storms should end as the plume moves east by early afternoon. Flooding is not expected today.

As the trough passes to the north today, increased surface winds are anticipated over the northern third of the state. With dew points dropping off rapidly, enhanced and possibility critical fire weather will be present this afternoon through this evening. Surface wind speeds are forecast to be in the 15 to 25mph range with gusts up to 40mph possible over the higher terrains.

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, Southeast Plains, Raton Ridge, Front Range, Southeast Mountains:

Drying will occur from west to east today as the trough passes through the area. This should bring some clear skies to the west later this morning and afternoon. The stronger showers and thunderstorms today should be confined to the far eastern plains though some weaker storms will be possible over the Southeast Mountains and Raton Ridge as the line of convection moves eastward. Max 1-hr rain rates up to 0.5 inches will be possible over the Raton Ridge. Stronger thunderstorm activity is forecast over the southeast corner of the state where some decent instability is able to build. Fairly quick steering winds should keep totals from reaching flood threat criteria. Max 1-hr rain rates up to 1.25 inches with small hail and gusty winds are possible. An isolated storm or two is also possible near the CO/NE border associated with a surface low. Max 1-hr rain rates up to 0.9 inches are possible with these storms along with small hail and gusty winds. Flooding is not expected.

Primetime: 10AM to 8PM

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

Drier air is being entrained from the WNW after the passage of the trough. Increased subsidence and low dew points should keep rainfall chances minimal today. It will be possible for some light, isolated showers over the higher terrains near the southern portion of the Continental Divide this afternoon. However, totals are expected to be under 0.1 inches with some brief wind possible, too. Surface winds will increase over the northern third of the state with the passing upper-level jet, so enhanced and possibly critical fire weather will be present in this region. Wind speeds are forecast to be in the 15 to 25 mph range with gusts up to 40 mph possible over the northern high terrains. Clear skies with the entrainment of the dry air will allow temperatures to increase this afternoon with highs over the lower elevations reaching 80F.  Flooding is not expected.

Primetime: 2PM to 7PM

 

 

 

 

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.