FTO 05-16-2019: Active Spring Pattern Continues into Next Week

Issue Date: Thursday, May 16th, 2019
Issue Time: 1:30PM MDT
Valid Dates: 5/17 – 5/31

Today’s SSEC RealEarth water vapor imagery continues to show a very dynamic and lively upper level pattern. Event #1 is taking shape as the west coast trough begins to slowly move eastward. By Friday, the upper trough will be located just to our west. As the image shows, not a lot of low level moisture in the area or around the low, so not expecting flooding with this system. By Friday afternoon, a lee trough will set up over eastern Colorado. With the dry line setting up east of this feature, storms over the mountains and adjacent plains should be high-based, which will limit accumulation. There is a slight chance for a couple severe thunderstorms over the Northeast Plains associated with convergence on the northwest side of the surface low. The chance for storms continues into Saturday as a cold front returns some low level moisture during the morning and a second shortwave passes through during the day from west to east. Widely scattered storms (snow and rainfall) are forecast over the mountains and adjacent plains, but severe weather is unlikely and accumulations are expected to stay under flood threat criteria.

Event #2 starts to form over the Gulf of Alaska with the conglomeration of several vorticity centers. This will form another trough that will affect the state at the beginning of next week. The latest runs of the GFS are placing a surface low over the Colorado, New Mexico and Oklahoma border. With cooler temperatures, this could mean some heavy snowfall for the Front Range and rain for the adjacent plains, so an Elevated Threat has been issued. Still plenty of time for the low to shift north or south, which would modify the areas of greatest accumulation. Also, the snow level will be monitored closely as this would also impact the threat level. Tuesday, showers and snow are likely to continue until the system pushes east. Please tune into Monday’s FTO and FTB for evolving details.

With multiple cold fronts moving through the state over the next week or so, there should be a brief pause in the melt out of the snowpack. Small streams will start to approach bankfull today and tomorrow, but the impending cool weather should allow surface levels to begin to drop starting on Saturday. Some warming is expected after Event #2, but with an active pattern expected, melting is not expected to accelerate for long or cause any major flooding issues.

Event #1: Friday (5/17) – Saturday (5/18)

No Apparent Threat as the next trough moves eastward from the west coast.

Moisture has started to slightly increase today with the approaching system and will continue to do so as the trough traverses east. Tomorrow, chances increase for rain and thunderstorms with some snow possible at the highest elevations. In the morning a line of storms will develop with a wave over western Colorado. With southwest steering winds, the storms will favor the Front Range as the wave travels eastward. Enhanced convergence and moisture along the Cheyenne Ridge will allow some higher amounts to fall over the northern Urban Corridor and Front Range. A couple severe thunderstorms are also possible over the Northeast Plains tomorrow afternoon on the northwest side of the surface low. Max 1-hr rain rates up to 0.8 inches may be possible with these storms. Saturday, cooler temperatures should produce snow or cold rain over the higher terrains and rainfall from weak thunderstorms over the adjacent eastern plains. Flooding is not expected.


Event #2: Monday (5/20) – Tuesday (5/21)

Elevated Threat as the active pattern continues and produces a surface low over the Colorado/New Mexico border.

Still lacking confidence in the details of this next pattern. This is mainly because slight movements in the low and changes to temperatures will impact where and how accumulations forms. However, widespread precipitation is forecast to start next week as the next trough forms to the west. With the current GFS track, the highest accumulations from this system will be over the Front Range, Urban Corridor and Palmer Ridge. The Northern Mountains will also likely have some decent accumulation with the current, more southern track. Hard to tell how much the cold front on Tuesday will cool things off, so can’t nail down the freezing level quite yet. However, if the majority of the precipitation can fall as snow on Tuesday, the Elevated Flood threat will be limited to Monday.


FTO 05-13-2019: Gorgeous Week Ahead with Storm Chances Increasing into this Weekend

Issue Date: Monday, May 13th, 2019
Issue Time: 11:30PM MDT
Valid Dates: 5/14 – 5/28

Cool start to the month of May across the state with the active pattern. Precipitation totals have also been above average for the higher terrains. The last weather system temporarily stopped the spring melting and added to the already high snowpack with the Central, Southeast and San Juan Mountains receiving the bulk of the snow accumulation. See the Upper Rio Grande Basin’s SWE (Snow Water Equivalent) below. With above average temperatures expected at the beginning of this week, we should start to see the melting of the snowpack pick back up at the higher elevations. At this time, flooding outside of minor flooding of small streams, is not expected.

Below is the SSEC RealEarth water vapor imagery from UW Madison, which shows a very active pattern lining up over the North Pacific. Currently, there is cutoff vorticity max over Texas and New Mexico mentioned in the last FTO. This should stay well south of the state as the high pressure begins to build in from the west. With residual moisture under the ridge, weak thunderstorm activity over the higher terrains is possible each afternoon with the diurnal heating pattern. Event #1 begins as the two vorticity maximums combine (marked X’s in the North Pacific) and a large trough moves in over the west coast and pushes east. Flow aloft will switch to southwesterly on Thursday, which should pull in drier air seen in the image below and limit precipitation chances. Higher moisture is expected on Friday as the ridge slides east, and a front on Saturday should help return low level moisture to the plains. This is expected cause an uptick in thunderstorm activity.

A lull in the pattern occurs Sunday into Monday before the next trough moves in from the west coast (Event #2; not marked above). The GFS is showing a trough west of Colorado at the beginning of next week, which could bring widespread rainfall to western Colorado. While, PW values aren’t looking too impressive at this time, multiple rounds of rain and a melting snowpack could cause some flooding issues. Still quite a bit of time for the details of this system to develop, but there is an Elevated Threat issued for this FTO.

Event #1: Friday (5/17) – Saturday (5/18)

No Apparent Threat as a trough moves eastward from the coast bringing favorable dynamics to area for severe thunderstorms.

Moisture will start to increase towards the end of the week as the trough moves eastward and sits west of Colorado. This will increase the chances of rain and thunderstorms to start next weekend. Saturday, models are showing a cold front drop through the plains, which may increase low level moisture. The GEFS moisture plumes are also indicating an increase in PW values out east. With plentiful lift and dynamics during the afternoon, paired with the moisture return, severe thunderstorms may be possible on Saturday over eastern Colorado. Activity Saturday night is also possible over the eastern plains if upper dynamics align properly. Mostly this would be isolated and associated with an overnight MCS in a boarding state. This could cause some very heavy rainfall totals near the Colorado/Kansas/Nebraska borders should activity spill back to the west. Please tune back in on Thursday for an update as the No Apparent Threat may be upgrade for Saturday.


Event #2: Monday (5/20) – Wednesday (5/22)

Elevated Threat as a slow moving trough sits to the west of Colorado next week.

Again, lacking confidence in the details of this next pattern, but widespread precipitation may be possible for western Colorado at the beginning of next week if the nearly stationary trough plays out. With snowpack high and temperatures rising, there could be a threat for some minor flooding. At this time, there is an Elevated Flood threat. However, if low level moisture is lacking and rainfall is gradual enough, flooding may not be an issue. Please tune back into the FTO on Thursday for evolving details.


FTO 05-09-2019: Scattered Showers for Southern Colorado then Warm Weather Returns for the Weekend

Issue Date: Thursday, May 9th, 2019
Issue Time: 12:15PM MDT
Valid Dates: 5/10 – 5/24

We start this FTO with the tail end of Event #1 from Monday’s FTO. Currently, a trough is exiting eastern Colorado with a break before the next wave moves in from AZ/UT/NV. This means flow aloft will turn to southwesterly to westerly on Friday. A plume of moisture, marked in the water vapor imagery below, will be pulled into southern Colorado. This will help fuel some snowfall and rain (lower elevations) over southern Colorado along the CO/NM border tonight into Friday morning. Expecting showers to continue tomorrow afternoon before the trough pulls westward and digs south creating a cutoff upper level low off the coast of CA.

Below is the 500mb geopotential height anomaly from the GEFS (Global Ensemble Forecast System) on Saturday morning. It very nicely illustrates the low becoming cutoff from the main, westerly flow. Once the system is cutoff, it moves south and slowly wanders east (Saturday-Tuesday). It should stay far enough south that it won’t affect the state. On Friday, high pressure starts to build over the state and a weak cold front gives the winds more of a northerly component on Saturday afternoon. This should prevent widespread showers as only minimal moisture remains trapped under the building ridge. Expect scattered storms over the San Juan Mountains with limited rainfall over the other high elevations. With high pressure to the north and low pressure to the south by Sunday, a nice a rex blocking pattern should keep the weather calm into next week. Warm temperatures will also be back in the forecast, so expecting widespread melting of the snowpack between the two systems. High temperatures over the lower elevations will start climbing towards 70°F by Sunday, and they be well into the 70°Fs on Monday and Tuesday.

Event #2 begins sometime between Wednesday and Thursday of next week. The next trough slides over the west coast and pushes the ridge eastward. Details of this event are still a little bit out, but right now the best moisture and dynamics don’t move into the state until Thursday or Friday. At this time there is No Apparent Threat; however, some severe weather may be likely towards the end of next week.

Event #1: Friday (5/10) – Saturday (5/11)

No Apparent Threat as the cutoff low moves south and westward of the state. The current wave over UT/AZ/NV will help provide lift and moisture for scattered storms across the southern border of the state into Friday morning.

With the next wave moving into Colorado this afternoon and tonight, the chances for rainfall will be greatest over the southern border. Light showers and snow accumulation are likely over these higher terrains by tomorrow morning. As the ridge begins to build over the state, some residual moisture on Saturday may help initiate some storms over the San Juan Mountains. Without a ton of moisture under the building ridge, totals should be much less than the last couple of days. Highest totals are forecast over the western facing slopes in the San Juan Mountains with lighter totals over the Southeast Mountains and Raton Ridge. Flooding is not expected.



Event #2: Wednesday (5/15) – Saturday (5/18)

No Apparent Threat as the next trough moves over the west coast and pushes the ridge east.

Not a lot of confidence in the details of this next pattern, but storms look to return to the forecast towards mid/end of next week. Best dynamics and moisture will likely arrive when a cold front drops south. Right now the GFS is predicting this sometime on Wednesday afternoon. This would allow for some moisture to return to the lower levels and provide some favorable dynamics for severe weather. Tune back into the FTO on Monday for evolving details. Due to the low confidence, please view the map below with caution. At this time, there is No Apparent Flood Threat.


FTO 05-06-2019: Scattered Showers and Thunderstorms Return to the Forecast for the Work Week

Issue Date: Monday, May 6th, 2019
Issue Time: 12:30PM MDT
Valid Dates: 5/7 – 5/21

After a weekend and Monday with gorgeous weather, an active weather pattern returns for the rest of the work week. The water vapor imagery below shows the low pressure system starting to move over southern California from the Pacific. This will change our upper level flows from westerly to more southwesterly, and it will also pull in a ribbon of moisture from the southwest over the state. An upper level jet stream along with lift out in front of this trough will provide sufficient lift for scattered showers and thunderstorms this week and marks the beginning of Event #1.

The cutoff low is expected to navigate into the Four Corners region on Monday night into Tuesday. This should increase shower and thunderstorm activity on Tuesday afternoon as easterly flow at the surface will keep low level moisture in place. So expected light showers and heavy cloud cover tomorrow morning with increasing coverage of showers during the afternoon. On Wednesday, the trough digs south on its backside, which should hold the unsettled pattern in place. Models show a a cold front sliding south through the state sometime between Wednesday morning and afternoon. By Wednesday evening, ongoing showers are expected to turn to snow as cold air takes control of the area. This cold front should drop freezing levels to 6-7K feet by late Wednesday into Thursday morning. Moderate snow accumulation (5-15 inches) is forecast over the higher elevations from Tuesday into Thursday with snow possible over the foothills as well. With two days of rain (Tuesday-Wednesday), recent burn scars may have some flooding issues, which is why there is an elevated threat in the middle of Event #1. However, freezing temperatures overnight on Wednesday into Thursday should nix this threat. By Friday, another cut off low forms over the southwest US, but it should be far enough west that only the southernmost portions of the state will be affected by another afternoon of scattered thunderstorms.

As far as snowmelt, there be a couple more days of melting (mostly south, central Colorado) before temperatures drop off enough to stall the melting. While most gages are on the rise, all major rivers are still well below action stage. Peaks in streamflow tend to occur in late May into June for the larger rivers. However, there are a couple gages that are near action stage on smaller rivers that should be watched closely this week. The first is Mancos River near Mancos in Montezuma County, and the second is Surface Creek in Pitkin County. Neither are expected to produce major flooding, but smaller rivers at lower elevations had some minor flooding issues during the last rainfall event.

Event #1: Tuesday (5/7) – Friday (5/10)

Elevated/No Apparent Threat as the cutoff low moves into the four corners region and helps provide lift and moisture for widespread showers, thunderstorms and snow.

Heavy cloud cover and light rain is expected by Tuesday morning as the low pressure system moves into the Four Corner region and moist, upslope flow continues. Showers and thunderstorms are expected to increase into the afternoon on Tuesday. A couple of severe storms may be possible out east. Rain continues into Wednesday with easterly flow and moisture in place, which may cause some issues for recent burn scars. By Wednesday night, temperatures are expected to drop drastically behind a cold front, which should bring the snow level down to 6-7K feet. A bit of a break with precipitation on Wednesday night, though storms are likely again Thursday afternoon. The unsettled pattern will finally start to ease up and there will be a downtick in coverage by Friday. At that time, only scattered showers and a few isolated thunderstorms are expected over the southern border of Colorado. Flooding is not expected at this time though burn scars may have some issues Wednesday before temperatures drip below freezing.