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FXUS65 KPUB 052045 AFDPUB

Area Forecast Discussion National Weather Service Pueblo CO 245 PM MDT Sun May 5 2024

KEY MESSAGES

- Red Flag conditions continue through 7 PM this evening for the San Luis Valley and return across all of southern CO where fuels are deemed critical for Monday.

- High winds will spread across the region tonight through Monday morning.

- Brief round of wind driven snow expected for the Continental Divide late tonight through Monday morning.

- Critical fire weather conditions will be widespread for the San Luis Valley and portions of the plains during the afternoon and evening hours on Tuesday and Wednesday.

- Very strong and gusty winds (near High Wind Warning criteria for some areas) are expected on Tuesday. Blowing dust will be possible across the lower elevations.

- A few showers and high elevation snow showers will be possible for areas mainly north of Highway 50 on Tuesday through Wednesday.

- Scattered showers and thunderstorms, with high elevation snow, will be possible on Thursday through Saturday, along with cooler temperatures.

SHORT TERM /THROUGH MONDAY NIGHT/
Issued at 241 PM MDT Sun May 5 2024

Upper low over NV/UT will move eastward across northern CO tonight and into western NE by Monday afternoon. This will send a brief round of wind driven snow into the mountains along the Continental Divide tonight before snow diminishes from south to north Monday morning. Still getting around 4 to 8 inches across the higher peaks and passes with the potential for brief hazardous travel impacts during the overnight hours. Have issued a short duration winter weather advisory to highlight this potential.

A bora cold front will cross the mountains late tonight into Monday morning spreading a round of high winds across the southeast mountains and into portions of the I-25 corridor around dawn on Monday. Gusts in the 60 to 75 mph range will be possible as the front crosses the mountains and strong downward forcing briefly transports higher momentum aloft to the surface. It will remain windy through the morning, but the high wind potential looks to diminish rapidly after 15z. Will upgrade the High Wind Watches to High Wind Warnings with the afternoon package. There is the potential for high wind gusts to impact portions of western Pueblo and southwest El Paso as well though coverage looks limited to locations west of I-25 and close to the mountains.

Very dry air behind the front will overspread southern CO on Monday resulting in a return of critical fire weather conditions across southern CO for locations where fuels are deemed critical by land management agencies. This will be confined to the San Luis Valley, the lower slopes of the Wets and Sangre De Cristo Mountains, the Wet mountain valley, and the Comanche grassland locations of Otero, eastern Las Animas and Baca counties where greenup has been delayed due to dry conditions this spring. However, given the magnitude of the winds on Monday, any activities which could start a wildfire is discourages as any fuel sources available to burn could become volatile with such strong winds.

Otherwise, temperatures will remain mild, though cooling to a little below climo for Monday behind the front. Winds tail down in the afternoon though it will still remain windy with critical fire weather conditions. Think any blowing dust will be confined to the morning hours with the strongest winds associated with the frontal passage. -KT

LONG TERM /TUESDAY THROUGH SATURDAY/
Issued at 241 PM MDT Sun May 5 2024

Monday night through Wednesday...

After passage of the bora front Monday night, there will be a lot of forward shear on the backside of the front within the westerly flow at the 700 mb level moving over the entire CWA on Tuesday, with some 50 kt pennants showing up over the southern I-25 corridor with some of the deterministic models. This is going to translate to very strong and gusty winds down to the surface, which could occasionally reach High Wind Warning criteria over certain areas by later in the day on Tuesday. Along with this will be blowing dust possible across the lower levels, as well as critical fire weather conditions for the San Luis Valley, and portions of the plains by later in the afternoon and through the early evening once RH values tank. The winds look to become the strongest right around peak heating in the middle of the day once there is the best mixing present. Although, confidence of persistent High Wind Warning criteria is not high at this time, given that cross sections display only forward shear, and thus deep mixing would be the only forcing that could get these stronger winds down to the surface.

Stronger winds will be more likely across the higher elevations of the Sangre de Cristo Mountains, which appear at this time to have a higher probability of needing a High Wind Warning vs other mountains. Again, there is still some uncertainty of this, depending on the position of the longwave trough and where the strongest 700-500mb flow will be. The San Luis Valley will also be another area in question for needing a potential High Wind Warning on Tuesday, if deep layer mixing does occur. With winds as the main concern, precipitation will be generally sparse on Tuesday, and more or less confined to areas north of Highway 50. The northern Sawatch and Mosquito Ranges will be the locations most likely to receive any measurable precip, with a few inches of snow possible. Downsloping winds will also adiabatically warm up the lower levels, with highs topping out in the upper 70s to low 80s across the plains. The higher terrain will be relatively cooler, and either at, or slightly below, the seasonal average for this time of year.

By Wednesday, a frontal boundary will move through with winds shifting more out of the northerly direction over the plains. This will help to allow for colder air advection, with temperatures being anywhere around 10 to 15 degrees cooler for highs. Strong and gusty winds will continue to be out of the more west to northwesterly direction over the higher terrain, yet not as strong. There will still be some showers possible over the central mountains, and also for areas of the Pikes peak Region (PPR), Ramparts, and Palmer Divide. There will still be widespread critical fire weather conditions over the San Luis Valley, although the northerly flow for the plains will help to mitigate fire concerns over the plains, although there could still be some areas which are vulnerable due to critical fuels over eastern Las Animas County that may need fire weather highlights for the afternoon hours.

Thursday through Saturday...

Chances of precipitation for all of SE Colorado will ramp up during this period in the forecast, along with cooler temperatures. The pattern will remain unsettled as there will be a deepening major shortwave trough that is going to be slowly progressing towards the south and over the region on Thursday, then splits with an upper level low retrograding back towards the southwest on Friday. There is a general consensus between the deterministic models as to what this U/L low will do once it becomes cut-off somewhere over the Great Basin region, although there is some deviation between the solutions. The GFS has this remaining further to the north, and then moving towards Colorado with a much more extensive mid-level moisture advection. The Canadian is more similar to what the GFS is showing, while the ECMWF is a much drier solution with the position of the U/L low being further to the southwest and only allowing for mid-level moisture to be more confined to the higher terrain with the plains remaining mostly dry. There is still some time to allow models to resolve this feature better in the upcoming days, and determine if the plains will be either more wet or more dry for both Friday and Saturday. It will be overall cooler, with highs running anywhere from 5 to 10 degrees below the seasonal average for most locations, especially on Friday. -Stewey

AVIATION /00Z TAFS THROUGH 00Z MONDAY/
Issued at 241 PM MDT Sun May 5 2024

Strong southerly winds will continue this evening with gusts up to 35 kts. Winds will decrease this evening but remain elevated and southerly through the night with the possibility of some periodic wind shear at KCOS overnight before strong winds increase again towards dawn Monday. All three terminals should see winds increase from the west gusting up to 40-45 kts on Monday. Conditions will remain VFR. -KT

PUB WATCHES/WARNINGS/ADVISORIES
Winter Weather Advisory from 9 PM this evening to 10 AM MDT Monday for COZ058-060.
Winter Weather Advisory from 9 PM this evening to 6 AM MDT Monday for COZ066-068.
Red Flag Warning until 7 PM MDT this evening for COZ224.
Red Flag Warning from 10 AM to 10 PM MDT Monday for COZ224-225- 232-233-237.
Fire Weather Watch from Tuesday morning through Tuesday evening for COZ224-225-232-233-237.
High Wind Warning from 9 PM this evening to noon MDT Monday for COZ072>075-079-080.
High Wind Warning from midnight tonight to noon MDT Monday for COZ078-081>083-087-088.

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