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FXUS65 KBOU 030234 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 834 PM MDT Thu May 2 2024

KEY MESSAGES

- Isolated showers on the northeast plains tonight.

- Another round of showers and storms late Friday/early Saturday.

- Warmer and breezy over the weekend.

UPDATE
Issued at 834 PM MDT Thu May 2 2024

A narrow band of showers has developed on the northeast plains, and appears to be driven by just enough mid level moisture and the right entrance region of an upper level jet. Due to the proximity of the jet, we've extended the lower pops into the early morning hours. Otherwise, not many changes needed tonight with partly cloudy skies and relatively cool temperatures. We may be a little warmer tomorrow, with only a mid to late afternoon arrival of the cold front and gusty winds, so nudged high temperatures up a couple degrees over most of the plains.

SHORT TERM /Through Friday/
Issued at 245 PM MDT Thu May 2 2024

Winds are starting to decrease as the surface gradient and winds aloft decrease. Mixing looks like it will produce lower dew points than earlier expected, so we've trimmed back PoPs for the late afternoon/evening hours. There will likely still be some isolated weak showers, and a thunderstorm isn't out of the question, but it won't be much and should stay east of the Front Range cities.

We'll have enhanced southerly drainage winds off the Palmer Divide later tonight, then southwest winds will increase in all areas during the morning. The previous forecast looks pretty good with gusts of 25-35 mph in most areas in the afternoon. The cold front should be moving across the area before 00z, with similar wind speeds from the north behind the front and temperatures dropping into the 50s. With the cold front moving into dry air, there's still not a lot to work with for convection. There will likely be some showers/storms with the front out near the eastern border, but it's more questionable further west and we've backed off the PoPs a bit. Some increase in mid level moisture and instability should also help promote scattered showers and a few storms over the northern mountains, again with lower chances further south.

LONG TERM /Friday night through Thursday/
Issued at 245 PM MDT Thu May 2 2024

An active weather pattern will continue across the central CONUS over the next several days, though for Colorado this will likely mean more wind than anything else.

We'll start the weekend with mostly dry weather under southwesterly flow aloft. Guidance is in reasonably good agreement with another round of isolated to widely scattered afternoon showers/storms, mainly across the high country into the adjacent plains. With near normal temperatures forecast (highs in the mid/upper 60s), snow levels will remain near or above 10,000ft for the high country.

Sunday should be the warmest day of the extended period as strong southerly flow develops in the warm sector of a broad, strong trough over the western U.S. Temperatures are forecast to warm into the mid to upper 70s across the region. Despite the warmer temperatures, only a few high-based showers/storms expected at this point... as moisture return in our area remains meager.
ECM/GFS ensembles have less than 20% chance of SBCAPE > 500 J/kg anywhere in our forecast area, with surface dew points generally remaining in the low 40s. We'll have to watch trends there, as moisture is the main limiting factor in an otherwise favorable convective environment.

The upper trough is expected to eject from the Four Corners region into the northern Plains by Monday, ushering in cooler temperatures to the region. With the storm track expected to be north of our forecast area, this would suggest some moisture for the mountains and along our northern border, with mostly wind elsewhere.

Wind will be the theme for Tuesday into Wednesday as zonal flow established behind the trough axis. The gradient flow should slowly relax through the week, though there's a decent amount of spread across the multi-model/ensemble suite of guidance. Guidance then hints at a return to a cooler/wetter pattern by the latter half of the week as a broad trough settles over the West. Have kept the current NBM blend that highlights near/below-normal temperatures along with "Chance" PoPs across most of the forecast area by Thursday.

AVIATION /00Z TAFS through 00Z Friday/
Issued at 549 PM MDT Thu May 2 2024

VFR will prevail through Friday. East/northeast winds are in place, and there's good confidence winds will slowly transition to more of a east/southeast winds through 06Z this evening.
Overnight, eventually southerly winds are expected to increase with gusts to 20-25 knots expected at KDEN and KAPA by/before 12Z.
After about 15Z Friday, there's more uncertainty in the wind forecast, but we do expect a transition to more southwesterly winds 16Z-20Z as long as we warm and mix sufficiently ahead of a cold front. That cold front could arrive anywhere from 21Z-01Z per recent model output, but typically the earlier arrivals win out so we'll go toward the front of that time. Wind gusts up to 25-30 knots possible ahead of the front, and then closer to 35 knots or briefly 40 knots behind it with a distinct northerly wind shift.

Mid/high level cloud decks will scatter out this evening. On Friday mid level clouds mostly above 10,000-12,000 feet AGL will thicken in the afternoon. The chance of showers will be limited by the high cloud bases. Behind the front, ceilings will likely (60-70% chance) lower to 3,000-5,000 feet AGL by 02Z-06Z, with a low probability (20% chance) of dropping under 2,500 feet AGL.

FIRE WEATHER
Issued at 245 PM MDT Thu May 2 2024

Fire danger will increase later this weekend into next week as an extended period of dry and windy conditions develops. Ensemble probabilities of >20kt wind gusts is nearly 100% from Sunday through Wednesday, with 60-100% probabilities of >34kt gusts Monday afternoon according to the 12z ECME. There are still some questions on how low RH dips each day in this period, and additional uncertainty in how dry fuels will get across the driest/windiest areas... but we'll be watching this period for potential highlights as we get closer to the weekend.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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