Sunrise 5:39 AM   Sunset 8:11 PM Moonrise 3:39 PM   Moonset 3:18 AM

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FXUS65 KBOU 181140 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 540 AM MDT Sat May 18 2024

KEY MESSAGES

- Warm through Sunday. Isolated to scattered high based showers and storms this afternoon and evening with strong wind gusts possible.

- Breezier Sunday into Monday.

- Cooler, wetter pattern late Monday into Tuesday as a couple weak systems track across the region.

- Warming/drying trend for the second half of next week.

SHORT TERM /Through tonight/
Issued at 413 AM MDT Sat May 18 2024

Surface observations and radar indicate a cold front is moving southward through Wyoming and Nebraska and will move through eastern Colorado around sunrise. The cold front is rather weak and it's only impacts will be a wind shift to the northeast and high temperatures being about 5 F cooler today.

Water vapor imagery shows a shortwave trough over Montana that will miss our area to the north. There is zonal flow over Colorado and an area of mid level moisture is seen over western Colorado and Utah currently that will move directly over our forecast area this afternoon. Weak instability will form this afternoon due to decent lapse rates. The moisture and weak instability will combine with light upslope flow to create enough lift for showers and weak storms to form across a decent portion of our CWA These showers and storms will not have very heavy rain associated with them and likely minimal hail. However, they may create strong wind gusts up to 45 mph. The primary time for these showers and storms will be between 20-02Z. However, the area of mid level moisture will continue to be over Colorado through tonight so showers may continue past midnight.

LONG TERM /Sunday through Friday/
Issued at 413 AM MDT Sat May 18 2024

Warmer and relatively quiet conditions are forecast for Sunday as westerly flow aloft gradually strengthens. Temperatures should warm back into the 80s across most of the plains. Scattered showers/storms are possible across the high country, mainly north of I-70. Generally dry conditions are forecast of the I-25 corridor. Further east, a dryline is expected to setup near the CO/KS border into SW Nebraska during the morning hours and remain nearly stationary through the afternoon. A few storms should develop along the dryline in the afternoon as a weak shortwave traverses the area. Still quite a bit of uncertainty as to where that dryline does stall out and how much capping exists in our far eastern CWA Overnight CAMs paint a mixed picture, with a few of the HRRR members implying a severe risk here while the NCAR FV3 ensemble keeps any severe risk well east of our forecast area.

By Monday, a broad upper trough axis is expected to dive into the intermountain West, with a series of shortwaves ejecting into the Plains. Guidance has generally come into better agreement, with a strong lead shortwave tracking across the region Monday evening into Tuesday, with a secondary wave Tuesday into Tuesday night. As a result, the initial surface low is much stronger as it develops and shifts east into the plains... with a fairly strong cold front tracking across the forecast area late Monday evening.
Guidance develops a broad swath of precipitation across our northern border into Nebraska Monday night, with the ECME/GEFS suggesting the potential for >1" of precipitation in the far northeast corner of the state.

Tuesday will be much cooler behind the front, with highs likely remaining in the upper 50s to mid 60s across the lower elevations.
Modest moisture/instability lingers across the plains during the day... and combined with shallow upslope flow and larger scale ascent from the trailing shortwave, should promote widespread showers and a few storms across the Front Range and adjacent plains. This likely wouldn't be a washout day but enough for a nice wetting rainfall for a large chunk of the forecast area.

The second half of the week should be quieter under a weak zonal flow pattern. A few shortwaves tracking to our north could provide brief glancing blows - slightly cooler temperatures/higher PoPs - but there are significant differences in the the timing/location of these features beyond Wednesday. In general, a gradual warming trend is expected through Friday with isolated/scattered PoPs, mainly across the higher elevations.

AVIATION /12Z TAFS through 12Z Sunday/
Issued at 534 AM MDT Sat May 18 2024

A cold front will move through the terminals between 12-13Z.
Winds will turn to the northeast after the front with potential for brief gusts to 20 knots. Winds will likely become east to southeast by 18z and then more south to southeast later in the day at 10 to 20 knots. The concern for the terminals is in the afternoon when elevated showers and weak storms may produce gusty winds. The dry airmass will lead to the potential for gusts up to 35 knots if a storm were to go directly overhead. Visibilities and ceilings should stay in the VFR category. There will be drainage winds tonight with increasing southwest winds tomorrow morning.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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