Sunrise 6:14 AM   Sunset 7:42 PM Moonrise 2:49 PM   Moonset 4:11 AM

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FXUS65 KBOU 181020 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 420 AM MDT Thu Apr 18 2024

KEY MESSAGES

- Colder with a few light showers today.

- Chance of accumulating snow Friday afternoon into Saturday morning.

- Drier and warmer early next week.

SHORT TERM /Through tonight/
Issued at 420 AM MDT Thu Apr 18 2024

The shower band that brought a few hours of steady light snow to areas north of Denver overnight is shrinking, fading, and moving east now. There's some very light precipitation, mostly snow, in an area ahead of the band, including the Denver metro area. Some lighter showers have developed over the Colorado/Wyoming border area from Cheyenne westward, and there are a few light showers coming into the central mountains from the west. Most of this is being driven by little ripples in the mid/upper level winds, though some flurries/drizzle may also be generated in the stratus layer below the frontal inversion.

All of this will be shifting east this morning, with a general decrease in the mid/upper level forcing and a little drying aloft.
Low levels probably won't change much as east to northeast winds will continue. This adds up to a decreasing chance of showers this morning, but still a non-zero chance this afternoon and evening.
Right now it looks like the banded structures will be headed mostly north and south of Denver. The shower chance should decrease further late tonight as there starts to be some warming and drying that will shrink the stratus layer and end the showers aloft. We may start to see holes in the clouds later tonight.

We bumped up PoPs a bit in some places, but it's for pretty light amounts. Persistent showers from about I-70 south into Park county and the gentle upslope into the east side of the Front Range are the two areas most likely to see a little snow accumulation today.
Temperatures probably won't climb much under the plains stratus.
The evening shift cut temperatures several degrees, and we cut a few more. There still should be a little warming, but lower 40s will likely be all we'll get.

LONG TERM /Friday through Wednesday/
Issued at 420 AM MDT Thu Apr 18 2024

The region will remain under zonal flow aloft Friday with weak synoptic ascent with the main upper jet(exiting) to the north and east. Expect light rain/snow showers in the morning along the northern border areas and some snow showers in the mountains.
Temperatures will be warmer than Wednesday with some rebound in the 700mb temperatures. This bring highs in the 50s across the plains and 30s/40s for most of the high country.

The next "wave" of precipitation will come late Fri afternoon through Saturday. This will be supported by another embedded shortwave trough in the flow aloft and the upward motion provided by the right entrance region of a jet. A front will be the initiator as it pushes across northeast Colorado from the north in the 20-00z timeframe. This will bring a push of northeasterly upslope winds behind it. Showers develop in the mountains first in the afternoon with steepening lapse rates and increasing moisture. Once the front is through by early evening and upslope is established, precipitation chances increase across across the lower elevations as well. Given the nature of the upslope flow, the higher chances will be confined to the typical NE upslope favored areas (Palmer Divide, south Denver metro, west I-25 corridor). Can't rule out the potential for some more organized shower banding with jet dynamics in place.

Shower activity continues overnight into Saturday. With the help of the cold air advection behind the front, temperatures generally drop toward the freezing mark across the lower elevations. Rain will begin to mix with and change over to snow Friday evening. There are differences among model guidance in how cold the air is and how far south and west it extends. This then results in uncertainty in snow amounts and some variance from run to run. Overall snow accumulations will follow the general upslope pattern favoring the Front Range, Palmer Divide and areas adjacent with some bands extending further onto the plains. Ensemble means keep totals on the lighter side at the lower elevations (< 3"). Front Range mountains/foothills could see moderate amounts at this point. We'll have more info on totals as this gets closer.

Synoptic subsidence works in Saturday afternoon/evening, gradually decreasing showers on the plains. Residual moisture and afternoon instability will support showers in the mountains. An upper level ridge moves eastward into the region on Sunday drying out the plains and bringing highs back into the 60s to near 70. A quick wave moves to the north bringing showers to the high country. Similar story for Monday with mainly dry conditions on the plains with mild temperatures and another wave of afternoon showers in the mountains.
By Wednesday, highs across the plains rise well into the 70s.

AVIATION /12Z TAFS through 12Z Friday/
Issued at 420 AM MDT Thu Apr 18 2024

MVFR conditions are expected through this evening. There will be areas of IFR, mainly through 16z. Most shower activity is expected to remain north of the Denver area, though some light rain showers or drizzle are possible especially early this morning. The low clouds will likely break up by 12z Friday.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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