textproduct: Grand Junction

KEY MESSAGES

- Snowfall picks up again this afternoon and a Winter Weather Advisory remains in effect for the ElkHead and Park Ranges from noon Friday morning.

- Multiple rounds of snow are expected in a progressive pattern over the coming days. Much of this snow will favor the northern half of the forecast area.

- Temperatures are expected to remain mild.

SHORT TERM /THROUGH FRIDAY/

Issued at 308 AM MST Thu Dec 26 2024

Moisture from the Christmas Day storm trapped beneath night time inversions has resulted in a a broad area of stratus and light fog for much of northwest Colorado, the Gunnison Valley and a portion of southwest Colorado. Meanwhile, very light snow lingered over the northern mountains according to the SBS Ski webcams. A weak transitory ridge developed over the area overnight ahead of a short wave trough moving over the Pacific Northwest.

The ridge will shift east of the area this morning as the short wave moves across the northern Great Basin. As this disturbance crosses Utah this afternoon the area will see another round of showers develop with mountain snow becoming widespread later this afternoon. Mild temperatures in the current regime continue to support valley rainfall.

The short wave passes over the forecast area this evening which should bring the heaviest snowfall rates as orographic lift combines with upward dynamic forcing. However, snow will continue overnight as orographic northwest flow milks the saturated 700-500 mb layer. Snow rates drop off and will likely end for some areas Friday morning as subsidence gradually dries the 7-5 layer. Clouds and the milder airmass will continue to buoy overnight lows.

The latest models appeared to be more progressive than the 12Z run and as a result, the timing of the Winter Weather Advisory for the Elkhead and Park Ranges appeared to be a bit off. Therefore, given event timing described in the previous paragraph, shifted the advisory start time from this evening to this afternoon and ended it at noon Friday as opposed to midnight Friday.

The Friday morning downturn in mountain snowfall will be short- lived as a more significant surge of AR moisture reaches the region on the nose of the 150+ Kt polar jet ahead of the next short wave trough in northwest flow. Consequently, snowfall becomes widespread over the mountains once again with the heaviest snow expected in the northern mountains where moisture is expected to be deepest. Despite clouds and precipitation, the airmass remains mild and highs will continue to run above seasonal norms.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Issued at 308 AM MST Thu Dec 26 2024

Snow will continue Friday evening in northwest flow as the more robust trough drops down the Front Range, allowing for additional snowfall accumulation favoring the northern and central Colorado mountains. Some light snow could linger into Saturday morning but rates should drop off after midnight Friday night with some additional light accumulation Saturday morning over the Park Range, favored in northwest flow. Ridging will try to build in across the Desert Southwest, providing a bit of a break during the day on Saturday. There is a weak wave that clips the north in northwest flow, providing another round of snow to the Park Range Saturday evening through Sunday morning. Feel like the snow generated Saturday night may be more orographically driven with little in the way of dynamic forcing, so feel the current blended guidance is a bit overdone for this period. The high pressure over the Desert Southwest gets flattened by another series of troughs moving into the PacNW and across the Intermountain West, allowing for more zonal flow late this weekend into early next week. The first in this series of waves drops in from the northwest and down the Plains Sunday night into Monday afternoon, with the northern and central Colorado mountains favored for snowfall. This trough looks to drag a cold front through the area, so temperatures could be much cooler to start next week as we transition from 2024 into the new year. Beyond Monday, the GFS is indicating an additional trough dropping further south through our area on Tuesday, bringing another round of snow with cooler temperatures while the ECMWF keeps us drier with more influence from the southwest high pressure ridge. Speaking of temperatures, they will warm up this weekend as mild, Pacific flow continues with highs approaching 10 to 15 degrees above normal by Sunday. Cooler air arrives with the trough passage Monday, dropping highs back to near to a few degrees below normal. How far south these troughs drop will determine exactly how much colder it gets, which is still in question due to model discrepancies.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1002 PM MST Wed Dec 25 2024

Occasional snow showers mainly over high terrain and areas along the divide will continue through Thursday morning but overall expect to see BKN to OVC skies as low stratus develops across much of the area due to recent precipitation. Could see brief drop to MVFR or IFR in showers and potential fog overnight in areas of recent precipitation although confidence is too low to include in TAF. Some areas become scattered overnight as the latest system exits to the east but clouds will increase Thursday late morning into the afternoon as another disturbance moves in with some snow showers possible over the high terrain.

GJT WATCHES/WARNINGS/ADVISORIES

CO...Winter Weather Advisory from noon today to noon MST Friday for COZ004. UT...None.