Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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335 FXUS65 KGJT 192115 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 315 PM MDT Sun May 19 2024 .KEY MESSAGES... - Isolated to scattered showers and storms are expected again on Monday, mainly north of I-70. Gusty outflow winds and hail will be the main risks from any stronger storm. - Dry, warm, and breezy weather will continue across the southern half of the CWA on Monday. Gusty winds of 35 to 45 mph will be common, especially in the higher elevations. - A larger system moves through Monday night into Tuesday, bringing fairly widespread precipitation and much cooler temperatures. Drier weather returns on Wednesday before another system approaches late in the week. && .SHORT TERM /THROUGH MONDAY NIGHT/... Issued at 315 PM MDT Sun May 19 2024 Scattered showers and storms have fired across northeast Utah and northwest Colorado as expected this afternoon, all in the vicinity of a stalled nearby surface boundary and a subtle shortwave aloft. These showers and storms are also taking advantage of a moist and unstable environment, characterized by a belt of PWs near 150 percent of normal and SBCAPE of 250 to 500 J/kg. Rounding out the parameter space is roughly 20 to 30 kts of effective shear, which is helping to loosely organize updrafts. As a result, showers and storms have become fairly sporty this afternoon, producing gusty outflow winds of 45 to 55 mph and some small hail in spots. Despite the above normal moisture across the entire column, the very lowest part of the atmosphere is still pretty dry... as evidenced by inverted V profiles on forecast soundings. This will only make outflow wind gusts more efficient at reaching the ground through the afternoon and early evening hours. The stalled surface boundary is not expected to move much over the next 24 hours, and additional shortwaves out ahead of the main trough digging southward across the Pacific Northwest will allow additional rounds of showers and storms to develop this evening, overnight, and into the day on Monday. By Monday afternoon, the deepening trough to our northwest will begin to phase with a potent positively tilted shortwave over Baja California, which will extend a very strong upper speed max northward across the Four Corners states. Combined with daytime heating and strong boundary layer mixing, a very breezy day is in store across most of the CWA, especially in southeast Utah, southwest Colorado, and the higher elevations. Gusts of 35 to 45 will be common Monday afternoon and evening. While we did consider a Wind Advisory, ultimately decided to hold off for now given winds should mostly top out just below criteria. Later shifts can re-evaluate as necessary. The winds will also lead to near critical fire weather, especially with relative humidities in the single digits and teens from the I-70 corridor southward. Fuels have not been deemed critical though, so no fire weather highlights have been issued. The boundary separating the moist air across northeast Utah and northwest Colorado and the dry air southward will again be the focus for additional scattered showers and storms Monday afternoon and evening. Forecast soundings and CAM guidance are hinting at storms potentially becoming strong to borderline severe along and north of the US-40 corridor towards the CO/UT and CO/WY state lines given adequate instability and more deep layer shear to work with. Strong and gusty winds would still be the main threat with any stronger storm, but plenty of CAPE in the hail growth zone and fairly low wet bulb zero heights could result in more of a hail threat as well. Certainly something to keep an eye on. By Monday night, the cold front will start pushing into northeast Utah and northwest Colorado as the deep parent trough now over the northern Rockies begins to swing eastward. This will result in the development of more widespread precipitation, and a push of much colder air into Tuesday. For more on that, continue on to the long term discussion below. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Issued at 315 PM MDT Sun May 19 2024 On Tuesday a closed low pressure clips northern portions of the forecast area as it swings eastward. With moisture still in place this should result in another round of showers and storms across the region. This system should force any lingering boundaries out of here leaving us with northwest flow. Cold air, cloud cover, and showers will see afternoon highs Tuesday some 15 degrees cooler than previous days. Due to this cold air aloft snow levels drop to about 8-9 kft. Accumulating snow will battle the high sun angle, but there could be a few inches in the high country on Tuesday. Impacts if any should be confined to the mountain passes. Conditions start to dry out Tuesday night as the low pressure proceeds over the Plains. Flow shifts back to the southwest on Wednesday as another system approaches from the Pacific Northwest. For the most part Wednesday will be dry, but could see enough lingering moisture for showers along the Divide. There is still minor disagreement about this next low pressure, but most of the models keep the track north of us over Wyoming. None the less this system should push another cold front into our area. Showers and storms associated with this front will favor the northern half of the forecast area through Thursday night. The end of the week looks to remain active with multiple waves diving into the persistent western CONUS trough. The solutions diverge at this point, but it appears this pattern could continue to keep us away from the summer heat and bring us occasional cold fronts with some rain. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1147 AM MDT Sun May 19 2024 A stalled frontal boundary has kicked off another round of isolated to scattered showers and thunderstorms north of I-70. Winds aloft remain strong and are expected to mix down to the surface with gusty southwest winds around the region. Terminals will see winds gusting around 25-35 mph, with a few stronger bursts from thunderstorm outflows. Small hail remains a concern as well this afternoon. Some showers will linger near the Wyoming border tonight with dry weather / VFR conditions elsewhere into Monday morning. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...MDM LONG TERM...KJS AVIATION...TGJT