Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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963 FXUS65 KGJT 111725 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 1125 AM MDT Sat May 11 2024 .KEY MESSAGES... - Widespread showers and thunderstorms are expected today as a system moves through the region. Soaking rains are possible at lower elevations, and a few inches of accumulating snow are expected above 9500 feet. Little in the way of impacts are anticipated. - An unsettled weather pattern remains in place through the coming week, with chances of mountain showers and thunderstorms each afternoon. More widespread activity returns Tuesday into Wednesday - A gradual warming trend will bring near normal temperatures tomorrow, and above normal temperatures from Monday onward. && .SHORT TERM /THROUGH SUNDAY/... Issued at 241 AM MDT Sat May 11 2024 The cutoff low pressure that has been dominating our weather the last few days is finally beginning to nudge eastward. This movement is pushing a corridor of enhanced moisture ahead of it which, combined with some little wiggles in the flow, has driven showers and thunderstorms over the San Juans tonight. These showers are expected to persist well into the morning, becoming more widespread as the cutoff low continues its trek east and the main vort max associated with it moves overhead this afternoon. Until that point, aside from the clouds and showers over the southern mountains, skies will remain mostly clear with near-normal to slightly below normal morning low temperatures. Moisture remains on the higher side as we move into Saturday, with last night`s 00z sounding showing a PWAT of 0.49 inches, which is right around the 75th percentile for PWATs at this date and time. Expect to see this value continue to rise through the day today as the low pressure tracks overhead. Diurnal heating and the moisture already present would be plenty to kick off showers and thunderstorms over the terrain this afternoon, but with the low pressure moving overhead and adding in some dynamic support as well, today will see the highest shower coverage we`ve seen so far. The southern and central mountains will be favored to see the most activity, but the majority of eastern Utah and western Colorado will see at least a passing shower or storm today, along with increasing cloud cover in the afternoon. These showers will be capable of producing light to moderate rain rates and even some small hail and lightning. Snow levels are expected to remain between 9000 feet and 9500 feet today, but strong showers will be able to drive that down briefly, so while the highest elevations will be the only ones to see accumulating snow, adjacent high valleys will at least have the potential to see flakes. Snow amounts have come up just a touch for the San Juans and into the Elks, West Elks, and Sawatch ranges, with totals now 3-5 inches, with locally higher amounts in the 6-8 inch range possible. Even still, impacts will be minimal, with just wet roads expected over the mountain passes. Activity will once again linger into the evening and overnight hours tonight, as the low continues east and just a bit of upper level support remains overhead. The center of the low moves east of the Divide by midnight, however, so do expect to see a slow tapering of activity from midnight through sunrise Sunday. Subsidence will move in behind the low, keeping things generally dry for much of eastern Utah and western Colorado on Sunday, with the exception of the Divide, where the influence of the low will remain longest, along with the best moisture, keeping isolated to scattered showers and storms in the forecast through Sunday evening. Increased cloud cover and shower activity today will keep temperatures 3-5 degrees below normal for much of eastern Utah and western Colorado, along with near to slightly above normal low temperatures. Tomorrow, with clearing skies and subsidence moving in, temperatures are expected to warm to near or a few degrees above normal, continuing the gradual warming trend we`ve seen over the last few days. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Issued at 241 AM MDT Sat May 11 2024 Any lingering showers from Sunday afternoons convection looks to come to an end after sunset for a relatively quiet Sunday night as that pesky low that is having a stronghold over our weather lately exits further east into the central Plains. Drier air will slowly advect in as a ridge of high pressure tries to build over the Great Basin. This ridge is not overly that strong and quickly gives way to a series of shortwave troughs moving down from the Intermountain West into the northern Rockies, keeping the weather pattern active and unsettled through much of the coming week. These shortwaves will keep the threat for daily afternoon and evening showers and thunderstorms in the forecast, focused mostly on the higher terrain Monday. The peak period of moisture and more widespread convection looks to hone in on the Tuesday and Wednesday time period as a more robust trough drops southward on Tuesday with its positively tilted trough axis swinging through the area from northwest to southeast on Wednesday. Meanwhile, there is a cut off low over the Desert Southwest during this period but it appears to become a non player as it is washed out and absorbed by this trough diving out of the northwest. Is it too early to be talking about PWAT (Precipitable Water)? Of course not! Moisture levels appear to peak on Tuesday as this initial surge moves out ahead of the trough passage on Wednesday, as PWAT anomalies rise to 160 to 200 percent of normal for mid May on Tuesday afternoon. This equates to PWAT near 0.6 to 0.7 inches, which is sufficient for some potential heavy rainers. Needless to say, expect showers and thunderstorms to be more widespread to numerous Tuesday and Wednesday. Storms may linger into Thursday due to lingering moisture and forcing from the trough as a cut off low will remain over Arizona by then, but storms should favor the central and southern mountains and adjacent valleys. Drier air tries to push in from the north and west on Friday as a ridge of high pressure tries to build over the western states and expand into the PacNW and Intermountain West according to the GFS but the ECMWF seems to have other ideas on the synoptic pattern. Models are not in the best agreement on what`s going to happen beyond Tuesday so low confidence in the forecast beyond mid week. Talking about temperatures, we will see some decent WAA Monday and perhaps into Tuesday before the moisture increase results in more widespread development of showers and storms. High temperatures will be around 5 or so degrees above normal early this week, cooling down slightly late Tuesday and Wednesday into Thursday with the trough passage to near to 5 degrees below normal. If the dry air pushes back in late this week, we are due to see highs creep back up to above normal levels. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1119 AM MDT Sat May 11 2024 Showers and a few storms continue to stream up from the south and will continue to do so as an area of low pressure slowly shifts eastward. All terminals along and south of I-70 have VCSH in their TAFs with some VCTS and -SHRA/-RA also included. Under and near the heavier showers/storms, some MVFR/IFR is possible though it should not last for long. Broken to overcast skies will be the rule today in those same areas. Best chances for ILS breakpoints to be reached will be KASE, KEGE, and KTEX today though other sites may flirt with those values as well. After sunset, shower activity will slowly decrease and skies will slowly clear except over mountainous terrain. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...BGB LONG TERM...MDA AVIATION...TGJT