895 FXUS65 KGJT 212346 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 546 PM MDT Sat Aug 21 2021 .SHORT TERM...(Tonight through Sunday night) Issued at 248 PM MDT Sat Aug 21 2021 Isolated to scattered storms developed this morning further south than most if not all of the hi res CAM models indicated across southeast Utah and southwest Colorado. These storms tracked northeast over the central valleys by mid to late morning, with a few rumbles of thunder and light to moderate rain, much to the surprise of many. However, these storms were very quick moving and shallow with a dry sub cloud layer as indicated by the 12Z GJT morning sounding and forecast model soundings. As a result, precipitation amounts were very light (a few hundredths to a tenth of an inch at best measured at gauges and estimated by radar). So flooding concerns are minimal at this time and not much a concern. After doing a deep dive in the mesoanalysis to see what is sustaining this convection, looks like steep low level lapse rates and an axis of effective bulk shear ahead of the shortwave trough that is currently moving through the Pacific NW and northern Great Basin. Makes sense. An 80 kt jet streak associated with this shortwave trough will track across northeast Utah and northwest Colorado tonight, helping sustain convection across the north overnight into Sunday morning before dissipating by sunrise. Temperatures have also been trending much cooler than guidance due to the increase in cloud cover and shower activity that models weren't picking up on as well, so backed off the high temperatures today as well as the next few days as the warming trend seemed a bit too quick given recent trends. Sunday will provide much drier conditions behind this shortwave trough with westerly flow up north helping pull more smoke in from the California wildfires. A bit of good news in regards to the smoke though is the latest HRRR smoke model seems to push most of the smoke out of the central and southern areas and keeps it concentrated across the north, thanks to more of a southwest component to the upper level winds across that portion of the CWA. While that is good news for areas along and south of I-70, not so good news for those locales further north towards the Wyoming border. Temperatures will be a bit warmer on Sunday compared to today, but still around 5 degrees below normal. .LONG TERM...(Monday through Saturday) Issued at 248 PM MDT Sat Aug 21 2021 Eastern Utah and Western Colorado predominately fall under southwesterly flow through the long term period. The region will remain sandwiched between a broad rotation of high pressure over the Southern Plains and lower heights anchored to the PacNW for several days. A series of shortwave troughs rippling through the PacNW low may generate a nudge of lift and instability aloft, favoring isolated showers over higher terrain each afternoon. However, the remaining forecast area will indulge in a warming and drying period, with only increased surface winds from said disturbances. High temperatures will climb from the low 90's across valley floors on Monday to nearly triple digits by mid-week in some remote desert areas of southeast Utah. Meanwhile, PWATs drop to around 0.25" to 0.5" across the Western Slope by Wednesday. Forecast soundings reveal an inverted V signature deepening each day, which will limit the showers that do try to wring out precipitation from reaching the ground and thus, further enhancing surface winds. In addition, this atmospheric profile is favorable for deep, boundary layer mixing, which can transport some of the stronger momentum aloft down to the surface. Therefore, near critical RH levels and increased winds will increase the concern for localized fire weather conditions each afternoon; though, fuels may very well be a limiting factor (considering all of the rain we've received earlier in the week). Model consensus tries to push the stagnant low inland by the middle to end of the week, which will suppress the mid level high to the southwest. This synoptic set up could be more favorable for the CWA to tap into Sub Tropical moisture, though, confidence in the strength of the plume and its trajectory remain low, attm. Looking ahead to next weekend, ridging slides back into the Western CONUS, which would return a dry and warming trend back across the Western Slope. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 546 PM MDT Sat Aug 21 2021 Isolated to low end scattered showers and thunderstorms will continue this evening, mainly over the higher elevations in the north. However, a disturbance passing north of the region overnight may sustain some activity across the northern border zones late. There is little chance this activity will impact TAF sites however, so left VFR conditions at all TAF sites. LLWS is expected as winds diminish this evening and will impact KHDN, KEGE, KASE, KGUC and KTEX through sunrise. Breezy southwest winds develop for most sites again Sunday afternoon. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...MDA LONG TERM...ERW AVIATION...NL