####018006302#### FXUS62 KGSP 032145 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 545 PM EDT Fri May 3 2024 .SYNOPSIS... Dry and warm high pressure moves off the Carolina coast as a front approaches from the west then stalls over our region for the weekend. This front will result in periodic thunderstorms and showers starting today and lingering through the weekend. A general summertime pattern sets up early next week, which will likely support scattered thunderstorm development each afternoon. && .NEAR TERM /THROUGH SATURDAY/... As of 520 PM EDT: Major change at this update is to reflect precip coverage in the next few hours, generally supporting lower PoP for most of the area. Convection has been on a downward trend in the last hour or so, along the persistent axis near I-77, seemingly being outflow dominant without enough instability or forcing to foster new development. Water vapor imagery and RAP analysis depict weak vort max over the CWA, which maintains some deeper cu west of that activity. This activity will move into the rain-cooled region and likely won't amount to much more, but remains worthy of an isolated or widely scattered shower mention. In the more unstable area from the Savannah Valley, Smokies and westward, area of rain with embedded storms will linger, but diminish nocturnally to some degree. At this point, main impacts are expected to be locally heavy rainfall, with whatever severe threat we had having peaked. The outflow wreaked havoc on our temp and dewpoint grids thru the evening; it is always tricky to get the grids back on track when guidance reflects current conditions as poorly as it did at the top of the hour, but we have done the best we could using HRRR and short-term consensus blend to make believable trends for the evening. Confidence is too low to say exactly how, but the increased sfc moisture from the activity could enhance low ceiling and fog potential in some areas toward dawn. For now we retain patchy fog wording in most zones. CAM guidance still shows an uptick in shower activity overnight in the continued moist and weakly forced atmos, with continuing southerly upslope flow. Coverage then continues to pick up through the day Saturday as forcing becomes better. Instability and shear will remain on the weak side, while forecast profiles show an even more saturated atmosphere. This suggests and even less chance of strong to severe storms, with a slight uptick in heavy rain potential. That said, the overall flood risk remains low given the relatively dry antecedent conditions. Highs will be near normal due to clouds and precipitation. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... As of 240 PM EDT Friday: The rest of the weekend looks active right into the first part of next week. A baggy upper trof overhead on Saturday night slowly lifts northeast with a short wave passage, and this bit of lingering forcing will be able to keep shower/thunderstorm activity on a slow wane into the early morning hours. Guidance suggests that it will never die off entirely, so the fcst retains some fairly high precip probs. That sets the stage for Sunday. Models show less forcing, but an uptick in the available buoyancy in the afternoon. That should make for a more thermodynamically-driven day, with better than climo coverage of showers and storms. Forecast soundings off the NAM show some pulse-severe wind damage potential with mid-level dry air and a shallow inverted-V, so it would not come as a surprise if it was a busier day than Saturday. A stronger short wave lifting northeast over the TN/OH Valley regions on Monday will continue to support diurnally-enhanced convection, so we continue with above climo precip probs. Temps look to be on the order of five degrees above normal. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 143 PM EDT Friday: The bulk of the medium range looks like a summer preview. After a baggy upper trof moves past Monday night, we should spend the remaining week underneath a low amplitude, relatively fast, WSW flow aloft. Within this flow, the model guidance shows a steady train of short waves moving through, mostly around peak heating each day, that will enhance our convective coverage each afternoon/evening. Overall, the air mass shows little change from one day to the next, as a wavy surface front will be strung out to our north in the WSW flow. Buoyancy will be modest and shear will be light, which suggests that chances for severe storms will be relatively low, but in such a pattern we eventually seem to manage to crank out a few pulse severe storms each day. Precip will be spotty and showery, which keeps the heavy rain threat at bay, but eventually there could be a few spots that start to see an increased risk of flash flooding, especially if a more coherent, stronger short wave comes along, such as what the GFS shows next Friday. Lots of uncertainty, though. Temps will remain in that 5-10 degree above normal range for most days, perhaps on the high side of that either Wednesday or Thursday, which one of those days might get a break in the wave train and thus reduced shower coverage and higher temps. && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... At KCLT and elsewhere: Convective activity diminishes somewhat this evening but returns overnight. Have PROB30s in place for that. Cig and vsby restrictions develop overnight as well, so have MVFR to MVFR before 12Z and IFR after 12Z. Light and variable wind expected overnight with S to SE wind for all but KAND, where it will be ENE, Saturday. Outlook: Enhanced moisture will combine with a weak/stalled front through early next week, resulting in a period of active/mainly diurnal convective weather each day. There will also be the potential for restrictions associated with widespread fog and/or low clouds each morning. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...RWH/Wimberley SHORT TERM...PM LONG TERM...PM AVIATION...RWH ####018009749#### FXUS65 KGJT 032148 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 348 PM MDT Fri May 3 2024 .KEY MESSAGES... - A system will brush the northern tier of eastern Utah and western Colorado today, bringing a few valley rain and mountain snow showers through this evening. Minor accumulations are expected with little to no impacts. - Scattered showers and isolated thunderstorms are possible late Saturday mainly in the mountains. Elsewhere expect warmer and dry conditions. - A strong system is expected on Sunday and Monday. It will bring widespread precipitation and strong winds. A High Wind Watch has been issued for much of eastern Utah and far western Colorado Sunday morning through Sunday evening. && .SHORT TERM /THROUGH SATURDAY NIGHT/... Issued at 348 PM MDT Fri May 3 2024 The cold front and upper level jet associated with the shortwave trough moving across the north is evident both on satellite and radar across the eastern Tavaputs in northeast Utah into northwest Colorado across the Flattops and into the northern Park Range. Some light showers are occurring in Craig and Hayden with rain at Hayden and rain flipping over to snow at Craig. Roads remain wet to dry according to webcams in that neck of the woods with trace accumulations on the grassy surfaces north of Craig where it's actively snowing. All in all, impacts remain minimal with maybe 2 to 5 inches of snow at the higher elevations of the Park Range but other than that, roads are expected to remain wet. Much different story along and south of I-70 where dry conditions are evident as relative humidity is in the teens with winds gusting in the 30s and 40s. Some locally higher gusts are occurring due to presence of virga showers but these gusty winds combined with the low relative humidities is leading to critical fire weather conditions at times. Temperatures today along and south of I-70 are sitting at 4 to 8 degrees above normal with areas north of I-70 cooler at 5 to 10 degrees below normal. Showers should come to an end early this evening as this shortwave over the north exits and the jet and cold front lift northward as a warm front by Saturday. Strong WAA is expected to take place Saturday afternoon with high temperatures warming by about 5 degrees along and south of I-70 with a warm up of 10 to 15 degrees from today across the north. Highs on Saturday will be 5 to 10 degrees above normal across most of the area. In this southwest flow, we will still see some breezy conditions, but winds are expected to be less than today as the jet lifts north and shortwave ridging takes place. The hi-res CAMs are indicating a bit of instability Saturday afternoon with a weak shortwave moving through the southwest flow, skirting the divide, so isolated to scattered thunderstorms are possible along the western Colorado mountains mainly along the divide. The gradient tightens Saturday night into Sunday ahead of a strong closed low that will dive southeastward from the PacNW into the Great Basin, settling over Nevada by Sunday morning. More on this in the Long Term discussion below. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Issued at 348 PM MDT Fri May 3 2024 By Sunday morning, eastern Utah and western Colorado are expected to be sandwiched between a ridge over the Great Plains and a strong Pacific Low dropping into the Great Basin. Wrapping around the base of this low, an intense southwesterly jet is expected to push into the region on Sunday. Strong winds are expected throughout the column, with 45-60 knots at 700mb and 95-110 knots at 250 mb. 700 mb is roughly the same altitude as some of the highest peaks in eastern Utah and western Colorado, so at a baseline, without factoring in any other daytime boundary layer mixing or virga shower enhancement, mountain locations are looking at least 50-60 mph gusts on Sunday afternoon, with valley locations looking at a baseline of at least 35-45 mph. But of course, we do have to account for those other factors, with strong diabatic heating allowing for deep boundary layer mixing to tap into and bring down the much higher windspeeds aloft, and virga showers breaking out ahead of the approaching cold front. With all these other factors accounted for, another 10-20 mph added onto the baseline makes a reasonable forecast, and is bared out by probabilistic guidance indicating a high probability (>99%) of gusts 45-55 mph in the valleys and 55-65 mph for the mountain regions. Peak gusts into the 60s across the lower elevations and into the 80s at higher elevations will also be possible especially across eastern Utah and far western Colorado zones. Eastern Utah will likely see some of the highest gusts as the jet remains overhead here the longest, providing ample time for deep mixing to tap into the jet and mix down stronger gusts through the day. A High Wind Watch has been issued for all valleys and most mountain areas of eastern Utah, as well as the lower valleys and mountains of far western Colorado where potential and confidence is highest for gusts 55 to 65 mph in those valley zones and gusts to 75 mph in those mountain areas. The High Wind Watch will begin 8 AM Sunday and last through 10 PM. Stay tuned for updates relating to this situation, and if you have outdoor furniture or other objects prone to being disturbed by strong, gusty winds, take the time now to prepare. The strong winds are just the first part of the impacts from this approaching Pacific low. An potent cold front is progged to move through late Sunday into early Monday morning, with substantially colder air moving in behind it. 700mb temperatures on Sunday morning are currently forecast around 4C, and within 24 hours are forecast to drop to nearly -7C. In reflection of this, snow levels will start out on Sunday morning at 9500-10000 feet, and will crash down to 5500-6000 feet by the same time on Monday. Only the highest elevations will see snow for the duration of this system, with most everywhere else beginning with rain showers on Sunday evening. Higher elevation valleys and lower slopes of the mountains will see a changeover to snow as the cold front passes. Current guidance doesn't keep much precipitation around in the post-frontal airmass, with the exception of orographic showers across the northern mountains, so little if any accumulating snow is expected for most locations. The northern and central mountains remain most favored to see the highest QPF, with totals 0.50" to 1.00" still in the forecast from Sunday morning through Monday night. The southern mountains may see 0.25" to 0.50" total through the same period, while the lower elevations can expect 0.25" or less. Most locations will see this all or mostly in the form of rain, although the central and especially northern Colorado mountains above 9000 feet will see a substantial chunk of that QPF in the form of several inches of snow. Travel over mountain passes may be a bit messy on Monday morning. Cold and unsettled northwest flow sets up in the wake of this low, which is forecast to eject into the northern Plains Monday evening. Some wrap around moisture from this low combined with favorable flow will keep light orographic showers going over the northern mountains. General troughiness is expected to linger from Tuesday on through the end of the week, with multiple waves riding the northwesterly to westerly flow over eastern Utah and western Colorado and keeping mountain showers a possibility most afternoons. The cooler air that moves in with the cold front late Sunday into Monday will remain in place through the late week period, with temperatures running 5-10 degrees below normal. That means highs in the 50s to low 60s across the lower elevations, with 30s-40s up high, until Friday when the blended guidance indicates temperatures warming to near normal values. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1120 AM MDT Fri May 3 2024 A cold front trying to drop into northeast Utah and northwest Colorado this afternoon will bring ceilings generally between 5000 and 10000 feet and a chance of showers. The main threat with any showers that do develop will be gusty and erratic outflow winds. The influence of this front is expected to stretch as far south as KEGE and KRIL, maybe KASE, but remaining terminals south of this will not see any direct impacts. Strong and gusty westerly to southwesterly winds will be the main issue across the entire region, with gusts of 30-40 knots possible especially along and south of the I-70 corridor. Due to a combination of these winds and ongoing work on the runway at KGJT, occasional reports of VIS less than 2SM and ceilings less than 200 feet are possible as dust interacts with the sensor. VIS is expected to remain past 6SM and ceilings above 10000 feet. Winds will diminish after sunset, becoming light and following typical diurnal patterns. VFR conditions will prevail through the next 24 hours. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...High Wind Watch from Sunday morning through Sunday evening for COZ001>003-006-011-017-020-021. UT...High Wind Watch from Sunday morning through Sunday evening for UTZ022-024-025-027>029. && $$ SHORT TERM...MDA LONG TERM...BGB AVIATION...TGJT