Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/29/21

Area Forecast Discussion
National Weather Service La Crosse WI
1030 PM CDT Sat Aug 28 2021 .SHORT TERM...(This evening through Sunday) Issued at 314 PM CDT Sat Aug 28 2021 Main forecast concern is the severe weather potential heading into tonight and ongoing flooding issues, particularly across northeast Iowa. Surface low pressure sits along the eastern South Dakota/Nebraska border early this afternoon with a warm front extending northeast toward Lake Superior. Meanwhile a mid-level shortwave is lifting through the Upper Mississippi Valley with a decaying MCV or two lifting into far northwest WI and the MN Arrowhead out ahead of an approaching cold front. Clouds have blanketed much of the forecast area today, and decaying showers and storms worked through portions of northeast Iowa and southeast Minnesota earlier. This has once again kept temperatures on the cooler side for much of the area (70s to low 80s), with the exception of our far south (mid 80s to around 90) where sunshine broke through earlier. As a result of the clouds/rain, there`s a big pool of more stable air centered over Austin/Rochester area, but MLCAPE of 1000-2500 J/kg wraps around to our north/east/south. Other parts of central/northern MN have also been worked over by storms earlier. There will continue to be some theta-e advection into our area heading into tonight, so the question is whether that will be sufficient to allow the atmosphere to recover. The cold front looks to cross into our area more overnight, which also complicates the severe potential. RAP suggests a narrow ribbon of 1000-2000 J/kg MUCAPE immediately out ahead of the cold front this evening as it crosses MN, with instability steadily diminishing thereafter overnight. Does appear to be some overlapping deep layer shear overnight as the low level jet/moisture transport gets underway. Overall impressions of this setup is that the greatest severe threat appears to lie north and west of our forecast area. Convection will develop into a broken line along the front, gradually weakening as it encounters waning instability by the time it crosses into our north/west overnight. CAMs have been indicating this same trend with the line fizzling out as it works into our area. If storms hold together, pockets of enhanced wind would be the main threat, but can`t write off isolated hail and tornadoes with the low level jet contributing impressive low-mid level shear once again. Some lingering rain chances in our southeast Sunday morning as the front finally exits, perhaps a few rumbles of thunder. But otherwise that looks to be it for wet weather for awhile. A cooler day on tap as cold air advection gets underway with highs generally in the mid 70s to around 80. .LONG TERM...(Sunday night through Saturday) Issued at 314 PM CDT Sat Aug 28 2021 A much-welcomed quieter period of weather comes into play early in the week as high pressure over Hudson Bay builds into the area with a drier airmass. Baroclinic zone off towards Nebraska/Missouri may support a developing MCS or two through Monday into Tuesday, but guidance generally keeps that off to our southwest so the forecast has been trending towards dry. The high drifts off to our east with developing return flow late in the week, so may see rain chances start to return towards next weekend. All in all, looks like a pleasant, cooler, less humid week ahead with highs in the 70s to low 80s. && .AVIATION...(For the 06Z TAFS through 06Z Sunday night) Issued at 1030 PM CDT Sat Aug 28 2021 Cigs: mostly VFR bkn cigs through the night, but potential for a few hour window of MVFR around cold front slated to move through near 12z. Then, looking at SKC/SCT conditions for the afternoon/night. WX/vsby: line of storms have developed along cold front to the west, with other storms going up north of the TAF sites on the edge of the low level moisture transport. A few meso models suggest the line will hold together as it reaches KRST, with weakening trend as it nears KLSE. Will follow these trends and add more timing for a shra/ts chances. Any thunderstorm could produce enhanced wind gusts and heavy rain. Winds: southerly through the night, swinging west/northwest toward 12z as the cold front moves through. && .HYDROLOGY... Issued at 314 PM CDT Sat Aug 28 2021 Additional rainfall of around 1 to 4 inches fell since early this morning across portions of northeast Iowa and far southwest Wisconsin. Much of northeast Iowa was already fully saturated. Headwaters of tributaries there have already crested or are in the process. The Turkey River is experiencing major flooding at Spillville with moderate flooding downstream. Cedar River is also in moderate at Charles City. Lots of standing water reported across northeast Iowa, so have an areal flood warning in effect into this evening. Will continue to check in with county officials to gauge impacts in case this needs to be extended. With CAMs indicating tonight`s line of convection should weaken/diminish as it gets into the area, it appears the threat for additional heavy rain impacting already flooded areas is low. However, if any storms hold together to move over this high impact area tonight, flooding could be exacerbated in some areas. Drier weather Sunday and beyond will allow conditions to improve. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ SHORT TERM...Kurz LONG TERM...Kurz AVIATION....Rieck HYDROLOGY...Kurz
Area Forecast Discussion
National Weather Service Bismarck ND
931 PM CDT Sat Aug 28 2021 .UPDATE... Issued at 931 PM CDT Sat Aug 28 2021 We extended at least low chances of showers area-wide until about 05 UTC with this update, with isolated storms also still possible. As of 02 UTC, the primary middle- and upper-level trough axis is roughly along the Highway 83 corridor, with dynamically-forced precipitation in advance of the wave gradually diminishing along with pre-trough, boundary-layer-based bouyancy. However, cyclonic flow and instability associated with the cold pool aloft behind the trough has allowed isolated to scattered low-topped convection to persist. CAMs are not capturing this post-trough activity well, and while it should diminish concurrent with diurnal cooling, radar trends supported extending its mention a few hours. Other- wise, guidance continues to support a cool night, with lows in the 40s F in western ND. UPDATE Issued at 547 PM CDT Sat Aug 28 2021 Changes with this update cycle were focused on recent observed trends, namely boosting shower chances into the likely category over south central ND the next few hours. Time-lagged HRRR runs capture that activity -- which is immediately ahead of a middle- and upper-level trough axis that`s advancing eastward -- well and served as the basis for near-term PoPs. Midlevel lapse rates are meager in the 6 C/km range, limiting lightning activity, but the CAPE-shear setting over the James River valley suggests the odds of a strong or marginally severe storm are still non-zero as the upstream forcing approaches that area the next few hours. && .SHORT TERM...(This evening through Sunday) Issued at 237 PM CDT Sat Aug 28 2021 Current surface analysis places low over western Manitoba, with frontal boundary dropping down into western Minnesota and secondary trough in its wake. Upper level analysis places trough sliding over the northern plains. The combination of these systems is resulting in some showers and a few weak thunderstorms popping up over our area. For the rest of this afternoon into tonight, expect showers with some thunderstorms to continue developing over the area with the upper trough gradually working towards the east. The only concern for severe weather, which is actually quite marginal, would be from far south central North Dakota into the James River Valley. This is where the higher instability is located over our area, though this is a bit marginal. With that said deep layer shear is elevated, so the threat is there for a storm or two to become severe. Shower and thunderstorms will come to an end from west to east overnight as the trough moves east, with skies clearing in its wake. On Monday, modest ridge passes over the area in the wake of the trough, resulting in a rather pleasant day with mostly sunny skies and near to slightly below average temperatures. .LONG TERM...(Monday through Saturday) Issued at 237 PM CDT Sat Aug 28 2021 An unsettled weather pattern develops for the upcoming work week as a variety of troughs deepen and swing around an upper low located over the far western Canadian provinces, which will eventually meander towards the east. This will keep chances for showers and thunderstorms in the forecast, with chances gradually increasing as we get later in the week. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 931 PM CDT Sat Aug 28 2021 Isolated to scattered showers and a few thunderstorms this evening will diminish by about 06 UTC as an upper-level trough exits the area. That will lead to dry weather into Sunday, along with widespread VFR conditions for western and central ND. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...CJS SHORT TERM...JJS LONG TERM...JJS AVIATION...CJS
Area Forecast Discussion
National Weather Service Cheyenne WY
924 PM MDT Sat Aug 28 2021 .UPDATE... Issued at 916 PM MDT Sat Aug 28 2021 Only minor changes made to the forecast this evening. We have removed the precipitation chances overnight, due to limited mid level moisture and more stable lapse rates in the 700-500mb layer. Still may seem some cloud decks around 4-5kft, but these clouds should not stick around long as things mix out fairly quickly. A much cooler day is expected tomorrow as cool high pressure builds over the area. && .SHORT TERM...(This evening through Monday) Issued at 250 PM MDT Sat Aug 28 2021 Current observations across the region show a surface cold front moving into Carbon and Albany counties this afternoon while the eastern plains are a little cooler and more moist behind the front after it pushed through earlier today. Thunderstorm forecast is tricky through tonight, because there is some chance for nocturnal convection across the southeast high plains due to cooler air aloft moving in associated with the upper level trough, and some elevated instability above the inversion. The frontal boundary will be nearby and may provide enough lift to initiate a few elevated thunderstorms this evening through tonight. As of right now, CAMs/high res models are not showing too much, but are hinting at some activity trying to get together along the Front Range. Added a slight chance for thunderstorms east of Cheyenne across the I-80 corridor. There is also the potential for fog across the I-80 Summit, given the moist east to southeast llvl flow. Kept it out of the forecast for now with the HRRR and Consensus model output not showing any fog at this time. Other than some fire weather concerns on Monday, hot temperatures and a dry/quiet forecast is expected into early next week. All models show the flow aloft backing into the southwest as a ridge of high pressure builds across the 4 corners region. Highs on Monday will likely reach the low to middle 90s for areas along and east of the I-25 corridor. Slight cooler further west, but afternoon temperatures should still be in the low to mid 80s through the day. .LONG TERM...(Tuesday through Friday) Issued at 230 AM MDT Sat Aug 28 2021 Key Messages: 1) Elevated to near-critical fire-weather conditions Tuesday with well above normal temperatures for the beginning of next week. Will need to monitor for a possible Red Flag Warning but winds might be just light enough. 2) Temperatures will cool to near normal and increased rainfall chances are likely starting Wednesday, climbing moreso Thursday, and continuing partly into Friday and Saturday next week. Pockets of moderate rainfall could be possible with sub-tropical moisure shifting into the region. Will need to monitor the Mullen Burn Scar for any possible flash flooding impacts. See hydrology section below for more information. Weather Discussion: Next Tuesday will be the last hot day (for next week anyway) across the region as a ridge over southern Colorado starts to break down with an incoming NW Pacific trough sweeping across ID/MT. Well above normal temperatures Tuesday with H7 temperatures of 16-18C in place leading to upper 80s to mid/upper 90s across the region. These H7 temperatures are in the 90-97.5 percentile of climatological observations for this region. Record highs are in the low to upper 90s so unlikely we will break records but likely be within 2-4 degrees of records. Did increase high temperatures 1-2 degrees above NBM model guidance. Wednesday will be the start of the cool down as more clouds shift into the region along with high PWATs. A moisture plume of 1-1.3" PWAT will stream in from the SW as the remnants of what is now Tropical Storm Nora that is forecast to become a hurricane later today in the eastern Pacific off the coast of west Mexico. These remnants will advect poleward to the NE in the conveyer belt flow between the Central Plains ridge and the trough across the Pacific NW and first shift across western WY Wednesday afternoon. Isolated to scattered showers will be likely Wednesday with more stratiform rainfall continuing overnight Wednesday into Thursday as the moisture plume slowly shifts east Thursday and Friday across east Wyoming and into Nebraska with embedded vorticity impulses in a slightly more zonal, yet unsettled pattern. Per ensemble suite and deterministic model agreement, Thursday appears to be the wettest day. Instability looks minimal so overall rainfall rates should remain low but can`t rule out moderate rates that could possibly cause impacts on the Mullen burn scar if training occurs. Temperatures will be more seasonable through mid to late next week. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 440 PM MDT Sat Aug 28 2021 VFR to possible MVFR conditions likely through the forecast period of all terminals. Overall, not too many changes to the forecast, outside of some gusty conditions tomorrow. HiRes models are picking up on some shortwave disturbances tomorrow afternoon, which is expected to kick up the wind speeds to around 20-25 knots. Moisture levels will remain low as Hurricane Ida effectively cuts off the moisture flow from the Gulf, limiting shower and thunderstorms potentials. Smoke from western wildfires will continue to limit visibilities in our western fringes, with RWL hovering around 6SM. && .FIRE WEATHER... Issued at 220 PM MDT Sat Aug 28 2021 Red Flag Warning remains in effect through this evening for areas west of the Interstate 25 corridor. A surface cool front will continue to push south and west across the region this evening with winds shifting into the east and higher dewpoint temperatures/humidities behind it. The front is expected to stall near the mountains, but should eventually lift northeast late Sunday and weaken. Although widespread critical fire weather conditions are not anticipated on Sunday, they will likely return on Monday with gusty southwest winds expected for most of southeast Wyoming. Will likely need additional Watches and Red Flag Warnings for Monday afternoon. Fire weather concerns will trend lower by late next week as another push of monsoon moisture is expected. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ UPDATE...REC SHORT TERM...TJT LONG TERM...JSA AVIATION...MD FIRE WEATHER...TJT
National Weather Service Hastings NE
642 PM CDT Sat Aug 28 2021 .DISCUSSION...(This evening through Saturday) Issued at 212 PM CDT Sat Aug 28 2021 Late This Afternoon Into Tonight... The big story will be the threat for strong to severe thunderstorms later this evening into tonight. Forecast models are in pretty good agreement that our forecast area should remain dry through at least 6 pm. Thunderstorms are likely to develop between 5-6 pm just northwest of our forecast area and then slide into our northwestern zones (Ord to Gothenburg) between 6-8 pm. Storms will be slower to reach our Tri-Cities with possible arrival time primarily between 9 pm and midnight. There is good model agreement in the late afternoon/early evening thunderstorm development. The questions reside more in the coverage and intensity of these thunderstorms. The 12Z NAM NEST continues to be the most aggressive in both coverage and intensity with the formation of a convective line that surges south with outflow boundaries bringing possibly severe winds. The HRRR and 12Z NAM indicate more scattered convection that could be strong at the onset, but then quickly decreases in coverage and intensity. The 12Z HRW NSSL and 12Z HRW ARW both are similar to the 12Z NAM NEST indicating that the convection should be rather widespread across the forecast area by late evening. Our official forecast follows more closely in-line with the wetter NAM and HRW models. Regarding the severe weather potential, the greatest threat for severe weather will be early on during the first several hours after thunderstorm development primarily between 6-11 pm across our northwestern zones. The wind threat seems to be the biggest threat although there could be a brief window for severe hail in that first 1-3 hours. Eventually, the belief is that these storms should merge into a line that could produce severe winds in the 60-70 mph range until the gust front gets too far ahead of the line and then it will just turn into a possibly heavy rain event for some areas during the late night hours. Will have to watch out for flooding if storms start training over the same areas, which is a possibility. Sunday Into Sunday Night... This should be the best day of the bunch with cooler temperatures behind the cold front holding highs down into the upper 70s to around 80 over Nebraska, to lower 80s over north central Kansas. There could be a few remaining showers/thunderstorms across our southeastern zones in the morning, but after these exit the area, odds are that most areas should be dry through the rest of the day. We will then see some return flow and a low level jet that could result in additional thunderstorms late Sunday night with northeastern zones being most favored. Monday Into Monday Night... We will start the warmup with decent southerly flow and highs back into the lower and middle 80s Nebraska zones to the upper 80s and around 90 over north central Kansas. The big thing to watch out for will be the chance for additional warm air advection nocturnal thunderstorms Monday night mainly across our eastern zones, although they may even set up east of our forecast area. We are already in a SPC marginal risk outlook for Monday. Tuesday and Wednesday... We will see an upper level ridge build across the western high plains and thus this period stands the best chance at being dry as well as warmer. Highs should be back to at least around 90 by Wednesday and probably well into the 90s over northern Kansas. Thursday Through Saturday... The upper level ridge should still be the dominate weather feature on Thursday, but there is a slight chance that thunderstorms could make it into our northwest zones by late day. Thursday should still be hot with a lot of folks around 90 or better. That next upper trough could start to influence our forecast area a little bit more by Friday and Saturday with cooling temperatures and increasing chances for thunderstorms. .AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Sunday) Issued at 212 PM CDT Sat Aug 28 2021 The big concern as noted above will center around the chance for strong to severe thunderstorms late this evening. The soonest that we could see thunderstorms at our TAF sites would probably be 8 or 9 PM, but likely it will be later than that. The wind will be gusty out of the south until the front comes through with the thunderstorms. Strong to severe thunderstorm winds can not be ruled out this evening and we`ll need to keep an eye out for how the thunderstorms develop and track later this evening. Behind the front and thunderstorms, the winds will become northerly. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Monday) Issued at 624 PM CDT Sat Aug 28 2021 VFR conditions expected to continue for the next few hours as a line of thunderstorms continues to develop to the northwest and eventually propagates across both terminals. This front will likely bring at least MVFR VSBYS with -TSRAs...and possibly some MVFR CIGS as well, but confidence of CIGS is lower. Winds should diminish ahead of the front before becoming northwesterly and gusting to near 20 KTS through much of the overnight hours. Conditions should begin to improve around daybreak Sunday...with VFR conditions returning around 29/12-13Z. && .GID WATCHES/WARNINGS/ADVISORIES... NE...NONE. KS...NONE. && $$ DISCUSSION...Wesely AVIATION...Rossi
Area Forecast Discussion
National Weather Service Grand Junction CO
544 PM MDT Sat Aug 28 2021 .SHORT TERM...(Tonight through Sunday night) Issued at 202 PM MDT Sat Aug 28 2021 Apart from the anticipated isolated storms over the far southwest San Juan Mountains this afternoon, conditions have remained dry and warm across the Western Slope. Near zonal flow aloft has started the transport of smoke from the ongoing western wildfires over the northern tier of the forecast area, as evident by the latest GOES satellite imagery. While not overly thick thus far, it has already moderated temperatures slightly across the north with the Craig Airport trending 3 degrees cooler than this time Friday (though this is also enhanced by yesterday`s trough passage). The HRRR Smoke remains consistent in the continued advection of this smoke through the short term period with the highest concentration centered along and north of I-70. As a result, temperatures will likely continue to trend slightly cooler than guidance. The aforementioned convection over the southern mountains will diminish after sunset, resulting in a quiet night. Westerly flow aloft will persist across the north on Sunday while a ridge of high pressure builds to the south. Residual moisture will once again fuel isolated afternoon showers and thunderstorms over the San Juans and potentially the West Elk Range. Otherwise, the status quo will prevail with smoky skies and dry conditions. Meanwhile, Hurricane Nora will continue to trek north through the Gulf of California Sunday night before its progress begins to slow down as we head into the long term period. .LONG TERM...(Monday through Saturday) Issued at 202 PM MDT Sat Aug 28 2021 The long term period will start off relatively quiet, with temperatures running around 5 degrees above average and relatively light winds. This all starts to change Tuesday night as the ridge that builds in over eastern Utah and western Colorado during the day begins to shift east and an upper level trough digs along the Pacifc Coast, creating a classic monsoonal pattern. This won`t be just a classic monsoonal push though, as moisture from Hurricane Nora will enhance the subtropical moisture tap. With this extra boost of moisture, PWATs are expected to increase quickly, with forecast values climbing almost half an inch over the course of 24 hours. PWATs are expected to peak Wednesday night into Thursday morning, with Thursday looking like the day for widespread precipitation as embedded shortwaves rotating around the trough combine with any lingering forcing from Nora. The concern here, with the expected widespread shower and thunderstorm activity, is heavy rain and localized flash flooding, with burn scars areas of high concern. Models are in good agreement through Thursday, that eastern Utah and western Colorado will tap into deep subtropical moisture and that Thursday will likely see the most widespread precipitation. With the expected cloud cover and precipitation from mid-week onward, temperatures will be at or below normal, with Thursday running around 10 degrees below normal. Confidence decreases from Friday into the weekend as discrepancies between models begin to crop up. However, generally speaking the weekend will continue to be unsettled with temperatures at or below average. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 534 PM MDT Sat Aug 28 2021 A plume of smoke will continue to filter into the area this evening and spread southward overnight. Right now, smoke is quite vivid on satellite imagery, covering areas mainly along and north of the I-70 corridor. Expect very little change in the next 24 hours, as near zonal remains overhead. VEL and HDN maybe see the biggest impacts in VIS, though have included smoke in nearly every TAF location. Otherwise, VRF conditions will prevail with light, terrain driven winds overnight and gusty winds (up to 25 kts) returning Sunday afternoon. && .HYDROLOGY... Issued at 202 PM MDT Sat Aug 28 2021 We are continuing to monitor the potential for heavy, widespread precipitation from midweek onwards. Most of this will rely on the track and strength of Nora. Regardless, subtropical moisture will once again stream into the region as southerly flow sets up on Wednesday in response to the high`s transition east. Passing embedded disturbances will provide enhanced lift, most notably on Thursday. Plenty of details need to be ironed out going forward, as any slight deviations could greatly impact the overall coverage and intensity of precipitation during this timeframe. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...MMS LONG TERM...BGB AVIATION...ERW HYDROLOGY...MMS
Area Forecast Discussion
National Weather Service Lubbock TX
616 PM CDT Sat Aug 28 2021 .AVIATION... VFR prevails for the TAF period. There exists a low chance of convection to possibly affect the KLBB and KPVW terminals, and areas west/northwest of the terminals, on Sunday afternoon. Check/monitor density altitude. Sincavage && .PREV DISCUSSION... /issued 219 PM CDT Sat Aug 28 2021/ SHORT TERM... Afternoon cumulus field showing congestus and towers developing near the New Mexico border where the mid level capping inversion was the weakest, and we have added late afternoon thunderstorm chances in the extreme southwest Panhandle along the NM border. Also seeing a few attempts toward deeper convection again along the edge of the Caprock escarpment, but inversion so far appears holding while bulk of short-range solutions do not indicate storms succeeding either. We favor retaining low thunder chances this evening across the southwest Panhandle with low shower chances later tonight spreading slightly further south and east, similar to as indicated by the HRRR which has been consistently indicating this throughout the day. Mild and humid conditions otherwise will dominate tonight with light southerly low level flow. Sunday will see weakness in the upper level heights continuing over the Panhandle and South Plains with a further increase in moisture aloft, as monsoonal flow bends out of New Mexico into the western Panhandle and South Plains. This will lead to chance mention for thunderstorms favoring this area during the afternoon. Also the gradual increase in moisture into the southern Rolling Plains justifies a low thunder mention this area as well Sunday afternoon. Temperatures Sunday should taper back another degree or two with the increase in clouds and showers, especially cooler in the southwest Panhandle. RMcQueen LONG TERM... Slight chance POPs will linger late Sunday night into the early morning hours of Monday. Weak instability aloft and deep boundary layer moisture supports light scattered showers with isolated convection in our northwest zones, but will taper off before sunrise Monday morning. It looks to be dry for the remainder of the week as Nora tracks NNW along the Baja of California and Ida shifts north into a zonal Polar Jet to begin the week. An upper level ridge just to our west begins to amplify Tuesday and Wednesday, as the jetstream begins to buckle under the weight of Ida as it moves across the southeast CONUS into the Mid-Atlantic region. As has been the case most of this summer, we will reside under the portion of the ridging aloft that will spare us from extreme heat. Temperatures will hover right around 90 degrees on the Caprock all week, and mid/upper 90s across the Rolling Plains. Surface winds during the afternoon will consistently be S/SE all week, keeping RH values elevated at times, especially in the Rolling Plains. Overall, it will be mostly sunny all week, a little humid at times, with light winds and little to no chance for rain. && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ 09
Please see the previous forecast discussion for more details on the
current warm episode and expected conditions next week. Keene
&& .AVIATION...28/18Z TAFs...Along the coast...VFR conditions will prevail through sunset over land areas even with persistent low stratus just offshore from Florence through Cape Blanco. South of Port Orford, wildfire smoke will be in play as northeasterly winds have brought the smoke to the coast and points offshore. Vsbys due to this smoke may drop into the MVFR category but are not expected drop any lower than that. After sunset, IFR with local LIFR conditions can be expected north of Cape Blanco as the marine stratus pushes onshore but said stratus is not expected to penetrate more than 5 miles inland. Inland...VFR conditions are expected through Sunday morning east of the Cascades before smoke starts arriving and reduces visibility there Sunday afternoon. From the Cascades westward, pockets of MVFR and localized IFR conditions due to low vsbys associated with wildfire smoke can be expected in most areas away from the coastline through this evening. Overnight much of this smoke may settle in the Umpqua and Rogue Valleys to maintain vsbys in those valleys at MVFR levels. -Sargeant/Keene && .MARINE...Updated 230 PM PDT Saturday 28 August 2021...A strong thermal trough along the coast will gradually weaken over the next couple of days. This will cause northerly winds to gradually diminish over the entire coastal waters such that by Monday morning, areas north of Cape Blanco should no longer experience Small Craft Advisory conditions. However, the thermal trof will remain strong enough to keep northerly winds cranking and keep areas south of Cape Blanco in Small Craft Advisory through Tuesday. Although by then, these conditions may only be south of Gold Beach. In addition to the high winds, areas that are in Small Craft Advisory will experience steep wind driven seas to add to the hazardous conditions. -Sargeant && .FIRE WEATHER...Updated 245 PM PDT Saturday, 28 Aug 2021... Northeast winds across the ridges are expected to briefly increase this evening to gusts in the 20 to 40 mph range, strongest in the Kalmiopsis Wilderness area, before diminishing overnight into Sunday morning. On Sunday the thermal trough along and near the coast will drift northeastward across the area resulting a dry, smoky, and unstable afternoon and evening across inland areas. Decided to go with Haines 5 conditions across the board tomorrow rather than 6, as extensive smoke is likely to mute T/RH potential, to some degree. Gusty westerly winds and very low humidity is expected to result in a period of critical conditions for portions of the area east of the Cascades Sunday afternoon and evening, specifically in FWZ624 east of Hwy 97, and across much of the Modoc FWZ 285. Sunday night into Monday a dry cold front will push across the area resulting in critical wind and RH conditions for much of the area east of the Cascades Monday afternoon and evening, specifically most of FWZ 624, FWZ 285, and FWZ 625. Winds are expected to be 5-10 mph stronger Monday afternoon and evening versus Sunday for the same time period. Cooler, more seasonable conditions are then expected through the rest of the week, though some guidance does warm up the latter portion of the week about 5 degrees F above seasonal averages again. ~BTL && .PREV DISCUSSION... /Issued 252 PM PDT Sat Aug 28 2021/ DISCUSSION...An upper level short wave ridge is over the area currently with a surface thermal trough extending from northern California to the SW Oregon Coast. Along the coast, this is bringing a Chetco effect to Brookings this afternoon with temperatures in the low-mid 90s as of 2 pm. North of Cape Blanco, conditions are more typical with more marine influence and temperatures in the 60s. Inland, nary a cloud can be seen, though smoke continues to emanate from area wildfires. This is resulting in areas of reduced visibility and air quality west of the Cascades and in Northern California, while areas east of the Cascades are getting a relative break from the thick smoke. Overall, it is a warm day with most areas in the 80-90 degree range and some locations in the west side valleys 90-95. The thermal trough and offshore flow will weaken a bit tonight into Sunday as an upper shortwave approaches the PacNW. This will turn the mid-level flow to SSW across the region and smoke from California wildfires will return from the south. The air mass aloft will remain quite warm, so Sunday will be another warm day inland. However, smoke from the fires could once again limit just how warm. For this reason, we`re forecasting temperatures a bit below the MOS guidance with highs widely in the upper 80s to the mid 90s. Expect an increase in afternoon breezes compared to today, highest east of the Cascades and in NorCal. It should be cooler in Brookings due to more marine influence compared to today. A dry cold front will push onshore Sunday night into Monday. This will result in a bit more of a marine push into the Umpqua Basin by Monday morning. Most noticeable, however, will be the 5-10 degrees of cooling expected -- perhaps even a few degrees more than that in some areas -- and some gusty afternoon west- northwest winds. This should carry most of the thickest smoke to the south and east and immediately downwind of the fires, likely giving many west side areas (except NE Jackson/eastern Douglas) another break from the smoke. Tuesday through Thursday will be cooler. Tuesday will likely be the coolest day of the next seven as the associated upper trough axis moves through. Back side energy digging into WA/OR should keep the trough in place long enough to prevent significant warming Wed/Thu, so we`ll remain near to slightly below average temperature-wise. Surface northerly flow could bring smoke back into portions of the Rogue Valley at night and into the morning hours, but upvalley NW breezes should help to clear it out in the afternoons. Mid-level westerly flow should also keep the thickest smoke to the east of the fires. Models show short wave ridging moving in Friday followed by some semblance of another upper trough next weekend. The GFS appears stronger with the trough Friday night into Saturday, actually suggesting some light rain is possible along the coast north of Cape Blanco. Other guidance, including the NBM keeps the trough weaker, so we have kept the forecast dry. -Spilde && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning from 2 PM to 8 PM PDT Sunday for ORZ624. Fire Weather Watch from Monday afternoon through Monday evening for ORZ624-625. CA...Red Flag Warning from 2 PM to 8 PM PDT Sunday for CAZ285. Fire Weather Watch from Monday afternoon through Monday evening for CAZ285. Pacific Coastal Waters...Small Craft Advisory until 5 PM PDT Monday for PZZ350-370. Small Craft Advisory until 5 PM PDT Tuesday for PZZ356-376. Gale Warning until 5 AM PDT Sunday for PZZ356-376. $$
National Weather Service Morristown TN
959 PM EDT Sat Aug 28 2021 .UPDATE... EVENING UPDATE. && .DISCUSSION... The isolated convection has increased again in the central valley, and given that the latest HRRR has it holding together for a bit as it tracks slowly north, will beef PoPs up a bit in these areas for a few hours. Will also tweak sky to better fit this scenario, but otherwise no additional changes. && .AVIATION... 00Z TAF DISCUSSION. Isolated convection impacting any of the terminals Sunday afternoon looks too improbable to include in TAFS. Fog, although possible late tonight, looks unlikely to impact vsby at any site. Thus will go with VFR conditions for the entire period all sites with just some high clouds around at times along with scattered daytime CU. Winds will generally be light. LW && .PREV DISCUSSION... /ISSUED 728 PM EDT Sat Aug 28 2021/ SHORT TERM...(Tonight and Sunday)... Key Messages: 1)A couple of showers/thunderstorms this afternoon across the high terrain. 2)Above normal temperatures continue tonight and on Sunday. Discussion... Afternoon water vapor imagery clearly shows Hurricane Ida moving NW on the SW periphery of a h5 anticyclone anchored over the Carolina Coasts. The surface reveals mainly high pressure across much of the Appalachians and mid Atlantic region. 19Z obs show temperatures warming into the upper 80`s to lower 90`s as expected. Dewpoints in the lower 70`s is contributing to heat index values in the mid to upper 90`s. Convection has remained fairly isolated as of discussion time with increasing subsidence aloft. Expect this isolated trend to continue through the rest of the afternoon with the better chances along the northern Plateau and higher terrain of the Southern Appalachians. Tonight will feature tranquil conditions as high pressure and ridging aloft continues to favor dry weather and above normal low temperatures. Cannot rule out patchy fog in favored river valleys tonight but not expecting this to be widespread given slightly higher dewpoint depressions tonight. Deep layer ridging remains in control across the Appalachians and Mid Atlantic states on Sunday with another warm day expected as highs rise into the upper 80`s to low 90`s. Showers and thunderstorms can be expected again with favored areas across the Plateau and higher terrain. Diegan LONG TERM...(Sunday Night through Saturday)... Key Messages: 1. The remnants of Hurricane Ida will impact the region Tuesday into Wednesday with a less active pattern afterwards. 2. With Hurricane Ida, confidence continues to increase in potential for strong winds and isolated tornadoes with locally heavy rainfall still expected in western portions of the area. However, these details are conditional on the track and evolution of the storm as well as the mesoscale structure of rain bands. Sunday Night through Wednesday At the start of the period, Hurricane Ida is forecast by the National Hurricane Center (NHC) to be making landfall in Louisiana as a major hurricane (Category 3 or greater). During this time, a 5,900 meter 500mb high will be receding over the Carolinas. During the day on Monday, the expectation is for Ida to move inland near or just east of the Mississippi River. A notable weakening trend is expected as it weakens to depression strength by Monday evening. This will result in an increasing southerly flow pattern and relatively scattered convection before the more notable effects take place Tuesday into Wednesday. The speed, evolution, and overall track of Ida`s remnants Tuesday onward still bears uncertainty within the latest model guidance. The NAM suggests a more notable right-turn of the storm into central Mississippi and northern Alabama on Tuesday. However, many GEFS members and the GFS/CMC/ECMWF deterministic solutions show a more progressive and northward track through west and middle Tennessee. With either solution, the bulk of local impacts will take place Tuesday into Tuesday night before a northerly flow/more settled pattern takes shape later in the week. If a more northerly track occurs coincident with the consensus, vertical wind profiles support strong (>200 m2/s2) 0-1km SRH, similarly high 0-3km SRH, LCL heights < 1,000 meters, and S/SSE 850mb flow of 30 to 40+ kts. As such, notable concern remains in the potential for isolated tornadoes. In addition to the track and evolution of the system, the tornado potential will be highly dependent on the mesoscale structure of rain bands and destabilization. Coincident with timing and structure, diurnal heating and breaks in clouds are both key in efficiency of destabilization. Synoptically-driven 850mb flow with the consensus would be sufficient for at least advisory-level winds in the mountains. However, local mountain wave effects may prove more than sufficient for warning criteria to be met. As such, a high wind watch could be needed in the coming days. Regarding the heavy rainfall threat, it still appears that the most impressive tropical moisture will stay along our western areas and even further to the west. Nevertheless, efficient rainfall rates and training of convection will be the main drivers of locally heavy rainfall and potential isolated flooding, especially along and near the Cumberland Plateau. Initial downsloping will likely inhibit rainfall totals further eastward. By Wednesday and Wednesday night, Ida is expected to move either east or northeast of the region, putting the area in a northerly flow pattern. This also comes ahead of high pressure to the north and a frontal boundary that looks to funnel drier air following a frontal passage. Thursday through Saturday For the end of the period, a more settled and seasonal pattern is expected as high pressure stays in place to the north. The GFS suggests an upper low forming to the south following Ida`s progression to the northeast. Nevertheless, all global guidance shows that an upper high is expected to expand across the Central Plains. The result will be fairly limited daily convective coverage and a more settled overall pattern. BW && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 73 92 72 89 71 / 10 20 10 40 40 Knoxville McGhee Tyson Airport, TN 72 92 71 91 71 / 20 10 10 30 30 Oak Ridge, TN 71 92 70 90 71 / 20 20 10 40 30 Tri Cities Airport, TN 67 92 68 91 68 / 10 20 10 30 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$
Area Forecast Discussion
National Weather Service Pocatello ID
125 PM MDT Sat Aug 28 2021 .SHORT TERM...Tonight through Monday night. A dry zonal flow will prevail over the region tonight and tomorrow. By Monday morning, an upper trough will work its way into the PAC NW, driving up some winds in the Snake Plain. Temperatures will be a bit above normal on Sunday and Monday as we continue under mostly dry conditions. Moisture should remain to the south through the short-term periods, so there`s no threat of any thunderstorms. Smoke should also remain to our south, though HRRR suggests some will creep into our southern zones Sunday afternoon. Increased smoke concentrations will be possible in the Central Mountains as early as Sunday evening. Hinsberger .LONG TERM...Tuesday through next Saturday. The operational GFS and ECMWF are in fairly good agreement that a low pressure system will linger over WRN Canada Tuesday and Wednesday as the remains of Nora work north through the Gulf of California. As a result the SSW flow aloft is expected to advect moisture from Nora northward through Utah and into the SE highlands as early as Wednesday morning and continuing through Thursday night before getting shunted eastward into Wyoming and Colorado Friday as the Canadian low and associated trough axis finally shift east into the Panhandle. By Saturday, the operational models fall out of phase which is also reflected in the Cluster analysis. Thus we are happy to float along with the going forecast and National Blend of Models which holds on to a mention of precipitation across the eastern half of the forecast area Wednesday through Friday. We may taking some liberties Saturday and deviate toward drier conditions as even the progressive/wet looking GFS is showing precipitation impacts well north of the region. Daytime highs remain warm Tuesday and Wednesday before trending lower toward climatology Thursday into Saturday. Huston && .AVIATION...VFR conditions will prevail under a dry west flow aloft. Huston && .FIRE WEATHER...We have increasing concerns for critical fire conditions Monday and Tuesday. Models continue to push sub 15% RH across much of the region and wind gusts 25 to 35 mph over zones 410 and 425, perhaps even into zones 422 and 476. There is some uncertainty on the windspeeds though, so we`ll be watching the trends over the next couple of model runs. As troughing digs into the PAC NW, we`ll see increasing chances of afternoon thunderstorms Wednesday and beyond. Humidity will be increasing after mid-week thanks to an influx of monsoon moisture. Hinsberger && .PIH WATCHES/WARNINGS/ADVISORIES... None. && $$
Area Forecast Discussion
National Weather Service Phoenix AZ
503 PM MST Sat Aug 28 2021 .UPDATE...Updated 00Z aviation discussion. .SYNOPSIS... The best storm chances will be over higher terrain areas of Arizona this weekend, but a few isolated showers or storms and gusty winds are likely to impact the south-central Arizona deserts. Hot temperatures with highs just above 110 degrees are expected this weekend across southeast California and southwest Arizona, while highs are likely to fall just short of 110 degrees in the Phoenix area. A much more unsettled weather pattern is expected for a good portion of next week as tropical moisture surges into the region by midweek. This will bring very good chances for rainfall through the middle of next week, likely focused across south central Arizona, while also bringing much cooler temperatures as well. && .DISCUSSION... Latest RAP streamline analysis depicts an upper-level anticyclone across central Arizona. This will generally result in a weak northeasterly steering flow this afternoon and evening. Meanwhile, in the lower levels, a well-defined gulf surge from a northern Sonora MCS pushed through the lower Colorado River Valley this morning. Gusts up to 30 mph were observed near Yuma, while further west in the Imperial Valley dewpoints reached the upper 70s, briefly yielding oppressive heat indices as high as 120 degrees. Across the Phoenix metro area, the morning moisture has also taken a bite out of afternoon temperatures. Current temperatures are generally running 5 to 7 degrees cooler than they were at this time yesterday. This is also evident in afternoon ACARS soundings, which depict the cooler boundary layer and the area of CIN just above that. However, further aloft temperatures are relatively cool, right around -7 deg C at 500 mb. Consequently, latest mesoanalysis indicates relatively steep mid-level lapse rates and a widespread area of 1000+ J/kg MLCAPE across the lower deserts. Consensus from the CAMs points to scattered shower and thunderstorm activity across the Mogollon Rim and higher terrain approaching the foothills north and east of Phoenix. Given the elevated DCAPE, an outflow boundary will likely push westward from this activity into the lower deserts. However, there is considerable uncertainty whether this boundary will be strong enough to break through the aforementioned CIN and generate new convection across the Valley. Latest HREF indicates roughly a 50% chance of an outflow boundary capable of producing winds up to 35 mph along with patchy blowing dust. Across southwestern Arizona, the chance of storms will be somewhat higher as the outflow boundary encounters a more favorable environment where CAPEs currently exceed 2000 J/kg. The strongest storms will also be capable of producing localized gusts up to 60 mph, particularly across portions of Pinal, southern Maricopa and La Paz counties. && .PREVIOUS DISCUSSION... Temperatures today will cool slightly off of the previous couple days, but the Excessive Heat Warning with highs of 110-114 degrees will remain across southeast California and southwest Arizona through Sunday. The increase in boundary layer moisture across southern Arizona should keep temperatures mostly in a 107-109 degree range in the Phoenix area, but it will still feel quite hot. Sunday`s temperatures look to be a near mirror image of today, but boundary layer moisture is expected to lower a bit due to the lack of a Gulf surge tonight. Afternoon scattered storms are again expected over the Arizona high terrain on Sunday, but due to increasing subsidence over the region the activity is likely to be more subdued. Slightly lower moisture levels and reduced MUCAPEs over the lower deserts on Sunday is likely to limit or even inhibit any storm development over the south-central Arizona deserts. For next week, there remains high confidence in a tropical moisture surge first starting on Monday, but intensifying Tuesday into Wednesday. A rather complex pattern is likely to take shape for the first half of next week. An upper level trough just to our southwest will become a major factor for our weather while combining with the increasing tropical moisture well out ahead of Hurricane Nora which is expected to gradually weaken as it tracks into the Gulf of California. Monday is likely to be a fairly limited storm day across most of southern Arizona as subsidence aloft and a capping inversion is likely to keep most storms confined to higher terrain areas. Increasing moisture into southeast California on Monday may present a favorable environment for some isolated to scattered storms, possibly strong if the GFS forecast sounding for KIPL comes to fruition. As a strengthening upper level jet associated with the trough to our west moves northward across southern California into the Great Basin on Tuesday, much of Arizona will eventually become perfectly positioned within a favored vertical ascent region. The combination of the deep tropical moisture overtaking Arizona Tuesday into Wednesday and the favorable ascent fields should give rise to fairly widespread shower and thunderstorm activity sometime late Tuesday, likely lasting through a good portion of Wednesday. Model ensembles continue to support this main area of likely moderate to at times heavy rainfall falling somewhere across south-central Arizona, but we are still a few days out and it`s still possible for some shifting in the expected heaviest rainfall. There is also a distinct possibility of some isolated to scattered strong thunderstorms at some point next Tuesday and Wednesday where higher instability and shear falls, likely farther west over southeast California and/or southwest Arizona. Forecast QPF amounts of greater than an inch are seen over a large swath of south-central into central Arizona for late Tuesday through Wednesday, but it is still a bit early to know the specific details of timing and location of the greatest heavy rainfall threat. By late Wednesday, the upper level support should be waining as the jet max lifts well to our north, but some model guidance shows at least some jet dynamics supporting our region into late next week. What happens with the remnant circulation of Nora is impossible to know at this point, but it seems unlikely an intact circulation will make it as far north as Arizona. Even without a direct impact of Nora, the increased moisture is likely to stick around over much of our region through the end of next week resulting in at least a chance for showers and storms. Forecast temperatures for next week take a big dive into the middle part of the week as highs are likely to dip into the 90s across a good portion of the lower deserts as early as Tuesday, but definitely by Wednesday. For now it seems likely the areas that see fairly continuous rainfall, or at least thick cloud cover on Wednesday will struggle to reach 90 degrees. The below normal temperatures are then likely persist through the rest of next week, especially if the deeper moisture sticks around the region. && .AVIATION...Updated at 0003Z South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Primary aviation concern through the TAF period will be the potential for convective impacts, mainly outflows from decaying thunderstorms. While the chances for VCTS at any terminals now looks to be quite low (10-20%), strong winds with dust from surroundings storms are more probable. Current thinking is that a relatively weak boundary may move thru first from the east or east-northeast. Wind speeds will likely be on the low side (gusts into the 20-25kt range at most). Then another outflow from more of a southeasterly direction will attempt to move into the region, bringing slightly strong winds and (perhaps) a bit of blowing dust int the Phoenix area during the 03-05Z timeframe. This 2nd outflow is expected to keep elevated southeasterly winds going thru sometime after midnight, with more typical lighter southeasterly winds thereafter. Cloud bases should remain elevated around 12 kft and above, outside of storms. There are indications high-based ACCAS showers may develop Sunday morning, but outside some brief gusty winds and shifts, they should be minimal impact. Another round (similar to today) of showers/TS is expected to develop along the Rim/White Mountains Sunday afternoon/evening, bring the likelihood of outflows back into the Phoenix area during the evening, with VCTS chances once again remaining quite low (10-20%). Winds to remain mainly out of a southeasterly direction at KIPL and a southerly direction at KBLH through the TAF period. Thunderstorms are still not anticipated at either terminal, but outflow winds from storms southwest of KIPL and east of KBLH cannot be completely ruled out. Elevated convection may also move into the region Sunday morning from the east, but confidence is too low to add any mention to the TAFs. Cloud bases should remain aoa 12 kft. && .FIRE WEATHER... Monday through Friday: Increasing moisture and rain chances will be seen early next week with temperatures eventually cooling to below normal by Tuesday. Shower and thunderstorm chances are likely to peak Tuesday into Wednesday with widespread wetting rains likely as tropical moisture surges into the region. Rain chances are likely to persist to some degree late in the period, but is likely to be more of the scattered variety. Minimum RH values will increase from around 25% on Monday to 40-50% by Wednesday before gradually lowering late in the period. Winds should be relatively light with an afternoon upslope component and overnight drainage expected for a good portion of next week, but southerly winds are also likely to be seen a bit more than typical. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Sunday for AZZ530>533-535- 536. CA...Excessive Heat Warning until 8 PM PDT Sunday for CAZ560>570. && $$ DISCUSSION...Hirsch PREVIOUS DISCUSSION...Kuhlman AVIATION...Percha/Benedict FIRE WEATHER...Kuhlman
Area Forecast Discussion
National Weather Service Sacramento CA
227 PM PDT Sat Aug 28 2021 .SYNOPSIS... Hot and very dry through the weekend. Gusty southwest to west winds early next week could bring critical fire weather concerns to the northern Sierra and southern Cascades. Cooler weather returns next week. && .DISCUSSION... GOES-West satellite imagery reveals smoky skies blanketing portions of interior NorCal this afternoon as wildfires continue to burn. Winds have subsided as surface pressure gradients are weaker than yesterday. Hot and dry conditions persist across the region this afternoon under flat ridging. Afternoon temperatures are generally running 2 to 6 degrees warmer across most of the area compared to 24 hours ago. Thick wildfire smoke may inhibit additional warming at some locations this afternoon. Forecast highs on Sunday will range from the upper 90s to around 103 resulting in moderate heat risk. Ensembles and cluster analysis indicate that an upper trough will start to take shape off the West Coast Sunday afternoon and gradually deepen into mid-week. This will promote increased onshore flow/southwest winds and cooler temperatures. However, these gusty winds will bring increasing fire weather concerns to the northern Sierra and southern Cascades Sunday into Wednesday. At this point, the strongest winds are expected Monday and Tuesday with gusts ranging from 20-35 mph. The strongest winds area expected in the afternoon and evening hours. A Fire Weather Watch has been issued for the higher elevations of the northern Sierra and southern Cascades from 11 AM Monday through 11 PM Tuesday given the potential for rapid spread of new or existing wildfires. The onshore flow will likely help with some smoke dispersal in the Valley. The HRRR smoke model shows improvement near the Delta influenced areas Sunday afternoon. A stronger onshore flow/southwest winds will get going Monday, which should push the smoke eastward out of the Valley and much of the foothills. A gradual cooling trend is expected during the Monday-Wednesday timeframe with mid 80s to low 90s returning by mid-week. && .EXTENDED DISCUSSION (Wednesday THROUGH Saturday)... Ensemble guidance is in good agreement large scale troughing will likely persist over the West Coast through the extended forecast period. This pattern will support a Delta breeze and slightly below average temperatures. Gusty southwest to west winds over the higher elevations of the mountains are possible in the afternoon into evening hours. && .AVIATION... Areas of MVFR to IFR due to area wildfire smoke. Gusts 15 to 20 kts vicinity Delta. Elsewhere, winds generally under 12 kts. Breezy conditions develop after around 21 UTC Sunday. && .STO WATCHES/WARNINGS/ADVISORIES... Fire Weather Watch from Monday morning through Tuesday evening for Burney Basin and Northeast Plateau in Shasta County Including Northwest Lassen NF north of Lassen NP-Northern Sierra Including Lassen NP and Plumas and Lassen NF/S West of the Sierra Crest (West of Evans Peak-Grizzly Peak-Beckworth Peak)- Northern Sierra Including the Tahoe and ElDorado NF/S West of the Sierra Crest-Stanislaus NF West of the Sierra Crest. && $$
Area Forecast Discussion
National Weather Service Tucson AZ
854 PM MST Sat Aug 28 2021 .SYNOPSIS...Scattered afternoon showers and storms are expected each afternoon and evening this weekend. Early next week an increase in storm activity is forecast as tropical moisture moves into the area and lingers through mid to late in the week. Concerns for heavy rainfall leading to flash flooding will also rise as a result. && .DISCUSSION...Rather boisterous convection around southeast Arizona with strong convection still occurring over far western Pima county. A few of the storm complexes caused damage and others were efficient rain producers resulting in some local flash flooding. Even had a decent surge down the CDO Wash thanks to heavy rainfall over the Catalina Mountains. For the remainder of the night most of the action will be across western Pima County where instability remains high and inhibition low allowing storm development with outflows. Elsewhere the HRRR continues to bubble up residual showers well into the night before it all ends before dawn. I went ahead and adjusted the forecast through the remainder of the night to account for current and expected trends. && .AVIATION...Valid through 30/00Z. FEW-SCT clouds at 8k-12k ft MSL (locally BKN into the early morning hours, mainly west of KTUS) thru the forecast period. ISOLD-SCT SHRA/TSRA thru 29/09Z and then again aft 30/19Z. MVFR conditions and mountain-top obscurations near TSRA, along with wind gusts up to 45 kts. Otherwise, SFC wind favoring an ELY/SELY direction and generally less than 12 kts. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Isolated to scattered showers and thunderstorms are expected for much of the forecast area through Monday. Deeper moisture will then overspread the area Tuesday through Thursday of next week as moisture associated with the remnants of Nora shifts northward. This will result in increasing precipitation chances mid to late next week across southeast Arizona, with potentially heavy rainfall at times. 20-foot winds will generally be less than 15 mph when not influenced by thunderstorms gusts. && .PREV DISCUSSION... /issued 330 PM MST Sat Aug 28 2021/ Scattered thunderstorms developing as expected this afternoon. Precipitable water values range from 1.2 inches east to 1.5 inches west. Easterly to southeasterly steering flow for storms with a decent shear environment for our corner of the state. Watch for isolated strong to near severe thunderstorms in and amongst the garden variety pulse storms, with some organized outflow pushing toward the lower deserts. We`ll see how things hold together for Tucson Metro over the next few hours and if we end up kicking up some dusty outflows. A chance of thunderstorms will continue through the weekend. Next we watch for deeper surge activity pushed up the gulf ahead of hurricane Nora. A convective complex that pushed from Sonora into the northern Gulf already assisted with a relatively deep moisture push through Yuma with southerly flow stacked 6k feet deep and the Yuma depot jumping 20 degrees over the past 24 hours. This will likely weaken before we see something stronger early in the new week. Current Nora projections bring her up very near the western coast of Mexico over the next 72 hours. She may be able to hang on to hurricane status as this happens, but not much more than that this close to the coast. A trajectory like this often ends up with the tropical system decoupling over southern Sonora with just mid level remnants making it across the AZ border, but we`ll have to see. A bit more to the east and we could see it shearing apart earlier than expected. A bit more to the west and it should hang on through the central Gulf. It is, however, becoming increasingly likely that we will see a deep and sustained surge through the Gulf of California as well as inland ahead of the storm. NAEFS and ECMWF ensemble means suggest an integrated water vapor transport maximum Monday night into Tuesday, with maximum precipitable water values Wednesday in excess of 1.75 inches. For SE AZ, our best precip chances (with possible heavy rain threat) could end up being multiple periods from Monday afternoon through most of the week. Tricky though. We get too much moisture and we could see a few days of light to moderate rainfall with storm totals in the 1 to 2 inch range, but not with rainfall rates that would suggest flash flooding. Or we could have multiple periods where we see twice as much storm total rainfall accompanied by flash flood threats. Or anything in between. Tropical systems (especially weaker ones like Nora) are a tough call. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ Public...Cerniglia/Meyer Aviation...Zell Fire Weather....Zell Visit us on Facebook...Twitter...YouTube...and at
Area Forecast Discussion
National Weather Service Las Vegas NV
843 PM PDT Sat Aug 28 2021 .SYNOPSIS...Hot temperatures and isolated thunderstorms are expected through Monday with Excessive Heat Warnings in effect for much of the region. Moisture will be increasing through the middle of next week aided by the remnants of Nora. This moisture will lead to better chances for shower and thunderstorm activity to Mohave County Sunday, expanding west and north into southern Nevada through mid-week. && .UPDATE...Isolated thunderstorms that developed late in the afternoon over southern Mohave County dissipated early this evening. One thunderstorm also developed in eastern San Bernardino near Essex. The gulf surge that occurred this morning will be a primer to the expected influx of moisture that will spread up the next few days as Hurricane Nora slowly works its way up the Gulf of California. We have at least until Tuesday before we should see a significant moisture increase and the latest model ensembles support the forecast trends from the previous discussion. No immediate changes needed. && .PREV DISCUSSION... 200 PM PDT Sat Aug 28 2021 .DISCUSSION...Through next Saturday What caught our eyes this morning was the ongoing gulf surge that was induced by the inverted trough presently crossing the northern Gulf of California. Moisture quickly spread northward up the Colorado River Valley and southern Mohave County with surface dewpoints climbing into the low 60s at Lake Havasu City and near 50 at Kingman. Radar indicates thunderstorms developing along the northeast slopes of the Hualapai mountains east of Kingman. Moisture may be too shallow but can not rule out a stray shower or thunderstorm over the mountains near Primm or southeast San Bernardino County later this afternoon or evening. With the moisture now in place expect better coverage in storms Sunday into Monday and relied on the camPoPs for the short term forecast. This moisture surge may dampen the temperatures a bit but overall readings will remain above normal Sunday and Monday. Through mid-week, moisture will continue to stream northward into the Desert Southwest well ahead of a weakening Nora. Combination of weak disturbance moving in from the west and strengthening jet streak interacting with that moisture will lead to widespread showers and thunderstorms on Wednesday. Still some uncertainty if there will be a heavy rain threat for Las Vegas and eastern San Bernardino County. But confidence is increasing that threat will exist probably from the Colorado River Valley east across Mohave County. Collaborated earlier with NHC, WPC and surrounding offices and we agreed no headline will be issued at this time. Will continue to brief primary partners. Its a given that temperatures will be cooler with the additional moisture and cloud cover. As dynamics wane and moisture slowly decreases late week, chances for showers and thunderstorms lower from west to east heading into the holiday weekend. && .AVIATION...For McCarran...Light winds favoring an easterly direction will remain before giving way to southwesterly winds this afternoon around 22Z. Expect winds around 10-12 knots with some occasional gusts around 15-20 knots lasting through 03-04Z. Winds will decrease overnight, eventually becoming light and variable. Skies will be mostly clear, with some FEW aoa 12 Kft this afternoon. For the rest of southern Nevada, northwest Arizona and southeast California...Typical wind patterns are expected across the region today with some afternoon southerly breezes possible. Gusts should generally remain below 20 knots with winds returning to typical drainage patterns tonight. Skies will be mostly clear with some FEW aoa 12 Kft across some of the higher terrain in the Mojave Desert. Although, haze from distant wildfire smoke will reduce slant range visibility at times, especially across the Sierra, western Mojave Desert and parts of the southern Great Basin. At KBIH, wildfire smoke is not expected to be quiet as dense tonight, and may not even drop below 7 SM based on the latest HRRR Smoke Runs. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && $$ UPDATE...Adair DISCUSSION...Pierce AVIATION...Peters For more forecast information...see us on our webpage: or follow us on Facebook and Twitter