Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/11/19


Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
903 PM PDT Sat Aug 10 2019 .SYNOPSIS...10/637 PM. Areas of low clouds and fog will develop over most of the coast tonight and gusty north winds are expected over southern Santa Barbara county through late tonight and then again on Sunday night. Temperatures will be on the rise Sunday through Tuesday as an upper level trough exits the region and a ridge moves in. && .SHORT TERM (TNT-TUE)...10/902 PM. The latest satellite imagery shows an upper-level trough over southeast Oregon, and lifting out into northern Intermountain region, while an upper-level ridge remains anchored over north Texas. As the trough`s influence wanes across the area, high pressure aloft will build in gradually. 500 mb heights slowly climb each day and a warming and drying trend will likely develop. The warming is well encapsulated and only a minor tweak will be made to mountain temperatures for Sunday. A stubborn and shallow marine layer remains in place this evening. Stratus is pushing a bit faster into the Central Coast this evening versus last night. The latest AMDAR soundings from KLAX indicate a marine layer depth near 700 feet deep this evening. With a shallow marine layer in place, dense fog could develop overnight tonight and into Sunday morning, especially along the Central Coast. Observations are being monitored closely this evening for the possibility of broader dense fog. Motorists traveling late tonight and early Saturday morning are advised to use caution. Slow down, use low beam headlights, and increase the space around your vehicle and the vehicles around you. Gusty Sundowner winds continue across southern Santa Barbara County this evening. KSBA-KSMX surface pressure gradients are a bit tighter tonight versus last night. A wind advisory remains in effect and drivers of high-profile vehicles, such as RVs and large trucks are advised to slow down and use caution. Gusty cross winds could make controlling your vehicle difficult. Marginal near- advisory level winds are also possible through Interstate 5 Corridor tonight and into Sunday morning. Local advisory level gusts could be reached on favored peaks, such as Whitaker Peak near the Los Angeles-Ventura County line. An update will be issued shortly. ***From Previous Discussion*** As heights continue to nudge upward Monday into Tuesday, look for gradual warming and drying trend to continue, especially interior mountains and valleys, as well as the deserts. As the marine layer becomes more shallow, looking for night and morning low clouds and fog to mainly be confined to coastal areas by Monday and Tuesday. .LONG TERM (WED-SAT)...10/214 PM. Warm temperatures will continue on Wednesday as the upper level pattern shows little change. Then from Thursday through Sunday the long range models are showing another upper level trough deepening across California. This will lead to a cooling trend Thursday through Saturday, along with increasing onshore winds in the mountains and deserts. && .AVIATION...11/0104Z. At 00Z, the marine layer depth was around 750 feet deep at KLAX. The top of the marine inversion was near 1400 feet with a temperature near 19 degrees Celsius. There was another inversion up to around 2500 feet. Moderate-to-high confidence in the current forecast. Higher confidence for inland terminals and in flight categories, less confidence for coastal terminals and in timing. Timing could be up to +/- 2 hours. LIFR to IFR conditions will likely develop at Central Coast terminals through at least 15Z. IFR to MVFR conditions will likely develop at coastal terminals south of Point Conception, except KSBA. VFR conditions should redevelop between 15Z and 17Z. There is a chance of moderate wind shear and turbulence at KSBA between through 08Z. KLAX...There is a 40 percent chance of VFR conditions through the period. The most likely time period for IFR conditions between 10Z and 14Z. VFR conditions should redevelop between 15Z and 17Z. KBUR...VFR conditions are expected throughout the period. && .MARINE...10/755 PM. For the Outer Waters, moderate-to-high confidence in the current forecast. Small Craft Advisory (SCA) winds are expected across the two northern outer coastal waters (PZZ670-673) through late Mon night and possibly into Tue. There will also be a 70% chance for the southern outer waters (PZZ676) to continue with SCA level winds through late Sunday night. There will then be a 50% chance of SCA level winds across the outer waters Wed and Thu. For the Inner Waters north of Point Sal, moderate confidence in the current forecast. There is a 60%-70% chance of SCA level winds during the afternoon and evening hours through Mon. After a lull Tue and Wed, there will be a 40% chance of SCA level winds Thu. For the Inner Waters south of Point Conception, moderate confidence in the current forecast. There is a 60% chance that SCA level winds across the western SBA Channel will continue through tonight. The strongest gusts will be south of Refugio to Gaviota with NW to N winds while the rest of the channel will be affected by westerly winds. There is a 30% chance of SCA level winds for the western portion of the Santa Barbara Channel on Thu as well. Otherwise, conditions are forecast to remain below SCA levels. && .FIRE WEATHER...10/326 PM. The strong upper level trough over the West Coast that brought cooler temperatures and higher humidities to most areas today will move north, as an upper level high builds over the area from the east during the next few days. Onshore winds will continue to range between 25 and 35 mph across interior sections (with isolated gusts to 40 mph in the foothills of the Antelope Valley) through this evening. The lingering dry air over the Antelope Valley and Los Angeles County mountains will remain through the early evening, with humidities generally ranging between 15 and 25 percent. The dry conditions combined with gusty onshore winds will result in elevated fire weather conditions through this evening across these areas. A gradual warming and drying trend will occur Sunday through Tuesday across interior areas, bringing elevated fire weather concerns. Gusty sundowner winds are expected to be stronger and more widespread late this afternoon into tonight across the Santa Barbara south coast and Santa Ynez mountains, strongest across western canyons and foothills from Gaviota to Goleta where wind gusts between 35 and 45 mph will be common. Isolated gusts up to 55 mph will be possible in and around Gaviota. Wind gusts of 30 to 40 mph are also possible near Montecito Hills. Temperatures will warm into the lower to mid 80s in the foothills and downslope coastal areas through the early evening hours. The combination of gusty sundowner winds, lowering humidities, and warm temperatures will result in elevated fire danger across southern Santa Barbara County late this afternoon into tonight, especially western portions. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory in effect until 3 AM PDT Sunday for zones 39-52. (See LAXNPWLOX). PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for zones 645-650. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Tuesday for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Monday for zone 676. (See LAXMWWLOX). && .HAZARD POTENTIAL OUTLOOK (TUE-SAT). No significant hazards expected. && $$ PUBLIC...Hall/Gomberg AVIATION...Hall MARINE...Smith FIRE WEATHER...Delerme SYNOPSIS...Stewart weather.gov/losangeles
Area Forecast Discussion
National Weather Service Phoenix AZ
845 PM MST Sat Aug 10 2019 .SYNOPSIS... Increasing moisture ahead of a fairly strong disturbance coming out of northern Mexico today will cause scattered to widespread showers and thunderstorms through Sunday morning over southern and eastern Arizona. Heavy rainfall is expected late this afternoon and evening across southeast Arizona and areas just south and east of Phoenix. Temperatures will remain slightly below normal for most areas except southeast California and southwest Arizona where temperatures will be near normal with drier air preventing any rainfall chances to the west. Dry air will begin to sweep eastward late this weekend through most of next week, pushing thunderstorm chances east into New Mexico as above normal temperatures return. && .DISCUSSION... Impressive and well defined upper disturbance/inverted trof over southeast and east-central Arizona continued to lift to the northeast early this evening ahead of a large upper trof moving into the Pacific Northwest. Latest SPC mesoanalysis page showed that the primary dynamics/differential vort advection associated with the feature was across far eastern AZ, mainly east and southeast of Globe. There was a bit of difluence/divergence aloft at 300mb mainly over southern Gila County ahead of the advancing inverted trof. 3 hour MLCAPE/surface based CAPE trends show values down substantially over most of Arizona except a small strip near the New Mexico border. Earlier southerly outflow winds helped to cool the boundary layer into the mid 90s and Phoenix is now at 88 degrees. So it now appears that convection and showers are mostly over for the central deserts including the greater Phoenix area for the rest of tonight as subsidence continues to move in behind the exiting disturbance. We have cancelled the majority of the Flash Flood Watch except for portions over southern Gila County which may still see some forcing and scattered showers (maybe a storm) past midnight. Given the high moisture in place and potential slow storm movement, flooding issues are not over to our east. Plus, the watch blends seamlessly with our surrounding office. Forecasts have been tweaked and POPs trimmed back across much of the area and now agree much better with expected trends for the rest of tonight. && .PREVIOUS DISCUSSION... Scattered to widespread showers and thunderstorms are ongoing across Pima County and southern Pinal County this afternoon in association with the inverted trough/MCV still located over northern Sonora. Additional isolated thunderstorms are developing along the Mogollon Rim with additional cells in southern Gila County near Globe. We expect that these cells will continue to increase in coverage along the fringes of the mid-to-upper level cloud deck associated with the MCC centered over Tucson whose deepest convection is continuing to expand on its south and west side towards the greatest instability. Although instability should increase a bit along the northern and western fringes of this MCC, significant mid-to-upper level drying and a relatively strong midlevel capping inversion over the Phoenix metro and to the north and east should prevent convection from holding together as it pushes southwest. Aircraft soundings from the east and southeast suggest that the midlevel cap is beginning to erode into a weaker stable layer that may erode more as deeper moisture moves in from the south. This should allow cells to increase in coverage over Gila County and potentially northern Pinal County, with clusters producing locally heavy rainfall and moist downbursts in this area for the next several hours. There is more uncertainty for convection developing east of Gila Bend where mid-to-upper level drying moving in from the southwest ahead of the longwave trough may preserve the midlevel stability, but moisture advection from the southeast may increase instability enough to allow for some locally heavy rainfall. Based on this, we will maintain the current spatial area of the Flash Flood Watch through 5 AM MST Sunday, but the western and northern fringes of which may be cancelled later this evening depending on how convection evolves over the next several hours. There is still concern that after a brief lull later this evening, we may see an uptick in convection later in the overnight hours as a new MCV or two associated with the stratiform region of the ongoing MCC forms. Although the broader inverted trough should continue to move north through eastern Gila County along the western fringes of the subtropical high centered over Texas, we cannot rule out the potential for a more localized circulation to develop further west and track northward. If this occurs, additional showers and thunderstorms may develop overnight over northern Pinal, eastern Maricopa, and Gila Counties with storm motions being very slow (given Corfidi vectors less than 5 knots possibly favoring backbuilding convection). The greatest potential for heaviest rainfall tonight appears to be over southern Gila County where multiscale interactions between any more localized MCV circulations and the larger-scale inverted trough may occur. Several model simulations still show 1-2 inch per hour rainfall totals for southern Gila and northeast Pinal Counties, with very few showing anything significant further south and west aside from light to moderate showers which should verify assuming a new MCV does not develop. On Sunday morning, the shortwave trough moving to our northeast will accelerate and weaken as it is picked up by the midlatitude shortwave moving through the Northern Rockies. The flow aloft across Arizona will remain out of the west with drying conditions taking over across the entire state. Sufficient lingering low and mid level moisture on Sunday will likely cause scattered showers and thunderstorms across eastern Arizona including Gila County, but they should be relegated to higher terrain areas only. The lower deserts will see drier air mixing down to the surface, especially west of Phoenix allowing high temperatures to warm closer to 105-107 degrees. Sunday`s highs for the Phoenix area look to remain slightly below normal, but warmer than previously thought with highs around 101-103 degrees due to the clearing skies and drier air aloft. that will eventually translate to surface drying by Monday. After tomorrow, next week looks dry and hot as the subtropical high rebuilds and strengthens to our southeast. This will allow for rising heights across the Desert Southwest with 500mb heights of 592-595dm for Tuesday and Wednesday. The higher heights and drier air will easily allow temperatures to warm to above normal as early as Monday, but especially Tuesday through Thursday. Highs by Tuesday should be hitting or even topping 110 degrees across the lower deserts with an Excessive Heat Watch possibly being needed on Tuesday with more of a likelihood on Wednesday. The heat should persist into at least Thursday, after which there are some indications of moisture seeping back into portions of at least southeast Arizona late in the week. A weak inverted trough loosely associated with a PV fracture that splits off from the longwave trough and front over the eastern half of the U.S. on Wednesday may eventually move west along the southern fringe of the ridge to improve rainfall chances over Arizona by next Friday or Saturday. && .AVIATION...Updated at 0000 UTC. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: A large upper disturbance was currently located over southeast Arizona, moving slowly towards the northeast. Most of the forcing should keep showers/storms off to the east of the terminals tonight but still expect at least isolated showers from 02z through 08z or so. Do not expect thunder at the terminals tonight but chances are not zero. As of 5 pm a few weak storms were near Ak-Chin and moving north but they will likely dissipate before getting into the terminals. Main impact weather wise will be outflow winds, initially mainly from the south and up to around 30kt, but they could vary between southeast and southwest over the next 2-3 hours. After 03z, winds should mainly focus out of the east/southeast and should dissipate below 20kt. Overnight may see some lower cloud decks - down to around 5k feet - develop with wrap around moisture coming into the area, but any CIGs likely to stay at 8k and above. For tomorrow should see thinning moisture and little if any chance for precip. Mainly FEW-SCT decks from 6k to 9k feet across the central deserts. Southeast California/Southwest Arizona including KIPL and KBLH: No significant aviation impacts expected over the next 24 hours. Dry southwest flow aloft will keep skies generally clear. Look for winds to favor the south to southwest at KBLH with some afternoon south breeze to near 20kt possible. Winds to favor the southwest/west tonight at KIPL becoming light variable or light southeast during the day on Sunday. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Tuesday through Saturday: A much drier pattern is expected for most of next week with very few thunderstorms expected even over higher terrain locations. Temperatures will warm several degrees above normal amidst the drier air mass, with winds following typical diurnal trends. Humidity values will generally drop into the upper single digits to mid-teens across the lower deserts while remaining above 20 percent over the higher terrain every day except on Wednesday. Overnight recovery will generally be poor to fair except at higher elevations where better recovery is expected. Moisture will begin to increase on Friday or Saturday as moist southerly flow aloft and isolated thunderstorms at higher elevations return. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Flash Flood Watch until 5 am MST Sunday for AZZ552-556-558- 560>563. CA...None. && $$ DISCUSSION...CB PREVIOUS DISCUSSION...Hopper/Kuhlman AVIATION...CB FIRE WEATHER...Hopper