Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 06/29/21

Area Forecast Discussion
National Weather Service Phoenix AZ
452 PM MST Mon Jun 28 2021 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... A major uptrend in humidity and thunderstorm activity will take place over the next few days. Strong winds will be the main impact from any storms today and Tuesday. Additional moisture on Wednesday will allow storms to produce more rainfall. However, many uncertainties remain exact locations of storms and rainfall amounts. There is higher confidence in high temperatures trending down, even dipping below normal by Wednesday and Thursday. Storm chances are anticipated to slowly decline from west to east during the latter part of the week and over the weekend. High temperatures are anticipated to slowly increase as well. && .DISCUSSION... Latest water vapor imagery depicts an anomalous trough across southwestern NM. The moisture plume from this trough extends southward towards Hurricane Enrique, off the west coast of Mexico. Meanwhile, the anticyclone producing historic record breaking temperatures remains situated across the Pacific Northwest. Between these two systems, a stronger than normal north- northeasterly flow is evident across Arizona. Latest KPSR sounding from 12z measured 30 kt at 500 mb. Mean layer flow off the higher terrain along with somewhat above normal PWATs will promote isolated convection reaching and possibly even developing across portions of the lower deserts this afternoon. Latest HREF indicates storms will initiate across eastern Gila County this afternoon. Latest U of A WRFs then suggest a strong westward-propagating outflow boundary will develop out of this convection. Latest HRRR indicates a 50% chance of 35+ mph wind gusts across the Valley, with the highest likelihood across Pinal County. Consequently, a Blowing Dust Advisory has been issued for the dust-prone areas of southeastern Maricopa and Pinal Counties for this evening. The boundary may also be strong enough to overcome any convective inhibition. Isolated storms are possible in the Valley tonight, though a general lack of CAPE will limit the overall coverage of storms. The environment also still remains more conducive for wind/dust/lightning, rather than heavy rain. Storm chances will increase Tuesday as total PWATs increase above an inch. Latest SREF indicates the aforementioned vort max across southern Mexico will migrate westward into a more favorable position for synoptic ascent across southeastern Arizona. However, CAMs are now displaying more variability. Some are developing activity early and with an expanse as far west as southeastern California. Others suggest storms will remain concentrated across south-central Arizona with another threat of an outflow boundary capable of producing blowing dust. Both scenarios could even materialize, resulting in a possible outflow boundary collision across the lower deserts. && .PREVIOUS DISCUSSION... Moisture availability continues to increase on Wednesday. That will enable any storms to be better rain producers. It remains to be seen what influence the aforementioned inverted trough will have at that point. Also, it remains to be seen how unstable the boundary layer will be which will be heavily influenced by the preceding day`s convection. Despite the increase in moisture, the GEFS plumes don`t depict much change in the CAPE from Tuesday to Wednesday. However, the SREF actually shows a decline (possibly due to some boundary layer stabilization). A lot of uncertainties remain. The big picture takeaway is that we will be seeing a major uptrend in thunderstorm activity and associated impacts over the region during the first half of the workweek. High temperatures trend down as well (below normal). Ensemble data depict a decline in moisture starting as early as Thursday over southeast California (remaining steady or even peaking a little more over south-central AZ). The NAEFS shows a decline over the weekend. The EPS does as well but more slowly. Meanwhile, high pressure becomes centered roughly over Arizona during the latter part of the week. But at this time it doesn`t appear to be overly strong. The PoPs follow the moisture trends. Temperatures slowly trend upward during the latter half of the week and into the weekend. && .AVIATION...Updated at 2350Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Wind speeds and directions will continue to be the primary aviation weather concern through this evening. For now, wind directions will continue to favor a south-southeasterly direction with speeds mostly between 8-12 kts and occasional gusts of 16-20 kts. Directions may veer more southerly at times creating temporary crosswinds for any east-west runway orientations. Meanwhile, attention remains focused on the thunderstorm activity moving westward from the White Mountains into Gila County. These storms are expected to send an easterly outflow through the terminal area late this evening between 2-6Z. There is less confidence assessing the potential wind strength of the switch for any particular airport, but gusts between 15-30 kts are anticipated, as is the potential for blowing dust (30% chance) at KIWA. There is a low chance for storms tonight, 20% or less, favoring the far eastern portion of the Phoenix area. The most current anticipated timing and strength of the wind shift is in the latest TAF package but will be amended to reflect any updates as the storms and winds evolve. For tomorrow, thunderstorm activity is likely to increase across the Mogollon Rim and westward through Yavapai County, thus increasing the chances for northerly outflows and VCTS in the terminal area late Tuesday afternoon. Southeast California/Southwest Arizona including KIPL and KBLH: There is some uncertainty regarding aviation weather towards the latter half of the forecast period. For this evening, southeasterly winds at 8-12 kts and occasional gusts are anticipated at KIPL, while winds maintain a more southerly heading at KBLH at 7-13 kts with some overnight gustiness. For tomorrow, there is potential that thunderstorm outflow winds move through the terminal area from the north-northeast late in the evening. Convection cannot be ruled out either but confidence in either of these two outcomes is too low to mention in the TAFs for now. && .FIRE WEATHER... Thursday through Monday: Humidities will peak midweek with Min RH values of 20-30% on the lower elevations (30-40% higher terrain). Max RH values will be highest on Thursday morning with readings of 40-60% most places (locally higher). Storms on those days, if any, would have the potential to produce localized flooding - especially on burn scars. High temperatures will also be at their coolest (several degrees below normal over south-central AZ). Atmospheric moisture and storm chances slowly decline from west to east late in the week and over the weekend. However, isolated showers and thunderstorms will remain a threat across much of the area. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST this evening for AZZ530- 532. Blowing Dust Advisory until 9 PM MST this evening for AZZ550-551- 553-554. CA...Excessive Heat Warning until 8 PM PDT this evening for CAZ560>570. && $$ DISCUSSION...Hirsch PREVIOUS DISCUSSION...AJ AVIATION...AD FIRE WEATHER...AJ/Hirsch
Area Forecast Discussion
National Weather Service San Diego CA
843 PM PDT Mon Jun 28 2021 .SYNOPSIS... Weakening high pressure and an influx of monsoonal moisture into Southern California through Wednesday, will bring some clouds and cooling, along with a chance for mainly afternoon and evening showers and thunderstorms, decreasing on Thursday. The best chance for showers will be over the mountains and deserts through Wednesday, while the marine layer and associated clouds hold over coastal areas with continued cool Summer weather. The moisture decreases on Thursday, along with the chance for showers, leading to a fair and dry weekend with seasonal temperatures. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... -Forecast Highlights- * Scattered thunderstorms Tue-Thu afternoon mountains/deserts * Main potential impacts: Lightning strikes, downburst winds * Less impact: Localized heavier rainfall/low flash flood risk Marine clouds held firm along the coast and offshore today and continue this evening, while higher clouds spread southwestward from the high deserts. A moderate coastal eddy continues to support marine stratus and south winds along the coast, which should spread inland tonight with moderate onshore sfc pressure gradients. Our 00Z sounding remained little changed from 24 hours prior. The marine inversion was based at 1900 FT MSL, and was about 16C, peaking near 31C at 4000 FT MSL. An elevated moist layer was at 16K FT where several high-based cumulus congestus developed over the mountains this afternoon, and spread anvils downwind over the valleys. The weakening of the ridge aloft is still expected to bring cooling, so the Excessive Heat Warning and Advisory will expire at 9 PM this evening. No other forecast changes. From previous discussion... Mid-high level moisture will be increasing from the northeast through Tuesday, underneath the anomalous ridge over the Pacific Northwest, which is resulting in record-shattering and very high impact heat there. The moisture on Tuesday will be highest aloft over San Bernardino County. Hi-res models of the HRRR and local WRF are continuing to show the only cells developing on Tuesday afternoon being over the San Bernardino County mountains and the Mojave desert. Most cells only dropping about 0.10-0.25", though the local WRF does show heftier cells over the Mojave Desert to about 0.50"/hr, but given the dry low levels this may be overdone. HRRR shows less activity and lower rainfall rates. The higher potential impact looks to be potential downburst winds versus flash flooding. There could be a few showers and thunderstorms moving southwest from Nevada Tuesday night, but model consensus keeps the bulk of this convection over SE California and just outside of our service area, but will have to monitor this as some of this could skim the Coachella Valley Tue night-Wed morning. The coverage of tstorms looks to increase across the mountains on Wednesday afternoon as better lower level moisture moves in from the southeast, but not looking too deep/significant as it had looked a few days ago. The prevailing flow will be westerly, so the coast and valleys likely will stay dry, except perhaps portions of the Inland Empire. The tstorms on Wednesday afternoon will favor the desert mountain slopes with the heaviest cells occurring over the Riverside (Santa Rosa Mountains) and San Diego County mountains where cells could drop about 0.50"/hr. Very localized flash flooding is possible, particularly along the desert mountain slopes and over the deserts. Again, the microburst/damaging wind potential looks to be a greater risk, though that would be localized as well. With the moisture aloft and fairly dry air continuing in the lower levels, thunderstorms will be capable of producing strong and potentially damaging downburst winds, which could lead to blowing dust over the deserts. The moisture will be advecting east on Thursday. There could still be isolated thunderstorms in the afternoon over the mountains and deserts, but less activity compared to Wednesday, and it is possible it could be dry if not much moisture remains. Friday and through the holiday weekend will see a slow warming trend along with expected dry conditions. Monsoonal moisture will be just off to our east over SE California and Arizona. The model consensus keeps moisture at bay here until perhaps later next week when a moisture return is possible. Until then, the upcoming weekend and into the following week looks tranquil with above normal temperatures likely. && .AVIATION... 290330Z...Coast/Valleys...BKN-OVC stratus will continue to spread overnight, up to 25 miles inland by 12Z Tue. Bases will be 800-1100 ft MSL with tops to 1300 ft MSL. Local vis 2-4 miles will occur over higher coastal terrain and in the coastal valleys. Most areas will clear 15Z-17Z Tue, except 18Z-21Z Tue within 5 miles of the coast, with BKN/OVC conditions continuing through the afternoon near the beaches. Conditions Tue night will be similar to tonight. Mountains/Deserts...SCT-BKN clouds above 20000 ft MSL will prevail through Tue evening. There is a chance of thunderstorms Tue afternoon/evening, with greatest likelihood in the mountains. CB bases will be 10000 ft MSL with tops to 40000 ft MSL, with strong up/downdrafts and local surface gusts to 50 knots possible in/near thunderstorms. && .MARINE... No hazardous marine conditions are expected through Saturday. && .FIRE WEATHER... An influx of monsoonal moisture will bring a recovery in humidity Tuesday into Wednesday with a chance for mainly afternoon and early evening thunderstorms, and mainly in the mountains and deserts. There is greater potential for dry lightning strikes on Tuesday afternoon as the moisture begins to increase, then again on Thursday afternoon as the moisture decreases. Wetting rains are most likely on Wednesday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ PUBLIC/FIRE WEATHER/...10/Gregoria AVIATION/MARINE...Maxwell