Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/28/21

Area Forecast Discussion
National Weather Service Denver/Boulder CO
857 PM MDT Mon Sep 27 2021 .UPDATE... Issued at 852 PM MDT Mon Sep 27 2021 Other than a few isolated showers in southern Park County, the region is mostly dry. Water vapor imagery shows mid-level moisture advecting into portions of central and eastern CO, although profiles remain dry near the surface reducing chances for showers overnight. Can`t rule out a stray shower over Park and Summit counties in the early morning hours. Dry air will likely prevent any rain from reaching the ground. We didn`t change the forecast for Tuesday much, it is still looking like it will be 5-10 degrees cooler than Monday with increasing clouds throughout the day. Shower and thunderstorm chances increase in the afternoon with the best chances over the higher terrain. Model profiles appear to be quite dry at the surface and instability is limited which will reduce heavy rain potential; however, gusty outflow winds up to 25 mph are possible. && .SHORT TERM...(This evening through Tuesday) Issued at 224 PM MDT Mon Sep 27 2021 Current observations across the region show dew points ranging from the upper 20s to lower 30s across the region while a high pressure system remains dominate over the state. This evening winds will decrease due to a low pressure system moving eastward decreasing the pressure gradients for areas east of Interstate 25. Above-normal low temperatures and party cloudy skies are expected tonight. A change of pace will occur Tuesday as high temperatures will be cooler due to a trough arriving in the afternoon. The GFS and HRRR are in agreement with dry air still remaining east of Interstate 25. PoPs were increased between 18Z-00Z for areas west of Interstate 25 due to NBM and NAM keeping dew points higher and scattered thunderstorms for that area. Any thunderstorm that does form will have difficulty to sustaining especially east of the Interstate 25 due to a lack of instability and dry surface to mid levels. Areas west of I-25 could receive QPF ranging from 0.10-0.25 inches through Tuesday evening. .LONG TERM...(Tuesday night through Monday) Issued at 224 PM MDT Mon Sep 27 2021 Synoptic pattern in the long term sees a series of slow moving shortwave troughs with main branch of westerlies well north into Canada. Second half of the extended has a cut off low over northern plains. Temperatures trend near to below normal from Tuesday night onward, with periodic chances for precipitation. Extended picks up at midnight Tuesday night, with lingering mountain showers and snow showers over the higher terrain behind departing weak shortwave trough. A cold front knocking on our door at midnight will sweep through the forecast area by sunrise, with a marked difference in temperatures and highs 15 to 20 degrees cooler than previous days. Wednesday morning a sharpening, slow moving 500 mb trough moves out of the NW US and only reaches UT/CO border by 12z Thursday. Mid levels dry during the overnight hours, with 700-500 mb specific humidity around 3.5 g/kg in the mountains Wednesday, down from over 5 g/kg in the mountains 24 hours earlier. Precipitable Water also drops from around 1/2 inch on Tuesday to .3 inch on Wednesday. Higher moisture remains on the plains, around 1-2 standard deviations above normal for this time of year. Even with the lower moisture content cooler air associated with the trough keeps RH and POPs high, with likely to categorical pops in the mountains and high chance to likely on the plains for Wednesday. Precip type will be snow over the summits during this period. Trough weakens and continues to move slowly Thursday, and by Friday is cut off from jet stream to north. However with trough axis and upper cold pool still over the region there will be enough instability to keep chance pops going mainly in the mountains. Snow levels in the center of the trough axis/upper cold pool drop to 8000 ft north to 9500 ft south early Thursday morning, then rise to over 10,000 ft west of the divide as heights rise behind the trough. Heading into Saturday another shortwave trough moves across WY/MT, then cuts off over the northern plains Sunday and Monday. Upper low even retrogrades into eastern MT/NE WY Monday, with northern jet stream into the northern Canada provinces and weak flow over the CONUS. A very odd pattern for early October. Chance pops in the mountains into northeast plains with some cold air aloft and QG ascent late Saturday into Sunday, and continued cool temperatures. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 605 PM MDT Mon Sep 27 2021 VFR conditions will continue tonight through Tuesday. A period of increased winds is possible after 03z; however, gusts above 15 kts are not anticipated. Winds shift SE this evening returning to southerly drainage by the early morning hours. All terminals should stay dry overnight with dry air in place near the surface. Winds will be primarily out of the SE during the day Tuesday. Showers develop over the mountains and foothills in the early afternoon. Chances are low for showers to extend east; however, it can`t be ruled out for a stray shower or two to wander onto the plains. This outcome could suggest the potential for gusty outflow winds in the 20-00z timeframe. && .FIRE WEATHER... Issued at 224 PM MDT Mon Sep 27 2021 A cold front will move through the region early Wednesday morning with strong north winds, cooler temperatures and chance for rain showers with snow on the summits Wednesday. For Thursday snow levels dropping to 8000-9000 feet. Some drying Friday with lower pops, then a chance again into the weekend. Inversions will limit dispersion overnight, and during the day mixing will only extend up to 5,000- 7000 ft AGL. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Mensch SHORT TERM...AD LONG TERM...Hanson AVIATION...Mensch FIRE WEATHER...Hanson
Area Forecast Discussion
National Weather Service Grand Junction CO
527 PM MDT Mon Sep 27 2021 .SHORT TERM...(Tonight through Tuesday night) Issued at 121 PM MDT Mon Sep 27 2021 Satellite imagery clearly shows circulation around the closed low that looks to be centered over central New Mexico at this hour. Short range CAM guidance was indicating some convection firing around noon over the San Juans but this has yet to really materialize thanks to cloud cover from earlier this morning. However, the best CAPE remains over the San Juans, along with some fairly strong divergence aloft. With some clearing taking place do expect some convection to take place...just a bit later than guidance suggested. Moving northward, CAM guidance was also showing some convection over the West Elk, Elk Mountains, Grand Mesa and a passing threat along the Bookcliffs. Thanks to the location of the low, convection will move from east to west (or southeast to northwest). Visible imagery and webcams do show some development at this hour so the going forecast for a few showers/storms looks good. PWATs have increased by about .2 inches over the last 24 hours so though the biggest threat remains gusty outflow winds, a quick downpour also can`t be ruled out. Latest 15min HRRR guidance is showing the strongest convection to move through the San Juans and southern valleys from about 5 to 6PM before dying down after 9PM. Again, look for some gusty winds with some brief downpours. A few showers may persist overnight but these will be very isolated in nature. Things get more interesting Tuesday as the low moves northeast to the Front Range while a trough approaches from the northwest. Once again, the San Juans will be favored for precip around noon but as the low continues to progress northeastward, plenty of lift and increased moisture will lend themselves to increased precipitation. Like today, the ingredients look to be in place for some convection but cloud cover may inhibit the timing and strength of any convection. For now, precip looks to favor all the higher terrain through 6PM and then shifts to the northern half of the CWA heading from mid-evening onwards...following the closed low. In fact, the heaviest QPF is progged to fall from 9PM Tuesday night through Wednesday morning for the northern valleys. The approaching trough/surface cold front will also aid in increased lift so some steady stratiform precip with some embedded convection looks probable. Snow? Wouldn`t be surprised to see a dusting to an inch near 11K feet. Expect temperatures to be cooler Tuesday thanks to increased clouds and precip with a noticeable dip Wednesday. .LONG TERM...(Wednesday through Monday) Issued at 121 PM MDT Mon Sep 27 2021 Model solutions continue to remain in decent agreement that the best forcing for ascent associated with the main upper level trough will focus precipitation generally from I-70 northward. This precipitation will last into the evening and is expected to come to an end overnight. Temperatures Wednesday will be 10-15 degrees below average across this portion of the area, while remaining more seasonal to the south. With the blocky pattern in place...and being the shoulder season...model consensus has been inconsistent at best. Models continue to indicate that energy from the stalled trough over the Rockies will split off and drop south, but agreement ends there. Some models, namely the EC, want to keep this parcel of energy further north over Arizona and bring wetter conditions to southwest Colorado and southeast Utah for Thursday night into Friday. The other camp, with the GFS and NAM on board, have the energy parcel much further south, over the Baja peninsula, and a much drier forecast. Stay tuned for subsequent forecasts, as model solutions will likely continue to change from run to run and, hopefully, will fall into better agreement for the late week period. Temperatures for this period are also a bit of a question mark due to the lack of model agreement and the subsequent large spread in the MOS guidance. So, for the time being, expect temperatures to be right around seasonal. At this point, the weekend forecast is looking drier as a shortwave ridge is expected to push up over eastern Utah and western Colorado. Should this forecast verify, the weekend will bring a welcome pause from unsettled weather with temperatures near seasonal values. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 519 PM MDT Mon Sep 27 2021 Showers and storms will continue through the evening for KDRO and KTEX, with lingering showers possible overnight as a system passes through to the south. Cloud cover will continue to increase from southeast to northwest over the course of the next 24 hours. VFR conditions are expected to prevail, although MVFR will be possible within any showers/storms. At any rate, expect mountain obscuration to intensify through the afternoon tomorrow. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...TGR LONG TERM...BGB AVIATION...TGJT
Area Forecast Discussion
National Weather Service Gray ME
1028 PM EDT Mon Sep 27 2021 .SYNOPSIS... Temperatures continue a downward trend this week as an upper level low settles in overhead. A weak area of low pressure will cross New England tonight, bringing rain showers overnight and into tomorrow as a cold front sags southward through New England. A mix of sun and clouds is expected through the duration of the week with the best chance for additional showers coming late Wednesday through Friday. The pattern becomes less certain this weekend as upper level low pressure attempts to make an exit, and high pressure works to build northeastward into the region. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 1025 PM Update...Cold front currently sagging into our northern zones at this time with scattered showers continuing ahead of it, as far south as KLEB. Forcing is pretty weak in association with this front, so we expect most locations to not pick up measurable rainfall overnight. However, we did increase PoPs across southernmost zones around 12z as upper support arrives and showers possibly become more numerous. A rumble of thunder would not be out of the question either with steep mid level lapse rates in place. However, the greatest threat would currently appear to be south of the area. 6PM UPDATE... Made some minor adjustments to precipitation chances over the next few hours based on radar trends. Very spotty showers in a streak across the southern part of the area are not likely to amount to much. More persistent streak of showers in the north stands a better chance of bringing some more widespread light rain. ORIGINAL DISCUSSION... Cold front shifts slowly across the CWA overnight, losing some steam as its dynamic support shifts NE. The areas of weak and scattered showers will continue to weaken in the south, while they should continue into the early evening in the north. The HRRR has had a good handle on this today. As the front moves from N to S late this evening and into the dawn hours, there will be little in the way of precip, but cannot rule out a few isolated showers or sprinkles. By tonight, skies will become mostly cloudy to overcast for most of the area, and with enough SW flow keeping winds up to around 5-10 mph in all but the very sheltered areas, temps will not fall too much tonight, with lows ranging from 45-50 in the ME mtns /where some cooler and drier air actually works in behind the front/, to around 50 in the NH mtns, to around 60 in the south. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Another 500 MB wave will move around the closed low to our N, and pass across the mid-Atlantic on Tuesday. This will allow a wave to form on the front to our S. Most of the showers associated with this front will stay to our S, but cannot rule out a few showers N of the front in srn NH and York County ME, mostly in the morning through early afternoon. There will be a lot of clouds in srn NH and along the coast through midday, with a slow clearing in the N. But even southern areas could see some breaks of sun by mid-late afternoon. Will have to wait for this second wave to pass for another surge of cooler air to work in, so highs, especially in the S, will be above normal for another day, generally 65-70. In the mtns, look for highs around 60. Expect partial clearing on N winds Tue night, and cooler lows. Given the N flow and the potential for a fair amount of clouds, it doesn`t look like a rad cooling night, except for some of the sheltered mtn alleys where skies will clear out quicker and decoupling occurs. Lows in the mtns will generally be 35-40, and there is some possibility of frost, although could be a case of fog before frost with Tds in the mid-upper 30s as well. Outside the mtns lows will generally settle in the mid-upper 40s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Sensible weather conditions for the mid to later part of the work week will be dominated by an upper level cut off low across the Northeast. During this time, anomalously strong ridging will build across Northeastern Canada, leading to the very slow progression of the cut off low. There is also near universal agreement among the models that this low will help to keep Hurricane Sam away from the Eastern Seaboard and eventually steer it toward the Northeast. By the weekend the low is likely to be pulling away through Atlantic Canada, and ridging will build into the Northeast bringing rebounding temperatures and more sunshine. Breaking it down day by day, the cut off low center is likely to drift southward into New England late Wednesday and Thursday, bringing with it the coolest temperatures of the stretch and an increased chance for a few showers to the area. The increased chance of showers will persist from Wednesday night through Friday, with the greatest chance being during the afternoon hours due to increased instability. It`s also likely that some of the highest elevations will see their first flakes of the season, with the best chances for this occuring during the overnight hours. At this time it looks likely by Saturday the cut off low will be pulling away from the area and more sunshine will return, along with moderating temperatures for Saturday and Sunday. A shortwave traversing the edge of the larger low may try to bring an increased chance of showers to northern areas Saturday night, but this remains low confidence at this time. A large scale blocking pattern will likely still be in place across the North Atlantic late this weekend and into next week, so the amplification of any ridging into the Northeast remains low in certainty at this time. Other factors including the path and progression and of the remnants of Sam during this time period, and the progression of any shortwaves that move southward into New England also factor into a high degree of uncertainty in the forecast by early next week. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Short Term...MVFR possible at times tonight at KHIE, and a better for a period of MVFR at both KHIE and KLEB Tuesday morning. Any breaks in the clouds tonight, and will likely see some fog at both those places as well. Otherwise, expect VFR tonight thru Tue night. Long Term... Scattered showers are possible from late Wednesday through Friday, briefly bringing restrictions at times. MVFR to IFR ceilings are possible at times during this period, especially across northern terminals. By next weekend mainly VFR conditions are expected. && .MARINE... Short Term...SCA in place for SW flow ahead of a cold front tonight. Expect winds to peak this evening thru around midnight. Otherwise, Tue and Tue night will see sub-SCA conditions. Long Term... A broad upper level trough is expected to keep northerly winds below SCA criteria into the weekend. By the weekend large swells to near SCA height are possible as Hurricane Sam passes by far outside of the waters. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ150-152-154. && $$ NEAR TERM...Ekster SHORT TERM...Cempa LONG TERM...Clair AVIATION...Cempa/Clair MARINE...Cempa/Clair
Area Forecast Discussion
National Weather Service Newport/Morehead City NC
955 PM EDT Mon Sep 27 2021 .SYNOPSIS... High pressure centered over the region this morning will slide offshore through Tuesday. A dry cold front will cross Wednesday followed by high pressure building in from the northwest late week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... As of 955 PM Mon...1019mb high continues to gradually push offshore tonight with light SW flow continuing over much of eastern NC, although more sheltered locales have managed to decouple and see efficient radiational cooling. Some patchy overnight fog is possible again in these spots overnight, although impacts should be minimal. Prev disc...No major changes this update as high pressure centered over the coast dominates the near term. Light seabreeze slowly working inland while the high continues to slowly drifts eastward over the coast and offshore tonight. Dry air mass in place keeps cloud coverage minimal save for some fair- weather CU working in from SW of the CWA. Tonight, mostly clear skies will allow for decent radiational cooling but steady flow from the SW will usher in slightly warmer temps keeping the overnight lows mild, lower 60s inland to mid to upper 60s for coastal areas. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... As of 350 PM Monday...High pressure offshore elongates and pushes south as a SFC trough drops into the area ahead of an approaching cold front from the north. Generally dry conditions will persist, but this will likely be the warmest day of this week as low level thicknesses increase and SW flow returns, allowing afternoon highs to return to the mid to upper 80s. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... As of 220 AM Mon...Strong ridge of high pressure lingers into Tuesday. A backdoor front will drop south midweek to bring another round of cool temps. Another sfc high pressure builds in from the north to keep temps seasonable through the weekend. Wednesday and Thursday...Global models pointing at a mid level trough developing across the East Coast mid week, bringing a backdoor front through the region late Wed. Trough turns into a cutoff low Thu, lingering across New England. Main impact is much cooler air moving in Thu with persistent NErly flow behind the front, causing aftn highs to drop from the low to mid 80s Wed to upper 70s Thursday. Latest guidance excludes much shower activity along the front given a relatively dry profile. Friday through Sunday...Reinforcing backdoor front will drop through the region Friday with high pressure building in from the north behind it. Guidance keeps a dry airmass in place through the weekend, limiting much shower activity along the front. Expect seasonable highs in the upper 70s to around 80 across the region. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... SHORT TERM /through Tuesday Morning/... As of 740 PM Mon...VFR conditions through the period as high pressure shifts offshore but remains firmly in control through the short term period. HRRR and NAM model soundings, and LAMP guidance to a more subtle degree point to just enough low level moistening to potentially see some lower stratus west of Highway 17, as winds should remain up just enough to keep fog from forming. Confidence is too low to mention in 00Z TAFs for now but will need to be watched overnight. LONG TERM /Tue through Friday/... As of 225 AM Mon...Prevailing VFR conditions through the period. Dry high pressure will continue through Wednesday with a dry frontal boundary pushing through the region Wed aftn, turning winds N. High pressure builds in from the north behind the front to keep VFR conditions across all terminals. && .MARINE... SHORT TERM /through Tonight/... As of 400 PM Monday...High pressure will slide offshore this this afternoon and tonight. SSWerly winds 5 to 10 kts builds to 10 to 15 kts this evening and tonight with the stronger winds northern tier. Seas will continue in the 2 to 3 foot range with 9-11sec periods. LONG TERM /Tuesday through Friday/... As of 230 AM Mon...High pressure will shift offshore Tuesday with SWrly winds 10 to 15 kt. Winds surge a little Tue night, up to around 20 kts, ahead of a backdoor front that will approach the northern and central waters by Wed, turning winds Nrly around 15-10 kts through Thu. Winds back to the NE by Fri as high pressure builds in from the north. Seas a general 2-4 ft through the forecast period. && .MHX WATCHES/WARNINGS/ADVISORIES... NC...None. MARINE...None. && $$ SYNOPSIS...MHX NEAR TERM...MS/CEB SHORT TERM...CEB LONG TERM...ML AVIATION...MS/ML MARINE...ML/CEB
Area Forecast Discussion
National Weather Service Marquette MI
658 PM EDT Mon Sep 27 2021 .SHORT TERM...(This evening through Tuesday) Issued at 230 PM EDT MON SEP 27 2021 Water vapor imagery and RAP analysis show a mid-level low over northern Quebec with broad troughing from this feature into the ne U.S. Upstream ridging over the western Plains is expected to amplify into the northern Plains by Tuesday as a sharp trough from the eastern Pacific digs into the western CONUS. Over Upper Mi today upslope stratocu over north central zones has generally dissipated with temps rising into the lower to mid 60s under mostly sunny to partly cloudy skies. Sfc high pres over northern Ontario will settle over Upper MI tonight. This will set the stage for a cool night as winds fall off to calm over much of the fcst area under mainly clear skies. Precipitable water values initially around .5 inch (or around 70% of the daily normal) during the evening and early overnight could enhance radiational cooling potential a bit, so will lean toward the low end of temp guidance, putting much of the interior down into the mid to upper 30s F. This is similar to what was observed early this morning in the vicinity of the high pres in northern Ontario. So, expect some fog formation overnight over the interior as temps fall through the min dew point crossover temps of the mid 40s this afternoon. Tuesday, under sunny skies and weak WAA southerly flow, expect mixing near fcst 850 mb temps of 10-14C to yield max temps generally to range from the upper 60s east half to lower to mid 70s west, although there could be a few upper 70s readings over the western third of the cwa. .LONG TERM...(Tuesday night through Monday) Issued at 315 PM EDT MON SEP 27 2021 Warm and dry continue to look to be the dominating conditions for the first half of the long term period. The main culprit is an amplifying ridge and height anomaly that`ll stretch from the Central Plains upwards toward James Bay. The anomaly is expected to stretch well into the Arctic. This will allow temps to return to the 70s and lows in the 40s initially, before returning to near normal late this weekend. Toward the end of the week, the combination of a nearly stationary broad trough and upper level low downstream over the Canadian Maritimes and an approaching shortwave lifting northeast out of the Central Rockies and east or southeast across the Northern Tier look to squeeze and then deamplify the ridge. Similarly to yesterday, this morning`s 12z guidance lifts a surface front up the ridge`s western periphery Thursday night. The consensus appears to initially keep this west of our forecast area. From there though, there`s still not a clear picture on the pattern evolution and how ridging to our southeast will or will not keep this out of our region Friday and Saturday. Given the uncertainty in this and that of an upper level low ejecting out of the 4 corners region, the track and evolution of subsequent systems for the remainder of the weekend is also uncertain. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 658 PM EDT MON SEP 27 2021 VFR conditions will prevail at most of the TAF sites through the fcst period. However, there will be the potential for ground fog development overnight under calm conditions/clear skies and KSAW could be impacted with MVFR to IFR vsbys at times. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 230 PM EDT MON SEP 27 2021 North to northeast winds gusting to 20kt this morning have generally diminishied blo 20 kt this afternoon as sfc high pres over Ontario has builds over the lake. High pres will remain in the area thru Tue, resulting in winds mostly under 15kt across Lake Superior. With high pres ridging setting up from Hudson Bay to the Lower Great Lakes and a weakening low pres trof moving across the Northern Plains to the Upper Mississippi Valley for Wed thru Fri, there will be some increase in winds, but gusts should remain mostly under 20kt. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...Voss LONG TERM...JP AVIATION...07 MARINE...Voss
Area Forecast Discussion
National Weather Service San Diego CA
202 PM PDT Mon Sep 27 2021 .SYNOPSIS... A deep marine layer will persist through Wednesday morning with well below average high temperatures in the valleys and below average high temperatures elsewhere. Areas of mainly upper level smoke will spread southward across the area through Tuesday. Weak Santa Ana winds are forecast by Thursday, which will bring warmer and drier conditions with gusty northeast winds near the coastal mountain slopes and below passes and canyons. Much warmer and dry conditions will continue into the weekend as winds lighten. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... -Forecast Highlights- * Below normal temps, solid marine layer through Wednesday morning * Weak Santa Ana winds/Elevated fire weather conditions Thursday * Turning much warmer Thursday-Sunday Marine layer low cloudiness is holding on tight from the coast and across much of the valleys this afternoon. Clearing has occurred over much of the Inland Empire, but the current GOES satellite loop is not encouraging on much, if any, clearing elsewhere where the clouds are socked in. Patchy mist/drizzle continues. Clouds will fill back inland to cover the IE overnight with clouds remaining for the coast. This marine layer will remain in place through Wednesday morning as onshore winds strengthen with an incoming longwave trough from the northwest. A coastal eddy may even develop over the California Bight. This would only provide more vigor to this marine layer. Patchy drizzle will again likely occur tonight into Tuesday and is a possibility all the way through Wednesday morning. HRRR shows smoke aloft from the southern Sierra wildfires moving across Southern California through Tuesday night. This will lead to hazy skies. Surface smoke won`t be high though as most of the smoke is elevated, but there is some small amounts of near surface smoke. So even where it is clear inland, haze will prevail and may even be cloudy for a time. Clearing will occur Wednesday afternoon behind the trough. Surface high pressure will build into the Great Basin and this will lead to weak Santa Ana winds developing Wednesday night through Thursday afternoon. East to northeast gusts of around 30 mph is expected below the passes and canyons and along the coastal mountain slopes, peaking Thursday morning through afternoon. Winds will relax Friday through the weekend while getting hotter as upper level ridge builds in from the west. Just how hot it gets is uncertain, case in point at San Diego where the spread is from 79 degrees to 90 degrees on Saturday off the ECMWF ensembles. No matter what, it will be a noticeable change, especially for the coast/valleys. Followed close to NBM in the extended with just a nudge towards the hotter guidance based on precedence. && .AVIATION... 272015Z...Coast/Valleys...P6SM OVC015-020 and tops 030 with areas of VIS 3-5SM in -DZ/BR. Patchy VIS AOB 1SM in -DZ/BR/FG developing far inland overnight with higher terrain locally obscured. The risk of bkn-ovc conditions at KSAN this evening is moderate to high so confidence in KSAN low cloud forecast is moderate to high. After 18Z Tuesday P6SM with areas of SCT-LCLLY BKN025, except remaining BKN- OVC020-025 within 5-10 miles of the coast. Mountains/Deserts...Mostly clear with scattered clouds AOB FL100. && .MARINE... Northwest winds will increase Tuesday afternoon over the outer coastal waters, with gusts near 20 knots possible. Otherwise, no hazardous marine weather is expected through Friday. && .BEACHES... A long-period south-southwest swell and a modest west-northwest swell will bring elevated surf and a high rip current risk to the beaches into Tuesday. Sets to 6 feet are possible at Orange County beaches, and sets to 5 feet are possible at San Diego beaches. The south swell will gradually diminish Tuesday through Wednesday, though the west-northwest swell will continue the elevated surf and the high rip current risk in San Diego County on Wednesday. && .FIRE WEATHER... Weak Santa Ana winds on Thursday will bring warmer and much drier conditions for inland areas with locally gusty northeast winds near the coastal slopes of the mountains and below passes and canyons. Lowest humidity on Thursday will be 10 to 15 percent over the inland valleys and deserts and generally 15-20% over the mountains. East to northeast wind gusts to around 30 mph is favored. The combination of low humidity and gusty winds will bring elevated fire weather conditions the lower coastal slopes of the mountains, the inland valleys, and inland Orange County on Thursday. It will continue warm and dry into the weekend but with weaker winds. Weak onshore flow may return during the weekend which would bring a greater recovery in humidity for the coast into the valleys. && .SKYWARN... Skywarn activation is not needed. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ PUBLIC...Gregoria AVIATION/MARINE...Small
Area Forecast Discussion...UPDATED
National Weather Service Shreveport LA
957 PM CDT Mon Sep 27 2021 .UPDATE... Deep layer moisture advection will continue to increase through the overnight hours and will be enhanced further by the development of a southerly low-level jet after midnight. At the same time, the flow aloft will become more difluent and a weak upper disturbance ejecting in advance of a strong upper trough over the Southern Rockies will move over the region. These factors should result in some showers, perhaps a few thunderstorms, developing between midnight and sunrise across Deep East Texas and into Northeast Louisiana. The HRRR keeps precip coverage relatively scattered and spotty, so PoPs will be kept in the slight chance range through sunrise Tuesday morning. No changes were made to this part of the forecast. Hourly temperature and sky grids were edited to slightly to better reflect observed trends, but the majority of the forecast was left intact. CN && .PREV DISCUSSION... /issued 658 PM CDT Mon Sep 27 2021/ AVIATION... For the 28/00z TAFs, VFR conditions should prevail initially with abundant high level cirrus clouds streaming over the area. MVFR/IFR flight conditions should develop after 28/06z in most locations as low-level southerly flow brings increasing moisture into the area resulting in low clouds and patchy fog. Ceilings should slowly lift and VFR conditions should return to all sites before midday. However, scattered showers and thunderstorms should begin to develop after sunrise across Deep East Texas and will then spread northeastward into North Central and Northeast Louisiana. KLFK and KMLU should be the TAF sites most likely to be affected by any convection. CN PREV DISCUSSION... /issued 307 PM CDT Mon Sep 27 2021/ SHORT TERM.../Tonight through Tuesday Night/ Low level moisture has increased in earnest this afternoon, with mid/upper 60s dewpoints already returning to areas along/S of I-20 across Lower E TX/N LA. Unfortunately, this nice stretch of beautiful and less humid days have come to an end as a prolonged period of unsettled weather will take shape through much of the forecast period, as the closed low analyzed over Cntrl NM this afternoon, begins to slowly eject NE into the Srn Rockies Tuesday before opening up into a trough over the Srn Plains Tuesday night. This opening trough will help to amplify ridging aloft over the nation`s midsection Tuesday/Tuesday night, with the ridge axis shifting E from the Great Lakes into the MS Valley by midweek, with troughiness aloft from the opening trough to our NW focusing periods of convection over the region. But in the meantime, the short term progs continue to focus the potential for isolated convection late tonight along a SW to NE oriented theta-e ridge extending from portions of Deep E TX across NCntrl LA and near a Nwd moving warm front, but have backed off on the timing and also extent of QPF. Have tapered back pops to slight chance late for much of this area, with this area favorable to again seeing more in the way of sct convection especially with the aid of diurnal heating Tuesday. However, no discernible focus aloft is hinted at by the models to suggest a more organized threat for convection, and thus have backed off on the higher NBM to mid and high chance for Lower E TX/N LA, although the flow aloft will become increasingly SW ahead of the approaching opening trough entering the Srn Plains late in the day. Did trend the higher temps (near/lower 90s) over much of E TX/extreme NW LA Tuesday with the greater cloud cover and sct convection helping to keep max temps just a tad cooler over NCntrl LA/SCntrl AR. While this convection should diminish with the loss of heating Tuesday evening, convection should begin to increase off to our W late as the trough axis nudges E across the Srn Plains. Have stepped pops up to low to mid chance late Tuesday night, with variability in timing of the trough`s movement leading to low confidence in the higher NBM pops currently advertised. Did not deviate much with the NBM min temps as readings should only fall to the upper 60s/near 70. 15 LONG TERM.../Wednesday through Monday/ The moistening process taking place in our atmosphere in the short term period will manifest in numerous showers and thunderstorms across the region by Wednesday and Thursday as a series of disturbances, emanating out of long wave trough in the Rockies, brush across our region. There will likely be enough wind shear and instability to at least loosely organize convection, but at this time there does not look to be enough of these ingredients to bring more than some isolated strong storms containing locally gusty winds, heavy downpours, and frequent lightning. In addition, there will be enough atmospheric lift associated with this synoptic situation to ensure some convection is in the overnight hours (i.e., not all diurnally driven). Of course the high amount of cloud cover and precipitation will keep high temperatures down a bit Wednesday and Thursday, mainly with maximums in the 80 to 85 degree range. Later this week there starts to be a little more model disagreement. In one camp are models keeping the disturbed regime around through early next week and in another camp are solutions that pivot the unsettled pattern more to our north by this weekend. To negotiate this, we basically stuck with the NBM blend of mainly lowering probabilities of precipitation gradually from Friday through early next week, with a more dramatic lowering across the Arklamiss. Stay tuned to later forecasts to get more clarity on which camp of solutions is likely to win. Despite the potential drying trend and lack of any considerable fropa, at this point we do not anticipate a big warming trend later in the official seven day forecast period. /50/ && .PRELIMINARY POINT TEMPS/POPS... SHV 71 90 71 83 / 20 30 40 90 MLU 70 87 70 84 / 20 50 40 80 DEQ 63 89 69 84 / 0 10 30 80 TXK 69 89 71 84 / 10 20 30 80 ELD 67 87 67 82 / 10 30 30 80 TYR 71 91 71 86 / 10 20 30 90 GGG 69 90 70 83 / 10 20 40 90 LFK 71 90 70 84 / 20 50 40 90 && .SHV WATCHES/WARNINGS/ADVISORIES... AR...None. LA...None. OK...None. TX...None. && $$ 09/24
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