####018005918#### FXUS66 KPDT 232136 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 214 PM PDT Tue Apr 23 2024 .SHORT TERM...Tonight through Thursday...The western USA is currently under an upper lever ridge of high pressure that is slowly moving eastward. This is in response to a split upper level trough over the eastern Pacific Ocean moving towards the west coast. The southern portion of the trough contains a closed low off the coast of southern California providing some instability showers over the Great Basin. The northern portion of the trough contains a closed low just off the coast of central British Columbia. Both of these system will move eastward over the next 24 hours and begin impacting the forecast area in different ways. Some of the moisture over the Great Basin will work its way into southern Oregon this evening triggering some showers and possible thunderstorms with some showers possibly clipping central Oregon. On Wednesday some of this moisture could clip eastern Grant, Baker and Wallowa counties with a few showers. Meanwhile, the northern low will move into Canada overnight and Wednesday with the southern portion of the low sweeping a weak cold front through the Pacific Northwest Wednesday. This will usher some showers into the Washington Cascades but more impactful will be the breezy to windy westerly winds that develop through the day and continue overnight. Wind speeds are expected to remain below advisory criteria in the range of 15-30 mph with gusts 30-40 mph. The movement inland of this split trough Wednesday will allow a more concentrated westerly flow pattern over the eastern Pacific. This westerly flow will usher in a better organized weather system directly into the Pacific Northwest on Thursday that will provide a good chance of precipitation to the forecast area. This system does not have much cold air associated with it as snow levels remain around 5000 feet through Thursday night. .LONG TERM...Friday through Tuesday...The long term will remain a progressive pattern as multiple systems move across the region, but aside from keeping temperatures on the mild to cooler side and producing mostly mountain precipitation, significant concerns are not anticipated during the period. Friday begins with a trough dropping across the region that will continue southeastwards through Saturday, becoming a cutoff low across the Four Corners region. The inland PacNW remains under troughing over the weekend, with a deep Alaskan low that will descend down the Canadian coastline and approach the US before fully moving over our area by the early to mid-week timeframe next week. Overall sensible weather concerns from this progressive pattern are expected to be fairly limited. Temperatures will remain near or slightly below normal with highs in our population centers in the upper 50's to mid 60's, with a few chances at low 70's in the Columbia Basin. Precipitation from the troughing pattern remains on the low side, particularly in the lower elevations. Ensembles only average a 10-40% probability of 0.1 inch QPF or higher for our lower elevation zones for the 24 hour period of Friday morning through Saturday morning (the best day for chances for precipitation). Otherwise the mountains have a widespread 70-100% chance of the same amount, with probabilities plummeting if we increase the amount to 0.5 inch outside of the highest elevations of the Cascades. The NBM also expects a few thunderstorms with Friday's precipitation across the Ochoco-John Day Highlands through the Blues and Wallowas, but probabilities are also on the low side (15-25%) as global models and ensembles show very little favorable support for this activity (wind shear, instability, etc). Expecting a few orographically driven storms to be possible with primary impacts being lightning, brief locally heavy rain, and some gusty non-severe outflow winds. With Friday into early Saturday being the best chance of precipitation, passing mountain showers and high elevation/mountaintop snowfall will continue through the long term period with the lower elevations having extremely low (15% chance of less) to nil probabilities of showers under the progressive pattern. But as the Alaskan low begins to approach on Sunday, ensembles are indicating the potential for some breezy winds Sunday evening into early Monday. Ensemble probabilities for gusts greater than 20 knots are high across Washington and Northern Oregon (60-100%), but probabilities for gusts of 34+ knots fall nearly completely off, meaning we'll likely see some breeziness as the pressure gradients tighten, but more significant activity that could lead to at least advisories is doubtful. Overall the pattern remains active enough, but not enough to bring noteworthy concerns to the forefront at this time. Goatley/87 && .AVIATION...18Z TAFs...VFR conditions over the next 24 hours with SCT to BKN high clouds. Winds light and northerly becoming diurnal and light overnight with westerlies to northwesterlies beginning tomorrow. Goatley/87 && .PRELIMINARY POINT TEMPS/POPS... PDT 37 67 43 62 / 0 0 0 20 ALW 40 70 47 66 / 0 0 0 20 PSC 41 72 48 69 / 0 0 0 10 YKM 40 70 43 64 / 0 0 0 20 HRI 38 72 46 67 / 0 0 0 10 ELN 39 62 43 61 / 0 0 0 20 RDM 33 65 37 57 / 0 0 0 30 LGD 39 67 40 61 / 0 10 0 20 GCD 39 70 40 61 / 0 10 0 30 DLS 42 69 48 60 / 0 0 0 40 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...91 LONG TERM....87 AVIATION...87 ####018004170#### FXUS65 KGJT 232136 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 336 PM MDT Tue Apr 23 2024 .KEY MESSAGES... - Warm and breezing conditions continue through Wednesday with temperatures 10-15 degrees above climatology and winds gusting 20 to 30 mph during the afternoon. - Precipitation chances increase Thursday afternoon with widespread rainshowers expected across the mountains with some light snow showers expected on the higher terrain Thursday night and beyond. - Cooler and unsettled conditions expected for the latter half of the forecast period. && .SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 326 PM MDT Tue Apr 23 2024 Moisture streaming through the ridge across the CWA, along with a weak shortwave is producing a few showers across northwest Colorado. A few lightning strikes have been detected in Rio Blanco and Moffat Counties this afternoon. Elsewhere, a generous cumulus field has sprouted over the region in the steep lapse rate environment depicted on this morning's sounding. Shower activity is expected to push more northward Wednesday as southwesterly flow increases ahead of the approaching wave coming ashore in California. Gusty winds will increase Wednesday afternoon, along with high temperatures. This will be the last day of this warm spell with near record temperatures expected in some locales. The frontal boundary pushes through the Great Basin Wednesday night and introduces a chance for more showers across the northern portion of the CWA. A weak moisture supply will keep much of this from reaching the ground and likely just produce some gusty winds under virga showers. Overnight lows will, once again, remain warm both Wednesday and Thursday morning, averaging 10 degrees above normal across the region. Fire fuels remain sub-critical, but weather conditions will remain at or near critical fire weather parameters on Wednesday. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Issued at 326 PM MDT Tue Apr 23 2024 Early on Thursday a shortwave trough makes landfall in Southern California and northern Baja. That trough lifts northeastward and passes just south of the Four Corners later in the day. This system will provide the lift and moisture needed for scattered to widespread precipitation across the forecast area. Thursday will be windy in the southwest flow ahead of the trough, and any showers that develop will only exaggerate the winds. That system experiences lee side strengthening, which keeps our area in the base of the trough. Moisture does not really get scoured out so the chances for showers linger Thursday night. This also sets up the next shortwave to track over the region on Friday and Saturday therefore expect increasing chances for showers during that time frame. On Sunday the low pressure makes it through the base and lifts out over the plains. Winds relax as this system moves overhead, but a cold front will cut temperatures down compared to the last few days. Snow levels in this active period hover around 7-8 kft, which should limit impacts to the mountain passes and higher peaks. As far as model differences the trough on Thursday has really good agreement with track, strength and timing. Confidence wains a touch with the second system, but overall the difference are subtle. Expect minor tweaks in the next few days, which may result certain areas having better chances for precip over others. As of now the highest amounts of liquid are in the northern mountains with decreasing amounts as you move southward. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1117 AM MDT Tue Apr 23 2024 VFR conditions are expected through the taf period. Winds will increase this afternoon and decrease after sunset. Isolated showers are possible around KHDN and perhaps KEGE. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...LTB LONG TERM...KJS AVIATION...TGJT ####018006381#### FXUS66 KLOX 232138 AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 238 PM PDT Tue Apr 23 2024 .SYNOPSIS...23/122 PM. Strong onshore flow and a deep marine layer will maintain much cooler than normal temperatures through at least Friday. Areas of night and morning fog and drizzle are expected across the coast, valley, and foothill areas with only partial afternoon clearing. Warmer weather is expected by the weekend into early next week. && .SHORT TERM (TDY-FRI)...23/147 PM. No significant changes to the forecast today as a series of low pressure systems move through California through Friday. Cooling aloft associated with these upper lows has deepened the marine layer to around 5000 feet while onshore flow to the east is approaching 9mb this afternoon. Today saw our first day of reverse clearing of the marine layer and this may be the case again Wednesday as well. With a little more sunshine today many coastal area temperatures were a couple degrees warmer than the previous couple days, but still well below normal. Some breezy winds have developed through the I14 corridor and into the Antelope Valley with that strong onshore flow but with the exception of the usual Lake Palmdale station winds are below 40 mph and expected to remain that way through early Thursday. There is low confidence in how the marine layer will behave Wednesday now that the it's so deep. The most likely outcome is another day very similar to today, with (not so) low clouds reforming overnight in most areas then another reverse clearing pattern tomorrow. Most of the high res forecast models favor this scenario along with some pockets of drizzle, especially near the south facing foothills. However, the next upper low will be quickly approaching the area Wednesday with an arrival expected Wednesday night into Thursday. So some additional cooling aloft is expected that could either reinforce the marine layer or potentially weaken it enough to where it clears out more completely in the afternoon. In any case, temperatures will remain well below normal with some breezy but again sub-advisory level winds across interior areas. With the arrival of the upper low Wednesday night into Thursday morning, chances for more widespread drizzle or light rain increase. But with northwest flow following the trough passage Thursday afternoon that should help generate better clearing. Increasing west to northwest winds expected in the afternoon and evening with wind advisories possible for some coastal areas and interior areas as well. Yet another trough quickly follows for Friday, though models have been tracking this one more inland. Temperatures will remain on the cool side with some gusty west to northwest winds but minimal chances for precip, except possibly across the northern mountains and interior SLO County. Still low confidence in the low cloud coverage but the most likely outcome is for less clouds across coast and valleys. Temperatures will remain below normal but should be 3-6 degrees warmer than Thursday. .LONG TERM (SAT-TUE)...23/153 PM. The warming trend that started Friday is expected to continue into early next week with weakening onshore flow and minimal, if any, marine layer stratus. Temperatures should be back to normal levels over the weekend and sneaking a few degrees above normal by Monday. Some cooling then expected Tuesday that will likely continue through the rest of next week as yet another cold upper low drops out of the Pac NW. && .AVIATION...23/1829Z. At 1744Z at KLAX, the marine inversion was based at 3700 feet. The top of the inversion was 4500 feet with a temperature of 11 C. Low to moderate confidence for coastal/valley TAFs and high confidence for desert TAFs. Lower confidence for coastal/valley sites due to uncertainties in timing of flight category changes. There is 30% chance of no afternoon clearing at sites with a clearing forecast. KLAX...Moderate confidence, due to uncertainty in timing of cig arrival and dissipation. No significant easterly wind component is expected. KBUR...Moderate confidence, due to uncertainty in timing of cig arrival and dissipation. && .MARINE...23/236 PM. For the Outer Waters, moderate to high confidence in current forecast. Today through Wednesday night, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels. For Thursday through Sunday, high confidence in combination of SCA level winds and seas. Across the two southern outer water zones (PZZ673/676), there is a 50-60% chance of Gale force winds Thursday and Friday afternoon/night. For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Wednesday night, high confidence in winds and seas remaining below SCA levels. For Thursday through Friday, there is a 60-80% chance of SCA level winds, especially in the afternoon and evening hours. For Saturday and Sunday, there is a 40-50% chance of SCA level winds, especially in the afternoon and evening hours. For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Today through Wednesday morning, high confidence in winds and seas remaining below SCA levels, expect for a 60% chance of SCA level winds for the SBA Channel this evening/night. Wednesday afternoon/night, there is a 60-80% chance of SCA level winds for all the southern inner waters. Winds will pick back up Thursday morning for the SBA channel (with a 20-30% chance of Gale force winds on Thursday), and reaching the waters south of Point Mugu Thursday afternoon. SCA wind or seas will last much of the time Thursday through Saturday. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect from 9 PM this evening to 9 AM PDT Wednesday for zone 650. (See LAXMWWLOX). && $$ PUBLIC...MW AVIATION...Schoenfeld MARINE...RAT/Schoenfeld SYNOPSIS...MW weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox