####018007461#### FXUS66 KPDT 041205 AFDPDT Area Forecast Discussion...UPDATED AVIATION. National Weather Service Pendleton OR 505 AM PDT Sat May 4 2024 .SHORT TERM...Today through Monday...The deep closed upper level low off the PacNW coast continues to move to the SE and will move over SW Oregon late today then into the Great Basin overnight into Sunday. Meanwhile, the cold front will be very slow to progress eastward as the low passes south of the forecast area. Will see increasing rain over the western portion of the forecast area this morning with precipitation slowly spreading east into the rest of the forecast in the afternoon and overnight. Models continue show a deformation band forming on the north side of the low where the cold front stalls across northern Oregon and southern Washington overnight into Sunday. This will lead to some significant rainfall amounts on the oder of .5 to 1.0 inches across the Columbia Basin and 1 to 2 inches over portions of the eastern mountains and along the east slopes of the southern Washington Cascades. Central Oregon should see the least amount of precipitation at .25 to .5 inches. The low begins to move off into the Rockies late Sunday and Monday which will cut off the wrap around moisture and allow a northwest flow to develop. This will shift the focus of precipitation Monday mainly to the Cascade crest and over the eastern mountains in the form of showers including a slight chance (15%) of thunderstorms over the eastern mountains in the afternoon and evening. River forecast continue to show that this significant rain will cause rivers to rise but with no flooding expected as rivers remain below bankfull. Snow levels start out this morning around 6000 to 7000 feet but begin to lower across central Oregon through the day and overnight as the low center migrates into SW Oregon and then into the Great Basin. Snow levels across central Oregon will lower to 2500 to 4000 feet overnight through Sunday morning before rising back to around 4000 feet Sunday afternoon. This will allow for some minor snow accumulations in the lower elevations but more significant accumulations above 4000 feet. Snow advisories are in effect for the East Slopes of the Oregon Cascades for 4 to 10 inches mainly along the crest and 3 to 6 inches in the John Day Highlands. South to southeast winds have increased across the region overnight with winds of 10 to 25 mph and some gusts 30 to 40 mph. These winds will continue through the morning and then decrease as a transition to westerly winds starts to develop this afternoon and evening. These westerly winds will increase overnight and continue through Sunday at speeds and gusts that warrant the issuing of a wind advisory for some zones across the Lower Columbia Basin mainly from the eastern Columbia River Gorge to Pendleton. .LONG TERM...Tuesday through Saturday...Deterministic models and ensembles are in good agreement particularly through Thursday then there are some differences in the evolution/amplitude of an upper ridge over the area for Friday and Saturday. On Tuesday a shortwave trough will move SEWD across the region in NW flow aloft. This will result in mountain showers and snow showers (50-75% chance) with snow levels 3500-4500 feet. QPF amounts are expected to be mostly less than .2 inches so significant impacts from snow are not anticipated. The NBM has low probabilities of TSTMS for Tuesday afternoon for the eastern Mountains (15-18%) but forecast soundings show little CAPE and insufficient depth for lightning so chose to keep TSTMS out of the forecast for Tuesday. The winds will be a concern on Tuesday as well. The GFS is forecasting the PDX-GEG surface pressure gradient to increase to 11- 14 mb which is indicative of significant west winds across the lower elevations. NBM 24 hour max gust probabilities of 45+ mph across the lower elevations exceed 70% over a wide area Tuesday. After Tuesday the weather will become quiet with the available guidance indicating a warming and drying trend. On Wednesday high temperatures will still be around 5 degrees below normal for this time of year but by Thursday high temperatures will be near normal. For Friday and Saturday the majority of the ensemble clusters favor a building upper ridge though there is a lower probability scenario (15-30% chance) for weak troughing over the area on Friday and then flatter westerly flow on Saturday. This is similar to the operational GFS and the GEFS ensemble and results in slightly cooler temperatures than what the NBM and ECMWF ensemble are forecasting. Given that the more likely scenario is for the upper ridge went with the warmer NBM temperatures for now. By Saturday the NBM probabilities of 85+ degree high temperatures in the Columbia Basin and Yakima Valley are 40-70%. 78 && .AVIATION...12Z TAFS...Increasing aviation concerns today that continue tonight between deteriorating flight categories, light gusts, and possible snow at central OR terminals tonight. Latest satellite shows an extensive cloud shield with clouds moving north across the area and obs denoting mainly high-end VFR ceilings (greater than 7 kft). This system will prompt precipitation to spread gradually north and east over the next 12-18 hrs as moisture gets ushered north and low levels and moisture in the column increases from increased forcing for ascent over time. Chances start ramping up (to and >80%) through 18Z across the western-most terminals before ramping up (>80%) across the KPSC, KPDT, and KALW terminals around 0Z-6Z, the former having the longest wait. High confidence (>80%) in MVFR conditions developing with precip and worsening flight categories, initially over central OR and the KDLS terminal today then KYKM, KPSC, KPDT, and KALW tonight with a strong consensus seen in the forecast envelope composed of hi- res deterministic guidance runs and past runs. Of note, winds will be gusty but confidence is high (80%) in peak gusts staying around 20-25 kts, except at KPDT when gusts are expected to increase late tonight to 30 kts. Lastly, snow mixing in with rain will be a possibility at KBDN and KRDM, however, confidence in predominately snow as the p-type is currently low (less than 30%) through 12Z tonight. && .PRELIMINARY POINT TEMPS/POPS... PDT 71 40 50 40 / 30 100 100 70 ALW 73 42 52 44 / 20 100 100 80 PSC 74 47 57 47 / 20 100 100 40 YKM 63 44 60 39 / 80 80 80 10 HRI 72 42 55 43 / 40 100 100 40 ELN 59 43 56 40 / 70 60 60 10 RDM 51 32 47 34 / 80 70 60 10 LGD 66 38 47 38 / 30 100 90 90 GCD 62 34 45 35 / 90 100 100 70 DLS 58 45 56 46 / 80 80 60 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory from 2 AM to 11 PM PDT Sunday for ORZ041-044-507- 508-510. Winter Weather Advisory from 5 PM this afternoon to 11 PM PDT Sunday for ORZ506. Winter Weather Advisory until 11 AM PDT Sunday for ORZ509. WA...Wind Advisory from 2 AM to 11 PM PDT Sunday for WAZ024-521. $$ SHORT TERM...91 LONG TERM....78 AVIATION...80 ####018005890#### FXUS65 KPSR 041207 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 507 AM MST Sat May 4 2024 .UPDATE...Updated 12z Aviation Discussion. && .SYNOPSIS... After another day of above normal temperatures today, a weather system passing by to the north will help to bring cooler temperatures Sunday into early next week. The system will also lead to widespread breezy to windy conditions today across southeast California and areawide on Sunday. Dry weather will persist through next week, and temperatures are expected to rebound into the low 90s by early next week. && .DISCUSSION... Temperatures will continue to run a few degrees above normal for one more day ahead of an approaching Pacific low now moving into northern California and the Pacific Northwest. Expect highs today very similar to yesterday with readings mostly topping out in the lower 90s across the lower deserts to as high as 95 degrees. The approaching weather system will also increase the gradient across the western deserts by this afternoon leading to increasing winds and wind gusts likely reaching advisory level (40 mph) over portions of southeast California by late this afternoon. As the Pacific low moves inland across northern California into northern Nevada tonight, it will start to weaken while also bringing in some high level cloudiness through the Desert Southwest. A dry cold front is also forecast to move through southern California by Sunday morning with the front attempting to move through much of Arizona, but it will likely somewhat wash out as the system continues to weaken as it moves through Utah and northern Arizona. Cooler temperatures will be realized on Sunday, especially over the western deserts where readings will only top out in the upper 70s to around 80 degrees, but the Phoenix area will still easily reach into the mid 80s. Windy conditions will also impact the region areawide on Sunday with gusts across the Arizona lower deserts mostly between 30-35 mph to as high as 40-45 mph across southeast California and over portions of the higher terrain north and east of Phoenix. The weather pattern for a good portion of next week should see a large trough set up from the Plains States through the Pacific Northwest with the southern fringe of the trough setting up over our region. This will allow for several days of seasonably dry westerly zonal flow over the Desert Southwest with heights aloft hovering near seasonal averages. As a result, temperatures will recover fairly slow into next week, eventually warming back into the normal range by around Tuesday or Wednesday. NBM forecast temperatures show highs in the upper 80s to the lower 90s from Tuesday through Thursday before warming a bit more by next weekend as ensemble guidance shows a ridge potentially building in from the west. && .AVIATION...Updated at 1207Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns are anticipated through the TAF period under extended periods of clear skies and at times FEW-SCT high clouds mostly aoa 20 kft. Winds will follow a similar pattern to that of the last 24 hours, with current E/SE winds veering out of the south over the morning and potentially going VRB. SW'rly directions become favored early in the afternoon. Occasional gusts up to 20 kt out of the SW to W can be expected late this afternoon and into the evening, though sustained speeds will generally remain aob 10-12 kt. Overnight, the typical diurnal E switch is still expected to occur (between 08-10Z), but with a more southerly component than usual. Southeast California/Southwest Arizona including KIPL and KBLH: The main aviation concern through the TAF period will be strong W winds at KIPL and SSW to SW winds at KBLH. Gusts will develop this afternoon at both terminals, with values peaking between 35-40 kt during the evening at KIPL and upwards of 25-30 kt at KBLH. Coinciding with the stronger winds, slight reductions in visibility from lofted dust will be possible, particularly at KIPL this evening. Winds are expected to become relatively light at KBLH overnight, whereas gusts may continue through the remainder of the period at KIPL. SW to W winds increase again tomorrow morning just after the end of the current TAF period. SCT to at times BKN mid and high level clouds move in late this afternoon. && .FIRE WEATHER... A weather system moving just to the north this weekend will bring breezy to windy conditions focused more during the afternoon and evening hours along with cooler conditions starting Sunday. Wind gusts above 30 mph are likely today across much of the western districts and then areawide on Sunday. The strong winds and dry conditions will lead to elevated fire weather conditions over much of the area this weekend. Min RHs through the weekend will be around 10-20%, while overnight Max RHs will be around 30-60% for most areas. For next week, weak high pressure will remain over the region allowing for temperatures returning to slightly above normal, while seasonably dry conditions persist. Lighter winds are expected by Monday, but some afternoon breeziness can be expected during the first part of next week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...Wind Advisory from 3 PM this afternoon to 9 AM PDT Sunday for CAZ560. Wind Advisory from 3 PM this afternoon to 8 PM PDT Sunday for CAZ563>567. Wind Advisory from 3 PM this afternoon to 11 PM PDT Sunday for CAZ562. && $$ DISCUSSION...Kuhlman AVIATION...Whittock FIRE WEATHER...Kuhlman