####018010557#### FXUS66 KPDT 031640 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 940 AM PDT Fri May 3 2024 .UPDATE...Current radar and infrared satellite imagery showing dry and clear conditions. However, there are still some lingering stratus that continues to dissipate over the Southern Blue Mountains and the John-Day Basin. Significant cloud cover is pushing inland ahead of the next robust weather system that will be passing through the Pacific Northwest over the weekend. Clouds will be increasing today as rain chances slowly extend into the east slopes later this evening. This system will bring with it ample moisture and breezy to windy conditions, with widespread precipitation expected Saturday afternoon through Sunday afternoon. A Winter Weather Advisory has been issued along the east slopes of the Oregon Cascades above 4000 feet beginning 5 AM Saturday as up to 10 inches of snow will be possible. There is also a potential for significant, advisory level snowfall across the John-Day/Ochoco Highlands and the Blue Mountains at elevations above 3500 feet Saturday evening through Sunday afternoon, but this will need to be further analyzed due to uncertainties in system track and strength. The secondary concern over the weekend resides with breezy to windy conditions Saturday evening through Sunday as a significant pressure gradient sets up along the Cascades in the wake of the passing cold front Saturday morning/afternoon. This will lead to wind gusts over the Simcoe Highlands early Sunday morning reaching between 35-45 mph, with these winds returning during the late afternoon and evening hours. These elevated winds will also extend across the northern Blue Mountain foothills, with gusts slowly intensifying and approaching advisory criteria Sunday night. 75 && .PREV DISCUSSION... /issued 452 AM PDT Fri May 3 2024/ SHORT TERM...Today through Sunday...A transitory ridge of high pressure will be passing over the region today. This will provide a mild Spring day with temperatures getting into the low 70s around the Basin and 60s in the mountains. High clouds will begin to increase and spread across the forecast area late today and overnight as the next weather system approaches. This closed upper level low pressure system is dropping SE out of the Gulf of Alaska with the center of the low taking a path into SW Oregon Saturday afternoon then continuing into the Great Basin on Sunday. This will bring the leading edge of a cold front into the Cascades tonight but its eastward progress overnight and into Saturday will be slowed as the low center moves into SW Oregon. Eventually the cold front turns into a deformation band of precipitation Saturday night into Sunday as moisture wraps around the low back across northern Oregon and southern Washington. 48 hour QPF amounts ending 12Z Monday continue to show a very high probability that lower elevations could see .5 - 1.0 inches of precipitation while the eastern mountains and Cascade crest could see 1 - 2 inches of precipitation. This amount of precipitation is expected to cause streams and rivers to rise and peak early next week but remain below flood stages. Snow levels will initially be high Friday night and early Saturday around 6000 to 7000 feet. They will begin to lower Saturday afternoon and night as the low passes south of the forecast area. Central Oregon will see snow levels down to 3500 to 4500 feet Saturday night but remain 4500 to 6000 feet across the rest of the forecast area. This could produce 4 to 10 inches of snow along the Oregon Cascade crest impacting travel over the passes so a Winter Weather Advisory has been issued Saturday morning through Sunday morning. Other concern will be some increasing S-SE winds overnight and Saturday. This will produce some gusty winds over the higher terrain of eastern Oregon and cause some downsloping off of the Blue Mountains along the Foothills. A wind shift back to windy westerly winds is expected to take place late Saturday and continue through Sunday. LONG TERM...Monday through Thursday...Another, weaker weather system will move across the Pacific Northwest on Monday and bring another round of precipitation, mainly to the mountains. However, there will be chances even in the lower elevations Monday afternoon. QPF amounts will be fairly light in most areas. In the mountains QPF will be a bit higher, ranging from 1/4 to 1/2 inch along the crest of the Cascades to around 1/4 inch in the Blues and Wallowas. Most other areas will see only a few hundredths. Precipitation chances will end everywhere except over the mountains by Tuesday morning. Some additional shortwave energy could enhance precipitation chances again Tuesday afternoon, mainly over the eastern Oregon mountains, but overall QPF is expected to be very light...only a few hundredths in most locations. Snow levels start out at 4000 feet or higher on Monday, but drop to between 2500 and 3000 feet by Tuesday morning. So, certainly the precipitation will mix with and change to snow in the higher elevations of the Cascades and Blues, and a few inches are possible along the crests with little elsewhere. The ECMWF EFI focuses on precipitation and snow over the Blue Mountains and nearby foothills with and area of 0.6 to 0.8 on Monday. Also on Monday, there is at least some chance of thunderstorms mainly over the eastern Oregon mountains, as this next systems moves through. CAPE values are expected to be in the 100 to 300 J/KG range, though the best CAPES look to be further southeast. LI values look to be between 0 and -2 degrees C. By Tuesday evening into Wednesday and for the remainder of the period, a ridge will build over the Pacific Northwest. This should bring drier weather and warmer temperatures. A few shwoers over the eastern mountains can't be ruled out on Thursday, but confidence is low (<30%) at this time. Winds will start out quite gusty as a result of the pressure gradient between the departing trough in the Great Basin and higher pressure to the west. WInds will gust 25 to 35 mph and possibly as high as 40 mph in portions of the Columbia Basin, Blue Mountain Foothills, Columbia Gorge. Winds will decrease during the day but remain gusty and become more widespread as the next system approaches. Gusty winds look to continue into Tuesday, with speeds 25 to 35 mph, before decreasing into Wednesday. The ECMWF EFI keys in on the Columbia Basin and Foothills of the Blue Mountains for winds on Monday, with values ranging from 0.6 to 0.8, with a core of 0.8 to 0.9 over the Blue Mountains. The NBM probabilities of wind gusts >= 39 mph on Monday are 70 to 90% across much of the Basin and Blue Mountain Foothills Simcoe Highlands and Cascade Gaps. On Tuesday, the NBM probabilities of wind gusts >=39 mph are 80% plus across much of the Basin, Gorge, Blue Mountain Foothills , Simcoe Highlands, and Kittitas Valley. The probabilities of wind gusts >=47 mph are 50 to 70% across portions of the Columbia Basin, Foothills of the Blue Mountains, Simcoe Highlands and 60-90% across the Kittitas Valley. High temperatures on Monday will start of 10 to 15 degrees below normal and will mainly range from the 50s in central Oregon to the 60s across the Columbia Basin. By Wednesday, high temperatures will begin to rise and by Thursday, highs will be close to normal in most areas and above normal in the Basin. The ECMWF EFI shows this trend as well for high temperatures. On Monday, there is a large area of -0.7 to -0.8 across most of Oregon, and -0.6 to -0.7 across much of southeastern Washington. On Tuesday, the area moves a bit eastward. There is a large area of - 0.7 to -0.8 across much of the region and even an area of -0.8 to - 0.9 over the Oregon Blue Mountains. By Wednesday, most of the anomalous temperatures are gone in the EFI. AVIATION...12Z TAFS...VFR conditions and little concerns area-wide before elevated aviation concerns begin right at the end of the TAF period. Latest nighttime microphysics RGB imagery shows large clear skies, except for a few swaths of thing high clouds crossing the Cascades and areas of low stratus in the higher terrain of central OR and the central OR mountains. The next weather system offshore in the eastern North Pacific will be approaching the OR coast tonight with its attendant cold front reaching the Cascades near the end of the TAF period. There will be increasing mid and high clouds out of the system late morning- afternoon before low-end VFR ceilings (less than 7 kft) materialize west to east early tonight as moisture gets transported from south to north in tandem with increasing large scale forcing for ascent. High confidence in low-end VFR ceilings late tonight, >70%, with increasing potential for sub-VFR ceilings across central OR. Latest LAMP ceiling probs have been growing the last three runs with chances for MVFR now >30% at KBDN and KRDM after 09 UTC. Current thinking is MVFR flight categories may need to be introduced if this trend continues and timing of the system speeds up. Already high chances for rain that coincide with this potential after 09 UTC tonight (>70%). Otherwise, increasing southerly to easterly winds this afternoon ahead of the system as it evolves south and east the next 24-hrs, however, potential for frequent gusts up to 20 kts is low (less than 50%) at all sites. && .PRELIMINARY POINT TEMPS/POPS... PDT 70 50 67 41 / 0 20 50 100 ALW 73 54 71 44 / 0 10 40 100 PSC 73 56 72 45 / 0 10 40 90 YKM 69 49 65 42 / 0 30 80 70 HRI 75 54 70 43 / 0 20 50 90 ELN 67 44 61 42 / 0 30 80 70 RDM 65 41 50 32 / 10 70 90 70 LGD 65 46 63 39 / 0 10 50 100 GCD 64 45 61 35 / 0 10 90 100 DLS 72 49 57 46 / 10 60 90 90 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory from 5 AM Saturday to 11 AM PDT Sunday for ORZ509. WA...None. && $$ UPDATE...75 SHORT TERM...91 LONG TERM....77 AVIATION...77 ####018008047#### FXUS61 KGYX 031643 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1243 PM EDT Fri May 3 2024 .SYNOPSIS... High pressure near the coast will provide a drier and quieter couple of days between today and Saturday, however, it will also contribute to a growing onshore flow this weekend. Thickening clouds, cooler temperatures and rain showers are expected by Sunday... with clearing likely not coming until Monday. Warmer and sunnier conditions are expected Monday and Tuesday, then more unsettled weather returns around the middle of next week. && .NEAR TERM /UNTIL 7 PM THIS EVENING/... 1245 PM Update... Another round of minor changes to the near term portion of the forecast through the remainder of the day. The earlier sunshine and heating has allowed for a cu field to develop with the greatest cloud cover located over southern NH. Partly sunny skies and a few additional degrees of warming can be expected through the remainder of the afternoon. Previously... 945 AM Update... Minor changes to reflect latest observational trends. Partly sunny skies will persist through the day with warmer high temperatures than yesterday. Previously... Impacts: *No significant weather impacts expected 1030 AM UPDATE...Breaks in the clouds are making for a sunny morning in many places. Fog is still present in many of the valleys, but that is expected to dissipate over the next couple of hours. This update was the usual refreshing of near term temperature, dewpoint, and sky trends with observations. Previous Discussion... Clouds continue to roll over the ridge this morning, however a clear slot did develop overnight allowing fog to form and some areas to quickly drop a few degrees. Now, as the mid- level cloud deck fills back in, fog is dissipating and temperatures are plateauing. As the ridge moves overhead and surface high pressure builds in today, skies will gradually clear and with BUFKIT soundings showing a return to good mixing, high temperatures should climb into the 60s areawide. The only exception would be the coast where the seabreeze will keep temperatures in the 50s. && .SHORT TERM /7 PM THIS EVENING THROUGH 6 PM SATURDAY/... Impacts: * No significant weather impacts expected Skies will remain partly cloudy overnight which will keep us from having a widespread radiational cooling night, but with continued light winds there is opportunity for patchy dense fog and some quick temperature drops in areas that can find some clear skies. Generally low temperatures look to be in the low to mid 40s across the area with some upper 30s north of the mountains. The 500mb ridge axis inches ever closer, but models suggest the offshore upper low keeps the pattern pretty blocked up for Saturday. Expect clouds to increase through the day as we see warm moist advection from the southwest. BUFKIT profiles suggest another well mixed day so the clouds shouldn't keep us from once again climbing into the 60s across most of the area, with the coast once again topping out in the 50s due to the seabreeze. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... An upper level ridge this weekend is replaced by an upper level trough to start next week, with rainy and cool weather eventually yielding to a drier, warmer couple of days to start the upcoming work week. Another frontal system approaches with increasing rain chances around the middle or latter part of next week. All in all neither of these systems look to be particularly impactful in terms of a significant hydrological or convective threat, and overall this will be a stretch of typical Spring weather with an active but ultimately benign pattern. Starting Saturday night... high pressure along the eastern periphery of Maritime Canada and a cold front approaching from the Great Lakes continue to produce onshore flow into New England. Clouds will fill in through the low and mid-levels especially south and east of the mountains into Sunday, with potential for fog and perhaps some patchy drizzle development during the morning as an upper level ridge rolls overhead. Shower chances meanwhile will increase from the west through the day Sunday amid pressure and height falls... culminating in a likely period of rain as a pre-frontal trough crosses Sunday afternoon and/or evening. Although the cold front itself won't cross until Monday, the moisture axis will be attached to the pre-frontal feature... with generally 0.2-0.4" of rainfall. Temperatures meanwhile won't warm too much on Sunday thanks to warm advection atop the cool marine layer, with highs generally in the 50s... coolest in the 40s along the coast. In terms of sensible weather conditions, a question will be the progression of the cold front itself as its passage will bring fresh westerly flow. There will be a gap between the bulk of the rain/deep moisture exiting late Sunday and the low-level humidity being flushed out with the cold front on Monday. Thus, would expect the overnight to remain a bit damp with fog and drizzle potential. Current model consensus mixes this out through the mid- or late- morning hours, with a mix of sun and clouds and far warmer temperatures on Monday. Highs are forecast to be in the 60s and 70s, coolest in the north where upsloping clouds and a few showers are expected to remain. Light winds and the warm temperatures should allow a sea breeze to develop. Upper level low pressure settles across Maritime Canada and a ridge axis nudges east toward New England. Resultant northwest flow reinforces the drier airmass with what looks to be a great day on Tuesday... featuring temperatures again warming into the 60s and 70s, light flow, an afternoon seabreeze, and what will likely be partly or mostly sunny skies. Forecasting the upper air pattern becomes a bit fuzzy toward the middle of next week with an increasingly blocked pattern and a general trend toward more zonal flow over the Northeast with the jet nearby or overhead. This introduces the potential for shortwaves moving through the jet to bring showers across the area... and indeed have PoP and cooler temperatures on the increase again toward the middle of the week. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... Short Term...A mixed bag of LIFR/IFR/MVFR ceilings early this morning will gradually improve to VFR as the day goes on. We will most likely return to areas of LIFR in fog tonight, but quickly improve back to VFR Saturday. Winds will be light and variable across the area. Long Term...Periods of IFR are likely Sat night through Mon morning with light SE flow turning N thru Sun, then SW or W Mon. Prolonged and more significant restrictions are most likely along the coast with low CIGs and some lowered VSBY... with all terminals expected to have at least a few hours of restrictions with -RA crossing the area on Sunday. Conditions trend back to VFR Mon, except potentially MVFR CIGs in the north... then all VFR on Tue. && .MARINE... Short Term...Conditions hazardous to small craft are not expected. High pressure building over the waters will keep winds light and variable through tonight, with an afternoon seabreeze developing. For Saturday, winds will be blowing onshore at around 8-10 kts. Long Term...SE flow across the waters Sat night increases to around 10-15 kts sustained by late Sun...with potential for fog and rain thru Mon morning. A front crossing the waters brings clearer conditions late Mon into Tue, with light winds generally out of the west (NW or SW) into midweek. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Tubbs