####018004594#### FXUS63 KBIS 032227 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 527 PM CDT Fri May 3 2024 .KEY MESSAGES... - There are low chances (20 to 40 percent) for rain showers through the day, mainly across the northern and eastern North Dakota. - Temperatures are forecast to warm up through the weekend, with windy conditions on Sunday. - Chances for rain return late Sunday night and continue through the work week. The wettest period will be Monday through Tuesday when most of western and central North Dakota will see medium to high chances (60 to 90 percent) of rain. && .UPDATE... Issued at 526 PM CDT Fri May 3 2024 Just a quick update to increase shower coverage across southern ND for the next few hours, based on latest radar imagery and trends. && .DISCUSSION... Issued at 302 PM CDT Fri May 3 2024 An upper level low located over southern Ontario will continue to push eastward. Wrap around showers will continue across the northern half of the state. Instability is a bit lacking this afternoon for thunderstorms, but a rumble or two is still possible. Showers will decrease later this evening as instability from daytime heating decreases. Overcast skies from low cumulus has resulted in below normal temperatures with high temperatures in the lower 50s. Breezy winds are being observed across the state from a surface pressure gradient from the aforementioned upper low. A surface trough continues to push across the central half of the state turning winds from southwesterly to northwesterly. Overnight lows could drop into the upper 20s across the southwest as surface high pressure passes through the region. High temperatures Saturday will begin to trend upward to near normal as surface high pressure clears out the region and ridging begins to build out west over the Northern Rockies. Sunday is forecast to be the warmest day as temperatures are forecast to climb into the 60s to 70s out west due to the upper level ridge pushing into the region. In addition a strong surface low will move into eastern Montana with a tight surface pressure gradient leading to windy conditions across western and south central North Dakota. Forecast soundings at this time have around 45 kts mixing down to the surface which will result in advisory level winds. This short term warm up will be short lived as another broad trough pushes across Western CONUS. A strong upper level low pressure system will move up from the Rocky Mountains Monday leading to widespread precipitation across the Northern Plains. The NBM has 50 percent chance of 1 inch rain across the Northern half of the state where the deformation band will likely set up. PWATs are pretty impressive for this event with values around 1.1 inches. Heavy rain is possible from stronger storms. However, there are some areas that could see significantly less rain depending on where the dry slot sets up. Thunderstorms are possible as the system first moves into the region. Instability around 500 j/kg which continues to decrease, however 0-500 mb shear is around 40 kts. CSU Machine Learning Program has backed off on severe weather parameters due to the ensembles having decreased instability, but there still is low chance for severe weather Monday. In addition to rain, windy conditions are expected Monday as a strong surface low with a tight pressure gradient moves through the region. Wrap around precipitation will continue through Wednesday leading to showers and cooler conditions. Temperatures are forecast to sit in the 50s through the middle of the week. After this system washes out near normal temperatures will continue until potential ridge moves into the region late next week. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1229 PM CDT Fri May 3 2024 MVFR conditions will continue for portions of North Dakota this afternoon due to low clouds. Clouds will slowly rise to VFR across the southern half of the state this afternoon before they dissipate later this evening. Breezy northwest winds will impact all terminals this afternoon with winds decreasing by the evening hours. Isolated showers are possible this afternoon across the state with showers diminishing by sunset. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...NH DISCUSSION...Johnson AVIATION...Johnson ####018009003#### FXUS66 KPDT 032229 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 329 PM PDT Fri May 3 2024 .SHORT TERM...Today through Sunday Night... Key Messages: 1. Significant rain and mountain snow through the weekend. 2. Some area rivers nearing or exceeding action (bankfull) stage. 3. Breezy winds late Saturday through Sunday evening. Current radar and visible satellite imagery showing light to moderate returns beginning to approach the west slopes of the Oregon Cascades as mid-to high level clouds extend into the Basin. This is in response to a robust upper level trough that is dropping from the the Gulf of Alaska and closing in on the Pacific Northwest coast. The low and associated cold front will pass through our area on Saturday as wrap-around moisture will keep widespread precipitation chances in the forecast through Sunday afternoon. This cold front will allow for snow levels to quickly drop 6000-7000 feet early Saturday morning to 2500-4000 feet early Sunday morning across Central Oregon. These dropping snow levels coupled with ample moisture will lead to significant, advisory level snowfall to occur across the east slopes of the Oregon Cascades and through the John Day-Ochoco Highlands. This has warranted to issuance of Winter Weather Advisories beginning at 5 AM Saturday across the east slopes of the Oregon Cascades and starting at 5 PM along the John Day-Ochoco Highlands above 4000 feet. 4 to 10 inches of snow is expected across the east slopes above 4000 feet and 3 to 7 inches of snow is likely across the John Day-Ochoco Highlands above 4000 feet. There is also a potential for significant snowfall across the southern Blue Mountains with 2-5 inches possible, mainly above 4000 feet. These amounts across the southern Blue Mountains are just below advisory criteria, but will need to be closely monitored. Confidence in these snow amounts are moderate to high (70-80%) as the NBM suggests a 65-85% chance of 6 inches or more snowfall across the east slopes of the Oregon Cascades Saturday afternoon through Sunday afternoon, a 70-90% chance of advisory level snow amounts (3 inches or more) across the John Day-Ochoco Highlands Saturday evening through Sunday evening, and a 40-60% chance of advisory level snow amounts (5 inches or more) along the southern Blue Mountains Saturday evening through Sunday evening. Substantial low and mid-level moisture is associated with this system as rain accumulations of 0.50 to 1.25 inches are expected across lower elevations of the Basin Saturday morning through Sunday night, with 1.5-2 inches likely across the Blue Mountains and Cascades. The only areas that are expected to see 0.25-0.50 of an inch include the Bend-Redmond area and the Kittitas Valley. Confidence in these rain amounts are moderate (50-65%) as the NBM suggests a 40-65% chance of 0.50 of an inch of rain across lower elevations, with higher chances residing along the northern Blue Mountain foothills and the John Day Basin. The NBM also highlights a 50-60% chance of rainfall of 1 inch or greater over the northern Blue Mountains and Elkhorns, with only a 10-30% chance over the Oregon Cascades. This moisture will also translate to rises across area rivers, with only the Naches River near Cliffdell currently expected to reach action (bankfull) stage briefly Saturday evening through Sunday afternoon. The John Day River at Service Creek looks to stay just shy of action (bankfull) stage Monday afternoon, but will continue to monitor as the weekend event unfolds. The incoming system will also attribute to breezy winds that will begin tonight ahead of the approaching cold front. Winds are expected to increase to 30-40 mph across the base of the northern Blue Mountain foothills beginning shortly after midnight tonight and extend through much of the morning on Saturday. The cold front will pass late Saturday morning to allow these winds to slacken through the afternoon as a pressure gradient begins to set up along the Cascades to increase winds through the Simcoe Highlands, eastern Gorge, and the northern Blue Mountain foothills beginning Saturday evening and extending through the day on Sunday. Winds are expected to peak between midnight on Sunday through noon Sunday as advertised by the GFS, NAM, and SREF indicating a 11-12.5mb pressure difference between Portland and Spokane. These values are just shy of advisory criteria as gusts of 35-45 mph will be possible. Winds will be slowly decreasing through the late afternoon and evening, but gusts of 30-40 mph will still be possible until early Monday morning. Confidence in these wind gusts are high (80-90%) as the NBM suggests an 85-95% chance of wind gusts of 47 mph or greater across the northern Blue Mountain foothills and the Kittitas Valley. This may warrant the need for wind highlights to be issued, so stay tuned. 75 .LONG TERM...Monday through Friday...Elongated troughing will bring about a cool weather pattern for much of the work week, before a high pressure ridge moves in and warms up temps toward seasonal averages and perhaps even above normal values by the start of next weekend. Ensembles are in pretty good agreement on the synoptic pattern next week, starting with a deep low centered over the Gulf of Alaska that partially envelops the PacNW with cold air. Guidance suggests that this low will essentially split into two systems: a low that remains over northern Canada and another low that gradually shifts eastward into the northern Plains. During this splitting process, the parent Alaskan low will advect in moisture into the forecast area on Monday, however QPF guidance early on indicates that this will primarily be a mountain/high elevation event. NBM probabilistic guidance depicts only about a 20% chance of much of the Basin seeing at least 0.05 inches, with chances increasing across our foothill zones (40-60%) and central Oregon (45-55%). The warm air advection from this weekend's system might shield the forecast area from lower snow levels, with Monday's levels in the 4000-5000 ft range, but cannot completely rule out our Cascade Passes from seeing some light accumulating snow. That being said, confidence is on the lower end (30-40%) due to how borderline snow levels are in the NBM for Monday. Once the low splits, our forecast area will find itself on the western flank of the departing low to the east, resulting in some cold air advection via northerly flow aloft. Temps look to remain below average Tuesday into Wednesday by as much as 15 degrees, however temperature ensembles do not currently suggest a freeze risk for the Basin. PoPs fall off on Tuesday as drier air prevails overhead with PWATs in the 0.2-0.3 range, leaving primarily light, orographically driven precip over the mountains thanks to N/NW flow aloft. For Wednesday onward, the forecast looks to be dry and warmer. Ensembles are in pretty strong agreement that a ridge will build in by the end of next work week, allowing temps to soar well into the 70s across our population centers. Should high pressure persist, as 8-10 day ensemble clustering suggests, highs in the lower Basin could even reach into the low 80s by next weekend. Confidence is high (70%) in this warm and dry forecast panning out based on what ensembles are showing. Evans/74 && .AVIATION...18Z TAFS...VFR conditions for today with currently high clouds at most sites, except for KPDT/KALW having clear skies. Cloud coverage will increase starting this afternoon into tonight/Saturday morning. KPDT might have winds gusting up to 24kts tonight as the low off OR coast pushes a cold front over PacNW. This will also bring rain showers into KDLS/KRDM/KBDN/KYKM Saturday morning as well. Winds will be less than 10kts, but will increase for KPDT/KALW this evening and overnight. Feaster/97 && .PRELIMINARY POINT TEMPS/POPS... PDT 51 68 37 47 / 20 40 90 80 ALW 55 72 41 50 / 10 30 90 80 PSC 56 72 46 56 / 10 30 90 70 YKM 49 63 44 62 / 30 80 70 40 HRI 54 70 41 54 / 20 40 90 80 ELN 44 61 42 57 / 30 80 50 40 RDM 40 49 31 47 / 70 80 50 50 LGD 47 65 37 47 / 10 20 90 80 GCD 46 61 34 44 / 10 80 90 90 DLS 49 56 45 55 / 50 80 70 50 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory from 5 PM Saturday to 11 PM PDT Sunday for ORZ506. Winter Weather Advisory from 5 AM Saturday to 11 AM PDT Sunday for ORZ509. WA...None. && $$ SHORT TERM...75 LONG TERM....74 AVIATION...97