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Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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923 FXUS66 KPDT 132350 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 450 PM PDT Tue Aug 13 2024 Updated Aviation Discussion .AVIATION...00Z TAFs...VFR conditions expected over the next 24 hours aside from BDN/RDM/YKM where local smoke from fires may be possible. Confidence is too low (<40%) to list in TAFs. Breezy flow expected to continue through the gaps for DLS, with diurnal flow 10 knots or less otherwise all other sites. Goatley/87 && .PREV DISCUSSION... /issued 340 PM PDT Tue Aug 13 2024/ SHORT TERM...This afternoon through Thursday...A vorticity maximum is slowly moving north-northeast across far NE OR, SE WA, and NRN ID this afternoon. The showers and thunderstorms associated with it have exited our forecast area, but a cumulus field is building across portions of the northeast Blue Mountains that cleared this morning. CAMs are advertising some isolated convection over the Blue Mountains, primarily Wallowa County, this afternoon. Any activity that develops will diminish this evening with dry conditions forecast overnight into Wednesday. Attention then turns to the next in a series of upper-level low pressure systems, a developing low offshore in the Pacific. Ensemble and deterministic guidance are in excellent agreement that the closed low will track onshore by Wednesday afternoon and evening, increasing large-scale forcing for ascent across central Oregon. Wednesday night through Thursday morning, the combination of the aforementioned forcing, ample mid-level moisture, and modest elevated instability (MUCAPE of 200-500 J/kg for parcels lifted from around 700 mb) should facilitate some high-based showers and thunderstorms. Have issued fire weather watches for OR611, OR640, and OR642 for abundant lightning potential given the high-based showers will have a low chance (10-30%) of producing a wetting rain. Thursday afternoon, the upper-level low will swing over the PacNW with another round of surface-based convection forecast for the majority of the Blue Mountains and Cascades. While the main jet will be across southeast OR and northern NV, hence bulk shear values will be low (10-20 kts), the cold core aloft will facilitate modestly steep lapse rates and MUCAPE of 500-1500 J/kg. Given weak steering flow and ample PWATs (~150% of normal), these storms will have a slow storm motion (5-15 mph) and a higher chance of producing a wetting rain (30-60% chance), so no fire weather watch has been issued for this activity. The low will track north-northeast out of our forecast area overnight into Friday morning with a slight chance (15-24%) of lingering shower activity overnight. Plunkett/86 LONG TERM...Friday through Monday...Ensemble guidance is in excellent agreement (>90% of members) that a deep, closed low will develop off the PacNW Friday through the weekend. However, analysis of ensemble clusters reveals a spread in solutions, ranging from a retrograding low with warm, dry conditions for the forecast area to a more progressive solution that tracks the low onshore overhead. The latter solution would result in cooler, more showery weather with potential for thunderstorms. Plunkett/86 && .PRELIMINARY POINT TEMPS/POPS... PDT 49 82 53 82 / 0 0 0 20 ALW 55 86 58 86 / 0 0 0 20 PSC 59 87 60 88 / 0 0 0 10 YKM 52 86 55 86 / 0 0 0 10 HRI 56 87 58 86 / 0 0 0 10 ELN 55 86 57 87 / 0 0 0 10 RDM 44 82 50 78 / 0 0 30 30 LGD 48 84 52 81 / 0 0 10 50 GCD 48 86 53 82 / 0 0 20 60 DLS 57 85 61 82 / 0 0 0 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Fire Weather Watch from Wednesday evening through Thursday morning for ORZ611-640-642. WA...None. && $$ SHORT TERM...86 LONG TERM....86 AVIATION...87