Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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900 FXUS66 KPDT 080504 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1004 PM PDT Sun Jul 7 2024 .Updated for Aviation... .AVIATION... 06Z TAFS...VFR conditions are expected to continue for the next several days. Winds should generally be 10 kts or less. && .PREV DISCUSSION... /issued 411 PM PDT Sun Jul 7 2024/ Updated for Aviation... PREV DISCUSSION... /issued 257 PM PDT Sun Jul 7 2024/ SHORT TERM...Tonight through Tuesday night...Water vapor imagery reveals the axis of an anomalously strong mid/upper-level ridge over the West Coast. Meanwhile, visible imagery shows mostly clear skies across the region. Ensemble and deterministic guidance are in excellent agreement (100% chance) that the ridge axis will propagate eastward through Tuesday night such that the ridge will be directly overhead on Tuesday. Hottest temperatures of this long-duration heatwave are anticipated Tuesday afternoon, while the warmest overnight lows are expected Tuesday morning or Wednesday morning, depending on location within our CWA. To provide an idea of how hot the region may get, NBM probabilities of exceeding 110 degrees range from 20-70% for much of the eastern Gorge, Columbia Basin, and adjoining valleys and foothills on Tuesday. Meanwhile, probabilities of overnight low temperatures at or above 70 degrees range from 50-95% across the same region Tuesday and Wednesday, especially for areas subject to westerly winds that will keep the lower levels of the atmosphere mixed overnight, thus limiting radiational cooling. Heat Advisories and Excessive Heat Warnings are in effect during the period. Regarding fire weather concerns, a subtle vorticity maximum and mid-level shortwave are increasingly apparent in NWP guidance for Tuesday afternoon into Wednesday. While mid-level moisture in forecast soundings appears meager to marginal, negative mid-level theta-e lapse rates coupled with modest synoptic lift may facilitate isolated afternoon and overnight convection (<10% chance). Convection, if any, would begin across central Oregon Tuesday afternoon and propagate northeastward across eastern Oregon overnight. Have opted to forgo any Fire Weather Watches for lightning due to low confidence. That said, the very dry air mass coupled with some instability over central Oregon on Tuesday afternoon will result in enhanced fire weather potential for any new fires that develop. Additionally, locally breezy northerly winds coupled with very low afternoon RHs will lead to a 30-50% chance in Red Flag criteria across central and north-central OR during Tuesday afternoon and evening. Plunkett/86 LONG TERM...Wednesday through Sunday... Key Points: 1) Heat continues through the period, though may lightly decrease enough that heat products, or at least excessive heat warnings, are not necessary. 2) Breezy conditions and critical RH`s will coincide on Wednesday to produce enhanced fire weather concerns. 3) Fire weather concerns relax on Thursday through the weekend, but areas of locally breezy winds may be possible. Models indicate the overall synoptic pattern as follows: high pressure will continue its slow progression eastwards through the end of the week, centering over the Four Corners region by Saturday. The ridge will still attempt to extend over our region and control the overall weather pattern, but various shortwave troughs will try and break through the stubborn high with mixed results between the major ensembles. By the end of the period Sunday night into Monday, ensembles are coming together that a deep trough just offshore may finally be the feature to break up the monotony. Confidence remains high (70-80%) in warm temperatures through the period, as afternoon highs start off very hot on Wednesday (95-105, locally approaching 110 in the Columbia Basin), dropping by around 3-8 degrees then on Thursday as a shortwave helps to flatten the pressure gradient and lightly cool us off. While the region will remain warm (90s to low 100s), overnight lows are expected to descend back down into the 50s to 60s, helping to reduce overall HeatRisk and perhaps dial back the need for heat related products. These temperatures should continue through the end of the period, though perhaps warming 1-2 degrees through the weekend as the ridging tries to regain control. Fire weather concerns are on the rise for Wednesday as the approaching system is expected to tighten our pressure gradient and bring breezy winds across the Cascade gaps and into the lower Columbia Basin. The NBM shows 55-100% probability of sustained winds 25+ mph from Pendleton across to the Columbia Gorge and up through the Cascade Gaps including both the Yakima and Kittitas Valley. With RH values still critically low, widespread teens for the day, probabilities are becoming moderate to high (60-80%) that elevated fire weather conditions will occur. Conditions should decline by Thursday, but winds may remain enhanced enough through some of the Cascade gaps to warrant another day of concern. Goatley/87 AVIATION... 00Z TAFS...VFR conditions are expected through the TAF period. There could be some gusty winds to around 20 kts at DLS, BDN and RDM for a few hours late this afternoon/early evening. Otherwise all site will have winds less than 10 kts. && .PRELIMINARY POINT TEMPS/POPS... PDT 59 102 62 106 / 0 0 0 0 ALW 62 105 64 108 / 0 0 0 0 PSC 64 105 66 110 / 0 0 0 0 YKM 65 105 68 108 / 0 0 0 0 HRI 63 106 64 111 / 0 0 0 0 ELN 62 105 64 108 / 0 0 0 0 RDM 54 101 59 104 / 0 0 0 0 LGD 53 98 58 102 / 0 0 0 0 GCD 56 100 60 106 / 0 0 0 0 DLS 67 108 71 111 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning until 10 PM PDT Wednesday for ORZ041-044- 505-507-508-510-511. Heat Advisory from noon Monday to 10 PM PDT Wednesday for ORZ049- 050-502-503. Heat Advisory from noon Monday to 10 PM PDT Tuesday for ORZ509. WA...Excessive Heat Warning until 10 PM PDT Wednesday for WAZ024- 026>029-521-523. Heat Advisory from noon Monday to 10 PM PDT Wednesday for WAZ030. Heat Advisory from noon Monday to 10 PM PDT Tuesday for WAZ522. && $$ SHORT TERM...86 LONG TERM....87 AVIATION...77