Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
417 FXUS66 KPDT 021148 AFDPDT Area Forecast Discussion...UPDATED AVIATION. National Weather Service Pendleton OR 448 AM PDT Tue Jul 2 2024 .SHORT TERM...Today through Thursday night...Limited concerns in the short term period. The main sensible weather highlights include: - Prevailing near seasonable high temperatures today and tomorrow. - Elevated fire weather concerns today stemming from dry and breezy to locally windy condition with the strongest winds across the Cascade gaps, eastern Columbia Gorge spilling into north central OR and Kittitas Valley. - Hot temperatures with highs 6-12 degrees above normal on Thursday. A shift from a large scale cyclonic flow regime to an anticyclonic flow regime will take place in the short term. Northwest flow aloft currently overhead with an extensive upper-level trough over the northwest and north central CONUS will give way to an upper ridge in the eastern North Pacific with the ridge axis evolving east to be near/over the PacNW coast by Thursday. Guidance is in very good agreement with the overall synoptic pattern. Of which, the ECMWF ensemble mean 500 mb height forecast for the center of the upper high is forecast to fall outside model climo for this time of year from now through Thursday night with these anomalous heights and ridge axis extending north across the PacNW coast by Thursday. A shortwave trough apparent in water vapor imagery west of Haida Gwaii that is embedded in the background flow is expected to rotate and move into northeast WA/northern ID today. This will provide large scale forcing for ascent outside the area to the far north and northeast. Of which, the combination of scant moisture with the best forcing outside our area and weak lapse rates will preclude any threat for precip/storms. High confidence (>90%) with the latest HREF bolstering this outcome that shows the best chances for dBZ >40 dBZ and 4-hr prob of thunder confined to extreme northeast WA into western MT. Otherwise, little to slight uptick in temperatures Wednesday that will give way to above average highs by Thursday. Limited heat risk signal on Thursday with highs 6-12 degrees above normal, greatest departures across central OR, Kittitas Valley, eastern Gorge, and the Lower Basin. A modest cross-Cascade gradient sharpening today in tandem with increasing flow aloft with an enhanced belt of 700 hPa winds moving in will promote breezy to locally windy conditions late today into early tonight. Current thinking is the strongest winds will be most likely along the Kittitas breezeway with KELN likely peaking 35-45 mph. While cannot rule out an isolated ~45 mph gust (50-70% chance) there, thinking the frequency and coverage does not necessitate a wind advisory at this time. .LONG TERM...Friday through Tuesday...The first heat wave of the summer looks to be more likely than not with triple digit temperatures forecast widely across lower elevations Friday- Tuesday, albeit with some increasing spread early next week. The main highlights include: - High-level moderate HeatRisk (category 2) to major HeatRisk (Category 3) Friday through Tuesday with the greatest confidence in triple digits this weekend - a good chance for some pockets of extreme HeatRisk (category 4) as well. - Less relief by way of mild, elevated overnight lows starting Friday night with lows 6-12 degrees above normal across the lower elevations. - Dry and light breezes through the weekend. Increased confidence in anomalous high temperatures affecting the region. Latest ECMWF extreme forecast index showing unusual temperatures highly likely (values of 0.6-0.8) based on forecast agreement amongst ensemble members through Monday. ECMWF ensemble mean 500 mb height forecast keeps the upper-ridge over the PacNW Sunday, albeit its 500 mb height forecast not as impressive compared to earlier in the period with its forecast still exceeding the 99th percentile by Sunday and then diminishing further on Monday. These less anomalous height forecasts speaks somewhat to the uncertainty and increasing spread in the temperature forecast starting early next week. Clustering scenarios show the potential for weak shortwave trough/disturbance affecting the area by way of lower heights along the eastern periphery of the upper-ridge Sunday and Monday. That said, this possibility appears low (less than 30%) but bears monitoring, alongside a very low threat for isolated precip/storms late in the long term. By Tuesday, there is an increased possibility of the upper-ridge weakening in magnitude and/or shifting more east. That said, odds still favor the heat to continue into early next week. Chances for exceeding 100 F peaks on Saturday and Sunday across the lower elevations with chances commonly seen to be greater than 80%. These chances start to decline Monday with the Lower Basin and foothills of the Blues falling to 50-70% for exceeding 100 F, and fall around 5-10% again on Tuesday. && .AVIATION...12Z TAFs...Low aviation concerns with fair conditions and increasing breezes today/early tonight. VFR conditions currently area-wide with some sct-broken mid clouds across parts of the eastern Lower Basin into the eastern mountains. Trend-wise, expect clearing sky and sunny skies today. Otherwise, increasing winds late today as surface pressure gradient sharpens and better wind flow aligns. Current thinking is strongest winds will be at KDLS terminal with 24-hr peak gusts highly likely to exceed 30 kts (>~90%). KYKM terminal likely (>75%) to see gusts greater than 22 kts starting late afternoon. Elsewhere, gusts generally 20 kts or less. Winds will then be elevated overnight with light breezes prevailing after 06 UTC. && .PRELIMINARY POINT TEMPS/POPS... PDT 83 52 83 54 / 0 0 0 0 ALW 86 54 86 57 / 0 0 0 0 PSC 89 56 89 58 / 0 0 0 0 YKM 86 52 89 54 / 0 0 0 0 HRI 88 54 89 56 / 0 0 0 0 ELN 79 54 85 55 / 0 0 0 0 RDM 83 44 84 48 / 0 0 0 0 LGD 80 47 78 50 / 0 0 0 0 GCD 82 46 83 49 / 0 0 0 0 DLS 81 54 87 59 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...80 LONG TERM....80 AVIATION...80