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
41
42
43
44
45
46
47
766 FXUS66 KPDT 181705 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1005 AM PDT Thu Jul 18 2024 Updated Aviation Discussion .AVIATION...18z TAFs...VFR conditions expected, with clear skies and light, terrain driven winds prevailing, except for BDN, RDM, and DLS which will see breezy conditions this afternoon with gusts up to 25 kts out of the NW. Haze will continue to obscure the horizon for many sites across the forecast area. Evans/74 && .PREV DISCUSSION... /issued 351 AM PDT Thu Jul 18 2024/ SHORT TERM...Today through Saturday night...The circulation that brought thunderstorms to the forecast area yesterday has exited to the northeast leaving dry conditions in its wake. Lightning associated with the storms initiated numerous fires across the region, and several "hot spots" are still present early this morning on satellite. Notably, the pre-existing Lone Rock and Falls fires remain active. Smoke from these fires has settled across the region, so have added haze and smoke to the forecast across much of Oregon and south-central and southeast Washington for the next 48 hours. Today, hot temperatures will continue across the region as a mid- to upper-level ridge of high pressure re-establishes itself over the PacNW. As a result, widespread Moderate to Major HeatRisk is forecast for the lower elevations. Have opted to downgrade the Excessive Heat Warning for the Yakima and Kittitas valleys to a Heat Advisory as forecast temperatures are no longer supportive of the warning. Elsewhere in the Columbia Basin and along the northern Blue Mountain foothills, afternoon highs are likely to approach or eclipse 100 degrees (75-100% zone-wide chances of exceeding 98 degrees per NBM probabilities). While Friday will still be warm, late July is climatologically the warmest time of year across the region and forecast temperatures are not quite supportive of Heat Advisories; thus, have opted to leave the expiration time of existing highlights. A weak shortwave is forecast to track southwest to northeast over northwest Oregon and Washington during the day Friday. Model-to- model spread in the amplitude of the shortwave and available mid- level moisture has precluded mention of thunderstorms across the Blue Mountains region at this time, but it I did increase PoPs across the mountains to convey a very slight chance of precipitation (5-10%). 00Z HREF output is advertising modest instability (MUCAPE of generally <500 J/kg except 500-1000 J/kg for the Wallowas), and coupled with negative mid-level theta-e lapse rates and modest upper-level Q-vector convergence, this should support at least some cumulus build-ups if not isolated showers and thunderstorms provided enough moisture is present. As the weekend rolls around, the mid- to upper-level ridge is expected to further amplify overhead, and confidence continues to increase that the weekend will be very hot. To avoid confusion with ongoing advisories, no Excessive Heat Watches have been issued, but there is high confidence (70-100% chance) in reaching or exceeding 100 degree afternoon temperatures across all of our low-elevation zones, and a 30-60% chance of at least 105 degrees. Plunkett/86 LONG TERM...Sunday through Thursday...A high amplitude ridge of high pressure will continue over the region on Sunday with a closed upper level low in the Gulf of Alaska and its trough extending south into the eastern Pacific. This will boost temperatures Sunday into the 105 to 110 range around the Columbia Basin with a 30-50% probability of some areas seeing over 110 degrees. This will place high temperatures within reach of record highs. The good news is that this will be the culminating event of this long heat wave. The upper level trough off the coast will begin to move inland Sunday night and Monday before slowly passing over the region during the week. This will lower high temperatures Monday by around 10 degrees followed by another 10 degrees of some on Tuesday with highs in the 80s to mid 90s of closer to normal for this time of year. These cooler, or normal temperatures, will continue Wednesday and Thursday as the upper level trough remains over the region. Precipitation wise this system keeps most of the moisture further north in Canada where the center of the lower pressure remains. There could be a low end 10-20% chance of some convection ahead of the approaching trough. This would occur over central Oregon Sunday afternoon and then shift to the eastern mountains on Monday. After Monday the flow over the region will be westerly pushing the convection east into Idaho and the northern Rockies. Wind will become an issue from a fire weather perspective as increasing westerly winds could cause fire spread concerns on new and existing fires from Sunday onward. This will begin Sunday as westerly winds increase along the east slopes of the Cascades in the late afternoon and evening coinciding with the very hot temperatures and low humidities. && .PRELIMINARY POINT TEMPS/POPS... PDT 98 63 96 61 / 0 0 0 0 ALW 102 67 101 65 / 0 0 0 0 PSC 103 68 102 65 / 0 0 0 0 YKM 101 62 100 61 / 0 0 0 0 HRI 103 66 101 63 / 0 0 0 0 ELN 101 65 98 63 / 0 0 0 0 RDM 96 53 94 54 / 0 0 0 0 LGD 96 61 95 61 / 0 0 10 0 GCD 99 58 98 60 / 0 0 10 0 DLS 95 64 96 65 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Heat Advisory until 10 PM PDT this evening for ORZ044. WA...Heat Advisory until 10 PM PDT this evening for WAZ026>028. && $$ SHORT TERM...86 LONG TERM....91 AVIATION...74