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
516 FXUS66 KPDT 071025 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 325 AM PDT Fri Jun 7 2024 .SHORT TERM...Today through Sunday... Key Messages: 1. Warm temperatures through the weekend. 2. Thunderstorm potential each day, peaking Sunday. Current radar and infrared satellite imagery showing dry conditions as some high level clouds stream in across the Basin from the west. These conditions are a result of an upper level ridge that has built over much of the western CONUS on Thursday, with a more pronounced ridge developing over the Pacific Northwest today into early Saturday. Today`s building ridge, coupled with southwest flow aloft, will attribute to warming conditions through Saturday. High temperatures on Thursday stayed in the upper 80s for much of the Basin, with the only exception being The Dalles which recorded a high of 90 degrees. Highs today will bump up 1 to 2 degrees from yesterday, with Tri-Cities expected to join the Dalles in the low 90s. Most of the Basin, Central Oregon, and the Yakima Valley will stay in the upper 80s. Confidence in these high temperatures is high (90%) as the NBM suggests an 80% chance at the Dalles, 53% for Tri-Cities, and 30% for Hermiston and Redmond reaching 90 degrees or above this afternoon. An approaching upper level trough on Saturday will enhance southwest flow to increase high temperatures another 2 to 5 degrees, as the Tri-Cities, Hermiston, the Dalles, and Yakima are all forecast to reach into the low 90s (which is about 10 degrees above normal). Confidence is high (90%) in these areas reaching highs in the low 90s, with the NBM highlighting an 87% at Tri- Cities, 86% at the Dalles, 71% for Hermiston, 61% at Yakima, and 35% for Pendleton reaching 90 degrees or above Saturday afternoon. Clouds will be increasing Saturday afternoon and evening as an upper level trough moves into the region, keeping overnight temperatures mild as Sunday morning lows only drop into the low to mid-60s through the Gorge, Lower Columbia Basin, Yakima Valley, and the Blue Mountain foothills. High temperatures will cool about 2 to 5 degrees on Sunday as the incoming system keeps clouds overhead and slight chances for rain develops across Central Oregon and our mountain zones. This decrease is minimal due to the continued southwest flow aloft and the overall lack of moisture with the system. The secondary concern resides with a slight chance (10-25%) of developing afternoon thunderstorms each day, with the greatest chance (15-25%) occurring on Sunday. There is also a potential for overnight thunderstorms Saturday into Sunday over Deschutes, Crook, and Grant counties. These conditions are a result from a weak shortwave undercutting the building upper level ridge today, leading to a slight chance (10%) of isolated thunderstorms over Deschutes, southern Crook, and southern Grant counties. Conditions are fairly marginal today, with most unstable CAPE (MUCAPE) of 100-150 J/kg, 10-20 knots of low level shear, and low level lapse rates of 6-7 C/km via the HREF and RAP. These parameters suggest low confidence (10%) in developing storms, with any developing cells being brief and unable to strengthen due to the lack of shear. The upper level ridge begins to exit to our east on Saturday, as an upper level trough and associated frontal system approach the coast. This system will begin to bring rain chances across Central Oregon by the afternoon before increasing chances and extending north across the Blue Mountains, Cascades, and portions of the Basin. Regarding thunderstorm potential for Saturday, it will begin over Deschutes county early in the afternoon before extending north and east into Jefferson, Crook, Grant, and southern Wheeler Counties through the evening. Conditions are slightly enhanced for thunderstorm development on Saturday as the HREF suggests MUCAPE of 200-300 J/kg, 35-45 knots of low level shear, and low level lapse rates of 7-8 C/km via the HREF and RAP. An incoming surface cold front from the northeast late Saturday into Sunday will keep MUCAPE elevated at 150-250 J/kg and low level shear between 35 and 45 knots over eastern Deschutes, Crook, and western Grant counties. These parameters Saturday and Saturday night provide low confidence (20%) of isolated thunderstorms forming over the aforementioned areas, with high confidence (80-90%) in storms staying sub-severe. The main upper level trough and frontal system passes over the area on Sunday, bringing the best chances (15-25%) of developing thunderstorms across Deschutes, Crook, Grant, Union, and Wallowa Counties. The GFS and NAM both advertise MUCAPE of 400-600 J/kg and 35-45 knots of low level shear. Low level lapse rates are not too impressive at 6-7 C/km, but precipitable water of 0.7-0.9" (100-130%) hint at an advanced trigger for convection and the potential for moderate to heavy rainfall under any developing storm cells. Even with these more enhanced thunderstorm parameters Sunday, confidence is still high (80%) in storm cells staying sub-severe as isolated, discrete cells are anticipated. However, there is still a potential for frequent lightning, gusty winds, and small hail with any developing storms - so stay weather aware and have multiple ways of receiving weather alerts. 75 .LONG TERM...Monday through Friday.... Key Messages: 1) Cooler pattern in store for the region 2) Breezy to windy conditions also return The long term looks to be staving off summer heat for a brief period thanks to a progressive pattern initiated by the system moving across the region at the end of the short term period. Models show the system over this weekend departs, leaving a transient ridge in its wake to start next week. There is high confidence (70%) that this ridge will be a short lived feature, and should quickly be swept out by a cold front Tuesday into Wednesday. Behind this front, flow becomes zonal during the mid- week period, then southwesterly on Friday in preparation for a deep low that approaches the West Coast at that time, with surprisingly good agreement from ensemble members. Still, there are outliers, and around 19% of members show ridging holding on rather than the progressive pattern, but the remainder expect some form of offshore troughing and southwesterly flow. With this pattern, expect a steady decay to temperatures, dropping us back to near normal conditions during the mid-week timeframe (upper 70`s to low 80`s), and then around 5 degrees below normal for highs by next Friday (upper 60`s to mid to upper 70`s). There is moderate confidence (60%) in these temperatures, but still some uncertainty thanks to the around ~20% of outliers in ensembles expecting ridging to hold off the progressive pattern, which would keep us seasonably warm. But with a progressive pattern and changing pressure gradients also comes winds. The NBM indicates a 60-90% chance of wind gusts of around 40+ mph Monday night into Tuesday as the cold front approaches, with a more widespread risk of these winds at a similar chance on Tuesday. The main areas of concern will be the Kittitas Valley, Simcoe Highlands, and Columbia Basin/Foothills of the Blues of Oregon. Once the front has passed and we reach the more zonal flow, winds should subside for Wednesday and Thursday, but by Friday as the gradients tighten with the approach of the next system, look for a similar risk of gusty winds in the aforementioned areas once again. We got a brief glimpse of summer, but the long term indicates we`re getting more spring-like conditions once again. Goatley/87 && .AVIATION...12Z TAFs...VFR conditions expected over the next 24 hours with a high probability (90-100%). BDN/RDM have a 10-15% of seeing a rogue shower or possibly thunderstorm which would bring conditions down briefly during the afternoon, but this threat is low and would be quickly over. Otherwise SKC or some high clouds/cirrus should be dominant. Winds 10 knots or less all sites except BDN/RDM during the afternoon when a few gusts 15-20 knots possible. Goatley/87 && .PRELIMINARY POINT TEMPS/POPS... PDT 84 55 87 60 / 0 0 0 10 ALW 87 56 90 62 / 0 0 0 0 PSC 90 58 92 64 / 0 0 0 0 YKM 88 55 90 60 / 0 0 0 0 HRI 89 57 92 63 / 0 0 0 0 ELN 84 53 87 60 / 0 0 0 0 RDM 86 53 84 56 / 0 0 0 20 LGD 83 52 84 58 / 0 0 0 10 GCD 88 54 88 57 / 0 20 20 30 DLS 92 61 90 63 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...75 LONG TERM....87 AVIATION...87