Sunrise 5:22 AM   Sunset 8:34 PM Moonrise 12:34 PM   Moonset 1:53 AM

  Print   HELP   Reset   Save   Recall  New

FXUS66 KPDT 170520 CCA AFDPDT

Area Forecast Discussion National Weather Service Pendleton OR 1019 PM PDT Thu May 16 2024

Updated Aviation Discussion

EVENING UPDATE
Despite decently strong cross-Cascade surface pressure gradients (5 mb SEA-ELN and 10-11 mb PDX-GEG), winds have dropped below advisory criteria for all sites this evening, and 00Z HRRR probabilities indicate a very good chance (80%) that winds outside of the Kittitas Valley will remain below advisory criteria through the night. Delving further into observations, VAD wind profiles indicate a low-level jet of 40-45 kts between 3-4 kft at KPDT, though winds reaching the surface are significantly weaker at 15-25 kts with gusts of 20-35 kts. Surface observations along area ridgetops corroborate the low-level jet; North Pole Ridge RAWS and Rattlesnake Mountain both show sustained winds of 30-35 kts with gusts of 40-45 kts. Given the lack of support in observations and high-resolution guidance, have opted to cancel all existing Wind Advisories except for the one in effect for the Kittitas Valley. Breezy to windy westerly winds are still forecast overnight through Friday morning, just not strong enough to warrant wind highlights. Plunkett/86

AVIATION
06Z TAFS...VFR conditions will prevail through the period. Clouds are developing and expanding across the area and SCT- BKN clouds at 040-070 are expected until around 12Z followed by clearing skies. It will be mostly clear on Friday with increasing mid clouds after 03Z Saturday mainly at KYKM and KDLS. Winds have slowly diminished this evening but expect sustained winds of 10-20 kt and gusts 20-30kt to persist for much of the period. There could be a little lull in the winds toward daybreak as the boundary layer decouples followed by an increase again after sunrise. 78

PREV DISCUSSION
/issued 449 PM PDT Thu May 16 2024/

SHORT TERM
Today through Saturday

Key Messages:

1. Windy conditions through Friday afternoon.

2. Elevated river levels on the Naches River.

3. Near to below normal high temperatures beginning Friday.

An upper level shortwave and an accompanying cold front will be passing through our area this evening through Friday morning.
These approaching synoptic features have already developed a pressure gradient along the Cascades, which have elevated winds across the Kittitas Valley, Simcoe Highlands, Eastern Gorge, and the northern Blue Mountain foothills as gusts of between 40 and 46 mph have already occurred at the Dalles, Pendleton, and Ellensburg airports. The current pressure gradient between Portland and Spokane is 10.8 mb, and is expected to continue to tighten through the afternoon to between 11.9 and 13.6 mb via the GFS, NAM, and SREF. Guidance suggests that the pressure gradient will tighten even further Friday morning to between 12.0 and 14.8 mb early Friday morning before slowly slackening into the afternoon. These gradient values are associated with winds of up to 50 mph, which has warranted the extension of the Wind Advisory over the aforementioned areas to 5 PM Friday. Confidence is high (85-95%) regarding advisory level winds as the NBM showcases an 80% to 95% chance of wind gusts of 47 mph or greater and a 50% to 70% chance of 55 mph wind gusts or greater across the earlier mentioned areas. There is also the potential for blowing dust to occur across areas where the advisory is active, which may decrease visibility and cause for potentially hazardous travel - especially for large profile vehicles.

Snow melt due to the event earlier in May coupled with persistent above normal temperatures have allowed some rivers to rise. At this time, all rivers are forecast to stay below action stage with the exception of the Naches River at Cliffdell. The current level at this reach is 29.08 feet, and is forecast to peak this evening around 11 PM at 29.17 feet before slowly subsiding to below action stage (29 feet) Saturday evening by 5 PM. The Naches River at Naches is forecast to stay about 6 inches below action stage (16 feet), peaking this evening before slowly dropping over the weekend.

This passing shortwave today will also bring with it mountain rain along the Cascades this evening before extending into the Blue Mountain overnight into early Friday morning. A transient upper level ridge will keep conditions dry on Friday ahead of another dropping upper level shortwave that digs over the area and ejects to our east as a trough, bringing more breezy conditions and mountain rain across the Cascades and northern Blue Mountains Saturday afternoon and evening. Lower elevations will stay dry through the period, but these features will usher in a cooler airmass associated with persistent northwest flow that will enhance on Saturday. High temperatures will drop 10 to 15 degrees Thursday to Friday as below normal high temperatures continue over the weekend and into the extended period. 75

LONG TERM
Sunday through Friday
The low over western Canada persists this work week as the NW flow aloft moves over PacNW with another potential low over Gulf of Alaska moving southerly.
Chances of precip remain on the low end (<15%) but increases to 10-20% in the low elevations and 20-40% at mountain areas with a cold front associated with the low over Gulf of Alaska moving southerly Tuesday onward. This will bring orographic lifting into the moisture-starved trough hence more showery activity.
Thunderstorms are possible but, chances are slim as this pattern doesn't seem to provide enough instability (<20%). Very light QPF amounts in the low elevations including Cascades but slightly more at the Blue Mountains to around 0.03-0.12 inch.

Gusty winds will continue this week at around 20-30kts mainly along Simcoe Highlands, Kittitas and Yakima Valley with strong surface pressure gradient as the front passes. The NBM probabilities of wind gusts >=22 mph shows high chances greater than 70%, but 40-60% over Ochoco-John Day Highlands. The agreement with the models and ensembles are improving with this pattern including potential showery precip impacting mountain areas. Temperatures will be slightly below or near normal, mainly 50s-60s within the mountains. Snow levels for this week will be 3000-5000ft but increase Thursday afternoon as precip dries out. Feaster/97

PRELIMINARY POINT TEMPS/POPS
PDT 43 64 39 67 / 10 0 0 0 ALW 48 68 45 70 / 20 0 0 0 PSC 50 72 46 73 / 10 0 0 0 YKM 41 69 40 69 / 0 0 0 0 HRI 47 70 43 71 / 10 0 0 0 ELN 41 62 41 63 / 10 0 0 0 RDM 42 65 34 66 / 0 0 0 0 LGD 45 60 36 66 / 20 10 0 0 GCD 46 63 36 69 / 0 0 0 0 DLS 48 66 46 67 / 10 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES
OR...None.
WA...Wind Advisory until 2 PM PDT Friday for WAZ026.

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

Pendleton, OR,