AgWeatherNet Weekly Weather Outlook Monday Update for October 5 to October 11, 2020

Continued warm and dry conditions with impactful weather for the weekend and beyond

Craig Oswald, AgWeatherNet Field Meteorologist

Synopsis:

Weather conditions are expected to remain warm and dry through the week as a broad low amplitude upper ridge rebuilds over the region after a brief transition to a zonal flow regime. This will help to promote calm to light winds, clear skies, and continued night time inversions with low temperatures remaining in the low 40s for the majority of the fruit growing regions. Western Washington will see a continuation of overnight and morning fog, primarily throughout coastal and low elevation areas. Conditions look to change drastically starting Friday night as a significant frontal system is anticipated to begin moving into Washington from the west. Precipitation statewide, even significant precipitation, likely on the order of 2+ inches for low elevation areas of western Washington, looks to be expected at this time. Even the driest region of the state, the Columbia Basin, is expected to receive rainfall, likely between 0 and 0.25 inches.

Discussion:

The week will continue to be pleasant and favorable for outdoor work and harvest activities as a modest ridge of high pressure continues to build over the Pacific Northwest. Overnight conditions will continue to be favorable for strong inversions, however with relatively warm air aloft, minimum temperatures, even in the cold spots of fruit growing areas, are likely to remain above 40F. The west side of the state will continue to experience overnight fog in low areas and near the coast, with a sea breeze expected to take hold through the course of the diurnal cycle. The greatest excitement expected is a few scattered rain showers for western Washington beginning Thursday and remaining into Firday with greater shower activity through the Cascades and Olympics. These showers look to be in conjunction with an offshore upper low that is expected to move into central/northern California, hopefully bringing a round of much needed rain to that region. This will also help to push the persistent ridge that has been providing the warm daytime temperatures to the east. Day time highs are expected to drop about 5F state wide by Friday.

Located further upstream from this feature is a rather robust trough currently centered over the Aleutian Islands and North Pacific. This system will move east into the Pacific Northwest, transitioning the region to a strong, moist southwest flow regime ahead of the approaching cold front. What appears to be the warm frontal boundary associated with this system is expected to be located across central British Columbia. This will provide rain showers for our neighbors to the north Friday, but also likely to the northern parts of western Washington as moist southwesterly flow is gradually lifted along the broad west to east frontal boundary to the north. Meaning the showers initiated by the upper low Thursday, likely won’t fully come to an end before the weekend. Winds will be quite breezy and windy by Friday as the cold front, the main forcing for the expectant showers, begins moving into the state from the west/northwest Friday night. Breezy and windy conditions are to prevail through the weekend. Widespread light to moderate rain showers with isolated areas of heavier rain will be in store for western Washington through Saturday with a transition to mostly scattered showers by Sunday. Initially, rain totals look to be around 2+ inches through much of the region. Of course the Cascades and Olympics will experience more consistent rainfall with higher totals and precipitation likely will not come to an end during the course of the weekend in the higher elevation areas. With significantly colder air aloft, mountain areas near and above 6000 feet are expected to see snow by Saturday night.

Precipitation will make its way east of the Cascades by Saturday with mostly light rain showers that will be more scattered in nature, aside from higher terrain areas where more consistent rain fall is expected. Snow levels again look to fall to around 6000 feet Saturday night. Showers look to exit most of eastern Washington by Sunday with just a low chance for a stray shower or two Sunday. A few rain/snow showers will likely linger over high terrain through Sunday. Totals are likely to be around 0 to 0.25 inches for south central Washington and the Columbia Basin, 0.25 to 0.5 near the Idaho border and low land areas of northern Washington, and around 1+ inch in high terrain. Winds will also become breezier by Friday with breezy to windy conditions prevailing through the weekend.

After the passage of the cold front, temperatures aloft are indicated to be cold enough to be worrisome for fruit growers in the midst of harvest. However, with elevated dew points, some lingering cloud cover, and ample wind, it is likely that overnight lows will remain near 40 or above. But please be cognizant that temperatures aloft are to be much cooler than they have been recently. High temperatures look to be 10 to 15 degrees cooler by Sunday state wide than they are forecast to be this week.

Additionally, another quite impactful weather system is being noted by several models to move into the state early next week, in the Monday time frame. Both of these systems seem to be kicking off a period of much more active weather. If the large scale pattern hinted at in the longer range models comes true, this looks to be the last taste of summer the region will have for some time as much cooler and unsettled weather looks to prevail.


Important Points About This Week's Weather

South Central Washington
Remainder of the week
  • Wind: Light and variable while becoming slightly breezier by late afternoon and trending much calmer during the overnight. Becoming S/SW and breezy Thu and Fri.
  • Precipitation: Dry conditions expected.
  • High Temps: Upper 70s Tue, upper 70s Wed, upper 70s Thu, low 70s Fri.
  • Low Temps: Upper 40s Mon night, upper 40s Tue night, upper 40s Wed night, mid 40s Thu night.
  • Sky Cover: Sunny and mostly clear. Turning mostly sunny to partly cloudy by Thu.

Weekend
  • Wind: S/SW and becoming windy Sat with gusts around 35mph. Remaining S/SW and generally breezy to windy through Sun.
  • Precipitation: Light and scattered rain showers Sat and Sat night. Likely dry Sun yet a continued low chance for a shower or two to remain.
  • High Temps: Mid 60s Sat, mid 60s Sun.
  • Low Temps: Mid 40s Fri night, low 40s Sat night, near 40 Sun night.
  • Sky Cover: Mostly cloudy Sat. Clearing to partly cloudy Sun.

North Central Washington
Remainder of the week
  • Wind: Light and variable while becoming slightly breezier by late afternoon and trending much calmer during the overnight. Becoming S/SW and breezy Thu and Fri, particularly through the Basin.
  • Precipitation: A high elevation rain shower or two near the Cascade crest Thu night through Fri. Otherwise dry conditions expected through the week.
  • High Temps: Upper 70s Tue, upper 70s Wed, mid 70s Thu, low 70s Fri. Cooler in high terrain.
  • Low Temps: Near 50 Mon night, low 50s Tue night, near 50 Wed night, upper 40s Thu night. Cooler in high terrain and deep valleys.
  • Sky Cover: Mostly sunny and mostly clear. Turning partly cloudy Wed and mostly cloudy by Thu. Greater cloud cover to the west, clearer through the Basin.

Weekend
  • Wind: S/SW and becoming windy Sat with gusts around 35mph, particularly through the Basin. Remaining S/SW and generally breezy to windy through Sun.
  • Precipitation: Rain showers and scattered rain showers region wide Sat and Sat night with greater activity through high terrain. Likely dry Sun yet a continued low chance for a shower or two to remain, especially through high terrain. A few snowflakes near 6000ft and higher likely Sat night.
  • High Temps: Mid 60s Sat, mid 60s Sun. Cooler in high terrain.
  • Low Temps: Upper 40s Fri night, low 40s Sat night, near 40 Sun night. Cooler in high terrain.
  • Sky Cover: Mostly cloudy Sat. Clearing to partly cloudy Sun.

Eastern Washington
Remainder of the week
  • Wind: Light and variable while becoming slightly breezier by late afternoon and trending much calmer during the overnight. Becoming S/SW and breezy Thu and Fri.
  • Precipitation: Dry conditions expected.
  • High Temps: Mid 70s Tue, upper 70s Wed, mid 70s Thu, upper 60s Fri. Cooler through the Blues.
  • Low Temps: Mid 40s Mon night, mid 40s Tue night, mid 40s Wed night, low 40s Thu night. Cooler through the Blues.
  • Sky Cover: Sunny and mostly clear. Turning partly cloudy by Thu.

Weekend
  • Wind: S/SW and becoming windy Sat with gusts around 35mph. Remaining S/SW and generally breezy to windy through Sun.
  • Precipitation: Rain showers and scattered rain showers region wide Sat and Sat night with greater activity through the Blues. Likely dry Sun yet a continued low chance for a shower or two to remain, especially through the Blues. A few snowflakes near 6000ft and higher likely Sat night.
  • High Temps: Low 60s Sat, upper 50s Sun. Cooler through the Blues.
  • Low Temps: Low 40s Fri night, low 40s Sat night, near 40 Sun night. Cooler through the Blues.
  • Sky Cover: Mostly cloudy Sat. Clearing to partly cloudy Sun.

Western Washington
Remainder of the week
  • Wind: Light and variable while becoming slightly breezier by late afternoon and trending much calmer during the overnight. Becoming S/SW and breezy Thu and windier Fri. Gusts around 35mph Fri.
  • Precipitation: Dry conditions expected early in the week. A few scattered rain showers creeping in Thu, primarily throughout the Cascades and Olympics and lingering through Fri with greater activity to the north.
  • High Temps: Low 70s Tue, low 70s Wed, upper 60s Thu, mid 60s Fri. Cooler through the Cascades and Olympics.
  • Low Temps: Mid 40s Mon night, upper 40s Tue night, upper 40s Wed night, near 40 Thu night. Cooler through the Cascades and Olympics.
  • Sky Cover: Sunny and mostly clear. Partly cloudy Wed. Mostly cloudy to cloudy Thu and Fri. Areas of fog expected in low areas and near the coast for the first half of the week.

Weekend
  • Wind: S/SW and windy Sat with continued gusts around 35mph. S/SW and lessening Sun yet remaining generally breezy to windy.
  • Precipitation: Widespread light to moderate rain showers, with isolated areas of heavier rainfall beginning Fri night. Showers trending scattered in nature Sun and lingering through Sun night. More consistent shower activity through the Cascades and Olympics. A few snowflakes near 6000ft and higher likely Sat night.
  • High Temps: Near 60 Sat, near 60 Sun.
  • Low Temps: Upper 40s Fri night, mid 40s Sat night, mid 40s Sun night. Cooler through the Cascades and Olympics.
  • Sky Cover: Mostly cloudy and cloudy.

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