AgWeatherNet Weekly Weather Outlook Monday Update for October 19 to October 25, 2020

COLD temperatures expected by mid week

Craig Oswald, AgWeatherNet Field Meteorologist

Synopsis:

The main weather story for the upcoming outlook period is defined by cold temperatures. A potent cold front is expected to move into the state from the north Wednesday dropping low temperatures into the 20s in many locations east of the Cascades. A surface low pressure system then looks to move into the state form the northwest beginning Thursday night, bringing fairly widespread precipitation across the state with non trivial totals. Given the cold overnight temperatures expected, snow may reach low land areas of northern and eastern Washington. After the passing of this system, a renewed surge of cold air is anticipated. Low temperatures for the weekend are indicated to drop to near 20 in many parts of northern Washington and even into the teens for eastern Washington, around 15 degrees below normal for the month of October in these locations. Low temperatures through lowland areas of western Washington are not completely safe from the cold either as temperatures are anticipated to be hovering around the freezing mark by the weekend after a steady drop through the week.

Discussion:

The broader synoptic setup currently influencing the weather across Washington consists of a ridge of high pressure over the central north Pacific, placing the region under strong northwest flow aloft. This, paired with a circulation northwest of Hawaii, is helping to draw moist tropical air to the north where it is subsequently directed around the apex of the ridge and into the Pacific Northwest. This is manifest in the generally mid to high level clouds expected to continue throughout the state for the course of the week. This moist northwest flow looks to continue to produce some orographically driven light and scattered rain showers throughout western Washington, primarily through the Cascades and Olympics, and even a shower or two throughout the Blue Mountains of southeast Washington and the ranges of northern Washington. Some modest upper level forcing is likely aiding in the production of these showers as well, yet the primary driver looks to be the effects of topography. Temperatures will remain seasonable Tuesday and for the day Wednesday before a strong cold front begins moving into the region from the north through the course of the day Wednesday.

The frontal passage Wednesday does not look to bring widespread precipitation as cold and dry air dominate conditions behind the front as in moves into the state from the north. An enhancement in shower activity throughout mountain regions however is expected with snow levels dropping to pass levels. Some scattered rain showers also look to continue throughout western Washington with a stray shower or two possible throughout low land areas of eastern Washington. Temperatures Wednesday night will be particularly cold throughout the state. With overnight lows having already reached the low 30s in some fruit growing areas the last several nights (and expected to continue to do so the next two nights, especially in the Okanogan) throughout the upper Yakima Valley and Okanogan, the exceptionally cold temperatures beginning Wednesday night look to bring widespread overnight freezes to these areas and eastern Washington in general.

While maintaining a northwesterly flow regime aloft, a surface low pressure system is anticipated to begin moving into northwest Washington Thursday night. Widespread rain and mountain snow are expected as precipitation moves southeast across the state. Snow levels look to lower to near 2000-2500 feet, and close to 1500 feet by Friday night. With this being said, low land areas of western Washington are expected to maintain rain showers while lowland areas east of the Cascades stand a good chance to see snow, particularly the northern half of the state and the Palouse. This system and its associated precipitation should be exited from the state to the southeast by Saturday morning. Precipitation totals, in liquid water equivalent, are generally anticipated to be 1.5+ inches in mountain regions such as the Olympics, Cascades, and Blues. Precipitation totals throughout the northeast corner of the state look to be substantially lower due to the northwest to southeast motion of the system. Totals of 0.10 to 0.25 inches are expected with slightly more throughout the mountains. Elsewhere, most lowland areas of western Washington are anticipated to receive around 0.75 inches with precipitation being much more variable east of the Cascades. Anywhere between 0.10 to 0.75 inches are expected with higher totals likely to be near the southeast corner of the state.

Fast on the heels of the departing low pressure system, another surge of cold and dry air from the north is expected. This will help to cool temperatures even more than what is likely to be observed during the second half of this week. Skies will trend mostly sunny and clear enhancing night time radiative loss and cooling overnight lows even further in areas that typically tend colder under such conditions.

Temperatures are expected to somewhat recover through the beginning of the following week.


Important Points About This Week's Weather

South Central Washington
Remainder of the week
  • Wind: Breezy W/SW winds Tue. Becoming windy and NW Wed. Switching N/NE and much lighter Thu. Remaining NE Fri and again becoming windy.
  • Precipitation: Dry through most of the week with a low chance for a rain shower or two Wed. Rain showers Fri and Fri night with snow likely above 1500 ft.
  • High Temps: Low 60s Tue, upper 50s Wed, low 50s Thu, upper 40s Fri.
  • Low Temps: Low 40s Mon night, mid 30s Tue night, upper 20s Wed night, mid 20s Thu night.
  • Sky Cover: Mostly sunny/mostly clear to partly cloudy through much of the week. Becoming mostly cloudy Fri.

Weekend
  • Wind: NE and windy Sat, trending much lighter yet breezy at times for Sun.
  • Precipitation: Any lingering rain/snow showers quickly trending dry early Sat. Dry conditions for the rest of the weekend.
  • High Temps: Mid 40s Sat, low 40s Sun.
  • Low Temps: Upper 20s Fri night, low 20s Sat night, near 20 Sun night.
  • Sky Cover: Mostly to partly cloudy Sat. Mostly sunny by Sun.

North Central Washington
Remainder of the week
  • Wind: Breezy W winds Tue, more so through the Basin. Becoming windy and NW Wed. Switching N/NE and much lighter Thu. Remaining NE Fri and again becoming windy. Much windier through N to S oriented valleys during the latter half of the week.
  • Precipitation: Scattered rain showers continuing near the Cascade crest with dry conditions expected elsewhere early in the week. Some mountain rain and snow showers Wed with a low chance for a rain shower in low land areas. Rain showers Fri and Fri night with snow likely above 1500 ft.
  • High Temps: Upper 50s Tue, mid 50s Wed, upper 40s Thu, low 40s Fri. Cooler in high terrain.
  • Low Temps: Mid 30s Mon night, low 30s Tue night, upper 20s Wed night, near 30 Thu night. Cooler in high terrain and deep valleys.
  • Sky Cover: Mostly sunny/mostly clear to partly cloudy through much of the week. Becoming mostly cloudy late Thu and reaming so Fri.

Weekend
  • Wind: NE and breezy Sat, windier through the Basin and N to S oriented valleys. Trending much lighter yet breezy at times for Sun.
  • Precipitation: Dry conditions expected.
  • High Temps: Upper 30s Sat, upper 30s Sun. Cooler in high terrain.
  • Low Temps: Mid 20s Fri night, near 20 Sat night, near 20 Sun night. Cooler in high terrain and deep valleys.
  • Sky Cover: Mostly to partly cloudy Sat. Becoming mostly sunny by Sun.

Eastern Washington
Remainder of the week
  • Wind: Breezy W/SW winds Tue. Becoming windy and NW Wed. Switching N/NE and much lighter Thu. Remaining NE Fri and again becoming windy.
  • Precipitation: Dry conditions expected early in the week. Some mountain rain and snow showers Wed with a low chance for a rain shower in low land areas. Greater chance for shower activity near the Idaho border. Rain showers Fri and Fri night with snow likely throughout the Palouse and Blue Mtns, and more generally, areas above 1500ft.
  • High Temps: Mid 50s Tue, upper 40s Wed, near 40 Thu, upper 30s Fri. Cooler through the Blues.
  • Low Temps: Upper 30s Mon night, mid 30s Tue night, mid 20s Wed night, mid 20s Thu night. Cooler through the Blues.
  • Sky Cover: Partly to mostly cloudy through the week.

Weekend
  • Wind: NE and windy Sat, trending much lighter yet breezy at times for Sun.
  • Precipitation: A few rain and snow showers to linger through Sat morning before trending dry and remain so for the weekend.
  • High Temps: Mid 30s Sat, low 30s Sun. Cooler through the Blues.
  • Low Temps: Mid 20s Fri night, mid teens Sat night, mid teens Sun night. Cooler through the Blues.
  • Sky Cover: Mostly cloudy Sat. Becoming mostly sunny by 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: Continued scattered rain showers early in the week with greater activity through the Olympics and Cascades. Enhanced scattered rain shower activity Wed with some mountain snow showers likely. Rain showers and mountain snow showers Thu night and Fri with snow likely down to pass levels.
  • High Temps: Upper 50s Tue, mid 50s Wed, low 50s Thu, near 50 Fri. Cooler through the Cascades and Olympics.
  • Low Temps: Mid 40s Mon night, low 40s Tue night, mid 30s Wed night, mid 30s Thu night. Cooler through the Cascades and Olympics.
  • Sky Cover: Partly to mostly cloudy through the week.

Weekend
  • Wind: NE and windy Sat, especially in the far northern part of the region and near the sound/straight. Trending much lighter yet breezy at times for Sun.
  • Precipitation: Trending dry Fri night with mountain snow showers lingering into Sat morning before coming to an end. Dry conditions expected for the remainder of the weekend.
  • High Temps: Near 50 Sat, near 50 Sun.
  • Low Temps: Mid 30s Fri night, low 30s Sat night, low 30s Sun night. Cooler through the Cascades and Olympics.
  • Sky Cover: Mostly sunny to partly cloudy.

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