AgWeatherNet Autumn 2011 Weather Review for Central Washington

Washington Experiences a Relatively Benign November in Contrast to the Freeze of November 2010

Nic Loyd, Meteorologist, 509-786-9357
Gerrit Hoogenboom, Director, 509-786-9371

Overview
Washington experienced fairly normal late autumn conditions, or at least typically variable weather, during the month of November, although there were several periods of interesting weather during the month. Most notably, western Washington recorded significant rainfall on several occasions, while areas in southern Washington near Walla Walla and the Tri-Cities experienced two periods of unusually warm and windy weather late in the month. Temperatures were generally slightly below normal by around one degree. However, there was a broad range of spatial variability over the state. A significant north-south temperature gradient for much of this month caused Walla Walla to record warmer than normal conditions, while Wenatchee and Mt. Vernon were cooler than normal. Low temperatures were well below normal by two to five degrees in most places, except again for Walla Walla which recorded normal overnight temperatures. High temperatures were generally below normal in the north and above normal in the south.

November 2011 Daily Average Temperatures (°F)
Location (Period of Record) Maximum Anomaly Minimum Anomaly Mean Anomaly
Prosser (WSU IAREC; 1990-2011)
49.9
1.5
28.5
-3.5
39.1
-0.8
Moxee (1990-2011)
48.4
0.0
21.7
-5.2
35.3
-1.8
Mt. Vernon (WSU NWREC; 1994-2011)
50.4
-0.6
35.3
-3.5
42.5
-2.2
Wenatchee (WSU TRFEC; 1994-2011)
45.8
-0.3
26.8
-3.1
35.7
-1.6
Gramling (Tri-Cities; 1989-2011)
48.0
1.6
31.4
-2.2
39.4
-0.2
Walla Walla (1992-2011)
51.7
2.6
35.0
0.1
43.1
1.3
Royal City East (2008-2011)
46.6
NA
29.1
NA
37.3
NA
Pullman (2008-2011)
42.8
NA
29.0
NA
36.0
NA

November Weather
Early November
A pattern change occurred during the middle of the first week of November, as the deepest trough of low pressure for autumn to that point entered the region, bringing a change from the warm weather of the previous three months. The month began with below average temperatures but dry conditions in central Washington on November 1st and 2nd, and morning temperatures dropping into the teens in cold locations like Broadview (Ellensburg) and Moxee. Most areas east of the Cascades and even some areas west of the Cascades fell below freezing overnight. High temperatures on Wednesday, November 2nd were generally in the low 50s, although southeasterly flow ahead of the approaching weather system caused significant downsloping and adiabatic warming as areas near the Blue Mountains like Walla Walla rose into the 60s. Rain fell in western Washington during the night of November 2nd, with 1.2 inches recorded at Mt. Vernon, while a few inches of snow fell in the Cascades. High temperatures in central Washington fell into the 40s or even upper 30s in some cases later in the week and into the first weekend of November.

Some cloudy locations in northern Washington were particularly cold on November 7th due to strong inversions and in spite of the warming conditions aloft. Frosty night-time temperatures gave way to warming conditions around November 9th. Highs were near 60 in the Walla Walla area, and reached into the low 60s in parts of western Washington that were exposed to down slope southeasterly winds on November 9th. A strong cold front brought brief heavy rain and winds to western Washington and snow to the mountains on Veterans Day, November 11th. More rain followed on Saturday with showers on Sunday and Monday for western Washington, while areas in the lee of the mountains had mostly dry and warm conditions with westerly Chinook winds.

Mid November
Two-day rain totals for Friday and Saturday, November 11 and 12, were around one inch at many locations in western Washington. Winds during the weekend of November 12th/13th gusted to around 50 mph in central Washington, while high temperatures reached nearly 60 degrees in the lower Yakima Valley. Peak winds on Friday, November 11th at St. John were 45 mph for a fifteen minute average and 58 mph for a maximum gust speed. Maximum sustained and gust wind speeds on Sunday, November 13th at Wenatchee Heights (elevation 2321 feet) were 30 mph and 60 mph, respectively. Some locations near the Columbia River and in the Walla Walla area reported very warm low temperatures in the upper 40s on Sunday, November 13th. Another strong storm affected the area on Wednesday, November 16th, bringing rain, snow, and wind to Washington. Even Prosser observed a dusting of snow, although there was little accumulation on paved surfaces. Many AWN locations in southwest Washington received around three quarters of an inch of rain, while the Leavenworth area received up to 6 inches of snow. St. John recorded wind gusts up to 35 mph, while several locations near Pullman and at the coast recorded wind gusts in excess of 30 mph. Snow continued to fall in the Cascades late in the week while several more inches of snow fell in the Pullman and Spokane areas on Friday, November 18th. Colder weather moved into the region during the weekend of November 19/20, bringing the first truly chilly air mass of the season to the region. Highs in the 30s were widespread in Washington on Saturday, November 19th, with up to several inches of snowfall Saturday in parts of eastern Washington.

Late November
Additional systems impacted Washington during the week of November 21st. A weak system on November 21st brought rain and even snow to certain places in the morning, with more snow for the Cascades. However, a warmer system Tuesday and Wednesday brought strong wind and heavy rain especially to western Washington, along with much warmer temperatures. Several inches of rain had fallen near the coast by Tuesday morning, November 22nd, with even more in the Coast Range and Cascades. 15 minute sustained winds and gusts were measured at over 35 mph and 52 mph, respectively, at the St. John site on November 22nd and 23rd. Along with the wind and rain came mild temperatures. A subtropical air mass along with warm southerly winds off of the mountains led to many locations near the Tri-Cities and Walla Walla reaching above 65 degrees on Tuesday, November 22nd. Some low temperatures were above 50 degrees on Tuesday, and many locations were well into the 60s on Wednesday morning. Some areas in western Washington received over 4 inches of rain in the Tuesday/Wednesday time period. After cooling down briefly around Thanksgiving with a quick round of rain for western Washington and snow for the Cascades, another warm spell occurred during the weekend of November 26th/27th, with some locations near Walla Walla again reaching to near 70 degrees. After receiving rainfall on Sunday, November 27th, western Washington was drier and cooler on Monday. The month ended with a weak weather system bringing light rain to western Washington on November 29th, while November 30th featured dry and seasonal conditions in Washington.



November-By The Numbers
The average temperature at Prosser (WSU IAREC) was 39.1 degrees, which is 0.7 degrees below the average of 39.8 degrees. The average high temperature at Prosser (WSU IAREC) of 49.9 degrees was 1.5 degrees above normal, while the average low temperature of 28.5 degrees was 3.5 degrees (1 standard deviation) below normal. The month was somewhat dry in central Washington with only 0.17 inches of precipitation recorded at Prosser, while the average wind speed was 4.2 mph. The warmest temperature of the month was 62 degrees on November 22nd, while the coolest temperature of the month was 18.5 degrees on November 20th. November 22nd recorded the warmest low temperature (44.5 degrees) and overall daily temperature (54.7 degrees) of the month. November 20th also recorded the coolest high temperature (32.2 degrees) and overall daily temperature (27.4 degrees) of the month.


Notable November Weather Events
  • November 2nd: 1.2 inches of rain falls at WSU's AWN site at Mt. Vernon.
  • November 13th: Winds at Wenatchee Heights gust to 60 mph.
  • November 16th: The first snowfall of the season accumulates to a thick dusting in the Prosser area.
  • November 27th: Walla Walla records a high temperature of nearly 65 degrees.

November Temperature Extremes
  Observed in 2011 Normal Range Record Monthly Extremes
Site (Period of Record) Warmest Date Coldest Date Warmest Coldest Warmest Date Coldest Date
Prosser (WSU IAREC; 1990-2011)
62.0
11/22/2011
18.5
11/20/2011
63.8
19.8
73.8
11/13/1999
0.9
11/24/2010
Moxee (1990-2011)
58.7
11/22/2011
9.2
11/19/2011
63.2
12.3
71.0
11/13/1999
-17.2
11/24/2010
Mt. Vernon (WSU NWREC; 1994-2011)
61.9
11/9/2011
25.8
11/20/2011
61.3
25.2
65.9
11/14/1995
7.5
11/28/2006
Wenatchee (WSU TFREC; 1994-2011
54.7
11/1/2011
19.1
11/6/2011
59.8
17.9
67.0
11/4/2007
-4.6
11/24/2010
Gramling (Tri-Cities; 1989-2011
63.6
11/23/2011
22.8
11/19/2011
61.9
21.0
72.8
11/13/1999
0.0
11/24/2010
Walla Walla (1992-2011)
64.7
11/23/2011
27.0
11/11/2011
65.5
21.1
79.2
11/12/1999
-3.2
11/24/2010
Royal City East (2008-2011)
59.6
11/23/2011
21.4
11/16/2011
NA
NA
NA
NA
NA
NA
Pullman (2008-2011)
55.4
11/23/2011
19.5
11/19/2011
NA
NA
NA
NA
NA
NA

Autumn Weather
Temperatures were generally above normal during the fall of 2011 due to the warm conditions in September and to a lesser extent October. September was mostly dry and very hot during the early and middle part of the month, while October featured several weak weather systems which kept low temperatures warm in places that normally experience strong overnight radiational cooling. While November temperatures were near average during the day, overnight low temperatures were below normal in Washington, leading to slightly below normal overall temperatures.

September and October Review
The autumn season began with above normal temperatures and dry conditions. Following cool weather for much of early 2011, summer weather continued well into September, with the most significant heat wave of the year occurring from September 9 to 13. While September featured particularly hot days, with high temperatures of three to four degrees above normal in eastern Washington, October brought warm overnight temperatures of two to four degrees above normal, especially in locations such as Moxee that typically feature cold low temperatures. The absence of an early freeze was beneficial since it allowed more time to harvest a delayed apple crop.


Autumn-By The Numbers
The average autumn temperature at Prosser (WSU IAREC) was 51.8 degrees, which is 0.9 degrees (0.8 standard deviations) above the average of 50.9 degrees. The average autumn high temperature at Prosser (WSU IAREC) of 64.7 degrees was 1.5 degrees above average mainly due to daytime heat in early September and several mild days in late November, while the average autumn low temperature of 40.0 degrees was 0.4 degrees above average. Prosser recorded 0.77 inches of precipitation during the autumn season, and the average wind speed was 3.7 mph. The warmest temperature of the season was 95.0 degrees and occurred on September 12th, while the coldest temperature of the period was 18.5 degrees on November 20th. Overall, autumn temperatures in Washington were above normal, especially in southeastern Washington. Average autumn temperatures ranged from near normal (0.1 degrees above normal) at Mt. Vernon to 2.1 degrees above normal at Walla Walla. Average autumn high temperatures ranged from 0.7 degrees above normal (Moxee and Mt. Vernon) to 2.6 degrees above normal (Walla Walla), while low temperatures ranged from 0.6 degrees below normal at Mt. Vernon to 1.7 degrees above normal at Walla Walla.

Autumn 2011 Daily Average Temperatures (°F)
(Autumn = Sept, Oct, Nov)
Location (Period of Record) Maximum Anomaly Minimum Anomaly Mean Anomaly
Prosser (WSU IAREC; 1989-2011)
64.7
1.5
40.0
0.4
51.8
0.9
Moxee (1989-2011)
64.3
0.7
34.4
0.6
48.8
0.8
Mt. Vernon (WSU NWREC; 1994-2011)
59.8
0.7
42.9
-0.6
51.2
0.1
Wenatchee (WSU TFREC; 1994-2011)
63.4
0.8
39.0
0.0
50.4
0.4
Gramling (Tri-Cities; 1989-2011)
63.3
1.9
43.8
1.1
53.0
1.5
Walla Walla (1992-2011)
65.4
2.6
44.3
1.7
54.5
2.1
Royal City East (2008-2011)
62.4
NA
41.8
NA
51.4
NA
Pullman (2008-2011)
59.6
NA
36.3
NA
48.2
NA
Notable Autumn Weather Events
  • September 9th: The high temperature of 98.8 degrees was the second warmest September temperature ever recorded in Wenatchee at the WSU Tree Fruit Research Station site.
  • September 12th: The AWN site at Orondo, north of Wenatchee, reached nearly 101 degrees.
  • October 26th: The low temperature at Pullman dropped to 19 degrees.
  • October 28th: Nearly an inch of rain fell at the WSU AWN weather station in Long Beach.

Weather Summary By Month
  • September: Hot early in the month with above average day-time temperatures.
  • October: Above average overnight low temperatures in central Washington.
  • November: Typically variable with a few periods of wind and rain.

Agriculture Report
The Washington apple harvest was complete at the end of November, with early indications suggesting an average crop yield for 2011 (Good Fruit Grower). Winter wheat had emerged in Walla Walla County, while dry corn harvest continued in Grant County in late November. Meanwhile, the Christmas Tree harvest is in full swing in preparation for the Christmas Season (Washington Agricultural Statistics Service).

This Month in History
On the morning of Tuesday, November 19th, 1996, residents in many areas in central Washington awakened to find more than a foot of snow had fallen overnight, in one of the earliest and most significant snowstorms in the history of the region. The snowfall was largely unexpected with many forecasts calling only for a mix of rain and snow. The cause of the anomalous winter storm was an unusual weather pattern featuring a split flow in the jet stream which included a southern branch of the jet containing Pacific moisture that collided with a northern branch of the jet bringing arctic air into Washington.

A Look Back at November 2010
The cold air outbreak that occurred last November has deservedly received significant attention from the media and from the public; and the full extent of its impact, including the damage to Washington agriculture, is only now being fully realized. The anecdotal evidence is clear: many people were surprised at just how cold it felt, and how much damage orchards received. However, a statistical analysis of Washington's Thanksgiving 2010 freeze helps to place this event in the proper quantitative context in terms of the extreme and unusual nature of this weather phenomenon. To say that this event was record setting is correct and yet does not fully appreciate the magnitude of this occurrence. The November 2010 cold snap was truly an outlier and a similar event may not be witnessed again in the foreseeable future. There are several aspects of this event that make it entirely unique.

  • The first notable aspect of the freeze event was the bitter cold. Many AWN locations fell below zero and recorded all-time (1989 to present) record low November temperatures on the morning of November 24th, 2010. While surpassing record values is impressive enough, many records were shattered last November. For example, Moxee fell to minus 17 degrees that morning, which was the first time since 1993 that the temperature at that AWN site had been below zero, and only the second time since 1989. The low temperature of -17 degrees eclipsed the old November record by an astonishing 13 degrees.
  • The November 2010 freeze happened unusually early in the winter for such an extreme outbreak of arctic air over the region, since most sub-zero temperatures in eastern Washington happen in December or January.
  • The cold snap was particularly long lasting, due in part to snow cover from snowfall that occurred near the beginning of the event. Prosser (WSU IAREC) temperatures were below freezing for a November record nine consecutive days from November 22 to 30, 2010, after having been above 60 degrees on four separate days earlier in the month. Prosser also recorded low temperatures below 20 degrees for a November record six consecutive days.
  • Temperatures were very cold in all meteorological categories and at all times of day. For example, November 24th, 2010 experienced the coldest temperature, daily high temperature, and average daily temperature ever in November at many locations in south central Washington. The high temperature of 14 degrees at Prosser (WSU IAREC) was nearly eight degrees colder than the previous November record cold high of 21.8 degrees set in 1993. The low and average daily temperatures (0.9 and 8.2 degrees) were also November records. In fact, the daily high temperature was about 15 degrees colder than the average low temperature for that date. The high, low, and average daily temperatures at Prosser on November 24th were each 30 degrees below average!
  • Finally, it was of particular consequence for the observed vineyard damage that the temperature dropped rapidly and significantly following a very warm first half of November in which many locations recorded several days in the 60s. Prosser (WSU IAREC) reached 60 degrees on November 16th; however, only eight days later, the high temperature was just 14 degrees and the low was 1 degree on November 24th. Therefore, many crops had accumulated relatively few chilling hours and thus had acquired very little cold resistance, making them unprepared for the arctic cold that was to come. Prior to November 21st, the coldest temperature of the month at Prosser (WSU IAREC) had only been 29.4 degrees! The following graph of Prosser¬ís November 2010 Temperature time series is provided in order to illustrate the rapid drop in temperatures that occurred late in the month.


The rapid decline from above average temperatures early in the month to record setting cold later in the month made November of 2010 the most variable month of November on record and one of the most changeable weather months in recent Washington history. Many Washingtonians sensed that this was a rare and remarkable weather event and the evidence certainly supports that claim.

Climate Outlook
Early December looks to be mostly dry with generally calm conditions for this time of year, as a large ridge of high pressure over the eastern Pacific Ocean prevents strong storms from reaching Washington. With La Niña conditions continuing in the equatorial Pacific Ocean, the outlook for later in the winter and spring continues to call for enhanced odds of wetter and cooler than normal conditions for Washington.

Washington State University