AgWeatherNet Spring 2015 Weather Review for Washington

Warmest Spring Since 1992 Ends With Warmest May Since 1993

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

Overview
The month of May marked the end of yet another abnormal season in Washington. In fact, the spring of 2015 was the warmest since the early 1990s. Prosser's temperature highlights from this impressive season include:

  • The Second Warmest Spring on Record (1992)
  • The Warmest Spring Low on Record
  • The Warmest May Since 1993
  • The Warmest May Low on Record
  • The Warmest March on Record

Interestingly, the low temperatures were particularly warm, which is indicative of the unsettled and somewhat humid conditions late in the spring. South central Washington was actually wetter than western areas in May, which represents a significant departure from normal conditions.

The non-temperature weather story of last month was the incredible May 13th rainfall in south central Washington. Much of the lower Columbia Basin from the lower Yakima Valley and Horse Heaven Hills eastward to the Tri-Cities and Walla Walla areas recorded in excess of one inch of rain, with isolated reports of more than 2 inches. The remarkable rainfall was widespread in the climatologically driest part of the state, and not isolated as would be the case with convective activity. Prosser recorded 1.37 inches of rain, which is an all-time daily record. The fact that this event occurred in May, rather than the cold season, is quite notable. The 13th was also a very cool day, with highs only in the 50s in much of south central and eastern Washington. In fact, temperatures seemed especially cool given the abnormal warmth of most of the month.

Earlier in the spring, March was nearly five degrees above normal at Prosser, and was the warmest on record. March 27th was an especially hot day, as Wapato reached a monthly record high of 80 degrees. However, several cool storms in early April brought wind, rain, and mountain snow to the region. The high was only 45 degrees at Garfield East on the 14th, and then Ritzville fell to 23 degrees on the morning of the 15th. However, the temperature soared to 83 degrees at Azwell on April 20th. Overall, April was only slightly warmer than normal and quite dry.

May 2015 Average Temperatures (°F)
Location (Period of Record) Maximum Anomaly Minimum Anomaly Mean Anomaly Soil Temperature
8 inches
Prosser (WSU IAREC; 1989-2015)
76.2
3.8
49.9
4.3
63.6
3.7
64.6
Moxee (1989-2015)
76.6
4.5
45.9
5.2
62.3
4.2
60.2
Mt Vernon (WSU NWREC; 1994-2015)
66.7
3.8
46.9
0.8
56.3
2.1
59.6
Wenatchee (WSU TFREC; 1994-2015)
77.8
6.0
51.1
4.3
64.3
4.4
65.1
Tri-Cities (1995-2015)
80.0
5.2
51.9
4.2
66.2
4.3
71.7
Walla Walla (1993-2015)
74.6
4.6
50.2
2.5
62.2
3.2
64.1
Moses Lake (1989-2015)
77.0
5.6
49.5
4.3
63.5
4.5
67.9
Omak (Pogue Flat; 2005-2015)
76.1
NA
48.4
NA
62.5
NA
65.8
Royal City East (2008-2015)
76.5
NA
50.6
NA
63.0
NA
65.3
Pullman (2008-2015)
69.0
NA
42.8
NA
56.8
NA
59.7
Long Beach (WSU Long Beach; 2005-2015)
58.6
NA
47.3
NA
52.6
NA
58.8
Sequim (2008-2015)
65.1
NA
45.9
NA
54.8
NA
54.5
Seattle (2011-2015)
68.5
NA
50.5
NA
58.9
NA
62.8
Vancouver (WSU RE; 2008-2015)
69.4
NA
48.9
NA
58.7
NA
60.1
2015 Rainfall and Evapotranspiration (ET) (inches)
Location (Period of Record) Rainfall ET Net
May 2015 May (Rain - ET)
Prosser (WSU IAREC; 1989-2015)
1.46
3.61
7.48
-6.02
Moxee (1989-2015)
0.88
2.62
7.57
-6.69
Mt. Vernon (WSU NWREC; 1994-2015)
0.60
12.25
4.33
-3.73
Wenatchee (WSU TFREC; 1994-2015)
1.21
4.29
6.85
-5.64
Tri-Cities (1995-2015)
1.54
3.72
8.55
-7.01
Walla Walla (1993-2015)
2.21
7.52
5.98
-3.77
Moses Lake (1989-2015)
0.90
2.87
7.91
-7.01
Omak (Pogue Flat; 2005-2015)
0.61
3.09
6.74
-6.13
Royal City East (2008-2015)
0.74
2.29
7.22
-6.48
Pullman (2008-2015)
1.35
8.10
6.90
-5.55
Long Beach (WSU Long Beach; 2005-2015)
1.07
22.89
3.02
-1.95
Sequim (2008-2015)
0.25
7.37
4.38
-4.13
Seattle (2011-2015)
0.57
13.57
4.47
-3.90
Vancouver (WSU RE; 2008-2015)
0.96
13.80
4.96
-4.00
May 2015 Daily Rainfall Time Series Graph for Prosser May 2015 Daily Rainfall Time Series Graph for Long Beach

May Weather
Early May-Variable Conditions
May began with warm temperatures and rather dry conditions. Highs on the 1st were in the upper 50s at the coast to the mid 80s in parts of south central Washington. However, the low on the 6th was a chilly 29 degrees at Ritzville. May 6th was a cool, breezy and showery day, with a few thunderstorms. A trend toward warming and drier conditions began on May 7th.

Mid May-Heavy Rain in Central Washington on the 13th
The highlight of mid May was the heavy rain event in the normally dry south central Washington region on the 13th. Several sites in the Horse Heaven Hills recorded daily rain values in excess of 2 inches.

Late May-Warm, With Isolated Showers
Late May was a warm and slightly unsettled time period, as occasional isolated showers were observed. The high temperature at WSU Tri-Cities on May 30th was 92 degrees.

May 2015 Daily Temperatures
2015 temperature Time Series Graph for Prosser 2015 temperature Time Series Graph for Moxee
2015 temperature Time Series Graph for Wenatchee 2015 temperature Time Series Graph for Tri-Cities
2015 temperature Time Series Graph for:Walla Walla May 2015 Temperature Time Series Graph for WSU
May 2015 Temperature Time Series Graph for WSUMoses Lake May 2015 Temperature Time Series Graph for WSU Omak
May 2015 Temperature Time Series Graph for WSU Long Beach May 2015 Temperature Time Series Graph for WSU Mt. Vernon

May-By The Numbers
The average May temperature at Prosser (WSU IAREC) was 63.6°F, which is 3.7 degrees (1.4 standard deviations) above average. The average high temperature was 76.2°F, which is 3.8 degrees (1.2 standard deviations) above average. The average low temperature was 49.9°F, which is 4.3 degrees (1.8 standard deviations) above average. The maximum temperature recorded last month was 88.4°F on May 30th, while the coolest daily high was 57.0°F on May 13th. Low temperatures ranged from 62.0°F on May 30th to 35.8°F on May 6th. Daily average temperatures ranged from 75.6°F on the 30th to 50.5°F on the 6th. The monthly precipitation total was 1.46 inches. The average wind speed was 4.5 mph, and the average 8 inch soil temperature was 64.6°F. Wenatchee (WSU TFREC) recorded an average temperature of 64.3°F, which is 4.4 degrees above average, while Walla Walla's average monthly temperature of 62.2°F was 3.2 degrees above average. Pullman was one of the cooler spots in the state, with an average May temperature of 56.8°F. In western Washington, Mt. Vernon's average temperature was 56.3°F, which is 2.1 degrees above average.


Notable May Events
  • May 1st: The temperature at Benton City soared to 86 degrees.
  • May 3rd: The temperature at LaCrosse fell to 28 degrees.
  • May 4th: The wind at Pullman gusted to over 43 mph.
  • May 6th: The temperature at Anatone reached only 56 degrees.
  • May 13th: 1.37 inches of rain fell at WSU Prosser.
  • May 30th: The temperature at the Tri-Cities rose to 92 degrees.

May Temperature Extremes (°F)
  Observed in 2015 Record Monthly Extremes
Site (Period of Record) Warmest Date Coldest Date Warmest Date Coldest Date
Prosser (WSU IAREC; 1989-2015)
88.4
5/30/2015
35.8
5/6/2015
98.4
5/12/1993
29.8
5/7/2002
Moxee (1989-2015)
89.2
5/29/2015
30.2
5/6/2015
98.0
5/23/2001
19.9
5/8/1996
Mt. Vernon (WSU NWREC; 1994-2015)
76.2
5/28/2015
36.1
5/3/2015
86.2
5/17/2008
32.6
5/7/2002
Wenatchee (WSU TFREC; 1994-2015)
89.9
5/30/2015
37.0
5/7/2015
97.7
5/17/2006
30.7
5/2/1997
Tri-Cities (1995-2015)
91.6
5/30/2015
39.0
5/3/2015
100.9
5/23/2001
29.8
5/1/2013
Walla Walla (1992-2015)
89.5
5/29/2015
38.4
5/3/2015
94.5
5/23/2001
32.7
5/2/2006
Moses Lake (1989-2015)
89.5
5/29/2015
38.2
5/6/2015
97.5
5/18/2006
27.8
5/8/2002
Omak (Pogue Flat; 2005-2015)
87.0
5/23/2015
36.1
5/9/2015
94.8
5/17/2006
29.1
5/4/2010
Royal City East (2008-2015)
93.2
5/19/2015
37.4
5/6/2015
93.3
5/17/2008
31.7
5/5/2010
Pullman (2008-2015)
80.5
5/29/2015
28.5
5/3/2015
85.2
5/17/2008
25.2
5/11/2012
Long Beach (WSU Long Beach; 2005-2015)
73.4
5/8/2015
37.5
5/6/2015
95.3
5/16/2008
31.1
5/1/2013
Sequim (2008-2015)
73.3
5/28/2015
35.0
5/6/2015
77.8
5/5/2013
26.5
5/1/2013
Seattle (2011-2015)
81.2
5/29/2015
41.5
5/3/2015
NA
NA
NA
NA
Vancouver (WSU RE; 2008-2015)
83.8
5/28/2015
38.2
5/3/2015
90.0
5/14/2014
31.7
5/10/2012

Spring Weather
March and April Review
March was the fifth record warm month of the previous nine months at that time. Temperatures at Prosser were nearly five degrees warmer than normal, including more than 6 degrees above normal during the day. March 27th was a particularly abnormal day where several stations in south central Washington set new all-time March high temperature records. Wapato reached an impressive 80 degrees, while Pullman topped out at 72 degrees. In fact, the final 20 days of the month were largely frost-free across Washington. Following a relatively cool and dry beginning, March trended somewhat wetter and much warmer for the remainder of the month.

April began with relatively cool and variable conditions. Temperatures were below normal on some days. High temperatures around Walla Walla were only in the 40s on April 5th, while the low at Broadview was 20 degrees. Frontal passages on the 10/11th and 13/14th brought wind, rain, mountain snow, and cooler temperatures. St. John's daily average wind speed on the 11th was 20 mph. 1.11 inches of rain fell at Long Beach on the 13th. The high on April 14th at Garfield East was only 45 degrees, and then the low at Ritzville on the 15th was 23 degrees. Temperatures were very warm on April 20th, as Azwell reached 83 degrees. Garfield East reached only 47 degrees on the 25th, and Ritzville fell to 22 degrees on April 26th. Heat returned at month's end, as Vancouver reached 81 degrees on the 27th, and Benton City climbed to 86 degrees on the 28th.

Overall, April was a dry month, which partly explains why Prosser's high temperatures were somewhat above normal, while low temperatures were near to slightly below normal. The relative lack of clouds and moisture allowed for sunnier and warmer days, and yet cool and stable nights. In fact, the mean low was slightly lower than it was in March, which is of course a testament to the warmth of March, rather than the chill of April. Interestingly, Moxee experienced a precipitation-free April.

Winter 2013 Daily Rainfall Time Series Graph for Prosser Winter 2013 Daily Rainfall Time Series Graph for Long Beach

Spring-By The Numbers
The average spring temperature at Prosser (WSU IAREC) was 55.5°F, which is 3.1 degrees (1.8 standard deviations) above average. The average high temperature was 68.1°F, which is 3.9 degrees (1.9 standard deviations) above average, while the average low temperature was 42.2°F, which is 2.6 degrees (1.8 standard deviations) above average. Daily high temperatures ranged from 88.4°F on May 30th to 48.0°F on March 3rd. Low temperatures varied from 62.0°F on May 30th to 22.9°F on March 4th. Daily average temperatures ranged from 75.6°F on May 30th to 38.0°F on March 4th. 2.55 inches of rain fell during the spring season. The average wind speed was 4.7 mph, while the average 8 inch soil temperature was 56.6°F. Other locations also experienced above normal spring temperatures. Wenatchee (WSU TFREC) had an average seasonal temperature of 55.5°F, which is 3.6 degrees above average.

Spring 2015 Average Temperatures (°F)
Location (Period of Record) Maximum Anomaly Minimum Anomaly Mean Anomaly Soil Temperature
8 inches
Prosser (WSU IAREC; 1989-2015)
68.1
3.9
42.2
2.6
55.5
3.1
56.6
Moxee (1989-2015)
67.9
4.2
36.9
2.6
53.1
3.0
52.6
Mt. Vernon (WSU NWREC; 1994-2015)
61.0
3.7
43.1
1.3
51.8
2.3
53.9
Wenatchee (WSU TFREC; 1994-2015)
68.1
4.9
42.7
3.0
55.3
3.6
55.8
Tri-Cities (1995-2015)
70.6
4.2
43.3
2.1
57.2
3.1
61.3
Walla Walla (1993-2015)
66.9
4.6
43.5
1.6
55
2.9
55.2
Moses Lake (1989-2015)
67.7
4.6
41.1
2.6
54.5
3.4
57.5
Omak (Pogue Flat; 2005-2015)
66.0
NA
40.8
NA
53.5
NA
55.0
Royal City East (2008-2015)
67.0
NA
43.2
NA
54.7
NA
55.9
Pullman (2008-2015)
60.4
NA
36.7
NA
49.0
NA
50.2
Long Beach (WSU Long Beach; 2005-2015)
57.5
NA
42.1
NA
49.8
NA
54.4
Sequim (2008-2015)
59.8
NA
40.8
NA
50.0
NA
50.3
Seattle (2011-2015)
62.9
NA
45.3
NA
53.4
NA
56.8
Vancouver (WSU RE; 2008-2015)
64.5
NA
42.1
NA
53.1
NA
55.1
Spring 2015 Rainfall and Evapotranspiration (ET) (inches)
Location (Period of Record) Rainfall ET Net
(Rain - ET)
Prosser (WSU IAREC; 1989-2015)
2.55
17.35
-14.80
Moxee (1989-2015)
1.46
16.85
-15.39
Mt. Vernon (WSU NWREC; 1994-2015)
4.59
9.87
-5.28
Wenatchee (WSU TFREC; 1994-2015)
2.19
14.82
-12.63
Tri-Cities (1995-2015)
2.41
18.51
-16.10
Walla Walla (1993-2015)
4.57
13.96
-9.39
Moses Lake (1989-2015)
1.75
17.84
-16.09
Omak (Pogue Flat; 2005-2015)
1.27
15.58
-14.31
Royal City East (2008-2015)
1.71
16.67
-14.96
Pullman (2008-2015)
4.11
15.75
-11.64
Long Beach (WSU Long Beach; 2005-2015)
9.84
7.81
2.03
Sequim (2008-2015)
3.24
9.74
-6.50
Seattle (2011-2015)
6.69
10.02
-3.33
Vancouver (WSU RE; 2008-2015)
7.00
11.13
-4.13
Notable Spring Events
  • March 11th: The low temperature at Mt. Vernon was a balmy 53 degrees.
  • March 15th: 1.76 inches of rain fell at Long Beach.
  • March 27th: The temperature at Wapato climbed to 80 degrees.
  • April 13th: 1.11 inches of rain fell at Long Beach.
  • April 15th: The low temperature at Ritzville plunged to 23 degrees.
  • April 17th: The temperature at Desert Aire rose to 80 degrees.
  • May 1st: The temperature at Benton City soared to 86 degrees.
  • May 30th: The temperature at the Tri-Cities rose to 92 degrees.

Spring Temperature Extremes (°F)
  Observed in 2015 Record Seasonal Extremes
Site (Period of Record) Warmest Date Coldest Date Warmest Date Coldest Date
Prosser (WSU IAREC; 1989-2015)
88.4
5/30/2015
22.9
3/4/2015
98.4
5/12/1993
11.5
3/2/1993
Moxee (1989-2015)
89.2
5/29/2015
18.2
3/4/2015
98.0
5/23/2001
9.7
3/1/1993
Mt. Vernon (WSU NWREC; 1994-2015)
76.2
5/28/2015
26.5
3/4/2015
86.2
5/17/2008
20.3
3/1/2007
Wenatchee (WSU TFREC; 1994-2015)
89.9
5/30/2015
22.7
3/4/2015
97.7
5/17/2006
15.6
3/2/1995
Tri-Cities (1995-2015)
91.6
5/30/2015
19.6
3/1/2015
100.9
5/23/2001
16.9
3/12/2009
Walla Walla (1992-2015)
89.5
5/29/2015
23.7
3/3/2015
94.5
5/23/2001
6.3
3/1/1993
Moses Lake (1989-2015)
89.5
5/29/2015
18.8
3/4/2015
97.5
5/18/2006
10.6
3/1/1993
Omak (Pogue Flat; 2005-2015)
87.0
5/23/2015
19.6
3/4/2015
94.8
5/17/2006
11.2
3/10/2009
Royal City East (2008-2015)
93.2
5/19/2015
21.4
3/4/2015
93.3
5/17/2008
16.3
3/10/2009
Pullman (2008-2015)
80.5
5/29/2015
19.1
3/4/2015
85.2
5/17/2008
-6.2
3/11/2009
Long Beach (WSU Long Beach; 2005-2015)
73.4
5/8/2015
28.3
3/4/2015
95.3
5/16/2008
25.4
3/11/2009
Sequim (2008-2015)
73.3
5/28/2015
26.0
3/4/2015
77.8
5/5/2013
19.5
3/12/2009
Seattle (2011-2015)
81.2
5/29/2015
28.8
3/4/2015
NA
NA
NA
NA
Vancouver (WSU RE; 2008-2015)
83.8
5/28/2015
25.1
3/4/2015
86.0
5/13/2012
21.0
3/12/2009
Weather Summary By Month
  • March: Record warmth.
  • April: From cool to warmer.
  • May: Record night-time warmth.

Agriculture Report
During early May, dry and warm conditions allowed for field work while leaving some crops in need of moisture. Winter wheat was in good conditions, but additional rainfall was necessary. Cherry and apple growers applied cover sprays for fruit fly and codling moth, and the planting of onions and corn continued. Unfortunately, the Roza water supply was shut off for much of the month in order to save water for later in the season (see the WSU drought page at http://Drought.wsu.edu). In mid May, raspberries and blackberries were in bloom. Heavy rain fell on May 12/13 in south central Washington, but cool and breezy weather minimized the impact on the early cherry crop. Irrigation water was critical in most districts during late May, as producers selectively watered crops, while others showed signs of water stress. Otherwise, early cherry harvest continued and grapes were at full bloom. Fungicide sprays were applied to peaches and other crops, while Spotted Wing Drosophila were seen in Klickitat County. Fruit thinning continued, and hops were 3 to 9 feet up the trellises (National Agricultural Statistics Service).

April 1 to May 31 Accumulated Growing Degree Days
  Base Temperature (°F)
32 43 50
Location 2015 5 Year Avg Difference 2015 5 Year Avg Difference 2015 5 Year Avg Difference
Prosser (WSU IAREC)
1551
1374
177
881
711
170
490
353
137
Tri-Cities
1703
1521
182
1035
851
184
623
459
164
Walla Walla
1540
1380
160
873
714
159
475
347
128
Wenatchee (WSU TFREC)
1604
1421
183
933
757
176
549
392
157
Moxee
1393
1222
171
732
571
161
400
258
142
Omak (Pogue Flat)
1491
1311
180
820
650
170
462
312
150
Moses Lake
1547
1372
175
876
708
168
487
345
142
Pullman
1134
987
147
493
377
116
208
143
65
Royal City East
1573
1383
190
903
716
187
513
353
160
Mt. Vernon (WSU NWREC)
1302
1185
117
631
519
112
249
171
78
Long Beach (WSU Long Beach)
1122
1065
57
452
399
53
119
88
31
Sequim
1193
1046
147
522
389
133
195
104
91

GDD are calculated by subtracting a base temperature from the average daily temperature (°F). If the resulting value is less than 0, then it is set to 0. Thus GDD are always 0 or greater.

GDD = (Tmax+Tmin)/2 - Tbase


This Month in History
On May 8, 1996, the temperature at Moxee dropped to 20 degrees.

Climate Outlook
According to the Climate Prediction Center (CPC), warm and somewhat dry conditions are expected from now through early 2016, as El Niño strengthens in the coming months.

Washington State University