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Washington, Lower Columbia Basin of Washington

Public Information Statement

Statement as of 12:29 AM PDT on May 03, 2015

... Month in review for northeast Oregon and southeast Washington for
the month of April 2015...

... Near normal temperatures and near record dry conditions observed
across the region in April...

I. Temperature and precipitation overview

April average temperatures were near normal across the region for the
calendar month. Maximum temperatures were generally slightly above
normal for the month while overnight lows were slightly below normal.
Total precipitation was well below normal, ranging from about 5 to 50
percent of average over much of the area; the only exception to this
was along the east slopes of the northern Oregon Cascades and parts of
the southern Blue Mountains where precipitation totals for the month
were between 70-90 percent of normal. Total snowfall for the month
was slightly above average of much of the mountains, where several
colder systems dropped a few inches of snow. Even with this added
snowfall the snow water equivalent remained well below average over
the entire forecast area. By the end of the month snow water
equivalent ranged from 0-20 percent in the mountains of Oregon and 5-
25 percent along the east slopes of the Washington Cascades. The
only exception to this was in the northern Blue Mountains of
Washington where snow water equivalent was reported to be near 50

April 2015 data and departure from normal for selected cities:

                   Max dep min dep Ave dep pcpn dep
                   temp norm temp norm temp norm totl norm

La Grande 60.5 +2.2 33.1 -2.0 46.8 +0.1 0.46 -1.12
Pendleton Airport 61.7 -0.4 36.2 -3.0 49.0 -1.7 0.39 -0.81
Redmond 60.5 +0.9 25.3 -3.8 42.9 -1.5 0.15 -0.58
The Dalles 67.4 +3.0 40.1 -1.4 53.7 +0.8 0.12 -0.67
Kennewick 67.2 +0.9 42.0 -0.3 54.6 +0.3 0.15 -0.41
Walla Walla 64.2 +1.7 41.4 -0.6 52.8 +0.6 0.90 -1.02
Yakima 68.2 +4.4 35.5 +1.1 51.9 +2.8 T -0.55

ii. Selected records

The month of April started off cool and wet for the first seven days,
then remained dry and cool through mid-month. The weather stayed mainly
dry with mild conditions for much of the second half of the month;
although there was a short cooler period from the 22nd through the
26th. The first system of note moved through the area on April 4th-
6th followed by another notable storm system which affected the
region on April 13th and 14th. Finally, the period of April 21st to
the 22nd was characterized by a strong, but mainly dry cold front
moving through the area. This brought gusty winds and much cooler
temperatures. More information on these weather systems can be found
in section iii: significant weather below.

The combination of these events resulted in a few top 10 April record
high temperatures in southern Washington state and central to northeast
Oregon. The following table lists the weather station, April rank of
the 1-day record high, the record temperature with date of occurrence,
and the current record temperature for the month of April.

City rank April 2015 Max T warmest Apr Max T

Meacham, or #4 76 on 4/28 78 on 4/22/2012
Hermiston, or #10 82 on 4/18 90 on 4/30/1998

The cold system that moved through the area on Easter Sunday (april 5th)
also lowered Max temperatures enough to set a few top 10 record low
maximum temperatures for the month of April, although no new number 1
records were set. The following table lists the weather station, April
rank of the 1-day record low Max temperature, the record low Max
temperature with date of occurrence, and the current record low Max
temperature for the month of April.

City rank April 2015 Max T coldest Apr Max T

Hermiston, or #2 49 on 4/05 43 on 4/01/2009
Milton Freewater #4 44 on 4/05 39 on 4/01/1936
Kennewick, WA #5 47 on 4/06 41 on 4/02/1936
Pendleton exp sta #5 43 on 4/06 38 on 4/01/1936

There were not many extreme minimum temperatures throughout the month.
There were no record warm minimum temperatures noted for the month.
There were no top 10 record cold minimum temperatures for the month,
but there were three daily record lows noted below, along with their
respective ranks and the coldest April minimum temperature on record.
A (t) indicates that the temperature tied the record with other dates.

City rank April 2015 min T coldest Apr min T

Madras, or #23 13 on 4/09 06 on 4/20/1927
Ellensburg, WA #41 24 on 4/05 18 on 4/03/2007
Pendleton dwntn #82 (t) 25 on 4/27 14 on 4/19/1966

The mean synoptic pattern for the month of April 2015 was characterized
as a generally zonal flow over the Pacific northwest. Of course this is
the overall average for the month; the reality was that throughout the
month there were periodic troughs and ridges over our region. There was
a slight overall negative height anomaly over the inland Pacific
northwest, which equates to troughs being marginally more prevalent
than ridging through the month. This height and flow pattern allowed
temperatures to end up within a few degrees either side of average at
all stations. With few major or moisture laden storm systems affecting
the area, precipitation values ended up well below average to record
low for the month, which will be discussed in further detail below. A
few top 10 average high temperatures were set throughout southern
Washington and central to northeast Oregon. The following table lists
the location, the rank, the average April high temperature, and the
record warmest average April high temperature.

City rank Apr 2015 avg Max T warmest Apr avg

Hermiston, or #4 66.8 69.8 in 2000
Ellensburg, WA #5 64.0 68.6 in 2004
Meacham, or #6 54.3 57.5 in 2000
Yakima, WA #8 68.2 70.4 in 1977

Due to the drier than average conditions and the periodic cold shots
throughout the month there was good opportunity for ideal radiational
cooling at many locations. Several top 10 coldest April average low
temperature records were set in the area, but none broke any of the
prior #1 records set. The following table lists the location, the
rank, the average April low temperature, and the record coldest April
low temperature.

City rank Apr 2015 avg min T coldest Apr avg min T

Antelope, or #2 27.4 25.8 in 2011
John Day, or #2 28.4 27.6 in 1970
Hermiston, or #3 35.3 32.8 in 1999
Sisters, or* #4 25.8 24.6 in 1983
grizzly, or #6 24.4 21.6 in 1964
Redmond, or #8 25.3 21.6 in 1964
Pendleton, or #9 36.2 33.9 in 2008

*station is missing 4 days of data for the month*

Considering the mean zonal flow over the region and that average
temperatures ended up within 2 degrees either side of normal for most
locations there were only Two Top ten April average temperature records
of note. Ellensburg, WA tied for its top ten warmest April average
temperature at 49.4 degrees, the current record for the warmest April
on record remains 52.6 degrees set in 2004. On the other hand, John
Day, or actually tied for its top ten coldest April average
temperatures at 43.8 degrees, the current record remains 40.0 degrees
set in 1975.

Precipitation totals were well below normal in most locations which
lead to many top ten lowest precipitation records and a few locations
had their driest aprils on record. Listed below are the locations,
rank, April 2015 precipitation and either the lowest recorded
precipitation for April, or the previous record if April 2015 is the
new record. A (t) and/or * means that the record tied with other
previous dates/years.

City rank Apr 2015 precip lowest Apr precip
Dayville, or #1 0.17 inches 0.22 inches in 1980
Ellensburg, WA #1(t) trace trace in 1956*
Yakima, WA #1(t) trace trace in 1985*
Milton Freewater #2(t) 0.12 inches 0.10 inches in 1966
Goldendale, WA #3(t) 0.06 inches 0.03 inches in 1956
Pendleton exp sta. #3 0.47 inches 0.21 inches in 1968
Meacham, or #4 1.18 inches 0.40 inches in 2004
Hermiston, or #5 0.28 inches trace in 1999
Condon, or #7 0.12 inches trace in 1924*
The Dalles, or #10 0.12 inches trace in 1977*
Moro, or #10 0.14 inches 0.01 inches in 1956

There were two daily snowfall records reported through the month,
the first being grizzly, or when 4.0 inches of snow fell on April
5th, breaking the old record of 3.2 inches set in 1938. The other
daily snowfall record was at Meacham, or when 2.6 inches of snow
fell on April 14th, tying the previous record of 2.6 inches set in

Iii. Significant weather

A storm system affected the area on April 5th and 6th. An upper level low
moved into the Pacific northwest bringing much cooler temperatures,
rain showers, light snow and even thunderstorms. Central Oregon
including The Bend and Redmond area reported a mixture of rain and snow
showers through the day on the 5th with even scattered reports of
thundershowers. Temperatures were very cold for early April, with most
locations remaining in the 30s and lower 40s through the day. Periods
of light snow even affected the northern Blue Mountain foothills
including locations near Pendleton during the mid to late morning hours
on the 5th... only traces of snow were reported here. Slightly higher
snowfall totals were observed in the Blue Mountains where locations
such as Meacham reported 1 - 4 inches of snow from April 4th - 6th.
Locations in Washington were not affected as much by this system,
however periods of light rain were observed and this rain lingered
into the early morning hours on April 6th. Below are some Sample
precipitation, and snow totals along with whether thunder was
observed from this system around the forecast area:

city precip total snow total thunder?

Pendleton, or 0.19 inches trace no
Meacham, or 0.45 inches 3.2 inches no
Redmond, or 0.03 inches trace no
Pasco, WA 0.18 inches 0.0 inches no
Walla Walla, WA 0.35 inches 0.0 inches no
Yakima, WA trace 0.0 inches no
La Grande, or 0.03 inches 0.0 inches unknwn
Joseph, or 0.02 inches trace no
Madras, or 0.07 inches trace yes
Prineville, or 0.05 inches trace yes
John Day, or 0.38 inches 0.5 inches yes
Hermiston, or 0.26 inches 0.0 inches no

From April 13th - 14th another strong cold front with an associated
low pressure system moved into the area bringing periods of rain,
wind, thundershowers with small hail and cooler temperatures.

A sharp upper level trough moved over the region during the morning and
early afternoon hours on the 14th. This brought a cold pool of air into
the mid and upper levels of the atmosphere. As the surface warmed from
daytime heating this lead to the destabilization of the atmosphere with
convective showers and isolated thunderstorms developing. With the very
low freezing levels some of the showers/storms produced small hail
and/or graupel; this was mainly observed over the Blue Mountains and
the Blue Mountain foothills region. Below are some precipitation and
wind reports from this event:

City precip total peak wind gust

Pendleton, or 0.04 inches 46 mph
Meacham, or 0.39 inches 22 mph
Redmond, or 0.00 inches 45 mph
Pasco, WA trace 44 mph
Walla Walla, WA 0.45 inches 34 mph
Yakima, WA 0.00 inches 39 mph
La Grande, or 0.13 inches 43 mph
Joseph, or trace 31 mph
Madras, or 0.00 inches 44 mph
Prineville, or 0.00 inches 39 mph
John Day, or 0.19 inches 46 mph
Hermiston, or trace 36 mph
Ellensburg, WA 0.00 inches 49 mph
*meacham, or also reported 2.6 inches of snow with this event*
        *pendleton, or reported small hail/graupel with this event*

After a calm, dry and mild day on April 21st a storm system approached
with a strong cold front by the late evening hours. This storm system
was lacking moisture but had plenty of cooler air behind it. As the
cold front move through the area some scattered showers were observed
along with gusty winds. Twenty-four hour temperature changes from the
afternoon maxes on the 21st to the afternoon maxes on the 22nd ranged
anywhere from 10 to nearly 20 degrees cooler over the forecast area.
With the dry frontal passage and increasing winds there was also
some minor, patchy blowing dust reported... mainly in the Columbia
Basin. Below are some rain and wind reports along with the 24 hour
temperature change during this event.

City precip total peak wind gust 24 hr temp change

Pendleton, or 0.00 inches 45 mph -15
Meacham, or trace inches 16 mph -18
Redmond, or 0.04 inches 31 mph -12
Pasco, WA 0.00 inches 28 mph -15
Walla Walla, WA 0.00 inches 30 mph -17
Yakima, WA 0.00 inches 41 mph -14
La Grande, or 0.00 inches 33 mph -17
Joseph, or trace inches -- mph -16
Madras, or 0.00 inches 33 mph -13
Prineville, or 0.00 inches 31 mph -13
John Day, or trace inches 38 mph -16
Hermiston, or 0.00 inches 40 mph -14

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