Office of the Washington State Climatologist

Transcription

1 Office of the Washington State Climatologist March 5, 2013 February Event Summary February was warmer than normal, on average, and extremely In this Issue dry for most of Washington State. Figure 1 shows February precipitation for SeaTac Airport compared to normal with the brown shaded area representing the precipitation deficit. February was among the top ten driest Februarys for several stations. February 2013 was the 3rd driest on record for Sunnyside (0.02 ), 4th driest for Ellensburg (0.27 ), 5th driest for Yakima (0.03 ), tied for the 6th driest for Omak (0.19 ), and the 7th driest for SeaTac (1.58 ). While not breaking the top ten, this past February was among the top 25 driest for several stations such as Colville Feb Event Summary...1 Snowpack...2 Mean Monthly Winds...3 CoCoRaHS...7 Climate Summary...8 Climate Outlook...10 (11th), Walla Walla (14th), Pullman 2 NW (15th), Hoquiam (19th), Olympia Airport (21st), and Spokane Airport (22nd). The weather during February was relatively calm, with the most noteworthy event occurring at the end of the month. A low pressure system impacted the state on the 22nd and 23rd, bringing windy conditions across the state; examples of peak gusts in western WA include 40 mph at SeaTac, 43 mph at Hoquiam, 46 mph at Snohomish Paine Field, and 51 mph at Whidbey Island Naval Air Station. Heavy rain fell on the coast and in the southern Puget Sound area with Olympia (1.31 ) and Quillayute (2.50 ) setting daily maximum precipitation records on the 22nd. Heavy snow fell in the mountains during this event, and snow at lower elevations in north central and northeastern WA was associated with this event. Figure 1: Precipitation at SeaTac AP during February (jagged line) compared to normal (straight line). The shaded area represents the difference from normal ( ).

2 OWSC Newsletter March 5, 2013 Page 2 of 10 Snowpack Summary While February was relatively dry, heavy snow fell in the mountains during the first week and over the last weekend of the month resulting in near-normal to above normal snowpack for most locations. Figure 2 shows the snow water equivalent (SWE) percent of normal as of March 4, The Olympic, North Puget Sound, Central Puget Sound, South Puget Sound, Lower Columbia, and Upper Columbia basins all have above normal snowpack, while the Central Columbia, Upper Yakima, and Lower Yakima have near-normal snowpack for this time of year. The Spokane and Lower Snake basins in eastern WA are lagging behind with 84 and 88% of normal SWE, respectively. Mar 04, 2013 Current Snow Water Equivalent (SWE) Basin-wide Percent of Median unavailable * <50% 50-69% 70-89% % % % >=150% * Data unavailable at time of posting or measurement is not representative at this time of year Washington SNOTEL Current Snow Water Equivalent (SWE) % of Normal Port Angeles 144 Olympic [( Olympia Bellingham [ Everett Seattle North Puget Sound Marblemount Central Puget Sound South Puget Sound Upper Yakima Cle Elum Central Columbia Winthrop Wenatchee Upper Columbia Spokane Spokane Yakima Lower Yakima Lower Snake Walla Walla 88 Lower Columbia Provisional Data Subject to Revision Miles The snow water equivalent percent of normal represents the current snow water equivalent found at selected SNOTEL sites in or near the basin compared to the average value for those sites on this day. Data based on the first reading of the day (typically 00:00). Prepared by the USDA/NRCS National Water and Climate Center Portland, Oregon Based on data from Science contact: Jim.Marron@por.usda.gov Figure 2: Snowpack (in terms of snow water equivalent) percent of normal for Washington as of March 4, Image is from the National Resources Conservation Service (NRCS).

3 OWSC Newsletter March 5, 2013 Page 3 of 10 Mean Monthly Winds in WA A message from the State Climatologist We expect that most regular readers of this newsletter have a good idea of how mean temperatures and precipitation amounts vary across the state over the seasons. These elements are typically used to summarize the climate of a location. But there are additional elements of the weather that vary systematically from place to place and month to month, of course, and here we consider one of those elements: the surface winds. There are significant temporal and spatial patterns in the winds due to the diverse landscape of Washington State. Our focus is on monthly mean wind speeds and prevailing, i.e., most common, wind directions from the ASOS stations at airports across Washington State for the period of This data set was compiled by the Western Regional Climate Center (WRCC) and is available from the following web site: While 11 years is a rather short interval from a climatological perspective, the monthly means presented here should be mostly representative of their longer-term counterparts. A spot check of this record with longer-term averages for a few of the stations revealed no substantial discrepancies. The wind information is shown in tabular form, separating the stations on the west side from those on the east side of the Cascade Mountains. Only 7 months and the annual values are shown here due to space constraints; the full tables can be found at the WRCC link above. Mean sea level pressure maps for January and July of from the NOAA s North American Regional Reanalysis (NARR), as provided by NOAA s Earth Systems Research Laboratory (ESRL), are included for context. The monthly mean winds for the western Washington stations are itemized in Table 1. The strongest winds are in Hoquiam (HQM) during December and the weakest winds are in Toledo (TDO) in January. Perhaps it is no surprise that the coastal location of Hoquiam gets the top prize, but note the mean speeds at Quillayute (UIL) are much slower presumably due to this station being a few miles inland. The low wind speeds at TDO can be attributed to sheltering within the Cowlitz River valley. The second windiest spot on the west side is Whidbey Island Naval Air Station (NUW). This location is subject to mean wind directions between southeast and east in the cool season (October-March) and west winds during the middle of the year. This seasonal cycle in the direction of the prevailing wind makes sense given the mean sea level pressure (SLP) patterns, as illustrated for January (Figure 3a) and July (Figure 3b). Given the reversal in the mean east-west pressure gradient between the seasons (i.e., the tendency for air to flow from high to low pressure), the lack of much of a seasonal cycle in wind direction at Port Angeles (CLM) may be a surprise. We suspect that the westerly component at CLM during the winter may be a very local effect, specifically a response to frequent troughing in the lee of the Olympic Mountains in the vicinity of Port Townsend. Seasonal changes in wind direction are also minor in the southern Puget Sound locations of McChord Air Force Base (MCC), Gray AAF (GRF), Shelton (SHN), and Olympia (OLM). The south to west-southwest winds are close to parallel to the isobars in winter and across them in summer, and in both cases, appear to be associated with marine air flowing through

4 OWSC Newsletter March 5, 2013 Page 4 of 10 Station Jan Mar May Jul Aug Oct Dec Annual Quillayute 6.5 ENE 6.5 S 5.2 W 4.6 W 4.2 S 4.8 ENE 6.3 ENE 5.4 S Hoquiam 11 E 10.3 E 9 W 8.4 W 7.9 W 8.5 E 11.1 E 9.3 E Bellingham 9 S 8.9 S 7.4 S 8 S 7.4 S 6.4 S 8.7 NNE 7.7 S Friday Harbor 7.2 SE 7.3 SE 5.2 SW 4.8 SW 4.1 SE 4.9 SE 7.9 SE 5.8 SE Whidbey Island 10.7 SE 10.9 SE 7.9 W W 8.3 ESE 11 E 8.6 W Port Angeles W 6.4 W 6.6 W 5.6 W 4.2 W 4.6 SW 5.2 W Arlington 5.6 SSE 6.2 S 4.8 NW 4.5 NW 4.3 NW 4.1 SSE 5.3 SSE 4.9 SSE Everett Paine Fld 9.3 S 9.2 S 7.6 N 7.1 N 6.9 N 7.3 S 9 S 8 N Boeing Field 6.4 S 7.1 S 6.5 S 6.1 NW 5.8 NW 5.7 SSE 6.3 SSE 6.2 S Renton 6.5 S 7.5 S 7.3 S 7.6 NNW 7.2 S 5.9 S 6.1 S 6.8 S SeaTac 8.3 S 8.5 S SW 6.4 N 6.9 S 8.3 S 7.5 S Tacoma Narrows 7 S 7.6 S 6.8 S 6.2 N 5.5 S 6.2 S 6.4 S 6.5 S Tacoma McChord 7.4 S 8.6 S 7.6 S 7 S 6.5 S 6.8 S 7.2 S 7.2 S Fort Lewis-Gray 6.4 S 7.5 S 6.6 S 6.1 S 5.8 S 6 S 6.6 S 6.4 S Bremerton NE Shelton 4.4 SW SW 4.5 SW 6 Olympia 6 S 6.6 S 5.9 S S 5.3 S 5.9 S 5.6 S Toledo 3.4 S 4.9 S 4.5 NW 4.7 NW 4.3 NW 3.6 S 3.5 S 4.1 S Kelso-Longview 5.9 SSE 5.4 S 4.6 N 5.8 N 5.4 N 4.1 SSE 5.8 SSE 5.1 SSE Vancouver 5.6 ESE 5 ESE 4.7 NW 5.5 NW 5.1 NW 4 ESE 5.6 ESE 5 ESE Table 1: The mean wind speed and direction for airport sites in western WA for a sample of months using data from 1996 through Full tables can be viewed at the WRCC website.

5 OWSC Newsletter March 5, 2013 Page 5 of 10 the conduit represented by the low terrain to the south of the Olympic Mountains (as indicated in Mass 1982). The three station of Boeing Field (BFI), Renton (RNT), and SeaTac (SEA) in King County are quite near each other, but display some interesting differences. BFI is tucked into the Duwamish River Valley and tends to have the lightest winds. SEA is at the highest elevation and has the strongest mean winds, except during summer. During that time of year the winds tend to be from the north, and hence the relatively stronger winds at RNT may be due to the reduced friction associated with the presence of Lake Washington immediately upstream. The mean monthly winds of eastern Washington are itemized in Table 2, and also feature plenty of quirks. The strongest winds by a large margin are the northwesterlies in Ellensburg (ELN) during summer. This location is near the downstream exit of one of the more prominent gaps in the Cascade Mountains. Too bad there are no large bodies of water because it otherwise might be a mecca for windsurfing, since the ELN winds are actually stronger than those in the Columbia River gorge at The Dalles, OR (not shown). The weakest east side winds are found not far away in Wenatchee (EAT) during the middle of winter. It stands to reason that this location, and to a lesser extent, Yakima (YKM) and ELN, tend to experience weak winds during this time of year because statically-stable temperature profiles are common in association with cold air banked against the east flank of the Cascades. It is not evident why the mean directions are from the west, but perhaps it is due to the drainage of cold air off the slopes to the west during the long winter nights. Most of the stations in eastern Washington tend to have stronger winds during the summer than the winter. This result contrasts with that for western Washington, which has stronger winds in winter on average at most locations. The three Spokane stations offer another opportunity to examine the variations in the winds over short distances. Fairchild Air Force Base (SKA) and Spokane International (GEG) are separated by only 3-4 miles and are situated in similar terrain to the west of the city of Spokane and their winds are comparable, with the exception of late in the calendar year. On the other hand, Felts Field (SFF) is located along the Spokane River just east of town, and while it is only about 12 miles distant from SKA and GEG, its mean winds are consistently weaker, and generally out of a different direction, during much of the year. The winter winds in Spokane area generally include a northerly component, at least at SKA, GEG, and Deer Park (DEW). This might seem inconsistent with the overall SLP pattern but could reflect down-gradient flow into relatively low pressure over northern Idaho (Fig. 1b). It should be noted that for the latter region of higher terrain the reduction of station pressure to sea-level may introduce errors. We have only begun to scratch the surface of the temporal and spatial structure in these wind data. We encourage readers to check out some of the other idiosyncrasies in this data set, and see if they can puzzle out their own explanations for the marvelous contrasts in this facet of the weather across Washington State. Reference: Mass, C.F. (1982): The topographically forced diurnal circulations of western Washington state and their influence on precipitation. Mon. Wea. Rev., 110,

6 OWSC Newsletter March 5, 2013 Page 6 of 10 Station Jan Mar May Jul Aug Oct Dec Annual Stampede Pass 7 E 7.5 E E 7.6 Wenatchee- Pangborn 3.3 W 7.1 W 9.3 WNW 9.8 WNW 9.2 WNW 6 WNW 3.3 WNW 6.9 WNW Ellensburg 4.3 NW 9.7 NW 12.9 NW 15.4 NW 13.5 NW 8 NW 4.2 E 9.5 NW Yakima 4 W 6.8 NW 7.5 W 7.2 W 6.7 W 5.6 W 3.8 W 6 W Omak 5 S 7.3 N 7.8 N 8.4 N 8.3 N 6.9 N 4.2 S 6.9 N Ephrata 6.9 N 8.8 N 9.5 S 9.7 S 8.8 S 7.6 N 6.6 N 8.3 N Moses Lake 6.4 N 8.1 N 8.5 S 7.9 S 7.3 N 7 N 5.9 N 7.3 N Hanford 7.5 NW 9.4 NW 9.9 NW 9.9 NW 9.2 NW 8 W 7.2 NW 8.8 NW Pasco-Tri Cities 6.7 NW 7.8 SW 8 SW 6.9 SW SW 6.1 NW 6.8 SW Walla Walla 8 S 9.8 S 9.1 S 9.1 S 8.8 S 7.8 S 7.6 S 8.5 S Deer Park 5.3 N 6.6 S 7 S 6 S 5.6 S 5.2 N 4.9 N 5.8 S Spokane 8.7 NE SW 8.3 S 8.1 NE 8.7 S Spokane- Fairchild Spokane-Felts Fld 4.5 SW 6.5 SW NNE 5.8 NNE 4.9 NNE 4.3 SW 5.5 SW Pullman-Moscow 9.1 E 8.8 E Table 2: As in Table 1, except for eastern WA. 6.6 E 9.3 E 7.3 E

7 OWSC Newsletter March 5, 2013 Page 7 of 10 a b Figure 3: Mean SLP during (a) January and (b) July of (contour interval 100 Pa) from the North American Regional Reanalysis (NARR). CoCoRaHS March Madness Thank you, CoCoRaHS observers, for continuing to measure precipitation throughout the state. The CoCoRaHS station located at OWSC on the University of Washington campus received 1.77 inches of precipitation for February, very similar to the precipitation measured at the Seattle NWS WFO. How does your station measure up to the official weather stations? CoCoRaHS March Madness has begun Though we compete with Oregon for new volunteers in October, the national contest for gaining the highest number of new recruits occurs in March. Please help spread the word about CoCoRaHS. New volunteers can sign up at

8 OWSC Newsletter March 5, 2013 Page 8 of 10 Climate Summary Mean February temperatures were above normal across most of the state, illustrated by the High Plains Regional Climate Center (HPRCC) temperature departure from normal map below. While most of the Puget Sound locations were within 1 F of normal, Bellingham was a warm spot on the west side of the Cascade Mountains with an average monthly temperature 3.4 F above normal (Table 3). Central WA was also warmer than normal, with temperature between 3 and 6 F above normal for the month. There were some cool spots, with monthly temperature departures from normal around -1 F in southwestern WA, parts of inland western WA, and northeastern WA. Total February precipitation was below normal, especially in central WA, where the precipitation percent of normal map indicates values between 2 and 25% of normal. Elsewhere in the state, percentage of normal totals ranged between 25 and 75% of normal. A few locations did receive near-normal precipitation or even slightly above: the northwestern tip of the Olympic Peninsula, the WA coast, the northern Puget Sound, and Lincoln County. Temperature ( F) Precipitation (%) February temperature ( F) departure from normal (top) and February precipitation % of normal (bottom). (High Plains Regional Climate Center ( relative to the normal).

9 OWSC Newsletter March 5, 2013 Page 9 of 10 Mean Temperature ( F) Precipitation (inches) Snowfall (inches) Avg Norm Departure from Normal Total Norm % of Norm Total Norm % of Norm Western Washington Olympia Seattle WFO Sea-Tac Quillayute Bellingham AP M Vancouver M M - Eastern Washington Spokane AP Wenatchee M Omak M M - Pullman AP M M - Ephrata M Pasco AP M - Yakima AP Table 3: February climate summaries for locations around Washington with a climate normal baseline of Note that the Vancouver Pearson Airport and Seattle WFO normals involved using surrounding stations in NCDC s new normal release, as records for these station began in 1998 and 1986, respectively. The Bellingham AP site has shown some indication of a faulty temperature sensor; use these measurements with caution until further notice.

10 OWSC Newsletter March 5, 2013 Page 10 of 10 Climate Outlook The conditions in the equatorial Pacific Ocean are ENSO-neutral, according to the Climate Prediction Center (CPC): In the last 4 weeks, sea-surface temperatures (SSTs) continue to be slightly below normal in the central and eastern tropical Pacific and have cooled to near normal in the western tropical Pacific as well. There is a consensus among the model predictions that near-neutral conditions will persist through spring The CPC three-class outlook for March has chances for below normal temperatures exceeding 50% for all of Washington State. The probability for below normal temperatures is higher than any of the WA seasonal forecasts the CPC has issued this past winter, indicating that there is more confidence in this prediction. For precipitation, however, there are equal chances of the three different categories for March statewide. The CPC 3-month seasonal outlook for spring (March-April-May; MAM) has an elevated chance of below normal temperatures for the entire state (exceeding 40%). There are equal chances of below, equal to, or above normal precipitation for spring for most of the state except for the southern-most part where there are increased odds of below normal precipitation. March outlook for temperature (left) and precipitation (right) from the CPC. March-April-May outlook for temperature (left) and precipitation (right) from the CPC.