Big Contrasts this Weekend: Roasting Out West, Soaking Back East

The atmosphere over North America will slide back into a familiar pattern this weekend, as a powerful upper ridge and record heat take hold of the Pacific Northwest and western Canada while an unusually strong upper low for late June brings wet, cool conditions from the Ohio Valley through the mid-Atlantic into New England. It’s yet another variation on the warm-west/cool-east pattern that predominated through much of 2014 and early 2015.

Sizzling temps on tap for Pacific Northwest
While it’s been an unusually hot, muggy June across much of the Southeast, the burners will soon be going full blast out West. Models are consistent in building strong high pressure across the western states late this week into next week. The results will be scorching temperatures, especially in parts of eastern Washington and Oregon where warm, dry weather in recent weeks has left the ground already parched. Highs are projected to range from 100°F to 110°F over most of the next 4 to 6 days across a large area. Excessive heat watches are in effect for both Portland and Seattle. Here are some of WU’s forecast highs compared to monthly and all-time records. (For more, see the roundup by Jon Erdman at weather.com).

—Spokane, WA: Forecast high 102°F (Sunday); All-time record is 108 degrees on July 26, 1928 and Aug. 4, 1961
—Boise, ID: Forecast high 106°F (Sunday); All-time record is 111 degrees on July 19, 1960 and July 12, 1898
—Salt Lake City, UT: Forecast high 103°F (Monday); June record is 105 degrees on June 28-29, 2013
—Portland, OR: Forecast high 99°F (Saturday); June record high is 102 degrees on June 26, 2006
—Reno, NV: Forecast high 102°F (Friday and Saturday); June record is 104 degrees on June 16, 1940
—Missoula, MT: Forecast high 102°F (Sunday and Monday); June record high is 100 degrees on Jun. 29, 1937 and Jun. 13, 1918.

The heat may abate slightly by the middle of next week over the Pacific Northwest, but longer-range models suggest unusual warmth continuing across much of Canada. There are also hints that a significant heat wave could develop over parts of Europe toward the latter part of next week and beyond, as a highly amplified jet-stream pattern sets up there. The WU extended forecast brings Paris into the mid-90s Fahrenheit for several days, starting next Wednesday.



Figure 1. Temperatures will be 10°F to 30°F above average across large parts of the western United States and Canada, while much of the eastern U.S. will be unusually cool, according to the forecast for 0000 GMT Tuesday, June 30, produced by the 1800 GMT Wednesday run of the GFS model. Image credit: Climate Reanalyzer/University of Maine.


Fire risk increasing over western U.S., Alaska
By recent standards, it’s been a relatively quiet year thus far for wildland fire across the United States. The total amount of land affected by fire through Tuesday, June 23, stands at 885,842 acres, according to the National Interagency Fire Center. That’s slightly above last year’s total through June 23, but well below each of the years from 2005 to 2013. The threat of wildfires should begin ramping up this weekend, though, with record heat and dry lightning storms over parts of California, Oregon, and Washington, as well as western Canada and Alaska. On Wednesday afternoon, more than 1,000 people had to flee a fast-growing 350-acre wildfire near Interstate 5 in Santa Clarita, CA, just north of the San Fernando Valley.



Figure 2. Smoke from the Washington Fire rises over the Sierra Nevada range south of Lake Tahoe as viewed from between Minden and Carson City, NV, on Monday, June 22. The wildfire had grown to over 20 square miles in hazardous and inaccessible terrain and was moving closer to structures, officials said. The Lake Tahoe area saw record-low amounts of snowpack this past winter. Image credit: Jim Grant/ Nevada Appeal via AP.


The greatest fire risk this weekend will be around the edge of the strong high pressure cell taking shape over the interior West. In and near the Cascades, enough moisture should be present for scattered thunderstorms with little rain but gusty winds and lightning. Combined with very hot weather and dry vegetation, this is among the most dangerous scenarios for wildfire risk. Lightning is the main cause of wildfires in the Pacific Northwest, according to Cliff Mass (University of Washington), who outlines the upcoming risk in detail in a blog post. “The bottom line is that with very dry conditions in place, multiple lightning-caused fires are quite possible. Fire folks need to get ready,” said Mass. The fire danger is also high to extreme over much of western British Columbia. The NOAA Storm Prediction Center has not yet outlined any high-probability areas in its 3-8 day fire weather outlook, but the discussion issued Wednesday afternoon notes the possibility of an upgrade as the time period draws closer and confidence in model solutions increases.


Figure 3. Smoke cloaks the skies above Fort Wainwright, Alaska, near Fairbanks, on Wednesday. The smoke is a byproduct of several large wildland fires burning in central Alaska. Image credit: Stephanie Frank.


Most of the major U.S. fires this year to date have been in Alaska, where sporadic bursts of record heat during the spring and early summer have dried out vast stands of forest and brushland. Eleven fires affecting more than 1000 acres each were in progress as of Wednesday, with six of those exceeding 10,000 acres. Several factors are pushing Alaska toward longer and more intense fire seasons, as outlined by Climate Central in a report published Wednesday. The state is warming twice as quickly as the U.S. average--almost 3°F since the 1950s—and the average fire season has lengthened by roughly 40 percent in the last 60 years. Hot temperatures from May to July are strongly related to the frequency and severity of fire seasons in Alaska.

Large fires (more than 1000 acres) have grown far more common in the tundra-dominated Arctic portion of Alaska: such fires occurred in only three years from 1950 through 1969, but 33 such fires have struck the Alaskan Arctic since 2000. “We’re starting to see a tundra-fire regime emerging within the past few decades,” said Todd Sanford (CIRES), the lead author of the report. Earth’s largest tundra fire on record occurred in 2007, when about 250,000 acres (380 square miles) were scorched in the vicinity of the North Slope’s Anaktuvuk River. Such a lightning-triggered fire was once virtually impossible on the damp, chilly tundra. Lake sediments from the region around the Anaktuvuk fire showed no evidence of any other major fires in the last 5,000 years. Further south, wildfire is paving the way for an infusion of deciduous trees into the evergreen forests of the Alaskan interior. According to the 2014 U.S. National Climate Assessment, “More extensive and severe wildfires could shift the forests of Interior Alaska during this century from dominance by spruce to broadleaf trees for the first time in the past 4,000 to 6,000 years.”

A stormy week for Midwest, mid-Atlantic
A strong polar jet stream from the Corn Belt to the East Coast has been ferrying intense thunderstorms from west to east all week. Tuesday brought one of the biggest severe weather outbreaks of 2015, with severe storms sweeping through the mid-Atlantic corridor into New England. At the peak of the storms, some 770,000 people were without power, and widespread tree damage was reported.


Figure 4. A huge mesoscale convective complex (MCS) sprawls across the upper Midwest in this infrared satellite image taken at 8:15 a.m. CDT on Monday, June 22. The pink shadings over northern Iowa and southeast Minnesota correspond to the highest cloud tops associated with the most vigorous thunderstorms. Image credit: weather.com.



Figure 5. Tornado paths and strengths across northeast Illinois on Monday evening, June 22. Image credit: NWS Chicago.


One of the most powerful storms pushed through southeast Pennsylvania into southwest New Jersey, where power outages exceeded those from Superstorm Sandy and the 2012 derecho. Winds gusted to 85 mph in Gloucester County, NJ, and to 72 mph at Philadelphia International Airport, just a few weeks after outflow from a weak shower on April 22 brought 71-mph winds. The city has recorded gusts that strong only four other times in its weather history.

The day before the mid-Atlantic got slammed, Monday brought a preliminary total of 19 tornadoes, with 9 of them from a long-lived supercell that carved a path just southwest of Chicago (see Figure 5). A long-track, high-end EF3 twister that struck near Coal City was the strongest observed in the Chicago metro area since the deadly F5 Plainfield tornado of August 28, 1990. Another EF3 was reported near Marysville, Iowa. At weather.com, Jon Erdman produced this assortment of eye-popping imagery from Monday’s and Tuesday’s storms.


Figure 6. Gary Rink walks behind his home on Tuesday, June 23, in Coal City, Ill., after a tornado passed through the area Monday evening. The community of about 5,000 residents is located about 60 miles southwest of Chicago. Image credit: AP Photo/Charles Rex Arbogast.


Wet weekend on tap for Northeast
Though at least it’s arriving a week before the Fourth of July holiday, a rainy, cool storm system will likely put a big damper on outdoor activities this weekend from the Ohio Valley into the mid-Atlantic and New England. The west-to-east jet stream that’s powered storms all week will buckle into a pronounced upper-level low that will move slowly across the region. A double-barreled surface low may develop, similar to the configuration seen in many nor’easters. Cool temperatures should tilt the odds away from thunderstorms toward steady rain over the coastal cities, where 1” to 3” of rain possible. Heavier downpours could fall over the upper Ohio Valley and Appalachians. With 9.57” reported this month through Wednesday, Baltimore has already landed the second-wettest June in its 145 years of weather history. The record of 9.95”, set in June 1972, could be eclipsed by an inch or more before the month is out.

Bob Henson


Figure 7. Projected three-day precipitation totals from the NOAA Weather Prediction Center, for the period from 1200 GMT June 25 to June 30. Image credit: NWS/WPC.


Figure 8.. The setting sun illuminates mammatus clouds over Pottsgrove, PA, in the wake of Tuesday’s severe storms. Image credit: wunderphotographer Jerry1481.