WILLIWAW WOES





http://en.wikipedia.org/wiki/Williwaw

 

According to the above Wikipedia link, the term Williwaw refers to katabatic winds (cold, heavy dense, arctic or antarctic air descending from continental higher-elevation sources) that blast into coastal areas, such as the Taku winds in Juneau. Most people that live in South-Central Alaska though understand the term Williwaw to describe the strong, often damaging and capricious winds we get here with the passage of low pressure/frontal systems, coming up from the south or southwest, from the Bering Sea or Gulf of Alaska. We have a Williwaw street, Williwaw Lakes in the Chugach State Park, just to the SE of the city, at 900 metres elevation, and a 1662 metre (5450') Williwaw peak, behind them.

 

An unusually strong, and unprecedented early event of this nature occurred earlier this week in the Anchorage "bowl", bringing winds across the majority of the city of 80-110 kph (50-65 mph), with gusts as high as 170-210 kph (100-131 mph, category 2-3 hurricane strength!) in certain favoured areas. Here at the Chugach Front Research Centre, we are estimating our peak gusts to be around 145 kph (90 mph), based upon the damage we observed to plants and trees around it, and the shaking of the entire building during the event. With thousands of downed trees across the "bowl" power was knocked out to more than half of the population, with a few unfortunate areas still without, as of this writing, five days later.

 

http://www.adn.com/2012/09/07/2615477/blackouts-remain-for-2700-customers.html

 

As this US National Weather Service graphic (from their NWS Alaska facebook site) shows, wind gusts as high as this, 131 mph (210 kph!) were observed. Since this local weather station is not an official NWS installed and maintained platform, it's accuracy is not entirely established, but it should be accurate to within +/- 10 mph (or 16 kph). Strong east through south winds in advance of low pressure/frontal systems are channeled by the Chugach Mountains, and in the right circumstances, flow down the mountainsides and accelerate. Giving much stronger winds in these favoured areas than what is observed across the middle and western portions of the city, e.g., where the Anchorage International Airport, and downtown, are located.

 

The surface map below from tuesday last, at 4 pm AKDT, shows the European (ECMWF) forecast model's initial analysis (what the model uses as the initial state of the atmosphere, which trillions of calculations then operate on, to provide forecast charts extending out 10 days) of  the surface low in the eastern Bering Sea at it's peak strength of near 970 mb. The yellow-green-blue colour contours are observed/forecast 850 mb (roughly 1500 metres/5000 ft) wind speeds in metres/second. Of note, is that the model is estimating that winds just to the east of Anchorage, over the Chugach mountains at this level are in excess of 40 m/s, or 143 kph (90 mph!). Why is that? Because this low was unusually strong, and surrounded by strong surface high pressure, leading to very strong pressure gradients.   

 

 

 

At 500 millibars, the low manifests as a deep 5250 metre centre, quite low for this time of year, which when combined with the fact that sea surface temperatures are at their summer seasonal peaks, allows for greater fueling of these systems winds and precipitation.

 

 

Right about this time, and about 5-6 hours before the strongest winds were occurring over the Anchorage bowl, this infrared satellite image shows the strong low just offshore of the southwest Alaska coast, with the occluded front about 150-200 km to our west. 

 

Following is the NWS Anchorage's "Area Forecast Discussion" written the afternoon of the strong wind event. These are a description of the basic weather pattern, problem(s) of the day, how the forecast models are handling it, and expected impacts. Prepared twice-daily in every US NWS office, by the lead forecaster on duty at the time, this one is exceptionally well-written, descriptive, and unfortunately accurate. Give it a read, it has some interesting details.

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
115 PM AKDT TUE SEP 4 2012

.ANALYSIS AND UPPER LEVELS...A POWERFUL STORM IS MAKING ITS WAY
ACROSS THE EASTERN BERING SEA AND TOWARD MAINLAND ALASKA THIS
MORNING. THE LATEST OBSERVATION FROM SAINT GEORGE ISLAND SHOWS
A SURFACE PRESSURE OF 972 MB...SO THE CENTRAL PRESSURE OF THE
NEARBY LOW IS LIKELY AROUND 970 MB. STANDARDIZED ANOMALIES ARE
IN THE RANGE OF 4 TO 6 FOR WIND SPEEDS AS THE LOW MOVES ACROSS
THE ALASKA REGION. THIS IS INDICATIVE OF HOW UNUSUAL IT IS TO
HAVE SUCH A STRONG STORM THIS EARLY IN THE SEASON. THE SIZE OF
THE STORM IS ALSO VERY LARGE...WITH GALE FORCE WINDS EXTENDING AT
LEAST 500 MILES IN ANY DIRECTION FROM THE LOW CENTER. IN ADDITION
TO WIDESPREAD STRONG WINDS THIS STORM IS ALSO PRODUCING HEAVY RAIN
ALONG THE FRONTAL SYSTEM...WHICH IS MOVING ONSHORE OF SOUTHWEST
ALASKA EARLY THIS AFTERNOON. 

.MODEL DISCUSSION...MODELS REMAIN IN VERY GOOD AGREEMENT WITH
HANDLING OF THIS SYSTEM AND FORECAST CONFIDENCE IS HIGH. THE
LATEST MODELS HAVE TRENDED TOWARD A SLIGHTLY MORE WESTWARD TRACK
OF THE LOW CENTER ALONG THE WEST COAST OF ALASKA WHICH MEANS THE
TIMING OF THE FRONT MOVING THROUGH SOUTHCENTRAL WILL BE A LITTLE
SLOWER.

.SHORT TERM FORECAST...STRONG WINDS AND HEAVY RAIN WILL BE THE
MAIN THREATS FROM THIS STORM. THE HIGHEST IMPACTS FROM WINDS ARE
EXPECTED TO BE IN THE TURNAGAIN ARM AND ANCHORAGE AREA WHERE HIGH
WIND WARNINGS ARE IN EFFECT. WINDS ARE ALREADY INCREASING THROUGHOUT
THE ANCHORAGE AREA. HOWEVER...EXPECT WINDS IN THE ANCHORAGE BOWL
TO COME DOWN LATE THIS AFTERNOON AND EARLY EVENING AS THE FRONT
MOVES INTO THE WESTERN GULF AND THE NORTH-SOUTH PRESSURE GRADIENT
INCREASES DOWN COOK INLET...WHICH SHOULD CAUSE WINDS CURRENTLY
BENDING INTO ANCHORAGE TO INSTEAD REMAIN OUT IN THE INLET. WINDS
ALONG TURNAGAIN ARM AND HIGHER ELEVATIONS WILL CONTINUE TO INCREASE
ALL THE WAY THROUGH THE EVENING HOURS UNTIL THE FRONT MOVES THROUGH
AROUND MIDNIGHT. CONDITIONS CONTINUE TO LOOK FAVORABLE FOR TRAPPING OF MOUNTAIN WAVES THIS EVENING WHICH WILL BRING SOME STRONGER WINDS DOWN THE HILLSIDE AND INTO PORTIONS OF EAST ANCHORAGE ALONG THE MOUNTAINS. WINDS WILL MOVE BACK IN TO ALL OF THE ANCHORAGE BOWL AS WE APPROACH MIDNIGHT AND THE FRONT MOVES THROUGH. AS HAS BEEN ADVERTISED THE PAST COUPLE DAYS...WITH LEAVES ON THE TREES AND FAIRLY SATURATED SOILS THERE IS AN INCREASED LIKELIHOOD OF FALLING TREES IN THESE HIGH WINDS.

WINDS ELSEWHERE WILL BE STRONGER THAN EXPECTED IN A MORE TYPICAL
WIND EVENT. HOWEVER...WINDS IN THESE AREAS ARE EXPECTED TO REMAIN
BELOW WARNING THRESHOLDS. WINDS WILL DIMINISH RAPIDLY BEHIND THE
FRONT IN MOST LOCATIONS. THE EXCEPTION WILL BE TURNAGAIN ARM AND
HIGHER ELEVATIONS WHERE THE PRESSURE GRADIENT WILL REMAIN QUITE
TIGHT AND SUPPORT STRONG SUB-WARNING LEVEL WINDS THROUGH WEDNESDAY.

AS WAS THE CASE WITH THE SYSTEM THAT MOVED THROUGH THE REGION
YESTERDAY...THERE WILL BE STRONG PRESSURE RISES BEHIND THE LOW
CENTER. THE MAX RISE WILL ONCE AGAIN BE OVER SOUTHWEST ALASKA
WITH WEAKER RISES OVER THE GULF AND SOUTHCENTRAL. THESE PRESSURE
RISES WILL CAUSE WINDSPEEDS TO INCREASE ONCE AGAIN ON WEDNESDAY.

HEAVY RAIN WILL FALL ACROSS MUCH OF THE REGION OUT AHEAD OF THE
FRONT. THE WIDESPREAD STRONG WINDS WILL RESULT IN LIGHTER QPF
AMOUNTS ALONG THE LEE SIDE OF THE MOUNTAINS. AREAS IN UPSLOPE
FLOW WILL SEE ENHANCED RAINFALL AMOUNTS ON THE ORDER OF TWO INCHES
OR MORE...PRIMARILY ALONG THE WESTERN SUSITNA VALLEY AND PRINCE
WILLIAM SOUND AREAS. THE FRONTAL RAIN BAND WILL MOVE THROUGH OVER
ABOUT A 3 TO 6 HOUR PERIOD FOR ANY GIVEN LOCATION. THIS HELPS LIMIT
THE FLOODING POTENTIAL. RIVERS AND STREAMS IN THE SEWARD AREA WERE
RUNNING HIGH AFTER YESTERDAY'S STORM AND A FLOOD WATCH HAS BEEN
ISSUED FOR TONIGHT THROUGH WEDNESDAY AS THE NEXT BATCH OF HEAVY
RAIN MOVES THROUGH. 

THIS STORM SYSTEM WILL EXIT TO THE NORTH ON WEDNESDAY WITH IMPROVING
TRENDS EXPECTED ACROSS THE REGION. HOWEVER...ANOTHER UPPER TROUGH
WILL DROP OUT OF THE RUSSIAN ARCTIC AND RAPIDLY TRACK TO THE GULF
OF ALASKA BY LATE FRIDAY. THIS WILL BE A MUCH WEAKER SYSTEM AND WIND
WON'T BE A MAJOR FACTOR...BUT PERIODS OF RAIN AND COOL TEMPERATURES
WILL PERSIST ACROSS THE SOUTHERN MAINLAND THROUGH THE END OF THE
WEEK.

.LONG TERM FORECAST...THE UPPER LEVEL PATTERN WILL REMAIN
PROGRESSIVE THROUGH THE EXTENDED FORECAST PERIOD WITH WEAK TO
MODERATE STORMS MOVING QUICKLY FROM WEST TO EAST ACROSS THE AREA.
AT THIS POINT IT LOOKS LIKE THESE STORMS WILL PRIMARILY REMAIN
ALONG THE SOUTHERN TIER OF THE FORECAST AREA...WHICH MEANS THE
SOUTHERN MAINLAND OF ALASKA MAY SEE A PERIOD OF DRY WEATHER.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 101 [Anchorage, eds..] 125.
MARINE...STORM WARNING...120.
         GALE WARNING...125 128 129 130 132 138 140 141 150 155
                        160 165 170 171 172 175 176 179 180 185.
FIRE WEATHER...NONE.

SEB SEP 12

Note the "standardised anomalies" referred to in the opening paragraph of the discussion. These are just a quantitative method of assessing the likelihood of occurrence (or rarity thereof) of whatever field is being described. In this case, SA's of 4-6 for the 850 mb wind field with this low, have a one percent or less likelihood of occurring in any given year, based upon the 60 year period of record that the NWS has for weather data.

The area that the Chugach Front Research Centre is located, sometimes called the "Chugach foothills subdivision(s)", has a notorious history/reputation for receiving stronger/more damaging winds from these type of lows than other lower and flat areas of Anchorage to the west. On the above 3-D representation of the eastern Anchorage area and Chugach front, this area is located just to the west of the "HORAGE" labeling, where the eastern-most large road, Tudor/Muldoon, curves from it's east-west orientation and becomes north-south. This small about 5 sq km area often can receive winds nearly as strong as those observed at the higher elevations on the Chugach front hillsides.

 

Why is that? Inspection of the map above, shows a 15 km long relatively straight canyon along the North Fork of Campbell Creek, labeled "Campbell Cr Canyon", that is aligned in a se-nw direction. Strong winds from the 900-850 mb levels (1000-1500 metre or 3300-5000 ft) are funneled through this long, narrow, straight canyon, and blast out onto the adjacent flat areas.

Here is the view of the canyon from directly behind the Chugach Front Research Centre.

Here is the lower reach of this North Fork Campbell Creek canyon, from our 3-day trip a few years ago, which we undertook entirely on foot from the CFRC.

http://akprogressive.blogspot.com/2010/08/going-neutral.html

 

This is looking in up-canyon toward the southeast, at an elevation of only around 700 metres (2300 ft.), but even at this low elevation, it is treeless. As often during the summer, cold winds funnel through here when lows are present in the Gulf of Alaska.

Further up-canyon, at about the 900 metre level (2950 ft), beautiful clear 4 km Long Lake fills the bulk of it. The source of the fresh waters of our much-loved North Fork of Campbell Creek. On this day, when a very weak low was in the Gulf, and light winds were observed in Anchorage, here in the canyon, winds were 60-90 kph (36-55 mph).

The headwalls of this beautiful 15 km long canyon are formed by the 1400-1662 metre peaks of this portion of the Chugach mountains, at the foot of which are more beautiful snowmelt-derived clear alpine lakes. Strong winds then descend this mountain headwall, then are funneled and accelerated down the canyon, roaring out onto the adjacent part of the Anchorage bowl, when the weather pattern permits.

What does that translate into, in terms of actual weather conditions, in these adjacent areas near the mouth of this canyon? This picture, above, is from the CFRC at about 1100 pm AKDT last tue., about an hour before the strongest winds were occurring. At this time, gusts of 90-110 kph (55-65 mph) were bending the birch trees behind our compound. The howling of the winds was also punctuated by the flashing of powerlines arcing and transformers exploding, like giant flashbulbs, or lightning strikes, all over the area. Which was quite terrifying, and we made sure to stay inside, away from the hazards of blowing/falling tree limbs/trees. This was even before stronger gusts made the entire building shake, which caused our assistant editor Mattie and research assistant Kluane to become quite nervous. Our power had gone out earlier, around 1045 pm AKDT. We tried sleeping by midnight that night, with limited success.

What greeted us the next morning were some of these same trees downed, and our raspberries shredded into ragged stalks. We also lost one of our young apple trees. But we were fortunate, as many people had downed trees in their yards and blocking their streets, also causing damage to fences, homes and cars.

We were left dazed and tired the next day after this event, and very uneasy, about the potential for stronger and more frequent occurrences of similar events.

By now, you are probably aware that the Arctic sea ice extent, volume, and thickness, have reached a new record low in the past few weeks, in the 30+ year period of satellite-derived measurement, with still at least another week or so left, in the melting season. The animation below shows the declining volume in stark detail, as of the end of August.

http://tamino.files.wordpress.com/2012/08/piomas.gif

Below, is a very good description of what happened this year with the Arctic sea ice, and what it means, by Dr. Jeff Masters, who is a well-respected researcher in the Atmospheric Sciences field.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2222

Half of the polar ice cap is missing: Arctic sea ice hits a new record low

 

Posted by: JeffMasters, 8:53 PM GMT on September 06, 2012

Extraordinary melting of sea ice in the Arctic this summer has shattered the all-time low sea ice extent record set in September 2007, and sea ice continues to decline far below what has ever been observed. The new sea ice record was set on August 26, a full three weeks before the usual end of the melting season, according to the National Snow and Ice Data Center. Every major scientific institution that tracks Arctic sea ice agrees that new records for low ice area, extent, and volume have been set. These organizations include the University of Washington Polar Science Center (a new record for low ice volume), the Nansen Environmental & Remote Sensing Center in Norway, and the University of Illinois Cryosphere Today. A comprehensive collection of sea ice graphs shows the full story. Satellite records of sea ice extent date back to 1979, though a 2011 study by Kinnard et al. shows that the Arctic hasn't seen a melt like this for at least 1,450 years (see a more detailed article on this over at skepticalscience.com.) The latest September 5, 2012 extent of 3.5 million square kilometers is approximately a 50% reduction in the area of Arctic covered by sea ice, compared to the average from 1979 - 2000. The ice continues to melt, and has not reached the low for this year yet.

Figure 1. A sunny, slushy day at the North Pole on September 1, 2012. Webcam image courtesy of the North Pole Environmental Observatory.

Figure 2. Sea ice extent on September 5, 2012, showed that half of the polar ice cap was missing, compared to the average from 1979 - 2000. Image credit: National Snow and Ice Data Center.

Why the Arctic sea ice is importantArctic sea ice is an important component of the global climate system. The polar ice caps help to regulate global temperature by reflecting sunlight back into space. White snow and ice at the poles reflects sunlight, but dark ocean absorbs it. Replacing bright sea ice with dark ocean is a recipe for more and faster global warming. The Autumn air temperature over the Arctic has increased by 4 - 6°F in the past decade, and we could already be seeing the impacts of this warming in the mid-latitudes, by an increase in extreme weather events. Another non-trivial impact of the absence of sea ice is increased melting in Greenland. We already saw an unprecedented melting event in Greenland this year, and as warming continues, the likelihood of these events increase.

Figure 3. August set a new record for lowest Arctic sea ice extent. Image credit: National Snow and Ice Data Center.


Figure 4. Arctic sea ice death spiral as plotted by Jim Pettit using data from the Japan Aerospace Exploration Agency.

Huge storm pummels Alaska
A massive low pressure system with a central pressure of 970 mb swept through Alaska on Tuesday, generating hurricane-force wind gusts near Anchorage, Alaska that knocked out power to 55,000 homes. Mighty Alaskan storms like this are common in winter, but rare in summer and early fall. The National Weather Service in Anchorage said in their Wednesday forecast discussion that the forecast wind speeds from this storm were incredibly strong for this time of year--four to six standard anomalies above normal. A four-standard anomaly event occurs once every 43 years, and a five-standard anomaly event is a 1-in-4800 year event. However, a meteorologist I heard from who lives in the Anchorage area characterized the wind damage that actually occurred as a 1-in-10 year event. A few maximum wind gusts recorded on Tuesday during the storm: [unfortunately, power outages and/or sensor damage occurred before the strongest winds occurred, eds..]
McHugh Creek (Turnagain Arm)... ... ..88 mph
Paradise Valley (Potter Marsh)... ... 75 mph
Upper Hillside (1400 ft)... ... ... ... 70 mph
Anchorage port... ... ... ... ... ... ... .63 mph

The storm has weakened to a central pressure of 988 mb today, and is located just north of Alaska. The storm is predicted to bring strong winds of 25 - 35 mph and large waves to the edge of the record-thin and record-small Arctic ice cap, and may add to the unprecedented decline in Arctic sea ice being observed this summer.

Figure 5. An unusually strong storm formed off the coast of Alaska on August 5 and tracked into the center of the Arctic Ocean, where it slowly dissipated over the next several days. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured this natural-color mosaic image on Aug. 6, 2012. The center of the storm at that date was located in the middle of the Arctic Ocean. Image credit: NASA.

Arctic storms may be increasing due to climate change
This week's Alaskan storm is the second unusually strong low pressure system to affect the Arctic in the past month. On August 4 - 8, a mighty storm with a central pressure of 963 mb raged through the Arctic, bringing strong winds that helped scatter and break up Arctic sea ice. According to a detailed post at NASA Earth Observatory, that storm was in the top 3 percent for strongest storms ever recorded north of 70 degrees latitude. A study of long-term Arctic cyclone trends authored by a team led by John Walsh and Xiangdong Zhang of the University of Alaska Fairbanks found that number and intensity of Arctic cyclones has increased during the second half of the twentieth century, particularly during the summer. Dr. Zhang explained that climate change has caused sea ice to retreat markedly in recent decades and has also warmed Arctic Ocean temperatures. Such changes may be providing more energy and moisture to support cyclone development and persistence. The strong storms of this week and a month ago would have had far less impact on the ice just a decade ago, when the sea ice was much thicker and more extensive.

A sea ice decline double-whammy
The monster Arctic storms like we've seen this year have sped up the rate of sea ice loss, but increased water temperatures and air temperatures due to human-caused global warming are the dominant reasons for the record melting of the Arctic sea ice. A July 2012 study by Day et al. found that the most influential of the possible natural influences on sea ice loss was the Atlantic Multi-decadal Oscillation (AMO). The AMO has two phases, negative (cold) and positive (warm), which impact Arctic sea ice. The negative phase tends to create sea surface temperatures in the far north Atlantic that are colder than average. In this study, the AMO only accounted for 5% - 31% of the observed September sea ice decline since 1979. The scientists concluded that given the lack of evidence that natural forces were controlling sea ice fluctuations, the majority of sea ice decline we've seen during the 1953 - 2010 period was due to human causes.

Joe Romm has a more in-depth look at the new Arctic sea ice record and what it means for the future over at climateprogess.org.  [well worth taking a look at, very informative, eds..]Angela Fritz and Jeff Masters

With the continued decline in, and imminent demise of summer sea ice coverage in the Arctic (likely by 2016-2018), we have reached a "tipping point", where positive feedbacks are now and will continue to amplify the warming we are already receiving from our increased levels of CO2 from fossil fuel combustion.

 

Thus, we at the APR fully expect now that greater losses of ice from the Greenland ice sheet will lead to significant coastal flooding/inundation world-wide within 10-20 years. As well as stronger and increased drought episodes (leading to greater wildfire acreages-another positive feedback, and greater instability in global food supplies) across continental land-masses in both hemispheres (North America, Eurasia, and Australia especially), stronger and more frequent heavy precipitation/flooding events, and stronger low pressure/frontal systems across the higher latitudes north and south. This is the reality we have now, and it's only going to get worse. Remember, we are nearing 395 ppm of CO2 in the atmosphere, and will reach close to 550 ppm by 2050, under current energy use/type trends. That means for us here at the CFRC, and in the Anchorage Bowl, stronger, and more frequent storms similar to that which occurred earlier this week. As well as greater instability and chaos in general in our climate, e.g., greater swings in winter conditions, freeze-thaw events, freezing rain, heavy snows and rains, more adverse aviation weather (turbulence/icing/wind shear) etc...

 

What will it mean for you, where you live? Feel free to inquire of us here at the Alaska Progressive Review, we have some knowledge and expertise to provide you with an informed assessment. Cheers.