Friday, June 21, 2013

Devastating Floods in Southern Alberta, Calgary

Downtown Calgary Friday
Credit: Justin Kripps - Twitter
Heavy rain falling just east of the Canadian Rockies in southwestern Alberta resulted in catastrophic flooding on Thursday and Friday across much of southern Alberta, including the city of Calgary.

More than a dozen towns in southern Alberta declared states of emergency after swollen rivers crested their banks Thursday, forcing mandatory evacuations for entire communities.  An estimated 100,000 people were evacuated from downtown Calgary.  There have been two fatalities attributed to the flooding.




The Province of Alberta. Calgary is red dot.
The flooding in southern Alberta resulted from a combination of an unusual upper level weather pattern and geography. The Bow River flows from near Lake Louise, through Banff and Calgary, eventually flowing into the South Saskatchewan River, which flows northeast to Hudson Bay. There are a number of rivers in the Bow River drainage area, which lies just east of the Rockies. The eastern part of the basin is 6,000 to 9,000 feet above sea level. Any precipitation that falls in the basin ends up in the rivers and eventually the Bow River. That's the geography part.



The Bow River basin in southern Alberta

Remember the unusually strong, nearly stationary upper level high pressure system that brought record hot weather to Alaska? Well, that high plays a part in the Calgary flooding. This high acted as a block to weather systems moving in from the Pacific. A trough of low pressure moving from west to east from the Pacific was forced south of the high.

The 700 mb map (about 10,000 feet) at 6:00 p.m. MDT June 20.

The combination of clockwise winds around the high and counter clockwise winds around the low streamed moisture-laden air from the central U.S. into southern Alberta. The formation of the rain was aided by the air being forced to rise as it encountered the Canadian Rockies.
This map shows the winds at 850 millibars (~5,000 feet)
and precipitable water at 6:00 p.m. MDT June 20.
The light green shading indicates PW values from 1.5 to 2.0 inches.
The dark green arrows show the general airflow.

Radar image for 10:30 p.m. MDT June 19. Note the more intense cells south and west of Calgary


Over half the Bow River basin received more than 50 mm (~ 2.0 inches) of rain, with many areas in the foothills seeing over 100 mm (~4.0 inches).

Radar estimated precipitation for period ending at 9:00 a.m. MDT June 20.


Here’s a graph of the rainfall from the rain gauge at Three Sisters Dam, 10 km south of Canmore, showing about 100 mm (~4.0 inches) of rain in less than 9 hours, and 245 mm (9.65 inches) for the event.This rain gauge is located within the area of maximum precipitation on the radar map.


This rain event was actually well forecast by the Canadian forecast model up to a week before.  Translating the precipitation forecast into specific river stage forecasts in advance is complicated, even more so over complex terrain.

Precipitation forecast by Canadian model valid for 6:00 p.m/ MDT June 20.
Credit; Environment Canada and The Weather Network
For photos and videos of the flooding, follow the links below.

Images shared on social media - The Globe and Mail

Photo gallery of Calgary streets before and during the flood - Global News


Flooding coverage by The Weather Network

Wednesday, June 19, 2013

Baked Alaska

While most of the lower 48 states were generally enjoying typical summer weather this week, Alaska residents suffered through a record-setting heat wave. It was just one month ago Tuesday that Anchorage had its last measurable snow.

The record heat was the result of a very strong ridge of high pressure in the upper atmosphere. The center of this "closed" high was located right over Alaska. Within the high air descends and warms, keeping skies clear allowing full sunshine. The high also moved very little during the last several days keeping any weather systems that might have brought relief at bay.

Upper level map (500 millibars, about 20,000 feet) showing the strong ridge over Alaska.

June 17 satellite image of Alaska showing cloud-free skies. Since Alaska is surrounded
by water, cloud-free days, especially over most of the state, are rare. Credit:  NASA

Here are the records set as of Tuesday.

All-time records set on Monday, June 17


Records for Tuesday, June 18.

One of our Alaskan CoCoRaHS observers included comments about the heat in his observations this week. The station is AK-MS-11, Palmer 1.7 WNW, located about 40 miles northeast of Anchorage.

June 17
Hot, dry weather has produced the warmest high temperature I have recorded in nearly nine years of record keeping in Alaska. Yesterday I reached 81.4° F and cooled only to 59.6° F, my warmest overnight low in nearly nine years. Winds reached 20.6 m.p.h. early in the evening which provided some relief. Today may be even hotter as winds are presently light and skies are clear.

June 18
Sunny, hot weather drove my high temperature in Palmer to a phenomenal 83.9° F and increased winds overnight prevented it from dropping below 65.7° F for the overnight low. My maximum gust earlier this morning was 41.2 m.p.h. A high cloud layer has developed this morning giving partly cloudy skies and the wind is continuing.


Residents headed out to beaches and parks seeking releif from the heat and/or just taking advantage of the unusual summer weather. Stores sold out of fans. Those who didn't have fans had to endure, as air conditioning is not common in most homes in Alaska.While for most of us here in the lower 48 an 81°F day is pleasant in the summer, it's a record in Anchorage. The heat also brought out the mosquitoes in large numbers, with some residents calling it the worst they have ever seen.

Fortunately for Alaskan residents the weather will be moderating this week. High temperatures in Anchorage, for example, will be in the 60s to low 70s into the weekend.

Tuesday, June 18, 2013

ET - Moving Water Back into the Atmosphere

If you Google "ET" or "E-T" the first several results returned are for the 1982 movie E.T. - The Extra-Terrestrial, about a boy who befriends an extra-terrestrial stranded on Earth.  The "ET" that is the subject of this article isn't about visitors from outer space, but it is a concept that may be a little "alien" to many people.

ET stands for evapotranspiration, the process in which water vapor moves back into the atmosphere.  Evapotranspiration is the sum of evaporation from ground surfaces and the transpiration of water to the atmosphere from plant leaves.  ET is a function of temperature, wind speed, relative humidity, and solar radiation. Transpiration occurs when the roots of a plant draw moisture from the soil where it moves up through the plant to be released as water vapor from the leaves. On average more than half the precipitation that falls is returned to the atmosphere through ET.  Studies show that transpiration by vegetation accounts for about 10 percent of the moisture in the atmosphere.  An acre of corn can transpire about 3,000 to 4,000 gallons of water per day.  The transpiration from agricultural crops is often significant enough contribute to the higher dew point temperatures that create muggy conditions during the summer and may enhance the formation of showers and thunderstorms.  Conversely, the reduction in transpiration, such during drought, reduces the return of moisture to the atmosphere which in turn inhibits the development of showers and thunderstorms.

The E-T Gauge
CoCoRaHS observers measure what falls out of the atmosphere, precipitation. Beginning last year, however, a number of CoCoRaHS observers have been measuring evapotranspiration, or what is going back into the atmosphere, the "return" side of the water cycle.  Evapotranspiration measurements actually began in mid-2011 with a few volunteers as a pilot project. Last spring the opportunity to make ET measurements was opened up to the observers at large. At present there are about 90 observers in 38 states making ET measurements across the country along with their rainfall (or in many cases, lack of rainfall) measurements.   ET does not vary to the same extent as precipitation (it's more similar to temperature), so multiple measurements in the same general area are usually not needed, unlike precipitation. ET measurements are only made during the warm season, since freezing temperatures can damage the gauge.



The measurements are made using a special ET gauge developed for this purpose.  The gauge consists of a water reservoir, with a cap consisting of a ceramic evaporator surface with a green fabric cover.  In our case the fabric simulates evaporation over turf, so the gauge needs to be sited in a sunny, exposed area and preferably over grass.  We are measuring "reference ET" which is defined as "the ET from an extensive surface of clipped grass… that is well-watered, and fully shades the ground."  This reference ET is referred to as ETo . Another cover is available which simulatesevaporation over alfalfa (ET1). The cap is connected to a supply tube which extends the length of the reservoir. There is a sight tube on the exterior of the gauge which measures the water level in the gauge.  The difference in water level from one observation to the next represents the evapotranspiration.


The measurement of both precipitation and evapotranspiration allows us to calculate an atmospheric water balance.  Water balance charts are available on the CoCoRaHS web site (I also had one in my last blog post about New Mexico). This plots precipitation, ET, and the accumulated difference over time.


Water balance chart for ME-CM-3, located about 20 miles north of Portland, Maine.

Water balance chart for TX-ER-4, about 60 miles WSW of Fort Worth, Texas


Water balance chart for UT-ML-1, about 80 miles SSW of Salt Lake City
 
These charts provide a good sampling of the relationship between ET and precipitation and the water balance. When viewing ET charts, keep in mind that the charts do show multi-day ET values (total E-T over a period of more than a day), but the charts don't plot multi-day precipitation accumulations. Only daily reports are reflected on the charts.

The measuring of ET is relatively easy but there is a commitment of time and money.  The ET gauges cost about $220, and there is a little more to setting up and maintaining them.  However, the ET measurements are very useful and more importantly fill a big data need. Most estimates of ET are calculated, and the deployment of these gauges to CoCoRaHS observers represents the first organized effort to measure ET other than in automated, specialized networks.

For more information on evapotranspiration and the CoCoRaHS measurement program, visit the CoCoRaHS web site and select Evapotranspiration in the Resources menu of the left side of the page.

Thursday, June 13, 2013

New Mexico in 2013 - Land of Dessication

New Mexico's official "nickname" is the Land of Enchantment. It really is a beautiful state, rich in natural beauty and cultural heritage. One of my lasting memories of a vacation out west years ago was while driving through New Mexico during the late afternoon and entering a flat desert plain surrounding by towering mesas. The late afternoon sun combined with the colors of the landscape was an amazing sight.

Unfortunately, New Mexico has become ground zero of the drought that has been in progress over the western U.S. the past two years. A little over 82 percent of the state is in Extreme to Exceptional Drought according to the latest U.S. Drought Monitor. That's the highest percentage of any state currently affected. Conditions have significantly worsened over the last three months.  At the start of the calendar year about 32 percent of the state was in Extreme to Exceptional Drought, and by March it was up to 50 percent.     

CoCoRaHS observers have been documenting the drought impacts, and some of the descriptions sound like they could have come from the Dust Bowl.  Here are two excerpts.

Santa Fe County
We are noticing that wild animals, birds and mammals, are increasingly desperate for water and therefore losing some of their instinctive fear of humans and other predators. The combination of severe drought and smoke from two wildfires nearby is making some mammals panic at times and come toward us rather than flee us when we are outside.
Rangeland in Lincoln County in April,
normally green at this time. Image credit: Twitter



Luna County
Because we've had so little moisture fall from the sky and we've had daily winds from 20 to 65/70 mph at least 80% of the population is suffering from "allergies" we didn't know we ever had! No one around here has a "lawn" of grass...instead we all measure just how deep the sand is now...the folks with the least amount of sand are considered lucky because they have less dusting/sand clean up to do on the inside of their homes. We've been told by a local farmer that he is now having to pay $20.00 for a bale of hay so he is going to have to sell all of his live stock next week - he can't afford to feed them any longer. And, we've heard that the local rancher spent over $100,000.00 in the last nine months trying to keep his cattle heavy enough to get them to market. We know that we haven't seen any of his cattle in our immediate area in the last 4 or 5 months...which means his heard head count is way down. Would you like us to start measuring the sand in our rain gauge rather than waiting for some moisture to land in it?


You can see the worsening of the drought in the water balance summary for a CoCoRaHS station in Bernalillo County in the north central part of the state. The station is NM-BR-56, Tijeras 3.7 N, located a few miles east of Albuquerque off of Interstate 40. This observer is not just measuring precipitation (or lack thereof), but also evapotranspiration (E-T).  It is the only location in New Mexico with this measurement at the time.  The average annual precipitation for this station is 18.54 inches. The annual total for NM-BR-56 in 2012 was 9.80 inches, just 53 percent of normal. So far in 2013 this station has only measured 1.85 inches of rain!  The observer started E-T- measurements on May 15, and since that time has had more than 8 inches of water loss, and no precipitation. E-T rates have been running from 0.25 to 0.45 inches per day, and without rainfall you can see how quickly the deficit accumulates.

Water balance summary for NM-BR-56. Water balance is precipitation minus E-T.

The precipitation shortfall since the beginning of the calendar year is remarkable. All of the areas in red have 20 percent or less of normal precipitation.

Percent of normal precipitation for January 1-June 13, 2013.
The gray area indicates the data is missing for far western New Mexico on this map.
Map from the National Advanced Hydrologic Prediction Service


The large precipitation deficits have had obvious effects on the streamflow in New Mexico. The Pecos River basin is located on the east side of the state.



Hot, dry weather and tinder dry vegetation also translates into a high risk for wildfires. Several wildfires are already burning encompassing about 50,000 acres in total. A new fire was started by lightning in northern New Mexico this afternoon.

Satellite image of two of the wildfires in northern New Mexico.
Santa Fe is located just west of the Tres Lagunas fire.
Speaking of thunderstorms, there has been storms that have actually produced rain, but they have been few and far between. On June 5 thunderstorms covered Interstate 25 near La Bajada in Santa Fe County with 6 inches of hail. The southbound lanes of the Intersate were closed for over an hour until hghway crews could clear away the ice.  As you might expect, the hail piling up on the highway caused several accidents.

New Mexico residents are looking forward to the onset of the summer monsoon season to provide some rainfall, but it certainly won't be enough to make much of a dent in the current drought. The outlook for the summer in the Southwest is for a higher than normal probability of warm and dry conditions persisting.




Monday, June 10, 2013

A CoCoRaHS History of Andrea

Tropical Storm Andrea developed in the Gulf of Mexico last week and moved up along the east coast finally moving well out to sea Saturday. Andrea began losing tropical characteristics on Friday and by late afternoon Friday was extratropical. The low picked up speed and raced northeast along the coast Friday and Saturday. It finally turned out to sea and was absorbed by another low near Newfoundland Sunday.

Here is an animation of the CoCoRaHS precipitation map from Wednesday, June 5 through Sunday, June 9.


7-day precipitation accumulation ending Sunday, June 9. Not all precipitation
along the eastern seaboard during this period was due to Andrea, but
her footprint is certainly evident.

Thursday, June 6, 2013

Andrea Poised to Soak Eastern Seaboard

Infrared satellite image at 10:31 p.m. EDT. The center of Andrea is
approximately 30 miles west of Jacksonville, FL.
Image credit: College of DuPage
Tropical Storm Andrea, which became the first named tropical system of the season in the Atlantic Basin yesterday, is currently crossing northern Florida after dumping 2 to 4 inches of rain on the southern half  of the state yesterday and last night. A tornado watch was in effect for much of Florida during the day. There were eight reports of tornadoes, most of which caused some damage.

The rain shield associated with Andrea has now spread north in to Georgia and South Carolina.

Radar image at 10:26 p.m. EDT. The red "L" indicates the center of Andrea.
The rain will continue spreading north as Andrea moves off the Florida coast and then takes a path hugging the east coast over the next several days.

Forecast track for Tropical Storm Andrea

Rainfall amounts from 2 to four inches, with locally higher amounts, are expected along the eastern seaboard from Georgia to Maine.

Rainfall forecast through 8:00 p.m. EDT Saturday, June 8.
CoCoRaHS observers - remember to submit Significant Weather Reports to report heavy rain, flooding, or other storm-related weather. These reports are immediately routed to your local National Weather Service Office. If you are going to be gone for part of the weekend and not able to make an observation be sure to review how to submit a multi-day accumulation if you aren't already familiar with this.  There should be some interesting rainfall maps to look at the next three days.

Saturday, June 1, 2013

Hurricane Season 2013 - What's Ahead

Hurricane Andrew, 1992
June 1st marks the start of meteorological summer, and probably more significant for those on the east and Gulf coasts, it's the start of the 2013 hurricane season.The National Oceanic and Atmospheric Administration issued it's hurricane season outlook for 2013 about a week ago.  The bottom line is that this is expected to be the fourth consecutive very active hurricane season in the Atlantic.

The outlook is based on current conditions in the Atlantic basin, expected atmospheric conditions over the course of the season, and model forecasts. The three key atmospheric factors that point to a very active hurricane season are:

  • A continuation of the atmospheric climate pattern, which includes a strong west African monsoon, that is responsible for the ongoing era of high activity for Atlantic hurricanes that began in 1995
  • Warmer-than-average water temperatures in the tropical Atlantic Ocean and Caribbean Sea
  • El NiƱo is not expected to develop and suppress hurricane formation.

NOAA estimates that there is a 70 percent probability that there will be

    13-20 Named Storms
    7-11 Hurricanes
    3-6 Major Hurricanes (Category 3 to Category 5) [link]

In other words, in all seasons with similar climate conditions to those expected this year, 70 percent of those seasons had activity that fell within the ranges above.

This compares to the official 1981-2010 seasonal averages of 12 named storms, 6 hurricanes, and 3 major hurricanes

How did the outlook verify in 2012?  In May 2012 the NOAA outlook was for 9-15 named storms, 4-8 hurricanes, and 1-3 major hurricanes. The outlook was updated in August to 12-17 named storms, 5-8 hurricanes, and 2-3 major hurricanes.  The actual count for 2012 was 19 named storms, 8 hurricanes, and 2 major hurricanes. The two major hurricanes were Michael, which did not make landfall, and Sandy, which did.

Tracks of the named tropical storms in the Atlantic basin in 2012
For a full-size, high resolution version of this map and track maps for previous years, visit the NHC Data Archive.


The 2010, 2011, and 2012 seasons each had 19 named storms in the Atlantic.

This Atlantic hurricane season outlook will be updated in early August, which coincides with the onset of the peak months of the hurricane season. The greatest frequency of tropical storms occurs in mid-September.

Number of tropical cyclones per 100 years

During the month of June tropical storm formation is favored in the Gulf of Mexico and the western Caribbean.



Here are the names of 2013 storms:

Andrea
Barry
Chanta
Dorian
Erin
Fernand
Gabrielle
Humberto
Ingrid
Jerry
Karen
Lorenzo
Melissa
Nestor
Olga
Pablo
Rebekah
Sebastien
Tanya
Van
Wendy


Hurricane preparedness week was May 23-June 1. For more information on tropical storms and how to prepare for them, visit  the National Hurricane Center's Hurricane Preparedness web site.  The site has video and audio presentations in both English and Spanish.