| | Precipitation | Snow pack | Data sources | Explanation of terms
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Summary
Since the November 7, 2007 drought report significant precipitation (30 to 50 mm) was recorded over much of the Peace Region and northern parts of the Northern Region. Moving southward, accumulations tended to decrease with the southern half of the Northern Region receiving 10 to 25 mm, and the Central Region receiving 5 to 15 mm. Across the Southern Region accumulations were variable, ranging from 5 to 10 mm in the south to 10 to 20 mm across much of the centre, with greater than 40 mm recorded in the west along the foot hills and in the Cypress Hills in the south east.
Cold season (Oct 1 to March 31) precipitation accumulations to date across most of the Peace Region and the northeast part of the Northern Region are near normal, while in the rest of the reporting area, precipitation accumulations varied from moderately low to very low, with several pockets mostly located in the Central Region graded down to extremely low.
Modeled snow pack accumulations for this time of year across most parts of the Peace and Northern Regions varied from very low to moderately low with a few exceptions grading up to near normal accumulation. In the Central and Southern Regions, although accumulation is minimal relative to the long-term normal, accumulations varied from near normal to moderately low with the exception few pockets classified as having moderately high accumulations.
A large selection of related maps can be found at http://www.agric.gov.ab.ca/acis, under the Quick Viewer tab.
Current Situation
Precipitation
Precipitation since the November 7, 2007 Drought Report (Figure 1) - Since the last report, significant precipitation was recorded over much of the Peace Region and the northern parts of the Northern Region, including southern foothill areas where some areas reported precipitation in excess of 60 mm. Across the Central and Southern Regions precipitation accumulations ranged from 5 to 20 mm, with large parts of the southern Central Region having less than 10 mm of accumulated precipitation.
Peace Region: Precipitation accumulation across the region, ranged from a low of 21.5 mm at the La Crete AGCM station in the north and 23.5 mm at Grande Prairie A in the southwest to more than 35 mm precipitation across most of the stations in the central and south eastern parts of the region.
Northern Region: Precipitation accumulations across the region grades from high of 51.9 mm at Cold Lake A station and 45.8 mm at Lac la Biche A station in the northwest to lows of 6.6 mm at Camrose and 11.8 mm at New Sarepta AGDM stations, in and around the County of Camrose.
Central Region: Precipitation accumulations across the region were lowest when compared to the rest of the reporting area with the exception of the foothills area near Calgary. An isolated station in the northwest and many stations across the central and southern part of the region recorded less than 10 mm. The COP Upper station near Calgary reported 46.4 mm, the highest in the region. The rest of the stations in the region reported less than 20 mm ranging from of 17.6 mm at Leedale AEDN in the northwest to 10.5 mm at Sundre A in the west.
Southern Region: Across most of the Southern Region, precipitation totals were less than 20 mm with some stations in south-central and north-central parts of the region recording less than 10 mm. Some exceptions were the Medicine Lodge station in the eastern part of the region with 43.3 mm and Champion AGDM in the mid west 27.1 mm. Along the foothills, many stations recorded precipitation in excess of 60 mm.
Cold Season Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 2) - Cold Season (Oct 1 to March 31) precipitation accumulations relative to long term normal across most of the Peace Region and northeastern parts of the Northern Region and extreme western and south eastern parts of the Southern Regions were near normal, while in the rest of the reporting plain area accumulations varied from moderately low to very to very low, with several pockets grading to extremely low, most of which were located in the Central Region.
Peace Region: Most of the Peace Region Cold Season precipitation accumulations are near normal with the exception of three widely scattered pockets having moderately low accumulations.
Northern Region: Cold season precipitation accumulations in the region ranged from extremely high in a small pocket in the north to moderately low in the west and to low and extremely low in the south central part of the region.
Central Region: Cold season precipitation accumulation across most of the region remains the lowest across the reporting area. It ranges from very low over an extended area across the central and southern parts of the region, and also includes few pockets classified as extremely low. Along the east and western borders of the region accumulations are higher, but are still classified as moderately low.
Southern Region: Cold season precipitation accumulations across the region varied from moderately low across most of the region with mixed pockets of low, extremely low or near normal. The foothills and part of the southwestern corner of the region are classified as near normal to moderately high.
Average Precipitation Accumulations for December (Figure 3) - Across the reporting area, on average 4.7 percent of the annual precipitation falls in December. During this month precipitation totals range from 10 to 20 mm across most of the central and Southern Regions, increasing in the west along the foothills. Across the Northern and Peace Regions, precipitation totals typically range between 20 to 30 mm.
Snow pack conditions (Figure 4 and Figure 5)
Modeled snow pack conditions expressed as snow water equivalent (SWE) are shown in Figure 4. Snow pack accumulations relative to long term normal are shown in Figure 5. These maps represent the current snow pack estimates in stubble fields and reflect a 30 percent precipitation loss due to blowing; in addition to losses due to sublimation and snow melt process.
Peace Region: SWE's ranged from 30 to 40 mm range across the central parts of the region down to 10 to 20 mm range in the south and less than 10 mm in the extreme northwest corner of the region. Snow pack accumulations relative to long term normal are variable across the region, with most of the region classified as low to moderately low and a few pockets classified as very low to near normal (Figure 5).
Northern Region: SWE's in this region graded from a range of 20 to 30 mm in the north and northeast to 1 to 10 mm across the south. However, the snow pack accumulations relative to long term normal varied from very low and low across the west and through a corridor, that extends up north starting just south of the City of Edmonton. These below normal accumulations grade to at least near normal in the east (Figure 5).
Central Region. The SWE's across the region are below 10 mm and these snow pack accumulation relative to long-term normal varied from a small pocket of moderately high in the southeast corner to near normal through central portions of the region, down to moderately low in the west and the north.
Southern Region: The SWE's across most of the region are less than 10 mm, but grade up to more than 10 mm in several areas including the southeast corner, one small pocket in the west central portions of the region and along the foothills areas in the west. The snow accumulations relative to long term normal across most parts of the region are at least near normal, except two pockets with moderately low accumulations located in the central and western portions of the region.
Data Sources:
Near Real Time Weather data
Daily and hourly near-real-time raw weather data is brought in via daily data feeds from Alberta Environment (AENV) and Environment Canada (EC). The data undergoes a preliminary computer assisted QA/QC check performed by Alberta Agriculture (AF) staff. Suspicious values are checked and verified and daily missing values are filled using archived data from AENV databases or from the EC web site. If daily data is still missing, it is estimated using data from nearby stations. Maps describing current conditions are based on preliminary data that is subject to change under further review by AF, AENV and EC.
Historical Weather data
Historical weather data was provided by Environment Canada. This data was then converted to a 10 km daily gridded weather data set that used all available daily data to generate historical climate and soil moisture normals.
Explanation of Terms
Precipitation Accumulations-Frequency of Occurrence
Precipitation accumulations, expressed as a frequency of occurrence are computed for various periods and can be found on our web site at www.agric.gov.ab.ca\acis, under the Quick Viewer tab. Maps are routinely produced for the following periods:
· Past 365-days
· Past 180-days,
· Past 90-days
· Past 30-days,
· Growing season to date -Starting April 1st
· Cold Season to date- Starting October 1st
Selected maps from this series are included in this report.
Precipitation accumulations for each period are then determined by ranking the precipitation accumulations during similar periods period dating back from 1961 to present. The current accumulation is compared to the ranked values, yielding the frequency of occurrence, based on percentiles. The percentile points were then put into arbitrary but intuitive classification fields that describe the current state as drier, near or wetter than the long term normal. The resulting map thus answers the question "how often does this occur?" The classifications are as follows:
| Description | Frequency of Occurrence |
| extremely low | drier than this, on average, less than once in 25-years |
| very low | drier than this, on average, less than once in 12-years |
| low | drier than this, on average, less than once in 6-years |
| moderately low | drier than this, on average, less than once in 3-years |
| near normal | on average, this occurs at least once in 3-years |
| moderately high | wetter than this, on average, less than once in 3-years |
| high | wetter than this, on average, less than once in 6-years |
| very high | wetter than this, on average, less than once in 12-years |
| extremely high | wetter than this, on average, less than once in 25-years |
This same scheme is then used for similar maps of soil moisture and snow pack accumulations so that comparisons can readily be made across the various map types.
Snow pack (reported during the winter season only)
Snow pack snow water equivalents (SWE) are modeled for stubble fields. SWE is defined as the equivalent depth of water (mm) that the snow pack contains if it were to be melted. SWE is computed from precipitation and subsequent losses due to blowing, sublimation and snow melt processes.
In the model, if precipitation falls when the mean daily temperature is below 2 °C that precipitation is estimated to be in the form of snow. If precipitation is estimated to fall as snow then to simulate drifting, only 70 percent of the total precipitation is allowed to accumulate resulting in a 30 percent loss due to snow "blow off". If precipitation occurs as rain on an existing snow pack, it is added directly to the snow pack as SWE.
Soil moisture (reported during the growing season months only)
Soil moisture is measured as millimetres (mm) of plant available water. Plant available water is approximately half of the total water that can be measured in the soil. Soil moisture is reported on from May through to October.
The crop gets the moisture it requires from the reserve of soil moisture, which in turn is replenished by precipitation. Soil moisture is a valuable indicator of drought potential because it indicates the reserve of water available to the crop at a given point in time. During peak growing periods, soil moisture reserves are consumed quickly and must be replenished frequently by rainfall. Poor soil moisture reserves during peak water use indicate a high risk of immediate crop stress. Prolonged stress becomes drought and results in significant unrecoverable yield loss.
Because the climate varies across Alberta, comparing current moisture levels to normal levels provides a valuable indicator of drought risk that can be applied to all localities during the frost-free season. Current soil moisture levels are compared against soil moisture levels for the same day in each year from 1961 to present. The frequency of occurrence is computed based on the percentile points, using the same method that was used for similar maps that were generated for precipitation. The frequency of occurrence is then plotted using the same class scheme as is used in the long-term (hydrologic) drought map (see table above). Soil moisture reserves with a modifier of low, indicate a need for more precipitation to restore reserves.
Soil moisture needed to return to average spring or fall conditions
Soil moisture needed to return to normal spring or fall conditions is computed by subtracting average soil moisture (spring or fall), computed using model runs dating back from 1961 from current soil moisture conditions. This yields the amount of recharge needed to bring current soil moisture levels to average. Historic model runs are then analyzed to determine how many years since 1961 that soil moisture recharge was similar to or greater than that currently needed. The number of years that this occurred is then used to compute the probability of returning to average. However, currently this process is unable to account for snow currently existing on the ground and as such is not as accurate where snow packs exist.
Report prepared by the Drought Reporting Team
Ralph Wright, Daniel Itenfisu and Isabel Simons-Everett
Conservation & Development Branch & Program
Alberta Agriculture and Food
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph 780-427-3556
This report was created on December 20, 2007.
Drought analysis is currently scheduled at monthly intervals between October 31 and April 31, and twice monthly from May 1 to September 30. This report updates the previous report of November 7, 2007. |
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