| | Precipitation | Snow pack | Data sources | Explanation of terms
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Summary
Since the last Drought Report (December 31, 2008) moderate amounts of precipitation (20 to 40 mm) were recorded over much of the Peace Region, northern parts of the Northern Region, and the extreme southwestern and southeastern parts of the Southern Region. Precipitation across rest of the reporting area was generally less than 20 mm, with most of the Central and Southern Regions, and southwestern parts of the Northern Region receiving less than 10 mm.
Average daily mean temperatures during the past 15-days, relative to the long-term-normal, across most parts of the Peace Region, the western parts of the Northern Region, and the northern and the eastern parts of the Central Regions were moderately high. Over the rest of the reporting area average temperatures were at least near normal (Figure 6).
Cold season precipitation (Oct 1 to March 31) accumulations relative to long term normal, to date, are low to extremely low across a large area straddling the border between the Central and the Northern Regions. In contrast, accumulations are least near normal across most of the Peace Region, the northern parts of the North Region, pockets in the eastern and western parts of the Central Region and a corridor extending from the north-west to south-eastern portion of the Southern Region. Cold season accumulations across the rest of the reporting area generally vary from moderately low to very low.
Modeled snow pack accumulations relative to long term normal are very low to extremely low across much of the southeastern parts of the Northern Region and northeastern parts of the Central Region. Low to moderately low accumulations are found over much of the other parts of the Northern and Central region. In contrast, accumulations are near normal across most of the Peace Region, the northwestern parts of the Northern Region, the extreme southeastern and southwestern portions of the Central Region and across most parts of the Southern Region.
A large selection of related maps can be found at http://www.agric.gov.ab.ca/acis, under the Quick Viewer tab. Note these maps are updated once a week (usually by Wednesday) providing updates between drought reports.
Precipitation
Precipitation since the December 31, 2008 Drought Report (Figure 1)
Since the last Drought Report (December 31, 2008) a moderate amount of precipitation (20 to 40 mm) was recorded over much of the Peace Region, the western and the northern and parts of the Northern Region, and the southeastern and southwestern corners of the Southern Region. Precipitation across the rest of the reporting area was less than 20 mm, with most parts of the Central and Southern Regions, and the southeastern part of the Northern Region receiving less than10 mm.
Peace Region: Precipitation accumulation ranged from 30 to 40 mm across much of the southern half of the region grading down the 10 to 20 mm range across the northern parts of the region. Precipitation accumulations across the southeastern part of the region sharply increased up to the 50 to 60 mm range. The highest precipitation accumulations were recorded at High Prairie Banana station (53.9 mm), followed by Spring Creek station (44.2 mm), both located in southeast, while the lowest accumulations were recorded at La Crete AGCM station (13.5 mm) in the north followed by Hawk Hills AGCM station (15.2 mm) in the north central part of the region. Precipitation accumulations relative to long-term-normal were at least near normal for the region, with the exception of a small pocket in the north that graded to low.
Northern Region: In general, precipitation accumulations ranged from 30 to 40 mm along the northwestern and northern portions of the region to 10 to 20 mm range across most other parts of the region, with the exception of large pocket in the southeastern part of the region that received less than 10 mm range. The highest precipitation accumulations were recorded at the Atmore AGDM station (31.5 mm) in the central north, followed by Cold lake A station (30.0 mm) located in northeast, while the lowest accumulations were recorded at Wainwright A station (5.0 mm) in the east followed by Bodo AGDM station (5.6 mm) in the southeast corner. Precipitation accumulations relative to long-term-normal for the region gradually graded down from at least near normal conditions northeastern parts of the region to very low and extremely low accumulations in the southeastern part of the region.
Central Region: Precipitation accumulations ranged from 30 mm across the northwestern tip of the region to less than 10 mm across the rest of the region, with the exception of a small pocket in the 10 to 20 mm range, located in the east. The highest precipitation accumulations were recorded at Rocky Mtn House A station (31.6 mm) followed by the Battle River Headwaters station (29.7 mm), both found in the northwest corner of the region, and the lowest precipitation was recorded at Acadia Valley AGCM Station (2.7 mm) followed by Sedalia AGCM station (3.2 mm) both in the eastern part of the region. The accumulations relative to long-term-normal grade from near normal in the southwest and southeastern corners, to moderately low across most of the region, then to very low and extremely low in the northeastern part of the region.
Southern Region: In general, precipitation accumulations rapidly graded down from 30 to 40 mm in southwestern and southeastern corners of the region to less than 10 mm across most of the region. The highest precipitation accumulations were recorded at Onefour CDA station (31.6 mm) in the southeast, followed by Prairie Bluff station (28.2) in southwestern corner, while the lowest accumulations were recorded at Shuller AGCM station (3.3 mm) in the east, followed by Barons AGCM station (4.5 mm) located in the central western portion of the region. Precipitation accumulations relative to long-term-normal varied from at least near normal across most of the region to moderately low in the northeastern part of the region.
Cold Season Precipitation Accumulations relative to Long-Term-Normal (1961 - 2005) (Figure 2)
Cold Season precipitation (Oct 1 to March 31) accumulations relative to long-term-normal, to date, are extremely low to very low along the border between the Northern and Central Regions. Accumulations range from low to moderately low across much of the Northern, Central and Southern Regions and are at least near normal across most of the Peace Region and the north-western parts of the North Region, including and two pockets in the Central Region and a large corridor running through the Southern Region that extends along from the north west to the south east.
Peace Region: Across most of the Peace Region, Cold Season precipitation accumulations are near normal with the exception of two isolated pockets in the northern and southern parts of the region that have moderately low accumulations.
Northern Region: Cold season precipitation accumulations in the region generally, grade from at least near normal across the western and northern parts of the region, to large pockets of very low and extremely low accumulations across the south-central and southwestern parts of the region.
Central Region: Cold season precipitation accumulations in the region rapidly graded up from very low and extremely low accumulations in central north and northeastern portions of the region to moderately low accumulations across most of the region with near normal accumulations found only across the extreme the southwestern and southeastern corner of the region.
Southern Region: Cold season precipitation accumulations across the region range from near normal across a long northwest to southeast trending corridor that runs through the center of the region, and then graded down to low and very low accumulations across the west and north eastern parts of the region.
Average Precipitation Accumulations for January (Figure 3)
February is typically the driest month in Alberta, receiving only about 3.5 percent of the annual precipitation. During this month precipitation totals range from 10 to 20 mm across most of the province, with the exception of a large area in the southeastern part of the Central Region that typically receives less than 10 mm. Areas that typically get more precipitation include parts of the Peace Region with 20-30 mm, and parts of the foothills in the Southern Region that receive up to 40-50 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: SWEs graded down from 70 to 80 mm across the extreme northwestern, eastern and southeastern parts of the region to 40 to 70 mm across most other parts of the region with the exception of a pocket in the north where SWEs are estimated to be 30 to 40 mm. The snow pack accumulations relative to long term normal are generally near normal to moderately high, with the exception of a small pocket in the north that grades to moderately low.
Northern Region: SWEs graded from 30 to 60 mm range along the northern and extreme northwestern parts of the region to 20 to 30 mm across most other parts of the region, with the exception of the southeastern parts of the region where only about 10 to 20 mm of SWE are estimated to reside. The snow pack accumulations relative to long term normal vary from at least near normal in the north to at least moderately low across most of the region with the lowest accumulations relative to normal found in the south east were they are classified as extremely low.
Central Region: SWEs graded from 20 to 30 mm in the west and southeastern portions of the region to 10 to 20 mm across the rest of the region, with the exception few pockets with less than 10 mm. The snow pack accumulations relative to long term normal graded from at least near normal in the southwest and southeast to a large pocket of very low and extremely low in northeastern parts of the region.
Southern Region: SWEs varied from 30 to 60 mm along the foothills and the southeast corner of the region and then grade to 20 to 30 mm in the center and northwest and finally down to 10 to 20 mm across the north and northeastern parts of the region. Snow pack accumulations relative to long term normal across most of the region are at least near normal with the exception of the northeastern parts of the region where they are moderately low.
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 and Rural Development (ARD) 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 ARD, 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 Accumulation - Frequency of Occurrence
Precipitation accumulation, 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 1
· Cold Season to date- Starting October 1
Selected maps from this series are included in this report.
Precipitation accumulations for each period are then determined by ranking the precipitation accumulation during similar 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 accumulation 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 if 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
Alberta Agriculture and Rural Development
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph (780) 427-3556
This report was created on February 12, 2009.
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 December 31, 2008. |
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