Notes and Weblinks for IWCS Information Sources

Recent Conditions: Notes and Web Links

The monthly average temperature and precipitation maps are derived from measurements at individual meteorological stations and interpolating (estimating) values between known points to produce continuous categories. Interpolation procedures can cause incorrect values in data-sparse regions. These maps are experimental products from the High Plains Regional Climate Center (temperature) and the NOAA’s Earth System Research Laboratory (precipitation). These data are considered experimental because they utilize the most recent data available, which have been subject to minimal quality control.

In the departure from average temperature map, average refers to the arithmetic mean of annual data from 1971–2000. In the percent of average precipitation map, average refers to the arithmetic mean of annual data from 1995–2010. This period of record is only 15 years long because it includes SNOTEL data, which was included in this dataset beginning in 1995.

* For temperature and precipitation maps, and for maps of other climate variables including individual station data, visit:
http://www.hprcc.unl.edu/maps/current/.
* For information on temperature and precipitation trends, visit: http://www.cpc.ncep.noaa.gov/trndtext.shtml.
* For a list of weather stations in Colorado, Utah, and Wyoming, visit: http://www.wrcc.dri.edu/summary.
* For information on past precipitation trends, visit: http://www.hprcc.unl.edu/products/current.html.
* For precipitation maps, which are updated daily visit: http://www.cdc.noaa.gov/Drought/.
* For National Climatic Data Center monthly and weekly precipitation and drought reports for Colorado, Utah, Wyoming, and the whole U. S., visit: http://lwf.ncdc.noaa.gov/oa/climate/research/monitoring.html.
* For a list of weather stations in Colorado, Utah, and Wyoming, visit: http://www.wrcc.dri.edu/index.html.

The SPI is an index based on the probability of recording a given amount of precipitation, and the probabilities are standardized so that an index of zero indicates the median precipitation amount (half of the historical precipitation amounts are below the median, and half are above the median). NOAA National Climatic Data Center (NCDC) computes the SPI for several time scales, ranging from one month to 24 months, to capture the various scales of both short-term and long-term drought. An index value of -1 indicates moderate drought severity and means that only 15% would be expected to be drier. An index value of -2 means severe drought with only 2.5% of years expected to be drier, etc. The SPI maps are from the Western Regional Climate Center, which uses data from the NCDC and NOAA Climate Prediction Center.

* For information on the SPI, how it is calculated, and other similar products for the entire country, visit: http://www.wrcc.dri.edu/spi/spi.html.
* For SPI products directly form the NCDC, visit: http://lwf.ncdc.noaa.gov/oa/climate/research/prelim/drought/spi.html. These maps use the same data as in the IWCS figures, but the categories are defined slightly differently.

The U. S. Drought Monitor and the Drought Monitor discussion are based on expert assessment of variables including (but not limited to) the Palmer Drought Severity Index, soil moisture, streamflow, precipitation, and measures of vegetation stress, as well as reports of drought impacts. It is a joint effort of several agencies. The U. S. Drought Monitor is released weekly (every Thursday) by the National Drought Mitigation Center, and it represents data collected through the previous Tuesday. The inset (lower left) shows the western United States from the previous summary’s map.

* For the most recent Drought Monitor, released every Thursday, visit: http://www.drought.unl.edu/dm/monitor/html. This site also includes archives of past drought monitors.
* Drought Impact Reporter (National Drought Mitigation Center): http://droughtreporter.unl.edu/.
* NIDIS Drought Portal: http://www.drought.gov.

Snowpack: Notes and Web Links

Snow water equivalent (SWE) or snow water content (SWC) refers to the depth of water that would result by melting the snowpack at the measurement site. Snowpack telemetry (SNOTEL) sites are automated stations operated by NRCS that measure snowpack. In addition, SWE is measured manually at other locations called snow courses. SWE is determined by measuring the weight of snow on a “pillow” (like a very large bathroom scale) at the SNOTEL site. Knowing the size of the pillow and the density of water, SWE is then calculated from the weight measurement. Given two snow samples of the same depth, heavy, wet snow will yield a greater SWE than light, powdery snow. SWE is important in predicting runoff and streamflow.

* For a monthly summary of snowpack conditions and streamflow forecasts for the western U.S. from the NRCS National Water and Climate Center, visit: http://www.wcc.nrcs.usda.gov/cgibin/westsnowsummary.pl
* For graphs visit: http://www.wcc.nrcs.usda.gov/gis/snow.html
-the basin-wide maps come out once a month; they are the % of Normal link under “SNOTEL & snow course snow water equivalent”
-the point maps (triangles) are updated daily and are the % of Normal link under “SNOTEL Snow Water Equivalent”
* For State Basin Outlook Reports, visit: http://www.wcc.nrcs.usda.gov/cgibin/bor.pl and select the state from the dropdown menu.
* For Surface Water Supply Index (SWSI) maps, visit: http://www.wcc.nrcs.usda.gov/wsf/swsi.html

Streamflow: Notes and Web Links

The streamflow forecast graphic (Figure STRM-1) shown in the October through May editions of the Summary is from the NRCS, but the forecast is a collaborative effort between the NRCS and the NOAA River Basin Forecast Centers. Forecasts of natural runoff are based principally on measurements of precipitation, snow water equivalent, and antecedent runoff, influenced by precipitation in the fall before winter snowfall. Forecasts become more accurate as more of the data affecting runoff are measured (i.e., accuracy increases from January to May). In addition, these forecasts assume that climatic factors during the remainder of the snow accumulation and melt season will have an average affect on runoff. Early season forecasts are, therefore, subject to a greater change than those made on later dates.

* For State Basin Outlook Reports, visit: http://www.wcc.nrcs.usda.gov/cgibin/bor.pl and select the state from the dropdown menu.
* For a monthly summary of snowpack conditions and streamflow forecasts for the western U.S. from the NRCS National Water and Climate Center, visit: http://www.wcc.nrcs.usda.gov/cgibin/westsnowsummary.pl
* The official NOAA streamflow forecasts are available through the following websites of individual River Forecast Centers:
- Colorado Basin (includes Great Basin): http://www.cbrfc.noaa.gov/
- Missouri Basin (includes South Platte and North Plate: http://www.crh.noaa.gov/mbrfc/
- West Gulf (includes Rio Grande): http://www.srh.noaa.gov/wgrfc/
- Arkansas Basin: http://www.srh.noaa.gov/abrfc/
* For more information about NRCS water supply forecasts based on snow accumulation and access to the graph on this page, visit: http://www.wcc.nrcs.usda.gov/wsf/.
* NOAA/NWS River Basin Forecast Centers in the Western U.S. have a collaborative and interactive website that shows streamflow forecasts as inputs to reservoirs: http://www.nwrfc.noaa.gov/westernwater/.

Reservoir Supply: Notes and Web Links

The size of each “tea-cup” is proportional to the size of the reservoir, as is the amount the tea-cup is filled. The first percentage shown in the table is the current contents divided by the total capacity. The second percentage shown is the current contents divided by the average storage for this time of year (not shown). Reservoir status is updated at different times for individual reservoirs.

* For current storage, average storage, and capacity data for reservoirs in the Great Plains region of the Bureau of Reclamation (Boysen, Buffalo Bill, Lake Granby, Pueblo, Seminoe, Turquoise): http://www.usbr.gov/gp/hydromet/teacup_form.cfm or http://www.usbr.gov/gp/hydromet/hydromet_arcread.cfm
* For current storage, average storage, and capacity data for reservoirs in the Upper Colorado region of the Bureau of Reclamation (Blue Mesa, Flaming Gorge, Fontenelle and Lake Powell): http://www.usbr.gov/uc/water/rsvrs/ops/r40day.html
* For operating information about Bureau of Reclamation Upper Colorado River reservoirs: http://www.usbr.gov/uc/.
* For current storage, average storage, and capacity data for reservoirs that are not operated by Reclamation (Bear Lake, Dillon, Strawberry and Utah Lake), use Basin-wide Reservoir Summaries from NRCS: http://www.wcc.nrcs.usda.gov/wsf/reservoir/resv_rpt.html
* For reservoir inflow forecasts as well as current data use one of these:
-- Water Resource Forecasts from NOAA/NWS (updated monthly between January and June): http://www.nwrfc.noaa.gov/westernwater/.
-- State Basin Outlook Reports from NRCS (updated monthly between January and June): http://www.wcc.nrcs.usda.gov/cgibin/bor.pl.
-- Water Supply Outlook Publications for the Colorado and Eastern Great Basins from the NOAA/NWS Colorado Basin River Forecast Center (updated monthly between January and June): http://www.cbrfc.noaa.gov/wsup/wsup.cgi.

ENSO: Notes and Web Links

The SST anomaly graphics from NOAA (Figure ENSO-1) show observed SST (upper) and SST anomalies (lower) in the Pacific Ocean, averaged over a recent 7-day period. Data are from satellite observations and the NOAA TAO array of 70 moored buoys spread out over the Pacific Ocean, centered on the equator. The buoys measure temperature, currents, and winds and transmit data in real-time.  NOAA uses these observations to predict short-term (a few months to one year) climate variations.     

The ENSO "Model Forecasts" graph (Figure ENSO-2) shows a spread of forecasts SST in the Niño 3.4 region for nine overlapping 3-month periods. “Niño 3.4” refers to the region of the equatorial central Pacific from 120°W to 170°W and 5°N to 5°S, which is used as an SST-based index for defining ENSO.  Abbreviations represent groups of three months.

* For a technical discussion of current El Niño conditions, visit the ENSO Diagnostic Discussion, a collaborative effort of the several parts of NOAA, including the research labs, the IRI, and other institutions funded by NOAA: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ (updated on the second Thursday of the month).
* For updated graphics of SST and SST anomalies, visit this site and click on “Weekly SST Anomalies”: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml#current.
* For more information about El Niño, including the most recent forecasts, visit: http://iri.columbia.edu/climate/ENSO/currentinfo/SST_table.html. The “forecast plume” showing multiple model projections is updated on the third Thursday of the month.
* The Multivariate ENSO Index is available at: http://www.cdc.noaa.gov/people/klaus.wolter/MEI/.

Temperature Outlook: Notes and Web Links

The NOAA CPC seasonal temperature outlooks (Figures TEMP-1 through TEMP-4) forecast the likelihood (percent chance) of temperatures occurring in the above-average, near-average, and below-average categories.  The numbers on the maps do not refer to actual temperature values, but to the probability, in percent, that temperatures will be in one of these three categories. The skill of the temperature outlooks largely comes from the status of ENSO and recent trends.  The categories are defined based on the 1971–2000 climate record; each 1- or 3-month period is divided into 3 categories (terciles), indicating the probabilities that the temperature in the period will fall into the upper third of the years (upper tercile), the middle third of the years (middle tercile, or around average), or the lowest third of the years (lower tercile). 

The forecast map depicts the probability that temperature will be in the above-average (A, orange shading) or below-average (B, blue shading) tercile--with a corresponding decrease in the opposite category. The near-average category is preserved at 33.3% likelihood, unless the anomaly forecast probability is very high for the above- or below-average tercile, or a near-average forecast is more likely than the other two categories. Thus, areas with dark brown shading indicate a 40.0–50.0% chance of below-average, a 33.3% chance of near-average, and a 16.7–26.6% chance of above-average precipitation. Light brown shading displays a 33.3–39.9% chance of below-average, a 33.3% chance of near-average, and a 26.7–33.3% chance of above-average precipitation and so on. Equal Chances (EC) represents equal chances or a 33.3% probability for each tercile, indicative of areas where signals are weak or conflicting and the reliability (i.e., ‘skill’) of the forecast is poor. “N” indicates an increased chance of near-average conditions, but is not forecast very often.

* For more information and the most recent forecast images, visit: http://www.cpc.ncep.noaa.gov/products/predictions/90day/. Please note that this website has many graphics and may load slowly on your computer.
* The CPC “discussion for non-technical users” is at: http://www.cpc.noaa.gov/products/predictions/90day/fxus05.html.
* For IRI forecasts, visit: http://iri.columbia.edu/climate/forecast/net_asmt/.
* More information about temperature distributions at specific stations in Colorado, Utah, Wyoming, and across the West can be found at the Western Regional Climate Center, http://www.wrcc.dri.edu/CLIMATEDATA.html

Precipitation Outlook: Notes and Web Links

The NOAA CPC seasonal precipitation outlooks (Figures PPT-1 through PPT-4) forecast the likelihood (percent chance) of precipitation occurring in the above-average, near-average, and below-average categories.  The numbers on the maps do not refer to actual precipitation values, but to the probability in percent that precipitation will be in one of these three categories. The categories are defined based on the 1971–2000 climate record; each 1- or 3-month period is divided into 3 categories (terciles), indicating the probabilities that the precipitation in the period will fall into the upper third of the years (upper tercile), the middle third of the years (middle tercile, or around average), or the lowest third of the years (lower tercile), each with a 33.3% chance of occurring. The middle tercile is considered the near-average (or normal) precipitation range. 

The forecast map depicts the probability of precipitation occurring in the below-average (B, brown shading) or above-average (A, green shading) tercile --with a corresponding decrease in the opposite category, The near-average category is preserved at 33.3% likelihood, unless the anomaly forecast probability is very high. Thus, areas with dark brown shading indicate a 40.0–50.0% chance of below-average, a 33.3% chance of near-average, and a 16.7–26.6% chance of above-average precipitation. Light brown shading displays a 33.3–39.9% chance of below-average, a 33.3% chance of near-average, and a 26.7–33.3% chance of above-average precipitation and so on. Equal Chances (EC) represents equal chances or a 33.3% probability for each tercile, indicative of areas where signals are weak or conflicting and the reliability (i.e., ‘skill’) of the forecast is poor. “N” indicates an increased chance of near-average conditions, but is not forecast very often.

The NOAA PSD experimental guidance for seasonal future precipitation (Figure PPT-5, and PPT-6 when available) is only shown in IWCS issues in January, March, July, and October. It depicts the shift in tercile probabilities for precipitation in the 3-month season shown. In order to be indicated on this map, a forecast tilt in the odds has to reach at least 3% either towards wet (above-average), dry (below-average), or near-normal (average). Shifts towards the wettest (driest) tercile are indicated in green (red), and are contoured in 5% increments, while near-normal tilts of at least 3% are indicated by the letter “N”. Shifts over 10% considered significant. Positive (negative) shifts between three and five percent are indicated by a green (red) plus (minus) sign, while minor shifts of one or two percent are left blank in this display.

* For more information and the most recent CPC forecast images, visit: http://www.cpc.ncep.noaa.gov/products/predictions/90day/. Please note that this website has many graphics and may load slowly on your computer.
* The CPC “discussion for non-technical users” is at: http://www.cpc.noaa.gov/products/predictions/90day/fxus05.html.
* For IRI forecasts, visit: http://iri.columbia.edu/climate/forecast/net_asmt/.
* More information about precipitation distributions at specific stations in Colorado, Utah, Wyoming, and across the West can be found at the Western Regional Climate Center, http://www.wrcc.dri.edu/CLIMATEDATA.html.
* The PSD experimental guidance product, including a discussion and executive summary, is usually updated by the 3rd Friday of each month, and is available on the web at:
http://www.esrl.noaa.gov/psd/people/klaus.wolter/SWcasts/

Seasonal Drought Outlook: Notes and Web Links

The Seasonal Drought Outlook (DO) depicts general, large-scale trends from that date through the end of the forecast period (3 to 3.5 months, depending on the date of issue).  The delineated areas in the DO are defined subjectively based on expert assessment of numerous indicators described above, including outputs of short- and long-term forecasting models, as well as consideration of the typical seasonal cycle (it is easier to come out of a drought during the wettest time of year, just as it is easier to worsen a drought situation during that time of year, depending on its moisture anomalies). Areas of continuing drought are schematically approximated from the Drought Monitor (D1 to D4). For weekly drought updates, see the latest Drought Monitor text on the website (updated weekly) see: http://www.drought.unl.edu/dm/monitor.html.  NOTE: The green improvement areas imply at least a 1-category improvement in the Drought Monitor intensity levels, but do not necessarily imply drought elimination.

* For more drought information, visit: http://www.drought.noaa.gov/.
* Forecasts of drought termination probabilities can be found at: http://www.ncdc.noaa.gov/oa/climate/research/drought/current.html.