IntermtntClimateSummaryJune2006 - Laserfiche WebLink

Home Browse Search

INTERMOUNTAIN WEST CLIMATE SUMMARY, JUNE 2006 Preci pitation Outlook July - September 2006 Source: NOAA Climate Prediction Center Summer seasonal precipitation forecasts, issued June 15th by the NOAA Climate Prediction Center (CPC), have changed little since the May forecast. The Intermountain West has "equal chanc- es" of above-average, near-normal or belo\v-average precipitation for the June 2006 and June-August forecasts period (Figure lla and 11 b). According to CPC, there are no significant skillful indi- cations for June precipitation anomalies from the forecast tools. The monsoon is one of the features that affects summer precipi- tation in parts of the Intermountain West. According to the NWS Weather Forecast Office in Grand Junction, the monsoon generally begins around the second week of July for western Colorado and eastern Utah. A high pressure area usually "breaks away" from the main Pacific ridge and settles in over the Great Basin by June, bringing hot temperatures during June and early July. As this high pressure Center moves eastward across the Continental Divide and into the Central Plains, a slightly cooler but much more moist environment \vill prevail in the south\vest flow behind the high. In most years, the monsoon is over by the end of August, but can last as late as October. Many areas in south\vest Colorado and southeast Utah experience a secondary precipitation maximum in October due to late-season tropical storm moisture carried north- \vard by the monsoonal flo\v. Monsoon start date is determined \vhen the average daily de\vpoint in Tucson, AZ is 540 F or greater for "3" consecutive days. Statistics on monsoon starts are: latest start, July 25, 1987; earliest start, June 17, 2000; average start: July 3rd. Last year's start \vas relatively late, July 18, 2005. To track the monsoon see the NWS/Weather Forecast Office in Tucson's Figure 11 a. Long-lead national precipitation forecast for June 2006. (released May 18, 2006) A = Above . 40.0-49.90/0 D 33.3-39.90/0 monsoon page: http://wW\v. wrh.noaa. gov /twc/monsoon/de\v- point_tracker. php. Notes The seasonal precipitation outlook in Figures 11 a-b pre- dicts the likelihood (chance) of above-average, near-average, and below-average precipitation, but not the magnitude of such variation. The numbers on the maps refer to the percent chance that precipitation will be in one of these three catego- ries, they do not refer to inches of precipitation. The NOAA-CPC outlooks are a 3-category forecast based largely on the status of EI Nino and recent trends. As a start- ing point, the 1971-2000 climate record for each particular 1 or 3 month period is divided into 3 categories or terciles, each with a 33.30/0 chance of occurring. The middle tercile is considered the near-average (or normal) precipitation range. The forecast indicates the likelihood of the precipitation being in one of the wetter or cooler terciles--above-average (A) or below-average (B)--with a corresponding adjustment to the opposite category; the near-average category is preserved at 33.30/0 likelihood, unless the anomaly forecast probability is very high. Thus, using the NOAA-CPC temperature outlook, areas with light brown shading display a 33.3-39.90/0 chance of above-average, a 33.30/0 chance of near-average, and a 26.7- 33.30/0 chance of below-average temperature. A shade darker brown indicates a 40.0-50.00/0 chance of above-average, a 33.30/0 chance of near-average, and a 16.7-26.60/0 chance of below-average temperature, and so on. Equal Chances (EC) indicates areas for which the models cannot predict the temperature with any confidence. EC is used as a "default option" representing equal chances or a 33.30/0 probability for each tercile indicating areas where the reliability (i.e., 'skill') of the forecast is poor. Figure 11 b. Long-lead national precipitation forecast for Jun. - Aug. 2006. (released May 18, 2006) B = Below . 40.0-49.90/0 D 33.3-39.90/0 EC = Equal Chances On the Web - For more information and the most recent CPC forecast images, visit: http://www.cpc.ncep.noaa.gov/products/predictions/ multi_season/13_seasonal_outlooks/color/churchill.html. 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/c1imate/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/CLlMATEDATA.html. FORECASTS 11 4