Global Precipitation & Temperature Outlook for December 2017

5 December 2017

OVERVIEW
The December Outlook indicates that Alaska is forecast to be warmer than normal, especially the western half of the state where temperatures are expected to be the hottest in 20 to 40 years. Malaysia, Indonesia, Papua, and New Zealand also stand out with intense hot anomalies predicted. Much wetter than normal conditions are forecast for northern Ukraine and across the border into the Don River Basin and parts of the Volga Basin in Russia.

PRECIPITATION OUTLOOK
The December precipitation forecast for North America is relatively benign, with some moderately drier than normal conditions in Canada along the southern shore of Hudson Bay and surrounding Ottawa and Montreal, and in southern Mexico's states of Michoacán and Guerrero. Wet anomalies are forecast for western Alaska, which could be severe on the Alaskan Peninsula.

Precipitation outlook. Reds indicate below normal monthly total precipitation. Blues indicate above normal monthly total precipitation. The darker the color, the more extreme the anomaly relative to a 1950-2009 climatic baseline. Colors are based on… — Precipitation outlook. Reds indicate below normal monthly total precipitation. Blues indicate above normal monthly total precipitation. The darker the color, the more extreme the anomaly relative to a 1950-2009 climatic baseline. Colors are based on the expected return period of the anomalies.

In South America a wide band of wet anomalies is expected in the middle of the continent from central Bolivia through northern Paraguay and eastward across Brazil to the Atlantic, and may be severe in south-central Bolivia and eastern Matto Grosso do Sul, Brazil. A large pocket of moderate to severe wet anomalies is also forecast encompassing La Pampa Province, Argentina. Wet anomalies of generally lesser intensity are forecast for eastern Ecuador and pockets in northern Colombia and Venezuela. An arc of dry anomalies reaching extreme intensity is forecast in southwestern Bolivia reaching into Argentina. Dry conditions of similar severity are also forecast in northeastern Colombia along the Meta River. Moderate to severe dry anomalies are forecast for Brazil's southernmost state of Rio Grande do Sul, with moderate conditions in nearby areas of Uruguay and Argentina.

Central Europe should be moderately wetter than normal, but a bit farther east wet anomalies may reach extreme or even exceptional intensity in northern Ukraine and across the border into the Don River Basin and parts of the Volga Basin in Russia.

Few significant precipitation anomalies are forecast for Africa.

Some moderate dry anomalies are expected in pockets of the Middle East, particularly northern Saudi Arabia and Iran. Primarily moderate dry anomalies are forecast for a vast expanse of eastern China including the North China Plain, and in Russia west of the Sea of Okhotsk. Dry anomalies of greater severity are expected in southern Japan.

Coastal Bangladesh is forecast to be exceptionally wetter than normal as will nearby regions of India and into Myanmar.

In Australia, wet anomalies of varying severity are forecast for the Gascoyne region of Western Australia, the Murray-Darling Basin in the southeast, and Queensland's central coast.

TEMPERATURE OUTLOOK
In North America, Alaska is forecast to be warmer than normal, especially the western half of the state where temperatures are expected to be the hottest in 20 to 40 years. Across the border into Canada's Yukon Territory moderate to extreme warm anomalies are forecast. Moderately warmer than normal temperatures are forecast for the US Southwest and Southern Rockies. In Mexico exceptionally hotter than normal temperatures are forecast surrounding Puerto Vallarta, while warm anomalies of lesser intensity are expected in north-central Mexico, Baja, and in the south from Chiapas through the Yucatan Peninsula. Some warm anomalies are forecast in Central America and may be more intense in southern Guatemala.

Temperature outlook. Reds indicate above normal monthly average temperature. Blues indicate below normal monthly average temperature. The darker the color, the more extreme the anomaly relative to a 1950-2009 climatic baseline. Colors are based… — Temperature outlook. Reds indicate above normal monthly average temperature. Blues indicate below normal monthly average temperature. The darker the color, the more extreme the anomaly relative to a 1950-2009 climatic baseline. Colors are based on the expected return period of the anomalies.

Moderate to severe warm anomalies are forecast across northern South America, particularly Brazil. Western Bolivia is forecast to be much warmer than normal, while slightly cooler than normal conditions are forecast for eastern Bolivia, Paraguay, and across the borders into Brazil.

Central Africa - CAR, South Sudan, and southwestern Ethiopia - are forecast to be cooler than normal. Warm anomalies are expected in West Africa and around the the Gulf of Guinea, especially in southern Cote d'Ivoire, where anomalies may be especially intense. Warm anomalies of varying severity are expected in the Horn of Africa which may be extreme in eastern Ethiopia. Madagascar will be moderately warmer than normal and similar conditions are expected in pockets across southern Africa.

A vast expanse of warmer than normal temperatures is forecast for Russia surrounding the Ural Mountains - where anomalies may reach exceptional severity - and trailing southwest through eastern Ukraine. Severe to exceptional hot anomalies are forecast for many parts of western China, including northern Xinjiang into Mongolia, and from the Tibetan Plateau down through India's far northeastern states and western Myanmar. Warm anomalies are also forecast for northern Pakistan; Jammu and Kashmir, India; and much of India's southern half.

Malaysia, Indonesia, and Papua are all forecast to be much warmer than normal and these extreme anomalies will reach into far northern Australia around the Gulf of Carpentaria. Exceptionally warmer than normal conditions are expected throughout New Zealand, with slightly less intense anomalies in Tasmania.

NOTE ON ADMINISTRATIVE BOUNDARIES
There are numerous regions around the world where country borders are contested. ISciences depicts country boundaries on these maps solely to provide some geographic context. The boundaries are nominal, not legal, descriptions of each entity. The use of these boundaries does not imply any judgement on the legal status of any territory, or any endorsement or acceptance of disputed boundaries on the part of ISciences or our data providers.

ABOUT THIS BLOG POST
Each week, ISciences processes an ensemble of 28 seasonal temperature and precipitation forecasts issued by the National Oceanic and Atmospheric Administration's Climate Forecast System Version 2 (CFSv2). We present our results in a proprietary weekly report titled Global Water Monitor and Forecast: Precipitation and Temperature Outlook. This blog post summarizes our Outlook released December 4, 2017 which includes forecasts for December 2017 through August 2018 based on NOAA CFSv2 forecasts issued November 24 through November 30, 2017.

Technical details:

Each CFSv2 forecast is bias corrected by:
- Constructing probability density functions from CFSv2 hindcasts.
- Fitting the hindcast probability distribution functions to a generalized extreme value distribution.
- Using an inverse lookup to an extreme value distribution fitted to the observed temperature and precipitation record (Fan & van den Dool 2008, Chen et al. 2002).
The map colors depict the return period of the median forecast anomaly.
Regions where the interquartile range of the ensemble spans both above normal and below normal conditions are hashed as having uncertain direction.
Regions where the interquartile range of the ensemble divided by the median forecast is large (>0.4) are hashed as having uncertain magnitude.
Results are reported in terms of return period using a 1950-2009 baseline.