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12/13/2018, 9:11 am EST

AG Hot Spot: More Heavy Rain Argentina

Discussion: The next heavy rain event is developing along a war, front in northeast Argentina this time centered between Rosario and Buenos Aires (Fig. 1). The outlook indicates this thunderstorm complex will expand today/tonight along the warm front and deposit several to 5+ in. of rain north of Rosario and east of Cordoba (Fig. 2). The rainfall event ends tomorrow. Fig. 1: Another thunderstorm complex is forming along a warm front in northeast Argentina. More showers and thunderstorms stretch across northern Argentina along a cold front although no excessive rainfall is indicated. The next heavy rain event is forecast for Sunday/Monday as an ocean fetch across a low pressure trough causes several in. of rain in northern Uruguay and northeast Argentina. That event lifts north into eastern Paraguay to southeast Brazil next Tuesday. The pattern goes dry for a few days followed by another excessive rainfall event affecting all of northern Argentina in the 11-15 day period (Fig. 3). Fig. 2-3: The GFS OP identifies a heavy rain event over the next 2 days in northeast Argentina (left). More heavy rain is forecast in the 11-15 day period (right).      
12/13/2018, 8:15 am EST

U.S. Medium-range Forecast

Highlight: Very warm outlook followed by reluctant cold (which will be reliant on returning snow cover). Chart of the Day: Comparing extended-range upper air forecasts by GFS Discussion: The GFS OP from overnight indicated a “polar vortex” cold event across the East U.S. on Christmas Day (left). The just-received GFS OP offers the opposing solution featuring a warm ridge in the East on Dec. 27th (right). Obviously, forecast confidence is low in the Holiday period thermal pattern. The model is struggling as to whether stratospheric warming over northwest Canada is positioned correctly to ignite excessive cold. Medium-range 6-10 Day Forecast Valid Dec. 18-22, 2018 Medium-range 11-15 Day Forecast Valid Dec. 23-27, 2018 Discussion: The super-warm 6-10 day forecast erases snow cover. That’s a concern for extended-range cold forecasts. Lack of snow cover will bias the climate warm especially in an evolving El Nino climate. The 11-15 day forecast is cold in Canada stretching to New England but forecast confidence is lower. Extended-range 16-20 Day Forecast Valid Dec. 28, 2018-Jan. 1, 2019 Discussion: Cold is farther north; warmer trend South. %Normal Precipitation Forecast for Medium-range using the ECM ENS Discussion: The 06Z GFS OP day 6-10 and day 11-15 snowfall forecast is indicated. Regenerating snow cover is required to allow any important cold to return to the U.S. The forecast indicates marginal increase for Interior Northeast snow cover in the 11-15 day period (also including the southeast quadrant of Canada). There is increasing support for cold into the Northeast U.S. in the 11-15 day period but not overwhelming.
12/12/2018, 8:59 am EST

Russia Week 2-4 Outlook

Highlight: Persistent colder than normal. Dec. 2-8, 2018 temperature anomaly/precipitation amount Discussion: Last week was temperate although colder-than-normal in southwest Ukraine. Widespread light snowfall was observed across most of southwest and west portions of Russia. Northwest Russia was milder than normal. Week 2 Ahead: December 16-22, 2018 Comment: A cold pattern settles over Southwest Russia although not pure arctic air. A swath of snow is likely east of the Black Sea and heavy amount is possible. Most of Western Russia to Ukraine is dry. Week 3 Ahead: December 23-29, 2018 Comment: Stratospheric warming episode triggers an arctic air mass across Central Russia which extends westward accompanied by no precipitation. Week 4 Ahead: December 30, 2018-January 5, 2019 Comment: The intense cold associated with deep arctic air eases but a colder than normal regime persists.
12/12/2018, 8:46 am EST

Australia Week 2-4 Outlook

Highlight: Expected Dryness/Anomalous Heat. Dec. 2-8, 2018 temperature anomaly/precipitation amount Discussion: A warmer than normal week across most of Australia with very dry weather northwest and central to southeast sections. Heavy rain occurred over the northeast Queensland drought area. Week 2 Ahead: December 16-22, 2018 Comment: Forecast models vary with GFS very hot and ECM less so…the forecast is a consensus of the 2 lead models. Most of the continent is dry except showers and thunderstorms along the East Coast. Week 3 Ahead: December 23-29, 2018 Comment: The East Coast is agreed upon by all models maintaining a tropical shower/thundershower risk suppressing heat. Elsewhere dryness and heat are dominant. Week 4 Ahead: December 30, 2018-January 5, 2019 Comment: Hot and dry weather covers most of the continent except thundershowers on the north coast. Unexpected Wet November 2018 Comment: Excessive rainfall which was unexpected given +IOD and developing El Nino unloaded on mainly Southwest Australia during November. The culprit was a semi-permanent upper trough extending to the north from offshore Antarctica. A similar deep upper trough was located southeast of South America.