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10/18/2018, 10:50 am EDT

Hot spot: NOAA/CPC Longlead Climate Forecasts for the U.S.

NOAA Probabilistic Climate Forecasts Discussion: The monthly long-lead probability climate forecasts issued by NOAA/CPC were released this morning. The primary contributor the winter/spring ahead forecast is ENSO. NOAA/CPC continues to forecast El Nino within 2 months but a weak event is expected making traditional El Nino/winter climate relationships less reliably forecast. NOAA/CPC identifies above normal snowfall across eastern Canada into October as a contributor to the late 2018 climate pattern. Fig. 1: The CPC/IRI ENSO probability forecast through MAY/JUN/JUL 2018. November 2018: The warm outlook is STRONGLY biased by warm tropical and non-tropical SSTA in the East Pacific and off the East Coast of the U.S. The wet pattern across the South and East U.S. is caused by approaching El Nino onset. Above normal snow cover across Eastern Canada leading into November will need to retreat for this warm forecast to verify. If the snow cover remains a colder scenario is likely for the Great Lakes to the Mid-South U.S. Fig. 2-3: The November 2018 temperature/precipitation probabilistic climate forecast for the U.S. issued by NOAA/CPC. Meteorological winter (DEC/JAN/FEB 2018-19): The outlook is biased by an El Nino climate and also warm SSTA into the northeast North Pacific. The result is warmer than normal climate across much of the U.S. An upper ridge pattern is favored in the West which leaves the East and particularly the Southeast States susceptible to an occasional cold upper trough. The precipitation forecast is a very typical El Nino amplified wet southern storm track. There are a lot of caveats here. First, warming of the northeast Pacific suggests emergence of the positive phase of the Pacific decadal oscillation. While this could happen there is no sign of this regime change yet. Second, the prediction of weak El Nino may be more related to the possibility of an El Nino episode with most of the East Pacific surface/subsurface ocean warming biased toward the Dateline rather than the northwest coast of South America. The caveats based on the PDO and Modoki-style ENSO potential is less warm Northwest and possibly colder East. Fig. 4-5: The DEC/JAN/FEB 2018-19 temperature/precipitation probabilistic climate forecast for the U.S. issued by NOAA/CPC. Meteorological spring (MAR/APR/MAY 2019): El Nino should linger into next spring. El Nino could be stronger than suggested. The NOAA/CPC outlook maintains an El Nino wet look in the Southeast U.S. while all but the Midwest to New England states is likely warmer than normal. Fig. 6-7: The MAR/APR/MAY 2019 temperature/precipitation probabilistic climate forecast for the U.S. issued by NOAA/CPC. Meteorological summer (JUN/JUL/AUG 2019): The summer 2019 outlook is almost exactly alike to the summer 2018 forecast with anomalous warmth just-about everywhere and wet climate across the Northeast. Fig. 8-9: The JUN/JUL/AUG 2019 temperature/precipitation probabilistic climate forecast for the U.S. issued by NOAA/CPC. Fig. 10: The seasonal drought outlook for the U.S. issued by NOAA/CPC. Seasonal (next 90 days) drought outlook: The NOAA/CPC seasonal drought outlook eliminates drought in the Southwest U.S. while maintaining drought in southern California and across the Great Basin. Drought eases on the Northwest Coast while the Columbia Basin stays dry.
09/27/2018, 1:21 pm EDT

Daily Feature: U.S. Winter 2018-19 Outlook

Colder than normal in the East arrives and departs with calendar winter Executive summary: The Climate Impact Company Winter 2018-19 Outlook is issued. The forecast is based on presence of weak El Nino with attendant oceanic warming biased toward the Dateline, susceptibility of a stronger than normal polar vortex to drop cold surges into the East followed by quick turn-arounds to a milder Pacific influence. By February the heat release of a cooling very (anomalous) warm  ocean surface east of New England causes a snowy pattern which enhances possible severe cold centered on the Mid-Atlantic States. California receives much needed rainfall during winter although the West averages warmer than normal. The forecast is made with below average confidence due to uncertainties in ENSO. Adjustments in the October update could be substantial depending on ENSO phase. CIC Temperature /Precipitation Anomaly Forecast for DJF 2018-19 November 2018: Onset of weak El Nino brought on by oceanic warming initiated by a western wind burst in the tropical Pacific during the mid-to-late warm season is expected. During this sequence increased Pacific influence on the U.S. climate pattern implies a warmer-than-normal regime. The anomalous warmth is likely most focused in central continent south of a strong polar vortex confined to the polar latitudes. The increased maritime influence of the Pacific cools the Western U.S. and energizes a southern latitude storm track causing above normal rainfall across Texas. Occasionally, cooler air masses extend south into the eastern U.S. following an active storm track through the Carolinas. Above normal southern Canada snow cover generated in October will retreat leaving bare ground also enhancing the Pacific warmth centered on North Dakota. Fig. 1-2: The CIC temperature and precipitation analog forecast for November 2018 is indicated. December 2018: The mild November pattern will continue through at least mid-December. A colder pattern change is likely mid-to-late month in the Central/East U.S. The warming influence of El Nino during late autumn is forecast to retreat somewhat as calendar winter begins. This process will allow the upper airflow to buckle and allow colder air masses from Canada to affect the U.S. Initially, these cold outbreaks are modified. However, southern Canada and the northern U.S. should regain snow cover later in the month allowing outbreaks of cold into the U.S. to reach farther south with intensity. During the colder transition expect an active storm track in the Southeast and East U.S. likely mostly rain with some snow likely in NY/New England. During the mild regime that begins the month California is wetter than normal. Fig. 3-4: The CIC temperature and precipitation analog forecast for December 2018 is indicated. January 2019: The susceptibility to cold air masses in Canada shifting south into the U.S. continues for mid-winter. During January 2 distinct weather patterns are likely. Timing of when each is present is difficult at this long-lead. During the Pacific pattern California is stormy with above normal precipitation while just upstream the mild Pacific air extends across much of the country. The second regime features a drier and warmer West U.S. ridge pattern in which downstream susceptibility to a polar vortex cold affects the East U.S. The Central/East temperature anomalies are the average between extreme warm and cold episodes. The January storm track likely features mainly snow from the Missouri Valley to the Northeast U.S. Florida is struck by at least 1 unusually cold event. Fig. 5-6: The CIC temperature and precipitation analog forecast for January 2019 is indicated. February 2019: In January snow cover is forecast to widen Midwest to Northeast U.S. (and possibly to the south). A strong cold outbreak (or 2) is indicated in February. The prime target is the Mid-Atlantic region. Implied is presence of deep snow cover. The concern is the exceptional warm SSTA off the New England coast entering the winter season finally cools to near normal mid-to-late winter after encountering offshore cold air flow. The heat release by the cooling ocean causes an energetic storm track occurring during the coldest part of winter justifying mostly snowfall episodes. The Snow and cold is not necessarily locked-in as with the 2013-14/2014-15 polar vortex winter seasons but choppy and extreme in character when they occur. The West U.S. is mostly dry and warm beneath a mean upper ridge pattern affecting much of North America. Typical of El Nino the storm track stretches across the entire far southern U.S. tilting northeastward on the East Coast. Fig. 7-8: The CIC temperature and precipitation analog forecast for February 2019 is indicated. March 2019: Although El Nino is weak and has an on-and-off influence on the U.S. climate pattern during the cold season a mature El Nino should be present by March. During mature El Nino the southern states are cool while the West Coast and Florida are stormy. Areas to the north are typically milder and drier than normal. Fig. 9-10: The CIC temperature and precipitation analog forecast for March 2019 is indicated. Population weight HDD forecasts for NOV-18 to MAR-19: The preliminary gas population weight HDD forecast for the U.S. for the 2018-19 cold season indicates warmer-to-near normal results versus the 30-year normal, coldest mid-to-late winter while the forecast is substantially colder than the 10-year normal. The CIC U.S. Cities HDD forecast (see CIC web site) indicates the NOV-MAR 2018-19 HDD forecast is 96.3% of the 30-year normal while the core winter months (DEC/JAN/FEB 2018-19) is 97.6% of the 30-year normal. The overall winter outlook is slightly warmer than normal BUT biased colder mid-to-late winter in the high energy demand areas of the East-Central and East U.S. Fig. 11: The CIC gas population weight U.S. HDD forecast by month for the cold season versus the 30-year normal. Fig. 12: The CIC gas population weight U.S. HDD forecast by month for the cold season versus the 10-year normal.