CPC says we not cold
6-10 DAY OUTLOOK FOR DEC 08 - 12 2022
Model solutions remain consistent that high latitude blocking develops over theNorthern Hemisphere early in December, consistent with a negative phase of theArctic Oscillation (AO). A very strong blocking ridge is forecast to retrogradewestward from the North Atlantic to Greenland during the first ten days ofDecember, resulting in a west-based negative North Atlantic Oscillation (NAO).Near normal temperatures are favored for the Great Lakes, Northeast, andMid-Atlantic since dynamical models have backed off on the magnitude ofanomalous cold shifting southward from Canada and statistical tools lean warmerfor the East. Likewise, dynamical models are less robust with anomalous coldspreading south of the 40th parallel and positive 500-hPa height anomaliesincrease probabilities for above-normal temperatures across the south-centraland southeastern CONUS. Surface high pressure, with anomalous cold, is forecastto remain centered over the Great Basin, which favors below-normal temperaturesthroughout much of the West.A more amplified 500-hPa trough over the West led to a wetter forecast todaycompared to the previous 6-10 day outlook. Above-normal precipitation isfavored throughout much of the West, Great Plains, and Mississippi Valley.Based on this predicted trough, a two-category change from below to above isnecessary for parts of the West. In addition, there is a greater chance of alow pressure system tracking across the central CONUS and the 6-10precipitation outlook reflects this trend in model guidance. The highestconfidence in the precipitation outlook exists across the lower Ohio Valley andMiddle Mississippi Valley where a mean surface front is likely to be a focusfor precipitation. The precipitation outlook is highly uncertain across thenorthern Mid-Atlantic and Northeast. The Greenland block and negative NAO wouldfavor an East Coast storm, but the ensemble spread is large on how close to theEast Coast a storm tracks, if it were to develop. Therefore, near normalprecipitation is favored for these areas.Positive 500-hPa height departures coupled with westerly surface flow favorabove-normal temperatures and precipitation for much of western and northernMainland Alaska along with the Aleutians. Surface high pressure is forecast tostrengthen across the Yukon and expand westward, which elevates theprobabilities for below-normal temperatures across southeastern Alaska.The official 6-10 day 500-hPa height blend consists of 35% of Today's 6z GFSEnsemble Mean centered on Day 8, 35% of Today's 0z European Ensemble Meancentered on Day 8, and 30% of Today's 0z Canadian Ensemble Mean centered on Day8FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Average, 3 out of 5, due to goodagreement among the ensemble means offset by poor continuity in theprecipitation tools.8-14 DAY OUTLOOK FOR DEC 10 - 16 2022The ensemble means continue to offer different solutions on the longwavepattern over the North Pacific and western North America during week-2. The GEFS and Canadian ensemble means maintain a more amplified 500-hPa ridge overthe North Pacific and Aleutians with a trough downstream and offshore of the West Coast. In contrast, the ECMWF ensemble mean shifts the anomalous ridging from the Aleutians eastward to the higher latitudes of western North America. Based on continuity and teleconnections derived from the well-agreed upon large positive 500-hPa height anomaly center near Greenland, the GEFS and Canadian ensemble means are preferred. However, the ECMWF ensemble mean is not completely discounted due to its higher 500-hPa anomaly correlation scoreduring the past 60 days. Despite these model differences, the temperature tools are in good agreementfor colder-than-normal temperatures across the western and north-central CONUS.The longwave pattern over North America with high latitude blocking would favorperiodic intrusions of anomalous cold southward from Canada. Similar to the6-10 day period, the reforecast tools have trended warmer across thesouth-central CONUS which is reflected in an increased coverage of favoredabove-normal temperatures for this region. This is likely due to a moreamplified trough upstream near the West Coast. Given the well-establishednegative NAO, the temperature outlook hedged colder across the Mid-Atlantic andSoutheast, compared to the reforecast tools.
*As the blocking ridge remainsstrong over Baffin Bay through the end of week-2, there is likely to be atendency for anomalous cold to shift southward away from the Great Lakes an New England. Therefore, near to above-normal temperatures are favored for much of these areas. *
Precipitation tools have trended wetter today across the western and centralCONUS, due to a predicted 500-hPa trough near the West Coast (by the GEFS andCanadian ensemble means) along with an increased chance of subtropical moisturebecoming entrained within the mid-latitude flow. A two-category change frombelow to above is necessary across the Midwest, based on the latest modelguidance. Since the storm track is expected to remain farther north duringweek-2, below normal precipitation is favored for parts of the Southeast. Basedon multiple ensemble members depicting a low pressure system near New England early in week-2, probabilities for above-normal precipitation are slightly elevated for this region. The manual 500-hPa height blend depicts a continuation of anomalous ridging over the North Pacific and Aleutians. Since the preferred GEFS and Canadian ensemble means feature only minor changes in the longwave pattern over Alaska and adjacent areas through week-2, the 6-10 and 8-14 day outlooks fortemperature and precipitation are similar.The official 8-14 day 500-hPa height blend consists of: 40% of Today's 6z GFSEnsemble Mean centered on Day 11, 30% of Today's 0z European Ensemble Mean centered on Day 11, and 30% of Today's 0z Canadian Ensemble Mean centered onDay 11
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Below average, 2 out of 5, due todiverging model solutions on the longwave pattern across the North Pacific andwestern North America along with large ensemble spread with the ArcticOscillation late in week-2.FORECASTER: Brad Pugh