FXUS06 KWBC 032046 PMDMRD Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks NWS Climate Prediction Center College Park, MD 300 PM EST Tue December 03 2024 6-10 DAY OUTLOOK FOR DEC 09 - 13 2024 Most model guidance indicates that a change in the 500-hPa pattern will start to evolve during this period. Beyond that, the situation is highly uncertain. The models are a little more consistent with each other today on the mean 6-10 day mid-level pattern, but overall, there is too much disparity in the guidance to justify anything more than a low-confidence forecast. In particular, the day-to-day evolution of individual mid-level features is highly uncertain, and the statistical temperature and precipitation tools are at odds with dynamical model output in many cases. Both the analogs and the teleconnections on prominent features are almost antithetical to the dynamic model output in some sizable areas, especially the temperature tools. Models start the 6-10 day period in decent agreement on the large-scale pattern. A moderate to strong mid-level ridge is forecast along or near western North America, with positive 500-hPa height anomalies extending westward in a band across the central North Pacific. The European ensemble (ECENS) mean and the Canadian ensemble (CMCE) are somewhat stronger with this feature than the GEFS mean, but all show the greatest positive height anomalies near the southwest Canada coast. A weak to moderate positively-tilted mid-level trough is anticipated in the middle of the Contiguous 48 states (CONUS), leading into above-normal 500-hPa heights ahead of this trough along the Eastern Seaboard. This is a considerable shift from yesterday, when most guidance kept heights along the East Coast closer to normal. A strong mid-level ridge is indicated downstream in the North Atlantic, although a preponderance of the guidance places it considerably farther southwest than yesterday, between Greenland and Atlantic Canada. Thereafter, models indicate a transitional regime with substantial changes in the 500-hPa features, but the evolution of these changes is highly uncertain, with substantial run-to-run and model-to-model differences. By day 10, the western North America ridge has retrograded into the central Pacific, subnormal 500-hPa heights should be centered near Hudson Bay, and a flat ridge should evolve from the eastern CONUS to the mid-level ridge over the north-central or northwestern Atlantic. There is not much agreement beyond that. The ECENS and CMCE are considerably stronger with the mid-level ridge that retrogrades into the North Pacific into southern and western Alaska. This leads to significant downstream disparities in the height field over the CONUS. The ECENS shows slightly positive 500-hPa anomalies along the southern and eastern fringes of the CONUS, with somewhat below-normal heights extending from north-central Canada into the northern tier of the western CONUS. In the CMCE, positive height anomalies extend considerably farther east, into central and western sections of the CONUS. Heights are close to normal farther north and east to the Appalachians, with positive height anomalies extending from the East Coast into the North Atlantic (similar to the ECENS). Meanwhile, the GEFS also retrogrades the western North American ridge into the central north Pacific, but is considerably weaker than the other models. This leads to differences downstream, with the GEFS bringing a moderate mid-level trough into northwestern North America which is not connected to the negative height anomaly in north-central Canada. So instead of relatively lower heights in the central CONUS, the GEFS builds a ridge there, downstream from its trough near the northwestern CONUS. The pattern is not too different farther east, with above-normal heights extending from the East Coast into the central North Atlantic. In the eastern CONUS, the GEFS has larger positive anomalies in the northeastern CONUS and near-normal heights in the Southeast. The other two ensembles show at least slightly positive anomalies along the length of the Eastern Seaboard, with slightly higher anomalies just off the Northeast Coast. Also, positive height anomalies in the Northeast reach considerably farther west in the CMCE than the ECENS. Given these discrepancies, it is not surprising the raw temperature and precipitation outputs are not particularly in concert, and the statistically-adjusted tools based on the ensembles diverge even further in some cases. However, there are a few areas of agreement, and the official temperature and precipitation forecasts are anchored on those features. With above-normal heights around the East Coast, the tools continue a trend from yesterday placing warmer air along the East Coast. Farther west, there is also general agreement that downsloping may contribute to enhanced chances for warmer than normal weather in the northern and central High Plains. With the mid-level ridge just upstream, most indicators show significantly increased odds for above normal temperatures across most of Alaska. Over the central and interior western CONUS, guidance is inconsistent, with the ECENS and CMCE raw and bias-corrected output favoring colder than normal conditions in many of these areas outside the northern High Plains. The GEFS raw and bias-corrected output is warmer throughout this broad area, and the reforecasts for all ensembles are significantly warmer in the central and interior western CONUS relative to the other tools. The forecast is further complicated by some of the most recent model runs bringing colder air southward briefly into southern portions of the Rockies, Plains, and Lower Missssippi Valley. The operational forecast is a compromise, favoring warmth along the East Coast and in the northern High Plains a bit more than other areas, which show little or no increased chances for abnormal warmth. Near normal mean temperatures are favored in areas potentially affected by the cold air outbreak. In Hawaii, the consolidation favors warm weather under above-normal 500-hPa heights, and the forecast follows suit. In the cyclonic mid-level flow pushing eastward from the nation’s mid-section into the flat East Coast ridge, one or more storm systems may develop and traverse through some part of this broad region, though there is little agreement in the guidance as to where and when this might happen. Still, with most guidance indicating some sort of unsettled weather, there are slightly increased odds for above-normal precipitation in the south-central and eastern CONUS. The raw and derived tools generally favor a slight increase of the odds toward surplus precipitation along the northern tier of the country as well. Meanwhile, a consensus of the tools slightly favors below-normal precipitation in the central and southwestern CONUS. Broad southwesterly mid-level flow is expected to favor above normal precipitation across most of Alaska especially in central and southeastern areas south of the Alaska range. The consolidation also leans toward wetter than normal conditions in Hawaii. The official 6-10 day 500-hPa height blend consists of 25% of Today's GFS Superensemble Mean centered on Day 8, 42% of Today's 0z European Ensemble Mean centered on Day 8, and 33% of Today's 0z Canadian Ensemble Mean centered on Day 8 FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Much below normal, 1 out of 5, with a broad array of guidance solutions tempered slightly by a few areas of agreement in the tools derived from the ensembles. 8-14 DAY OUTLOOK FOR DEC 11 - 17 2024 The divergent model solutions noted during the 6-10 day period continue through week-2.The ensemble means generally trend toward deamplification of the 500-hPa height pattern, although this could be the result of a broad array of ensemble member solutions where significant height anomalies average relatively close to normal in aggregate. The operational models show more amplification, lending credibility to this possibility. Mean features generally consistent across the guidance for week-2 are mid-level ridging and above-normal heights over Alaska, a broad area of slightly above-normal heights over the CONUS, with the greatest anomalies from the south-central through the eastern and especially the northeastern CONUS, with somewhat lower heights in southern Canada. There remain significant differences among the tools driven by divergent model solutions in the southwestern and northwestern CONUS, where some models indicate relatively low 500-hPa heights relative to the surroundings (like the GEFS mean) while others favor above-normal heights (like many of the CMCE members). As with the 6-10 day period, the temperature and precipitation outlooks are anchored on a few areas of relative agreement. Most week-2 tools slightly favor warmth over most of the CONUS, Alaska, and Hawaii. A few areas closer to larger positive 500-hPa anomalies show slightly higher odds, including parts of the eastern CONUS and southern Alaska, in addition to downsloping potential in the northern Plains. The only exception is a swath of near-normal temperatures from the southern Rockies eastward across the Lower Mississippi Valley, where there may be unusually cold air early in the period followed by warmer weather late week-2. The possible storm track from the Lower Mississippi Valley through the East Coast slightly increases the odds for surplus precipitation there, and many of the tools also favor above-normal amounts along the northern tier of the CONUS as well. A preponderance of the precipitation tools show relatively heavy week-2 precipitation in much of the Northwest, where odds for wetness are slightly more enhanced. The tools are inconsistent in other parts of the CONUS, but the consolidation slightly favors subnormal precipitation in much of the central and southwestern CONUS, which is also consistent with yesterday’s tools. Slightly increased odds for dryness are shown there. Across Alaska, the broad southwesterly flow driving unsettled weather should be on the wane, especially if the GEFS mean verifies, but in the mean, above-normal precipitation is slightly favored in most areas, especially south of the Alaska Range. Anomalously wet weather is also forecast for Hawaii, consistent with the consolidation. The official 8-14 day 500-hPa height blend consists of: 15% of Today's 6z GFS Ensemble Mean centered on Day 11, 25% of Today's GFS Superensemble Mean centered on Day 11, 25% of Today's 0z European Ensemble Mean centered on Day 11, and 35% of Today's 0z Canadian Ensemble Mean centered on Day 11 FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Much below normal, 1 out of 5, due to inconsistent model guidance, including run-to-run differences in individual models, tempered slightly by a few areas of relative consistency in the temperature and precipitation tools. FORECASTER: Rich Tinker Notes: Automated forecasts are issued on Saturday and Sunday. Occasionally manual intervention is necessary to address quality control and consistency issues. In these cases, forecasts are manually drawn but a full discussion is not issued. The notation for the categorical forecast indicated on the maps is the same as that in the tables: A-above N-near normal B-below The temperature map shows regions with > 33% chance of being warmer (orange, "A"), colder (blue, "B"), or close to (unshaded, "N"). Historical average values for the calendar period of the forecast (dashes, "f"). Labels on the shaded lines give the probability (> 33%) of the more likely category (B or A). Probability of N is always < 40%. The precipitation map shows regions with > 33% chance of being wetter (green, "A"), drier (tan, "B"), or close to (unshaded, "n"). Historical median values for the calendar period of the forecast (dashes, "inches"). Labels on the shaded lines give the probability (> 33%) of the more likely category (B or A). Probability of N is always < 40%. In the southwest and other climatologically dry regions - there will be a greater than 33.3% chance of no precipitation and occasionally even a normal (i.e. Median) value of zero - especially during the dry seasons. In such cases a forecast of near normal is effectively a forecast of little or no precipitation. The climate prediction center uses 1991-2020 base period means as reference in the climate outlooks. The next set of long-lead monthly and seasonal outlooks will be released on December 19. Analogs to the 5 day mean observed pattern centered 3 days ago (D-3) for the region from 20N to 70N latitude and 175E to 60W longitude include the 5 day periods centered on the following dates: 19581211 - 19551127 - 19621209 - 20021130 - 19761123 Analogs to the 7 day mean observed pattern centered 4 days ago (D-4) for the region from 20N to 70N latitude and 175E to 60W longitude include the 7 day periods centered on the following dates: 19581212 - 20021130 - 19621210 - 19761123 - 19551127 6-10 DAY OUTLOOK TABLE Outlook for Dec 09 - 13 2024 STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A A OREGON A N NRN CALIF A B SRN CALIF A B IDAHO A N NEVADA A B W MONTANA A A E MONTANA A A WYOMING A N UTAH N B ARIZONA N B COLORADO N N NEW MEXICO N B N DAKOTA A A S DAKOTA A N NEBRASKA A N KANSAS A N OKLAHOMA N N N TEXAS N N S TEXAS N A W TEXAS N B MINNESOTA A A IOWA A N MISSOURI A N ARKANSAS N N LOUISIANA N A WISCONSIN A A ILLINOIS A N MISSISSIPPI N A MICHIGAN A A INDIANA A A OHIO A A KENTUCKY A A TENNESSEE A A ALABAMA A A NEW YORK A A VERMONT A A NEW HAMP A A MAINE A A MASS A A CONN A A RHODE IS A A PENN A A NEW JERSEY A A W VIRGINIA A A MARYLAND A A DELAWARE A A VIRGINIA A A N CAROLINA A A S CAROLINA A A GEORGIA A A FL PNHDL A A FL PENIN A A AK N SLOPE A A AK ALEUTIAN A A AK WESTERN A A AK INT BSN A A AK S INT A A AK SO COAST A A AK PNHDL A A 8-14 DAY OUTLOOK TABLE Outlook for Dec 11 - 17 2024 STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A A OREGON A A NRN CALIF A N SRN CALIF A N IDAHO A A NEVADA A N W MONTANA A A E MONTANA A A WYOMING A A UTAH A N ARIZONA N B COLORADO A N NEW MEXICO N B N DAKOTA A N S DAKOTA A N NEBRASKA A N KANSAS A N OKLAHOMA N N N TEXAS N N S TEXAS N N W TEXAS N B MINNESOTA A N IOWA A N MISSOURI A N ARKANSAS N N LOUISIANA N A WISCONSIN A A ILLINOIS A N MISSISSIPPI N A MICHIGAN A A INDIANA A N OHIO A N KENTUCKY A N TENNESSEE A A ALABAMA A A NEW YORK A A VERMONT A A NEW HAMP A A MAINE A A MASS A A CONN A A RHODE IS A A PENN A A NEW JERSEY A A W VIRGINIA A A MARYLAND A A DELAWARE A A VIRGINIA A A N CAROLINA A A S CAROLINA A A GEORGIA A A FL PNHDL A A FL PENIN A N AK N SLOPE A N AK ALEUTIAN A A AK WESTERN A A AK INT BSN A A AK S INT A A AK SO COAST A A AK PNHDL A A LEGEND TEMPS WITH RESPECT TO NORMAL PCPN WITH RESPECT TO MEDIAN A - ABOVE N - NEAR NORMAL A - ABOVE N - NEAR MEDIAN B - BELOW B - BELOW THE FORECAST CLASSES REPRESENT AVERAGES FOR EACH STATE. NORMAL VALUES - WHICH MAY VARY WIDELY ACROSS SOME STATES - ARE AVAILABLE FROM YOUR LOCAL WEATHER SERVICE FORECAST OFFICE. FOR ADDITIONAL INFORMATION SEE MESSAGE FXUS06 KWBC - ON AWIPS AS PMDMRD. $$