FXUS06 KWBC 091916 PMDMRD Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks NWS Climate Prediction Center College Park, MD 300 PM EDT Thu May 09 2024 6-10 DAY OUTLOOK FOR MAY 15 - 19 2024 Today's dynamical model solutions are in fairly good agreement on the predicted 500-hPa circulation pattern across North America and surrounding regions during the 6-10 day period, and are quite similar to yesterday. Yesterday, the operational GFS and ECMWF models showed a more amplified 500-hPa height pattern than the ensemble means, but these have shifted toward the less-amplified ensemble means today, supporting this solution. The ECMWF and Canadian ensemble means are very similar, featuring a strong anomalous mid-level mean ridge southwest of Alaska, subnormal 500-hPa heights across Alaska and adjacent Canada, positive mid-level height anomalies in the Pacific Northwest extending into the northern Rockies, near- to slightly below-normal 500-hPa heights in the eastern CONUS, and a downstream mid-level ridge east of Atlantic Canada. The only substantial difference across the CONUS is that the Canadian ensemble mean keeps slightly higher mean 500-hPa heights in the South Atlantic region, but this has little effect on sensible weather. The GEFS ensemble mean is slightly different, featuring less mid-level troughing across southern Alaska, less anomalous ridging in the Pacific Northwest, and slightly greater 500-hPa heights in the Southwest, and a moderate anomalous mid-level ridge centered near northeastern Canada. The pattern shown by the ECMWF ensemble mean is favored given slightly better agreement with its solution than yesterday, but all three show a relatively flat pattern with weak mid-level features affecting Alaska, Hawaii, and the CONUS. GEFS and European ensemble mean raw, bias-corrected, calibrated, and reforecast temperatures all favor above-normal temperatures for most or all of the CONUS, with the weakest odds in portions of the Lower Mississippi Valley and interior Southeast. Here, slightly below-normal 500-hPa heights and moderate to heavy rainfall on the cooler side of a quasi-stationary front could serve to keep temperatures closer to normal. The highest probabilities favoring above-normal temperatures exceed 70% over southern Florida, with odds topping 60% over the entire Florida Peninsula, the Great Basin and adjacent areas, and locations near and west of the Appalachians in the Northeast, all similar to the consolidation. 500-hPa mean heights near Hawaii are forecast to be near or slightly below normal by all ensemble means, with weak anomalous mid-level ridging to the west and the east, leaving the island chain in an area with no marked shift of the odds toward either above- or below-normal temperatures. Farther north, despite decent model agreement, dynamic model temperatures and especially the derived tools were in conflict across Alaska. Analogs were cold throughout the state. The consolidation shows cold weather favored in southeastern and southwestern parts of the state, with warmer than normal weather favored closer to the Arctic Circle. The reforecasts were sharply different, with the GEFS showing subnormal temperatures dominating almost the entire state while the ECMWF reforecast confines enhanced chances for below-normal temperatures to part of southwestern Alaska, with increased odds for above-normal temperatures over the northern half of the state. The official forecast is a compromise of the tools, with increased odds for colder than normal weather across the southern half of the state and no tilt of the odds indicated farther north. Below-normal precipitation is favored from the interior western CONUS (outside climatologically dry areas), with no tilt of the odds toward wetness or dryness closer to the Pacific Coast. This is supported by GEFS and ECMWF reforecast precipitation, as well as the raw ECMWF ensemble mean output. For most of the remainder of the CONUS, these two reforecasts depict increased odds of above-normal precipitation, which is consistent with broad, low-amplitude cyclonic flow. The highest probabilities for above-normal precipitation, in excess of 60%, are indicated over the central Gulf Coast region. This is associated with increased onshore flow from the Gulf Coast states interacting with a quasi-stationary front in a region of weak mid-level troughing. The ECMWF ensemble mean depicts more than 2 inches of rain during the period over portions of the central Gulf Coast region while the GEFS mean, in the same location, keeps the totals closer to 1.5 inches. The consolidated tercile probabilities show the greatest odds of above-normal rainfall in this region as well. In Alaska, above-normal precipitation is weakly favored over most of the state associated with broad mid-level troughing. Similarly, slightly enhanced chances for above-normal precipitation cover Hawaii the proximity of weak 500-hPa troughing. The official 6-10 day 500-hPa height blend consists of 20% of Today's 0z GFS Ensemble Mean centered on Day 8, 30% of Today's 0z European Ensemble Mean centered on Day 8, 20% of Today's operational 0z ECMWF centered on Day 8, and 30% of Today's 0z Canadian Ensemble Mean centered on Day 8 FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Above average, 4 out of 5, due to good agreement among model solutions and forecast temperature and precipitation tools in most areas. 8-14 DAY OUTLOOK FOR MAY 17 - 23 2024 The ensemble means start to diverge during the 8- to 14-day period, particularly across the western CONUS. All models keep slightly below-normal 500-hPa heights from the Upper Mississippi Valley through most of the eastern CONUS, but differences begin to evolve farther west. The Canadian and ECMWF ensemble means increase 500-hPa heights in the western CONUS, leading to a weak but distinct anomalous 500-hPa ridge over much of western North America. The GEFS, on the other hand, lowers mid-level heights in the Pacific Northwest and keeps any weak anomalous ridge development flat and confined to the Southwest. The manual blend favors the weak anomalous ridge covering the western CONUS as it is more consistent with the 6- to 10-day 500-hPa mean pattern, and is depicted by a preponderance of model solutions, but with low confidence given the low amplitude of the pattern and the weakness of individual mid-level features. Farther west, the moderately strong 500-hPa ridge southwest of Alaska is expected to remain essentially unchanged during week-2 while mid-level heights across Alaska slowly climb toward normal, slightly more markedly in the ECMWF ensemble mean than the Canadian ensemble mean or the GEFS mean. A weak trough and near-normal 500-hPa heights are predicted in the vicinity of Hawaii, although the placement and magnitude of features are not consistent among the models. With the official forecasts leaning with low confidence toward a solution featuring a fairly well-defined mid-level ridge in the western CONUS with a weak trough to the east, there is more uncertainty in the temperature pattern from the Plains eastward, and in much of this region, the forecast shows no tilt of the odds favoring either unusually warm nor unusually cool weather. Farther west, the weak mid-level ridge favors above-normal temperatures, with the best odds across the interior West and Southwest where there is better model agreement on positive 500-hPa height anomalies. Across Alaska, the tools differ significantly on temperatures, as during the 6- to 10-day period. Each individual tool, however, is at least slightly warmer during week-2 than it is for days 6-10, and the official forecast has followed this scenario. Odds for below-normal temperatures are less enhanced and confined farther to the south while slightly enhanced chances for above-normal temperatures extend across portions of northern Mainland Alaska. 500-hPa heights increase slightly across Hawaii during week-2, but remain close to normal in a pattern slightly favoring above-normal temperatures over the western half of the state. The uncertainty in the evolving 500-hPa pattern is reflected in the week-2 precipitation outlook. Across most of the western half of the CONUS, the official forecast shows equal chances of all precipitation terciles, save for below-normal precipitation slightly favored in the southern Rockies and High Plains, where there is slightly better model consensus that the region will be downstream from anomalously high 500-hPa heights. Farther east, the lower than normal mid-level heights marginally favor above-normal precipitation in most locations, with better odds over the Southeast, where the GEFS mean drops 1.5 to 2.5 inches of rain during the period. The ECMWF ensemble shows significant odds for a deepening trough to bring heavy rainfall farther north later in the period, toward New England, but none of the other tools are as amplified at this time, and for now this solution is not preferred. The weak mid-level flow pattern across Alaska slightly elevates the chances for above-normal precipitation statewide, and in Hawaii, the proximity of a surface frontal system marginally enhances the odds for surplus precipitation in the western islands, but prevailing surface high pressure may serve to slightly reduce precipitation totals across the Big Island. The official 8-14 day 500-hPa height blend consists of: 30% of Today's 0z GFS Ensemble Mean centered on Day 11, 35% 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: Below average, 2 out of 5, with model disagreement on the overall circulation pattern increasing with time, and weaker signals in the precipitation and temperature 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 May 16. 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: 19750427 - 19760424 - 19750502 - 19850513 - 19650507 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: 19750428 - 19760424 - 19820518 - 20060505 - 19750503 6-10 DAY OUTLOOK TABLE Outlook for May 15 - 19 2024 STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N N OREGON A B NRN CALIF A N SRN CALIF A N IDAHO A B NEVADA A B W MONTANA A B E MONTANA A N WYOMING A N UTAH A B ARIZONA A N COLORADO A A NEW MEXICO A A N DAKOTA A A S DAKOTA A N NEBRASKA A N KANSAS A A OKLAHOMA A A N TEXAS A A S TEXAS A A W TEXAS A A MINNESOTA A A IOWA A A MISSOURI A A ARKANSAS A A LOUISIANA A A WISCONSIN A A ILLINOIS A A MISSISSIPPI A 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 N A AK ALEUTIAN B N AK WESTERN B A AK INT BSN N A AK S INT B A AK SO COAST B A AK PNHDL B A 8-14 DAY OUTLOOK TABLE Outlook for May 17 - 23 2024 STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A N OREGON A N NRN CALIF A N SRN CALIF A N IDAHO A N NEVADA A N W MONTANA A N E MONTANA A N WYOMING A N UTAH A N ARIZONA A N COLORADO A N NEW MEXICO A N N DAKOTA N N S DAKOTA N N NEBRASKA N A KANSAS A N OKLAHOMA A N N TEXAS A N S TEXAS A B W TEXAS A B MINNESOTA N N IOWA N A MISSOURI N A ARKANSAS N A LOUISIANA A A WISCONSIN N N ILLINOIS N A MISSISSIPPI N A MICHIGAN N A INDIANA N A OHIO N A KENTUCKY N A TENNESSEE N A ALABAMA N A NEW YORK N A VERMONT N A NEW HAMP N A MAINE A A MASS N A CONN N A RHODE IS N A PENN N A NEW JERSEY N A W VIRGINIA N A MARYLAND N A DELAWARE N A VIRGINIA N A N CAROLINA A A S CAROLINA N A GEORGIA N A FL PNHDL A A FL PENIN A A AK N SLOPE N N AK ALEUTIAN B B AK WESTERN B N AK INT BSN N N AK S INT B N AK SO COAST B N AK PNHDL B N 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. $$