845 FXUS06 KWBC 261902 PMDMRD Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks NWS Climate Prediction Center College Park, MD 300 PM EDT Fri April 26 2024 6-10 DAY OUTLOOK FOR MAY 02 - 06 2024 Model solutions depict a persistent longwave pattern into the beginning of May. The GEFS along with the ECMWF and Canadian ensemble means feature a 500-hPa trough of varying amplitude near the West Coast, a broad ridge over the central contiguous U.S. (CONUS), and a trough across the western Atlantic. Positive 500-hPa height anomalies support increased above-normal temperature probabilities from the Rockies to the East Coast. However, recent model guidance shows at least a brief period of cooler-than-normal temperatures affecting the Great Plains and Upper Mississippi Valley and this is reflected in the ECMWF reforecast tool. Also, a cooling trend is forecast for the Northeast and Northern Mid-Atlantic from day 6 to 10. Therefore, above-normal temperature probabilities are lower today in portions of the central and eastern CONUS. Anomalous mid-level troughing and enhanced onshore flow favor a slight tilt towards below-normal temperatures across parts of the Pacific Northwest and California. An upstream trough along the West Coast generally favors a wetter-than-normal outcome for much of the western and central CONUS. This is supported by the GEFS and ECMWF reforecast tools. Enhanced onshore flow leads to increased above-normal precipitation probabilities from the Pacific Northwest and northern California eastward to the northern Rockies. Near normal precipitation is forecast for the Great Basin and climatological dry areas of the Southwest. Downstream of a mid-level ridge axis, near to below-normal precipitation is favored across the eastern CONUS. A 500-hPa trough over the Bering Sea favors above-normal precipitation for much of Alaska. The uncalibrated model output is colder than the GEFS and ECMWF reforecast tools. Given the lower 500-hPa heights in todays manual blend and expectation for more widespread cloudiness and increased chances of precipitation, near normal temperatures are forecast for the southern two-thirds of Alaska. Good model agreement continues on the favored below-normal temperatures across the North Slope. Based on the GEFS and ECMWF ensemble means, near normal temperatures and precipitation are favored across much of Hawaii. The official 6-10 day 500-hPa height blend consists of 35% of Today's 6z GFS Ensemble Mean centered on Day 8, 35% of Today's 0z European Ensemble Mean 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: Average, 3 out of 5, due to good model agreement on the longwave pattern offset by increasing forecast uncertainty across the eastern CONUS. 8-14 DAY OUTLOOK FOR MAY 04 - 10 2024 The GEFS, ECMWF, and Canadian ensemble means maintain the persistent longwave pattern with 500-hPa troughs near both coasts of North America and a broad ridge centered over the central CONUS. By the second week of May, the ensemble means indicate a retrogression of the longwave pattern over North America with a 500-hPa ridge axis shifting from the Mississippi Valley to the Rockies and an amplifying trough closer to the East Coast. The Northeast and Mid-Atlantic is vulnerable to backdoor cold fronts and cold air damming during the spring and model guidance continues to show an increased chance for this to occur. A slight lean towards below-normal temperatures is forecast for southern New England and the coastal Northeast. Compared to yesterday, coverage/probabilities for above-normal temperatures are reduced across the eastern CONUS. The ridging aloft and associated positive 500-hPa height anomalies favor above-normal temperatures from the Rockies to the Appalachians. Conversely, a mid-level trough and negative 500-hPa height anomalies supports slightly elevated below-normal temperature probabilities for southwest Oregon and California. The mid-level longwave trough upstream yields a relatively wet outlook across much of the western and central CONUS. Forecast confidence is not high though since the GEFS reforecast tool indicates weak probabilities. In addition, as the ridge axis shifts westward to the High Plains, that would lead to a drier pattern across the Great Plains later in week-2. Due to the amplifying trough near the East Coast, a cold front may shift south and become stationary across the southeastern CONUS. This could provide a focus for precipitation which tilts the outlook towards the wet side for parts of this region. Farther to the north across the eastern Great Lakes, Mid-Atlantic, and much of the Northeast, below-normal precipitation is slightly favored and supported by the GEFS and ECMWF reforecast tools. A broad 500-hPa trough over the Bering Sea and western Mainland Alaska supports increased above-normal precipitation probabilities nearly statewide for Alaska. Similar to the 6-10 day period, the likelihood for enhanced precipitation and cloudiness supports near normal temperatures for a majority of Alaska. The GEFS ensemble mean features a mid-level trough lingering over the Central Pacific. This is expected to promote cooler-than-normal temperatures for Hawaii and increased chances of above-normal precipitation except for the Big Island. The official 8-14 day 500-hPa height blend consists of: 35% of Today's 6z GFS Ensemble Mean centered on Day 11, 35% of Today's 0z European Ensemble Mean centered on Day 11, and 30% 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, due to a predicted retrogression of the longwave pattern and weak signals among the precipitation tools. FORECASTER: Brad Pugh 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: 19660425 - 19900507 - 20040416 - 19900418 - 19740429 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: 20040415 - 19640407 - 19740428 - 19900418 - 19900508 6-10 DAY OUTLOOK TABLE Outlook for May 02 - 06 2024 STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N A OREGON B A NRN CALIF B A SRN CALIF N N IDAHO A A NEVADA A A W MONTANA N A E MONTANA A A WYOMING A N UTAH A N ARIZONA A N COLORADO A N NEW MEXICO A A N DAKOTA A A S DAKOTA A A NEBRASKA A A 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 N WISCONSIN A N ILLINOIS A A MISSISSIPPI A A MICHIGAN A N INDIANA A N OHIO A N KENTUCKY A N TENNESSEE A A ALABAMA A A NEW YORK A B VERMONT A B NEW HAMP A B MAINE A N MASS A B CONN A B RHODE IS A B PENN A B NEW JERSEY A B W VIRGINIA A B MARYLAND A B DELAWARE A B VIRGINIA A B N CAROLINA A B S CAROLINA A N GEORGIA A N FL PNHDL A N FL PENIN A B AK N SLOPE B A AK ALEUTIAN N A AK WESTERN N A AK INT BSN N A AK S INT N A AK SO COAST N A AK PNHDL N A 8-14 DAY OUTLOOK TABLE Outlook for May 04 - 10 2024 STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON N A OREGON N A NRN CALIF B A SRN CALIF B N IDAHO A A NEVADA N A W MONTANA A A E MONTANA A N WYOMING A N UTAH A N ARIZONA A N COLORADO A N NEW MEXICO A A N DAKOTA A A S DAKOTA A A NEBRASKA A A 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 N WISCONSIN A N ILLINOIS A N MISSISSIPPI A A MICHIGAN A B INDIANA A N OHIO A B KENTUCKY A N TENNESSEE A N ALABAMA A A NEW YORK N B VERMONT N B NEW HAMP N N MAINE N N MASS B N CONN B B RHODE IS B N PENN A B NEW JERSEY B B W VIRGINIA A B MARYLAND N B DELAWARE N B VIRGINIA A B N CAROLINA A N S CAROLINA A N GEORGIA A A FL PNHDL A N FL PENIN A N AK N SLOPE B A AK ALEUTIAN N A AK WESTERN N A AK INT BSN N A AK S INT N A AK SO COAST N A AK PNHDL N 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. $$