677 FXUS06 KWBC 011902 PMDMRD Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks NWS Climate Prediction Center College Park, MD 300 PM EDT Tue October 01 2024 6-10 DAY OUTLOOK FOR OCT 07 - 11 2024 During early to mid-October, the GEFS, ECENS, and CMCE are in good agreement that an expansive and anomalous 500-hPa ridge develops and persists over the western and central contiguous U.S. (CONUS). This ridge begins to become established just prior to the 6-10 day period and the ridge axis is forecast to be centered across the Rockies. The ensemble mean solutions depict positive 500-hPa height departures for the western two-thirds of the CONUS. The anomalous mid-level ridging supports increased above-normal temperature probabilities from the West Coast eastward to the Mississippi Valley. The largest probabilities (more than 80 percent) are forecast across the interior West and Northern to Central Great Plains where 5-day temperatures are likely to average near or more than 15 degrees F above-normal. For the eastern CONUS, an amplified 500-hPa trough is expected to result in cooler-than-normal temperatures across the Mid-Atlantic on days 6 and 7. Given the relatively strong cold signal in the uncalibrated model guidance and a negative phase of the North Atlantic Oscillation, a slight lean towards below-normal temperatures is forecast for parts of the Northeast, Mid-Atlantic, and Central to Southern Appalachians. Closer to the Gulf Coast and across Florida, above-normal temperatures are more likely based on the reforecast tools. In addition to the unseasonably warm temperatures, the anomalous 500-hPa ridge is likely to result in a very dry pattern with little to no precipitation for a majority of the CONUS. Along and to east of the predicted ridge axis, below-normal precipitation is favored across most of the western and central CONUS. An amplified trough offshore of the West Coast slightly favors above-normal precipitation for parts of the Pacific Northwest. According to the National Hurricane Center at 2pm EDT on October 1, there is a 40 percent chance of tropical cyclone (TC) development over the northwestern Caribbean Sea and southern Gulf of Mexico during the next 7 days. Until this potential TC forms, model guidance will vary on its strength and track. Many GEFS and ECMWF ensemble members depict a TC tracking slowly east from the Gulf of Mexico to Florida or as far north as southern Georgia next week. Despite the uncertainty on the eventual strength and track of this potential TC, precipitation tools are in good agreement with increased above-normal precipitation probabilities for parts of the Southeast. The model solutions have a sharp cutoff in the precipitation amounts farther to the north with below-normal precipitation favored for the Southern Appalachians and Tennessee Valley. The GEFS and ECENS favor low pressure development near New England by day 7, tilting the 6-10 day outlook towards the wet side for that region. The GEFS, ECENS, and CMCE agree with an amplified trough over Alaska which leads to increased above-normal precipitation probabilities for southeastern parts of the state. Downslope surface flow results in elevated below-normal precipitation probabilities across northern Mainland Alaska. Onshore flow favors above-normal temperatures across eastern Mainland Alaska. The elevated below-normal temperature probabilities forecast for coastal western Alaska and the Aleutians are related to below-normal sea surface temperatures. Based on the GEFS and ECENS, near to above-normal temperatures along with near to above-normal precipitation are favored for Hawaii. The official 6-10 day 500-hPa height blend consists of 40% of Today's 6z GFS Ensemble Mean centered on Day 8, 40% of Today's 0z European Ensemble Mean centered on Day 8, and 20% of Today's 0z Canadian Ensemble Mean centered on Day 8 FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Forecast confidence: Above average, 4 out of 5, due to good model agreement on anomalous ridging and its effects on temperature and precipitation for the central and western CONUS. 8-14 DAY OUTLOOK FOR OCT 09 - 15 2024 The GEFS, ECENS, and CMCE maintain a stable longwave pattern with the anomalous 500-hPa ridge anchored over the west-central CONUS. The ECENS has this mid-level ridge strengthening late in week-2 with daily 500-hPa height departures peaking to more than 180 meters above normal across North Dakota and Montana. Strongly enhanced above-normal temperature probabilities are forecast throughout the western and central CONUS. Probabilities exceed 80 percent across the Northern Great Plains given the excellent model agreement on a stable longwave pattern and the highly amplified ridge. Temperatures are favored to be near normal for much of the eastern CONUS due to a trough just offshore of the East Coast. Due to the broad and amplified 500-hPa ridge, a dry pattern is likely to persist for a majority of the CONUS through mid-October. Any TC that forms in the Gulf of Mexico by early next week is expected to move slowly which elevates above-normal precipitation probabilities for parts of the Southeast. A low pressure system is forecast to move away from New England on days 8 and 9. Therefore, the 8-14 day outlook is drier for this region compared to the 6-10 day outlook. The GEFS favors a TC in the East Pacific tracking northwest towards the Baja Peninsula and Gulf of California by the beginning of week-2. This could lead to enhanced low to mid-level moisture spreading north to the Desert Southwest. Although the GEFS reforecast tool depicts slightly elevated above-normal precipitation probabilities for the Southwest and Great Basin, the 8-14 day outlook preferred the drier ECENS reforecast and uncalibrated model solutions at this time. An amplified 500-hPa trough and enhanced onshore flow favor above-normal precipitation across southeastern Alaska. Downslope surface flow leads to elevated below-normal precipitation probabilities across the northern third of Mainland Alaska. Model guidance remains consistent and in good agreement with increased above (below)-normal temperature probabilities for eastern Mainland Alaska (coastal western Alaska and the Aleutians). Based on the GEFS and ECENS, above-normal precipitation and above-normal temperatures are favored for Hawaii. The official 8-14 day 500-hPa height blend consists of: 40% of Today's 6z GFS Ensemble Mean centered on Day 11, 40% of Today's 0z European Ensemble Mean centered on Day 11, and 20% of Today's 0z Canadian Ensemble Mean centered on Day 11 FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Above average, 4 out of 5, due to a stable longwave pattern and excellent agreement among the temperature tools with the highest uncertainty in the precipitation outlook for the Southwest. 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 October 17. 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: 20051014 - 19640920 - 19841012 - 20051009 - 20090919 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: 20051013 - 19841011 - 20030910 - 19640920 - 20041009 6-10 DAY OUTLOOK TABLE Outlook for Oct 07 - 11 2024 STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A N OREGON A B NRN CALIF A B SRN CALIF A N IDAHO A B NEVADA A B W MONTANA A B E MONTANA A B WYOMING A B UTAH A B ARIZONA A B COLORADO A B NEW MEXICO A B N DAKOTA A B S DAKOTA A B NEBRASKA A B KANSAS A B OKLAHOMA A B N TEXAS A B S TEXAS A B W TEXAS A B MINNESOTA A B IOWA A B MISSOURI A B ARKANSAS A B LOUISIANA A B WISCONSIN A B ILLINOIS A B MISSISSIPPI N B MICHIGAN A B INDIANA N B OHIO N B KENTUCKY N B TENNESSEE N B ALABAMA N N NEW YORK N B VERMONT N A NEW HAMP N A MAINE A A MASS N A CONN B A RHODE IS B A PENN N B NEW JERSEY B B W VIRGINIA B B MARYLAND B B DELAWARE B B VIRGINIA B B N CAROLINA B N S CAROLINA N A GEORGIA N A FL PNHDL A A FL PENIN A A AK N SLOPE N B AK ALEUTIAN B N AK WESTERN N N AK INT BSN A B AK S INT N N AK SO COAST N A AK PNHDL N A 8-14 DAY OUTLOOK TABLE Outlook for Oct 09 - 15 2024 STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN WASHINGTON A N OREGON A B NRN CALIF A B SRN CALIF A N IDAHO A B NEVADA A B W MONTANA A B E MONTANA A B WYOMING A B UTAH A B ARIZONA A B COLORADO A B NEW MEXICO A B N DAKOTA A B S DAKOTA A B NEBRASKA A B KANSAS A B OKLAHOMA A B N TEXAS A B S TEXAS A B W TEXAS A B MINNESOTA A B IOWA A B MISSOURI A B ARKANSAS A B LOUISIANA A B WISCONSIN A B ILLINOIS A B MISSISSIPPI A B MICHIGAN A B INDIANA A B OHIO A B KENTUCKY N B TENNESSEE N B ALABAMA N B NEW YORK N B VERMONT N B NEW HAMP N B MAINE A N MASS N B CONN N B RHODE IS N B PENN N B NEW JERSEY N B W VIRGINIA N B MARYLAND N B DELAWARE N B VIRGINIA N B N CAROLINA N B S CAROLINA N N GEORGIA N A FL PNHDL N A FL PENIN A A AK N SLOPE A B AK ALEUTIAN B N AK WESTERN N N AK INT BSN A N AK S INT A 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. $$