923 FXUS06 KWBC 171903 PMDMRD Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks NWS Climate Prediction Center College Park, MD 300 PM EDT Thu September 17 2020 6-10 DAY OUTLOOK FOR SEP 23 - 27 2020 Today's models show fair agreement and feature a relatively amplified pattern across the forecast domain. An amplified trough is forecast over the North Pacific, with below normal heights predicted over Alaska. A weak ridge is expected over the western and central CONUS, and a weak trough is predicted off the East Coast. Above normal 500-hPa heights are forecast over much of the western and central CONUS due to the mean ridging. Below normal 500-hPa heights are favored over the Pacific Northwest, much of the East Coast, and the Southern Tier states, underneath the negative 500-hPa height anomalies. Below normal temperatures are favored in western Mainland Alaska and the eastern Aleutians underneath negative 500-hPa height anomalies and predominantly easterly to northeasterly surface flow. Despite the eastward extension of negative 500-hPa height anomalies over the Alaska Panhandle, onshore surface flow and above normal sea surface temperatures favor above normal temperatures in Southeast Mainland Alaska and the Panhandle. Enhanced probabilities of above normal temperatures are predicted for much of the western CONUS, extending northeastward to the Great Lakes, underneath mean ridging centered over the Upper Midwest and Great Plains. Elevated odds for below normal temperatures are favored across the Southeast and Gulf Coast, in association with an amplified trough just off the East Coast. The models show some disagreement in the temperature fields for the Northeast and the strength of this trough. However, the ECMWF ensemble mean has shown greater day-to-day consistency with regard to this feature, so the height blend is weighted more toward the Euro. In association with the broad mean trough over the North Pacific and the increased potential for an atmospheric river event, above normal precipitation is favored for much of eastern Mainland Alaska and the Panhandle. Weaker probabilities of above normal precipitation in the Central Aleutians are associated with the passage of surface low pressure systems. Weak probabilities of below normal precipitation are favored in western Mainland Alaska, associated with easterly and northeasterly surface flow. Enhanced odds for above normal precipitation are predicted over the Pacific Northwest ahead of the mean North Pacific trough. Despite the need for rainfall in drought-stricken areas, increased odds for precipitation in the Pacific Northwest bring with them an increased threat for landslides/mudslides in areas with burn scars from ongoing wildfires. So residents in regions affected by wildfires should exercise caution. Below normal precipitation is favored for the eastern two-thirds of the CONUS underneath mean ridging. Enhanced probabilities of below normal precipitation in the Mid-Atlantic are favored behind the mean trough off the eastern seaboard. Weak probabilities for above normal precipitation along the western Gulf Coast are associated with a potential tropical disturbance that is expected to develop and slowly move northward into the beginning of the 6-10 day period. Uncertainty remains whether the system remains offshore throughout the valid period. Probabilities for above normal precipitation are reduced in the Four Corners Region, compared to yesterday's 6-10 day forecast, due to some uncertainty in the forecast tools. The official 6-10 day 500-hPa height blend consists of 20% of Today's 6z GFS Ensemble Mean centered on Day 8, and 80% of Today's 0z European Ensemble Mean centered on Day 8 FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Above average, 4 out of 5, due to fair agreement among the models and tools over Alaska and most of the CONUS, offset by uncertainty in the Northeast and Four Corners. 8-14 DAY OUTLOOK FOR SEP 25 - OCT 01, 2020 During the Week-2 period, a similar 500-hPa circulation pattern is forecast as during the 6-10 day period, but de-amplified, with a trough over the North Pacific, weak ridging over the western CONUS, and weak troughing favored over the eastern CONUS. Below normal 500-hPa heights are predicted over most of Alaska, except for extreme Northeast Mainland Alaska. Near to above normal 500-hPa heights are favored over the western CONUS, extending to the Great Lakes and the Southeast. Weak below normal 500-hPa heights are predicted over Texas and the East Coast, as the mean trough centered off the East Coast is forecast to deamplify during the 8-14 day period. Despite below normal 500-hPa heights, above normal sea surface temperatures and onshore surface flow favor weak probabilities of above normal temperatures along coastal areas of southeastern Mainland Alaska and the Panhandle. Similar to the 6-10 day period, below normal temperatures are favored for much of western and northern Mainland Alaska, in association with easterly to northeasterly surface flow. Broad mean ridging across the central CONUS increases odds for above normal temperatures across much of the CONUS, particularly across the Northern Plains and Upper Midwest. Weak probabilities of below normal temperatures are predicted in the Southeast, in favor of good agreement among the dynamical model and reforecast guidance. Similar to the 6-10 day period, a second, weaker atmospheric river event is predicted to occur, resulting in elevated odds for above normal precipitation in the Alaska Panhandle and the Pacific Northwest, with weaker probabilities extending northwestward into eastern Mainland Alaska. Below normal precipitation is predicted in southwestern Mainland Alaska, with easterly and northeasterly flow favored. Mean surface high pressure over much of the central and eastern CONUS is expected to dominate through much of the 8-14 day period, favoring below normal precipitation in the central CONUS, extending to the Ohio Valley. Increased odds for tropical activity in the Gulf of Mexico, combined with the passage of a frontal boundary late in the period, favor above normal precipitation along the central Gulf Coast and portions of the interior Southeast. However, probabilities remain weak at this time due to large spread in the model guidance. The official 8-14 day 500-hPa height blend consists of: 30% of Today's 6z GFS Ensemble Mean centered on Day 11, 60% of Today's 0z European Ensemble Mean centered on Day 11, and 10% of Today's 0z Canadian Ensemble Mean centered on Day 11 FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Average, 3 out of 5, due to good agreement in the surface fields across Alaska and the central CONUS, offset by uncertainty in the 500-hPa height features and large model spread related to potential tropical activity in the Gulf of Mexico. FORECASTER: Adam Hartman 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 1981-2010 base period means for temperature...precipitation...and 500-hpa heights as reference in the climate outlooks. The next set of long-lead monthly and seasonal outlooks will be released on October 15. 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: 19550908 - 19900910 - 19560914 - 19560907 - 19640911 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: 19550908 - 19900909 - 19560912 - 19560907 - 20070914 6-10 DAY OUTLOOK TABLE Outlook for Sep 23 - 27 2020 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 B WYOMING A B UTAH A N ARIZONA A N 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 B B S TEXAS B A W TEXAS A B MINNESOTA A B IOWA A B MISSOURI A B ARKANSAS N B LOUISIANA B A WISCONSIN A B ILLINOIS A B MISSISSIPPI B B MICHIGAN A B INDIANA A B OHIO A B KENTUCKY N B TENNESSEE B B ALABAMA B B NEW YORK A B VERMONT N B NEW HAMP N B MAINE N B 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 B B N CAROLINA B B S CAROLINA B B GEORGIA B B FL PNHDL B B FL PENIN B B AK N SLOPE B A AK ALEUTIAN B A AK WESTERN B B AK INT BSN N A AK S INT N A AK SO COAST A A AK PNHDL A A 8-14 DAY OUTLOOK TABLE Outlook for Sep 25 - Oct 01, 2020 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 N E MONTANA A B WYOMING A B UTAH A N ARIZONA A N COLORADO A N 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 N N WISCONSIN A B ILLINOIS A B MISSISSIPPI N N MICHIGAN A B INDIANA A B OHIO A B KENTUCKY A B TENNESSEE A B ALABAMA B A NEW YORK A N VERMONT A N NEW HAMP A N MAINE A N MASS A N CONN A N RHODE IS A N PENN A B NEW JERSEY A N W VIRGINIA A B MARYLAND A N DELAWARE A N VIRGINIA A N N CAROLINA A N S CAROLINA N N GEORGIA B N FL PNHDL B A FL PENIN A B AK N SLOPE B A AK ALEUTIAN N N AK WESTERN B B AK INT BSN N A AK S INT N N 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. $$