Prognostic Discussion for Monthly Outlook NWS Climate Prediction Center College Park MD 300 PM EDT Fri Sep 30 2022 30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2022 The October updated monthly outlook is adjusted by utilizing model forecast guidance from the short, extended and subseasonal time range as well as considerations from potential MJO influences (primarily for the second half of the month). Model predictions of the RMM index indicate the development of a MJO signal that will propagate eastward to the western Pacific (Phase 6) by the middle of October. Although tropical extratropical connections are generally not as robust this time of the year (as compared to the winter/spring seasons), this evolution would tend to develop warmer conditions for the eastern CONUS and troughing and colder conditions for the western CONUS late in October. The revised October outlook for monthly mean temperatures is generally not significantly changed from the previous outlook for most of the forecast domain. Above-normal temperatures remain favored for most of the CONUS, however, the area of focus is shifted westward so that the highest odds are now forecast for the western and central CONUS. Elevated odds for below-normal temperatures are forecast for the mid-Atlantic. The primary reason for the change in this region is cooler conditions at the start of the month from (1) cloudiness and rainfall associated with the remnants of Hurricane Ian, (2) northerly flow behind this system and trough development forecast by medium and extended range model guidance over Southeast Canada and the Northeast. The area is modest in size because anticipated cooler than normal conditions the first 10 days of October are favored to be modified during the remainder of the month consistent with subseasonal guidance and tendencies noted earlier by lagged composites of the MJO from Phase 6 during the later part of October. Model guidance across time scales favors above-normal temperatures for much of the western and central CONUS with the greatest probabilities forecast for parts of the Pacific Northwest, northern Rockies and northern and central Plains. For Alaska, anticipated troughing to the west of the state with a west- southwesterly flow favors high odds for above-normal temperatures for most of the state during the first 1-2 weeks and signals thereafter are not particularly strong and reliable for sufficient confidence that colder conditions would develop for the second half of the month so the area of below-normal temperatures favored in the mid-month outlook has been removed with an increase in coverage across the state for favored above-normal temperatures. For precipitation, in the short-term in the mid-Atlantic region, the forecast is driven by the eventual rainfall from the remnants of Hurricane Ian that are forecast to occur the first few days of October. High probabilities of above-normal monthly precipitation totals are depicted for a small area in the coastal mid-Atlantic. The favored below-normal precipitation area from the mid-month outlook has been shifted eastward and oriented more north-south in the revised outlook. Anomalous northerly, drier flow after the transition and departure of Ian along with forecast trough development over eastern North America favors below-normal precipitation for the central CONUS from the Canadian border to the Gulf of Mexico. A change was made from the mid-month outlook for the western CONUS as precipitation is anticipated during the first 1-2 weeks of October at various times for portions of the Southwest, central Rockies and Far west resulting in considerable uncertainty for the western CONUS. The forecast area of EC is increased from the mid-month outlook and an area of elevated odds for above-normal precipitation is depicted for parts of the central Rockies and Southwest. For Alaska, the aforementioned trough west of Alaska and southwesterly flow favors above-normal precipitation for much of interior part of the state and Alaska Panhandle. ************ Previous mid-month outlook discussion is below ************ A review of background climate conditions continues to show established La Nina conditions which are forecast to remain in place at least into the upcoming winter months. Both the Nino4 and Nino3.4 latest sea surface temperature (SST) values remain near -1.0 degrees C and tropical atmospheric conditions (i.e., convection/rainfall, low-level and upper-level winds) continue to be consistent with La Nina. Although this is a monthly outlook and impacts from La Nina to the mid-latitudes are generally weak at this time of the year, the La Nina base state was considered in the October monthly outlook to some degree. The MJO signal is not particularly coherent especially in certain indices such as the RMM index which is being heavily influenced by interference from ongoing La Nina conditions. Some predictions of other variables such as 200-hPa velocity potential show some potential for more MJO organization as we enter the month of October with the enhanced convective phase located in Phases 1-2-3. This may promote enhanced convection to develop in the Central America and Caribbean region at a time of the year when primary tropical cyclone development begins to shift from the eastern and central Atlantic westward to these areas. In addition to the considerations noted above, dynamical model guidance from the North American Multi-Model Ensemble (NMME), Copernicus model suite (C3S) and extended (30-day) ensemble model systems from the CFS, ECMWF and GEFS that target the Week 3-4 period were utilized in preparing the outlook. The October 2022 temperature outlook depicts favored above-normal monthly mean temperatures for the majority of the CONUS with the only exception being the far Pacific Northwest. The greatest odds are forecast for an area from the central Rockies to the central Plains where the anomalously warm signal was most consistent amongst all the forecast tools and potential La Nina influence. The Week 3-4 dynamical model guidance and multiple linear regression forecast tool (ENSO, MJO, trend as predictors) supported a warmer than average start to October across the CONUS associated with forecast ridging and northward shifted westerlies. For Alaska, the signals overall were quite weak and conflicting. Slight tilts toward above-normal (below-normal) temperatures are depicted for coastal northwest Alaska (south-central Alaska) driven primarily by long-term trends (model guidance). For the October 2022 precipitation outlook, elevated odds for below-normal monthly total precipitation amounts is depicted from north-central California eastward across the central Rockies to the central and southern Plains and parts of the central Mississippi and Ohio Valley's. The La Nina base state, dynamical model guidance and long term trends contributed to this outlook. A slight tilt toward above-normal precipitation is shown for parts of Washington and the Alaska panhandle associated with model guidance and potential La Nina impacts. Probabilities in all locations are modest due to the low predictability common during this time of the year. Considerations of tropical moisture from the Gulf of Mexico or Caribbean Sea region related to any potential intraseasonal influence noted above resulted in an Equal Chances (EC) forecast for parts of the Gulf coast and Southeast despite considerable forecast guidance favoring drier-than-normal precipitation. There were weak and conflicting signals for mainland Alaska so EC is currently forecast in this area. FORECASTER: Jon Gottschalck The climatic normals are based on conditions between 1991 and 2020, following the World Meteorological Organization convention of using the most recent 3 complete decades as the climate reference period. The probability anomalies for temperature and precipitation based on these new normals better represent shorter term climatic anomalies than the forecasts based on older normals. The next monthly outlook...for Nov ... will be issued on Thu Oct 20 2022 These outlooks are based on departures from the 1991-2020 base period. $$