Prognostic Discussion for Monthly Outlook NWS Climate Prediction Center College Park MD 300 PM EDT Tue Oct 31 2023 30-DAY OUTLOOK DISCUSSION FOR NOVEMBER 2023 The November Temperature and Precipitation Outlooks are updated considering current Weather Prediction Center (WPC) Outlooks for week 1, Climate Prediction Center (CPC) Extended Range and Subseasonal Outlooks, dynamical model guidance for week 2 and weeks 3-4, snow cover, background climate states, and recent Climate Forecast System version 2 (CFSv2) monthly forecasts of temperature and precipitation. Equatorial sea surface temperatures (SSTs) are above average across the central and eastern Pacific Ocean, and El Niño conditions are observed. Evolution of the Madden Julian Oscillation (MJO) is uncertain due to destructive interference from the active El Niño, and as such, El Niño remains the dominant teleconnection for temperature and precipitation over North America. Other influencing factors for the updated November Outlooks include sea surface temperature (SST) anomalies, which are above normal along much of the coast of Alaska, along the west coast of the Contiguous United States (CONUS), in the Gulf of Mexico, and along most of the East Coast. Additionally, anomalously high snow cover is present in the north-central CONUS, and sea ice is lower than the average near Alaska, which are also taken into consideration. CPC 6-10 day forecasts (early November) of the 500-hPa circulation pattern favor ridging over western CONUS and troughing over eastern CONUS, with slight eastward progression of the pattern into the 8-14 day period (early to mid-November). Dynamical model predictions of Weeks 3-4 (mid- to late November) 500-hPa heights generally feature broad ridging across much of the CONUS, indicating that the pattern may shift near the middle of the month. Thus, the pattern is somewhat transient for at least the eastern part of the CONUS, which adds uncertainty to the forecast over the east, particularly for temperature. The updated Monthly Temperature Outlook remains similar to the previously released Outlook. A broad area of above normal temperatures is favored for the western half of the CONUS and the Gulf States. Given the persistent ridging over the western CONUS in early to mid-November, Week 34 guidance that favors broad ridging, and recent monthly CFSv2 forecasts of temperature that favor strong probabilities of above normal temperatures over the western half of the CONUS, confidence on above normal temperatures is increased compared to the mid-month Outlook (50 to 60 percent). In contrast, the early November troughing over the eastern CONUS is expected to bring short-lived below normal temperatures into the region, though later parts of the month may shift toward weakly above normal temperature probabilities. Above normal temperature probabilities over the Gulf States are weaker (33 to 40%) and shifted toward the coast compared to the mid-month Outlook due to the possibility of short lived below normal temperatures that may dip into the region early in the month. However, most models maintain some above normal probabilities over the Gulf States throughout much of November and Gulf of Mexico SST anomalies are above normal, both of which support the weak tilt toward above normal. Equal chances of above, near, and below normal temperatures (EC) are favored for the region stretching from the north central CONUS to the east coast, where model uncertainty is high, as well as due to anomalously high snow cover over parts of the north central CONUS that could lead to cooler temperatures. A weak tilt toward below normal temperatures (33 to 40 percent) is indicated for New England, where most models and tools maintain the below normal signal throughout the month of November. The main change from the mid-month Temperature Outlook over Alaska is expansion of the region of above normal temperature probabilities given the lower than average sea ice and above normal SSTs. Larger changes are evident for the updated November Precipitation Outlook, especially given model uncertainty for the mid-month Outlook which led to large areas of EC. Probabilities of above normal precipitation are elevated (50 to 60 percent) over the Northwest given expected early to mid-November above normal precipitation, and in agreement with the expected El Niño teleconnection. The area of below normal precipitation, previously favored over parts of the Great Lakes, is expanded to include parts of the Middle Mississippi, Lower Mississippi, Ohio and Tennessee Valley regions due to strong below normal precipitation probabilities in recent monthly CFSv2 forecasts, supported by Week 3-4 ECMWF forecasts of precipitation. Recent CFSv2 forecasts favor below normal precipitation all the way to the Gulf and east coasts, however, a weak tilt toward above normal is maintained over coastal parts of the Southeast due to potential for El Niño teleconnections and supported by Week 3-4 ECMWF forecasts. EC is favored for the Middle Atlantic and Northeast, again despite below normal monthly CFSv2 predictions, due to amplified storminess and risk of heavy precipitation along the coast as noted in the CPC U.S. Week-2 Hazards Outlook, however, there is considerable uncertainty surrounding this feature. Over Alaska, the updated Precipitation Outlook remains similar, with slight decrease in the area of favored above normal precipitation over the northern parts of the state, and expansion of the area of favored below normal precipitation over the southwestern parts of the state, consistent with updated dynamical model forecasts. ****************************************************************************** Previous mid-month discussion below ****************************************************************************** El Niño conditions are currently observed, and equatorial sea surface temperatures (SSTs) are above average across the central and eastern equatorial Pacific Ocean. The tropical Pacific atmosphere is consistent with El Niño, and as such we expect El Niño to be the dominant teleconnection for November, though impacts are generally weaker than during winter and early spring. While the Madden Julian Oscillation (MJO) showed some renewed activity recently, an incoherent MJO is favored in forecasts of the Realtime Multivariate MJO (RMM) index given destructive interference from the ongoing El Niño and an emerging positive Indian Ocean Dipole (+IOD) event. Thus, the MJO was not significantly considered for the November Outlook. However, given climatology and a broad-scale environment predicted in the models that is consistent with a Central American Gyre (CAG) formation over the tropical Americas, conditions are favorable for tropical cyclone (TC) development over a broad area from the south of Mexico to the western Atlantic during early parts of November as forecast in the latest CPC Global Tropics Hazards Outlook (GTH). In addition to these influencing factors, the November Temperature and Precipitation Outlooks consider local SST anomalies, dynamical model guidance from the North American Multi-Model Ensemble (NMME), Copernicus model suite (C3S), and the Climate Forecast System version 2 (CFSv2), as well as statistical models that include the influence of trend and ENSO. Week 3-4 forecasts from CFSv2, ECMWF, and GEFSv12 for the early part of November were also considered, as was the expected evolution from the Week 2 forecast period. The November 2023 Temperature Outlook favors a broad area of above normal temperatures for the western contiguous United states (CONUS) stretching into the Southern and Central Plains, the lower half of the Mississippi Valley, the Tennessee Valley, parts of the Ohio Valley, and the Southeast. Week 2 Temperature Outlooks feature a tilt toward below normal temperatures over much of the western CONUS for the period of October 25 through October 1, that shifts eastward toward the central CONUS for October 26 through November 1. In contrast, CFSv2, GEFSv12, and ECMWF predictions of week 3 and 4 temperatures through mid-November broadly favor warming over CONUS, including the western and central parts of the country. This suggests that any potential cooler start to November, particularly over the western CONUS, will be a transient feature with uncertainty on how long it may persist. While recent forecasts from CFSv2 favor strong probabilities for above normal temperatures over the western third of the CONUS, probabilities in the November Temperature Outlook are comparatively damped (40 to 50 percent) to reflect this uncertainty. Higher probabilities (40 to 50 percent) of above normal temperatures are indicated over the Southwest where dynamical models agree. The tilt toward above normal temperatures over the west is also supported by the typical El Niño teleconnection, which favors above normal or milder temperatures over the western half of the CONUS. In contrast, below normal temperatures are more typical over over the eastern half of CONUS during El Niño, however, this is at odds with CFSv2 predictions that favor (relatively) strong probabilities for above normal temperatures over parts of the Mississippi, Ohio, and Tennessee Valleys and the Southeast, and with NMME and C3S predictions that also slightly tilt above normal. A weak tilt toward above normal is maintained over parts of the southeastern CONUS (33 to 40 percent), with higher probabilities (40 to 50 percent) over parts of the Gulf States and Florida Peninsula where there is stronger model agreement, and coincident with above average SST anomalies. Equal Chances (EC) of above, below, and near normal temperatures are indicated for the Northern Plains, Great Lakes, parts of the Mid-Atlantic and New England where statistical tools and dynamical models showed weak or conflicting signals. Mixed positive and negative SST anomalies off the coast of New England adds to uncertainty. Finally, a gradient of above normal temperature probabilities to EC is favored for Northern Alaska to Southern Alaska, with the strongest probabilities of above normal temperatures found over the northernmost part of the state where there was strong model agreement and anomalously warm SSTs. More uncertainty is apparent in the November 2023 Precipitation Outlook, with EC indicated for a large part of the CONUS given weak and inconsistent model results, and significant day to day differences in recent CFSv2 predictions. A region of favored above normal precipitation is indicated from parts of Texas eastward across the Southeast and up the East Coast of the CONUS. This region of elevated above normal precipitation probabilities is supported by the NMME and C3S, and agrees with the expected El Niño teleconnection and the potential for increased precipitation that may be associated with elevated TC development. However, probabilities are damped given CFSv2 guidance that favors a tilt toward below normal precipitation probabilities. A slight tilt toward below normal precipitation is depicted over the western Great Lakes where NMME, C3S, CFSv2, and expected El Niño teleconnections all support below normal. Both statistical and dynamical models support enhanced probabilities of above normal over Northern Alaska. Guidance is mixed for the southern coast, but recent CFSv2 forecasts consistently favor stronger probabilities of below normal precipitation, additionally supported by a subset NMME and C3S models, and thus below normal precipitation probabilities are elevated over coastal regions. FORECASTER: Johnna Infanti 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 Dec ... will be issued on Thu Nov 16 2023 These outlooks are based on departures from the 1991-2020 base period. $$