528 FXUS07 KWBC 311901 PMD30D Prognostic Discussion for Monthly Outlook NWS Climate Prediction Center College Park MD 300 PM EDT Mon Aug 31 2026 30-DAY OUTLOOK DISCUSSION FOR SEP 2026 The updated September temperature and precipitation outlook is primarily informed by model guidance across time scales including short- and medium-range (next 7 days), extended-range and subseasonal-range forecasts. Near coast sea surface temperatures (SSTs) and surface wetness anomalies adjust the outlook in some areas. There are considerable changes in the updated temperature outlook from the mid month outlook. Troughing is forecast to impact much of the western contiguous U.S. (CONUS) early in the month and so cooler conditions are now expected in these areas. The area of favored above-normal temperatures is shifted eastward to encompass the central U.S., Great Lakes and mid-Atlantic in the outlook update. There is now a slight tilt for below-normal monthly mean temperatures for a small region in the Pacific Northwest and Equal-Chances (EC) is now forecast in remaining areas as cooler than normal conditions to start the month may be offset during the second half of the month. Elevated odds for above-normal temperatures remain for the southern tier of the U.S. and Southeast Alaska. The highest likelihood for above-normal temperatures is forecast for the central Great Plains where the GEFS and ECMWF model guidance predict strong ridging during much of the first ten days of September as well as substantially below-normal surface wetness conditions. Potential troughing in the Northeast along with favored above-normal precipitation increases uncertainty and so Equal-Chances (EC) for above-, near- or below-normal temperatures are forecast in this area. For Alaska, troughing forecast in proximity to the state supports elevated odds for below-normal temperatures for parts of western and northern Alaska. There are also substantial modifications in the updated precipitation outlook from the earlier release in mid-August. Above-normal monthly total precipitation amounts remain favored for California and much of the Intermountain West, Rockies and Southwest. For the Pacific Northwest and parts of the northern Rockies, however, above-normal precipitation is now favored due to troughing over approximately the first ten days of the month. The greatest odds are forecast for areas in Oregon where significant precipitation is forecast over the next 7 days and where the monthly precipitation climatology is lower than nearby areas. In the short-term, tropical moisture elevates odds for above-normal precipitation for the southern half of the Florida Peninsula and heavy rains from Potential Tropical Cyclone 5 increases the likelihood for parts of southeast Texas. Enhanced precipitation on the northern periphery of subtropical ridging highlighted in the mid-month outlook is shifted northeastward in the updated outlook. Model guidance is consistent in predicting ridging to be more amplified in the central CONUS and so elevated odds for above-normal precipitation is now focused for the eastern Great Lakes and much of the Northeast. Forecast ridging in the central U.S. for much of the first ten days of September limits precipitation potential and tilts the odds to below-normal precipitation for areas in the central Plains and central Mississippi Valley. Model guidance across multiple time scales supports the weak tilt for below-normal precipitation for a small area along the central Atlantic coastline. There are only slight changes from the mid-August outlook for the state of Alaska. ***************************************************************************** ***** Previous mid-month outlook discussion ***** ***************************************************************************** El Nino conditions in both the ocean and atmosphere have continued to strengthen entering mid-August 2026. Sea surface temperatures (SSTs) are near or greater than +3 degrees C in the equatorial eastern Pacific and the latest weekly Nino3.4 SST index value is +1.8 degrees C. A vast reservoir of above-normal ocean temperatures exists along the equator from the Date Line eastward to the South America coast to a depth of 200 meters. The atmospheric response to these ocean characteristics has been quite strong, namely enhanced convection over the central and eastern Pacific, strongly reduced Trade Winds and upper-level anticyclonic circulations symmetric about the equator. Response to the El Nino conditions is the primary driver of anomalous upper-level divergence, convection and winds in the global Tropics. Any Madden-Julian Oscillation (MJO) related forcing is minor in this context and given the time of the year. Below-normal surface moisture conditions encompass much of the Contiguous United States (CONUS) with severe, extreme and exceptional drought conditions as defined by the U.S. Drought Monitor covering many areas across the western U.S., Great Plains and coastal Southeast. The September Temperature Outlook favors above-normal monthly mean temperatures for the western CONUS, the southern Plains, the Southeast, and Southeast mainland Alaska and Southeast Alaska (i.e., Panhandle). Equal-Chances (EC) for above-, near- and below-normal temperatures are forecast for the Northern Plains, Midwest, Northeast and parts of the Ohio Valley and Mid-Atlantic. The greatest probabilities for warmer than normal temperatures are forecast for the north-central Rockies and Intermountain West. Dry surface conditions, dynamical and hybrid model guidance from the North American Multi-Model Ensemble (NMME) and Copernicus Climate Change Service (C3S) suites, the Seasonal Forecast System (SFS)-Beta and very strong positive (warmer) long-term temperature trends strongly support the forecast for above-normal temperatures. The above outlined factors and model guidance also support the Southern Plains and Southeast forecast for above-normal temperatures. Potential El Nino influence (i.e., slight tilt toward cooler than normal temperatures), closer to normal surface conditions and considerable spread in forecast guidance including that targeting the Week 3-4 period, particularly from the European Centre for Medium-Range Weather Forecasts (ECMWF) model, is the reason for the EC forecast area. Throughout the summer months, frequent troughing and cooler temperatures has impacted this area. The forecast in this region will be refined with the updated monthly outlook later this month. Below-normal SSTs off the coast of the Pacific Northwest lower the odds for above-normal temperatures for near coast areas in this region. Potential for above-normal precipitation over the Southwest U.S. and southern Rockies lowers the likelihood for above-normal temperatures in this area. For Alaska, El Nino conditions, above-normal SSTs in the Gulf of Alaska and the majority of model guidance support the above-normal temperatures depicted for much of the state. EC is forecast for remaining areas due to considerable forecast guidance spread. Ongoing El Nino conditions, statistical, dynamical and hybrid model guidance and positive (wetter) long-term precipitation trends support the favored wetter than normal conditions across the western CONUS. NMME, C3S and SFS-Beta model guidance is utilized for the forecast in interior Alaska and elevated odds for below-normal precipitation in the Pacific Northwest and western Great Lakes. The signals from the model guidance noted here are quite weak and marginally linked to potential El Nino impacts. The slightly elevated likelihood for above-normal precipitation over the Ohio Valley, Central Plains and central Mississippi Valley is primarily based on general persistence from what we have observed much of the recent couple of months. Subtropical ridging across the southern tier of the U.S. has been overall quite persistent while shifting zonally. In association with this ridging, enhanced rainfall has occurred on the northern periphery of the ridge due to residual surface boundaries and mesoscale convective system (MCS) activity. 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 Oct ... will be issued on Thu Sep 17 2026 These outlooks are based on departures from the 1991-2020 base period. $$