Prognostic Discussion for Monthly Outlook 
NWS Climate Prediction Center College Park MD 
830 AM EDT Thu Sep 21 2023 
 
 
30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2023 
 
El Nino conditions remain strongly in place across the equatorial Pacific Ocean 
both in the ocean as well as the atmosphere and so is considered in the 
preparation of the October outlook. Potential impacts, however, are less likely 
and generally weaker than that sometimes observed during winter and early 
spring. Recent MJO activity has not been strong in recent weeks as compared to 
earlier in 2023. Some model forecasts of the RMM index and other MJO forecast 
tools indicate potential strengthening in the western Pacific (WPAC), but there 
is considerable uncertainty overall in this outcome especially given ongoing 
robust El Nino conditions. 
 
Eventual evolution of the MJO amplitude and phase notwithstanding, conditions 
in the WPAC remain quite conducive for tropical cyclone development over the 
next few weeks in the WPAC as forecast in the latest CPC Global Tropics Hazards 
Outlook (GTH). Since late September and October is near the peak for 
extratropical circulation influencing WPAC re-curving typhoons, predictability 
and overall forecast confidence is generally at a minimum for October within 
the seasonal cycle. The October outlook will be updated on the last day of 
September utilizing the latest information including that related to the above 
uncertainties. 
 
The October 2023 temperature outlook favors above-normal monthly mean 
temperatures for the majority of the forecast domain with the only exceptions 
being Southeast Alaska and the Alaska Panhandle as well as a region from the 
central Rockies to the central Plains where Equal-Chances (EC) of either of the 
three categories are equally likely. The greatest probabilities for 
above-normal temperatures are forecast for areas in northern and western Alaska 
and for the Great Lakes, Northeast, mid-Atlantic and parts of the Southeast and 
Gulf coast. 
 
For Alaska, reduced sea ice coverage and above-normal sea surface temperatures 
(SSTs) in surrounding waters elevate odds for warmer than normal conditions as 
well as El Nino considerations and dynamical model guidance from the NMME and 
C3S contributing ensemble systems. Chances for above-normal temperatures 
decrease moving south and east across Alaska. 
 
Through a considerable period of the first half of the month of October, model 
forecasts from extended-range and subseasonal systems (ECMWF, GEFSv12, JMA, CFS 
and others) indicate the likelihood of substantial positive 500-hPa height 
anomalies associated with both ridging as well as a general northward shift in 
the mean westerlies over central North America including the northern CONUS. As 
a result, above-normal temperatures are most likely for the northern tier of 
the U.S., the eastern CONUS and southern Plains. Considerably above-normal SSTs 
in the Gulf of Mexico and along the Atlantic seaboard also support favored 
above-normal temperatures in these areas. Short-term climate prediction models 
as part of the NMME and C3S ensemble systems indicate this forecast outcome is 
maintained in the monthly mean temperature forecast. 
 
Elevated probabilities for above-normal temperatures for much of the western 
CONUS are low due to uncertainty in model guidance and other forecast tools at 
the start of October. Conflicting forecast tools and El Nino considerations 
(i.e., potential below-normal temperatures) led to a forecast of EC for a 
region in the interior CONUS. 
 
For precipitation, elevated odds of above-normal October monthly total 
precipitation amounts are forecast from the Southwest eastward to include parts 
of the central Rockies, central and southern Plains, Ohio Valley and 
mid-Atlantic. The forecast for the center of this region is mainly supported by 
the likelihood of more unsettled conditions underneath forecast ridging to the 
north as noted above and this is consistent with much of the extended-range and 
short-term climate prediction model guidance. Although only slightly elevated, 
above-normal precipitation is forecast for some areas in the Southwest due to 
potential tropical influences of overall enhanced moisture, tropical cyclone 
impacts and El Nino considerations. Potential unsettled conditions underneath 
ridging, partial model guidance support and positive precipitation long term 
trends slightly favor above-normal precipitation for the Ohio Valley and 
mid-Atlantic. 
 
Above-normal precipitation is also favored for western and northern Alaska 
supported by more open and warmer waters both over a larger area in the 
northeast Pacific as well as more nearby waters of the Bering Sea, Chukchi Sea 
and Beaufort Sea. 
 
Northward shifted westerlies and ridging as indicated by extended-range and 
subseasonal model guidance in early October and short-term climate prediction 
models (NMME and C3S) elevate odds for below-normal precipitation for parts of 
the Pacific Northwest and an area from the northern Great lakes to New England. 
El Nino considerations (i.e., potential below-normal precipitation) also 
supports the forecast for the area highlighted in the Pacific Northwest. 
 
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. 
 
An updated monthly outlook... for Oct will be issued on Sat September 30 2023 
 
These outlooks are based on departures from the 1991-2020 base period. 
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