Prognostic Discussion for Monthly Outlook 
NWS Climate Prediction Center College Park MD 
830 AM EST Thu Apr 18 2024 


30-DAY OUTLOOK DISCUSSION FOR MAY 2024 

El Niño conditions are currently observed, and equatorial sea surface  
temperatures (SSTs) are above average across the much of the central and  
eastern equatorial Pacific Ocean, reaching 0.9 degrees Celsius above normal in  
the Niño3.4 region, 0.6 degrees Celsius above normal in the Niño3 region, but  
have decreased to -0.2 degrees Celsius below normal in the Niño1+2 region.  
Above average SSTs have weakened across most of the equatorial Pacific Ocean in  
the last 4 weeks, and tropical Pacific atmospheric anomalies are weakening as  
well. Given the weakening signals in the equatorial Pacific, a transition from  
El Niño to El Niño Southern Oscillation (ENSO)-neutral conditions is likely by  
April-May-June 2024. The Madden Julian Oscillation (MJO) has continued to  
weaken recently and though there has been eastward propagation in the past  
week, the amplitude has dropped. Dynamical model forecasts of the Realtime  
Multivariate MJO (RMM) index through close to the end of April are weak and  
incoherent due to an emerging low-frequency feature over the western Indian  
Ocean which appears to be interfering with the MJO. While we may see some  
lingering impacts to temperature and precipitation due to El Niño, the  
influence is expected to weaken throughout the next few months. Moreover, the  
weak amplitude of the MJO does not support much of a teleconnection response  
over the Contiguous United States (CONUS). As such, the May 2024 Temperature  
and Precipitation Outlooks are mainly supported by the lingering influence of  
El Niño, local SST anomalies, influence of soil moisture 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. The Week  
3-4 Outlook for the early part of May was also considered, as was the expected  
evolution from the Week 2 forecast period.  



The May 2024 Temperature Outlook favors above normal temperatures over the  
Northwest, much of the eastern half of the CONUS, and southeastern Alaska. A  
relatively small region of near normal temperatures is indicated over parts of  
California, Arizona, Nevada, and Utah. The highest probabilities of above  
normal temperatures, 50 to 60 percent, are located over Washington, the Great  
Lakes, northern New England, southeastern New Mexico and parts of southwestern  
Texas, the southern tip of Florida, and southeastern Alaska. Probabilities are  
enhanced over these regions given good consistency among tools on above normal  
probabilities. Decadal trends also support above normal probabilities over the  
northwest and northern New England. Anomalously warm Great Lakes temperatures  
provide additional support for above normal probabilities over the region.  
Lower than normal soil moisture along with forecasted below normal rainfall in  
dynamical models, and strong probabilities for above normal temperatures in  
recent CFSv2 forecasts of May temperatures adds to confidence over the  
Southwest. Signals were more mixed over western Alaska given cooler SST  
anomalies and sea ice, but NMME and C3S favor a transition to warmer  
temperatures over the southeast part of the state. Near normal and equal  
chances of above, near and below normal temperatures (EC) are indicated over  
southern California and the Four Corners where there are observed coastal below  
normal to neutral SSTs, near normal temperature forecasts from NMME and C3S,  
and a below normal CFSv2 temperature forecast. While tools tilt toward above  
normal temperatures over the Gulf States (particularly coastal regions),  
partially supported by warmer Gulf of Mexico SSTs, high amounts of recent  
rainfall over eastern Texas and Louisiana have resulted in high soil moisture,  
and as such probabilities are still above normal but damped. EC is favored  
where models were inconsistent and/or where there was a lack of support from  
statistical tools.  



There is more uncertainty in the May 2024 Precipitation Outlook than the  
Temperature Outlook, as evidenced by lower overall probabilities and larger  
areas of EC. Models favor above normal precipitation over parts of the central  
and southern CONUS, including parts of the Mid-Atlantic, Middle Mississippi and  
Ohio Valley regions. Some lingering influence from El Niño further supports the  
tilt toward above normal precipitation over the Southeast, as well as enhanced  
soil moisture. Though El Niño can lead to below normal precipitation over the  
Great Lakes, Middle Mississippi Valley, and Ohio Valley, this influence is  
overshadowed by above normal precipitation trend. EC is indicated over the  
Great Lakes where models had weak or inconsistent signals and trend and El Niño  
influence are opposite. However, over the Mississippi and Ohio Valley regions  
C3S and NMME favored above normal rainfall and thus a weak tilt toward above  
normal is indicated. Dynamical models and dry soil moisture led to the favored  
probability of below normal precipitation over parts of the southwest, which is  
also indicated in the Seasonal Outlook for May-July 2024. However, this is at  
odds with the recent Weeks 3-4 Precipitation Outlook for early May that tilted  
weakly toward above median precipitation. We expect below normal precipitation 
 over the region by mid- to late- May. Tools were again mixed over the  
northwest, but influences from El Niño and trend tilt the odds toward below  
normal. Finally, over Alaska, above normal precipitation is favored over the  
southwest where there has been recent above normal precipitation, with a weak  
tilt toward below normal precipitation over southeastern Alaska due to expected  
influence from El Niño. 
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. 

An updated monthly outlook... for May will be issued on Tue Apr 30 2024 

These outlooks are based on departures from the 1991-2020 base period. 
$$