Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
830 AM EDT Thu May 20 2021


30-DAY OUTLOOK DISCUSSION FOR JUNE 2021

The June 2021 monthly outlook was prepared based on current surface conditions 
such as soil moisture and coastal sea surface temperatures (SSTs), potential 
impacts from the currently active MJO, dynamical model and statistical forecast 
guidance and newly derived long term trends from the 1991-2020 base period. 

La Nina conditions present during the winter and spring months has ended as 
both SSTs in the equatorial Pacific Ocean have warmed and coupling to the 
atmosphere has weakened. The MJO, however, has been active since mid-March and 
has been strong and is starting its third "cycle" around the global Tropics. 
The enhanced phase of the MJO is currently centered in the Indian Ocean and is 
forecast to continue to propagate eastward to the western Pacific by the 
beginning of June. The teleconnection to the mid-latitudes from MJO forcing 
during late spring and summer, even during a moderate to strong event, is 
typically considerably weaker, has a lower likelihood to occur and impacts 
highly variable. For this event, the forecast phase of the MJO at the start of 
June would favor above-normal temperatures for the western CONUS based on 
composites and statistical forecast tools as well as, but to a considerably 
lesser degree below-normal temperatures in the vicinity of the Great Lakes, the 
Ohio Valley and parts of the mid-South. These impacts, however, would be mainly 
during the first 10 days of the month June and impacts based on MJO composites 
and other tools are not statistically significant in subsequent MJO phases 
thereafter. 

Favored above-normal temperatures for the western CONUS from the MJO 
perspective is consistent and further supported by overwhelming dynamical model 
forecast guidance, statistical tools, low soil moisture considerations and 
positive long term temperature trends. Conflicting and/or weak signals related 
to the MJO, dynamical model and statistical guidance, areas of very wet surface 
conditions in addition to favored above-normal precipitation for the month of 
June as a whole results in low confidence for the eventual category of June 
monthly mean temperatures for the southern Plains, lower Mississippi Valley and 
parts of the Southeast. Equal-chances (EC) for either of the three categories 
is forecast in these areas. Above-normal SSTs in the lower Bering Sea favor 
above-normal temperatures for southwest Alaska which is somewhat supported by 
model forecast guidance. Climate signals were weak for most of the remainder of 
the state. 

The June 2021 precipitation outlook favors below-normal precipitation for a 
region from the Pacific Northwest and northern Rockies to the central Rockies 
southward to include parts of the state of New Mexico and Texas primarily based 
on consistent dynamical model forecast guidance. Elevated probabilities for 
above-normal precipitation is forecast for the western portion of Alaska 
supported by model guidance as well as potentially greater moisture 
availability for precipitation due to more open and warmer waters in the Bering 
Sea, especially the first half of the month. The likely MJO phase over the 
course of the month of June would tend to favor at various times enhanced odds 
of above-normal precipitation for the Gulf Coast, Southeast and Ohio Valley. 
This along with support from dynamical model guidance and long term positive 
precipitation trends favor above-normal monthly total precipitation amounts for 
these areas.

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 Jun will be issued on Mon May 31 2021

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