Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT Sun May 31 2020


30-DAY OUTLOOK DISCUSSION FOR JUNE 2020

The updated monthly temperature and precipitation outlooks for June 2020 are 
based on the latest dynamical model guidance, including the NCEP CFS and GEFS 
and ECMWF ensemble prediction systems, WPC temperature and precipitation 
forecasts for the first week of the month, the CPC 6-10 day, 8-14 day, and week 
3-4 temperature and precipitation outlooks, and current climate conditions. The 
enhanced phase of the Madden-Julian Oscillation (MJO) propagated eastward 
across the Western Pacific during late May and is now in the Western 
Hemisphere. Enhanced convective activity over the Caribbean and southern Gulf 
of Mexico may enhance precipitation for parts of the southeastern CONUS in the 
second week of June. ENSO neutral conditions are present at this time and 
likely to continue into summer. 

Dynamical model circulation forecasts for the first week of June predict a 
mid-level trough over the North Pacific extending along the Pacific coast of 
North America with an amplified ridge downstream over the central and eastern 
CONUS. Models including the ECMWF and GEFS ensemble prediction systems indicate 
a de-amplification of the circulation pattern in the second week of the month, 
while maintaining troughing from the Gulf of Alaska to the Pacific Northwest 
and ridging and above normal heights over the Southwest into the southern 
central CONUS. Uncertainty between model forecasts increases in the second half 
of the month, while dynamical models generally persist positive 500-hPa height 
anomalies for much of the western CONUS and, in the case of the ECMWF ensemble 
mean forecast, across the entire CONUS. Weak negative 500-hPa height anomalies 
persist over parts of the North Pacific in dynamical model forecasts, including 
the ECMWF, NCEP CFS and the Subseasonal Experiment (SubX) multi-model ensemble 
(MME), for late June.

The updated June temperature outlook indicates increased probabilities of above 
normal average temperatures for the month over most of the CONUS under a 
persistent ridge through at least the first half of the month. Probabilities 
exceed 60 percent for parts of the Central Plains, where the probabilities of 
above normal temperatures during weeks 1 and 2 are greatest and predicted to 
persist in the CPC week 3-4 outlook. Equal chances (EC) of below, near and 
above normal temperatures are indicated for parts of the Pacific Northwest, 
where below normal temperatures are likely during much of the first half of the 
month, under a predicted trough, and a warming is likely later in the month, as 
500-hPa heights are predicted to rise. Above normal temperatures are likely for 
all of the state of Alaska for the June average, under primarily positive 
500-hPa height anomalies throughout the month. 

The updated June precipitation outlook indicates increased chances of below 
normal rainfall over parts of the central and eastern CONUS, including parts of 
the Southern and Central Plains from northern Texas northward across Oklahoma 
into Kansas and much of Nebraska and northeastward across the Central 
Mississippi Valley as far as Illinois, under a predicted ridge particularly 
during the first two weeks of June. An additional area of enhanced 
probabilities of below normal precipitation is indicated over the Mid-Atlantic 
region into southern New England, supported by a consolidation of weeks 1 
through 4 precipitation forecasts from the NCEP GEFS and CFS. Above normal 
precipitation continues to be likely for the Gulf Coast region, as in the 
half-month lead precipitation outlook, due to predicted enhanced convective 
activity over the Gulf of Mexico by dynamical models primarily during week 2. 
Dynamical model forecasts, including the ECMWF and GEFS, of likely above normal 
precipitation extending from the Southeast northward into the Central 
Mississippi, Tennessee and Ohio Valleys during week 2 decreases the probability 
of below normal June average precipitation for these regions, despite the 
prediction of large scale ridging and below normal precipitation for the first 
week of the month. A predicted trough along the Pacific Coast early in June 
increases the likelihood of above normal precipitation for the Pacific 
Northwest in the June outlook. Dynamical model forecasts indicate likely above 
normal precipitation for parts of Arizona and New Mexico into the Four Corners 
region during the first week of the month, however precipitation amounts are 
likely to be small, and dynamical model forecasts predict a drying of this 
region from the week 2 period forward. Therefore, equal chances (EC) is 
indicated in the June precipitation outlook for the Southwest region. Above 
normal precipitation continues to be likely for much of southern Alaska from 
the Aleutians across the south coast of the Alaska Mainland to the Alaska 
Panhandle, as indicated by dynamical model forecasts of predicted weak positive 
or negative 500-hPa height anomalies and potential storm tracks. 

----------- Previous message (from May 21) is below ------------

The June 2020 temperature and precipitation outlooks are based primarily on 
dynamical model guidance, statistical tools, and current soil moisture 
conditions. ENSO-neutral conditions are currently present across the Tropical 
Pacific, and the consensus forecast indicates that ENSO-neutral conditions are 
likely to remain in place throughout the month of June and into the next 
several seasons. SSTs have cooled across most of the equatorial Tropical 
Pacific during the last several weeks and are near or below average over the 
eastern equatorial Pacific. The Madden-Julian Oscillation or MJO has recently 
become active with convection centered over the Indian Ocean. Dynamical model 
forecasts, including the NCEP CFSv2, indicate that the MJO is expected to 
remain active and propagate across the Maritime Continent into the western 
Pacific Ocean, potentially influencing the climate over North America in three 
to four weeks from the present time. Statistical tools show that the active MJO 
in the current phase will potentially enhance the chances of below normal 
temperatures across much of the eastern CONUS and above normal temperatures for 
parts of the western CONUS in early June. The transient MJO impact will 
potentially influence June monthly average temperatures and increase the 
uncertainty in the June outlook. Absent a signal from ENSO, the June 
temperature outlook is somewhat impacted by decadal time scale temperature 
trends, moderated by shorter timescale climate impacts, including soil moisture 
feedbacks. If the MJO or related atmospheric Kelvin wave propagates eastward 
over the Western Hemisphere during early June, this would provide a favorable 
large scale environment for tropical cyclone development across the northwest 
Caribbean and southern Gulf of Mexico and may impact precipitation for parts of 
the southeastern CONUS.

The June temperature outlook calls for enhanced probabilities for above normal 
temperatures for all of Alaska with probabilities exceeding 50 percent for 
southwestern areas of the state, where nearby sea surface temperatures are 
above average. The week 3-4 temperature outlook indicates likely above normal 
average temperatures for the first half of June for Alaska, and dynamical model 
forecasts from the CFS as well as the NMME support above normal temperatures 
for the month. Above normal temperatures are also likely for the month of June 
for the western CONUS, primarily to the west of the continental divide, 
supported by dynamical model forecasts from the CFS and NMME, and similar in 
extent to predicted likely above normal temperatures in the first half of June 
by the CPC week 3-4 outlook. Probabilities exceed 50 percent for much of the 
Great Basin and Southwest regions, where the signal due to decadal temperature 
trends is greater. Uncertainty increases across much of the central and eastern 
CONUS, due in part to the influence of shorter timescale climate signals such 
as the MJO. A large area of equal chances of below, near or above normal 
temperatures is indicated for the month of June from the Northern and Central 
Plains across the Upper and Central Mississippi Valleys, where there is greater 
ensemble spread among individual models of the NMME. Temperatures for the month 
of June may also be moderated across this area by current positive soil 
moisture anomalies and an above normal precipitation forecast. Probabilities of 
above normal temperatures increase for the Gulf Coast states as well as the 
Eastern Seaboard and Northeast regions, supported by dynamical model forecasts 
including the CFS and NMME models. Models consistently show a high probability 
of above normal temperatures for the southern Florida Peninsula where the 
probability of above normal temperatures exceeds 50 percent. Above normal 
temperatures for the Northeast region are also supported by larger positive 
decadal temperature trends for this region. 

The June precipitation outlook calls for enhanced probabilities of below normal 
precipitation for western areas of the states of Washington and Oregon, 
supported by dynamical model forecasts including NMME probability forecasts, 
where seasonal climate signals indicate a broader area of likely below normal 
precipitation. However, dynamical models indicate uncertainty is greater in the 
individual month of June. Probabilities of above normal precipitation are 
enhanced over a large area of the eastern CONUS stretching from eastern areas 
of the Great Plains across the Central and Lower Mississippi Valleys and the 
Southeast region to the southern Atlantic coast, supported by probability 
forecasts from the NMME. Dynamical models, including the CFS, indicate an 
active Gulf of Mexico in June. Skill in precipitation forecasts is limited but 
a clear signal is apparent in dynamical models for a large area of the eastern 
CONUS. Models are less consistent for the Northeast region June precipitation 
forecast where equal chances of below, near and above normal precipitation is 
indicated. Dynamical model forecasts from the NMME indicate much of the 
precipitation signal over Alaska is along the southern coast, where 
probabilities of above normal precipitation are increased. 

FORECASTER: Dan Collins

The climatic normals are based on conditions between 1981 and 2010, 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 Jul ... will be issued on Thu Jun 18 2020

These outlooks are based on departures from the 1981-2010 base period.
$$