Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
830 AM EDT Thu May 18 2023


30-DAY OUTLOOK DISCUSSION FOR JUNE 2023

The June 2023 temperature and precipitation outlooks are based on the Climate 
Forecast System Model version 2 (CFSv2), North American Multi-Model Ensemble 
(NMME) and Copernicus model (C3S) suites for June, the week 3-4 model 
solutions, statistical tools, and soil moisture conditions. The Madden-Julian 
Oscillation (MJO) remains active with its enhanced phase over the west-central 
Pacific. The MJO influence on the mid-latitude circulation pattern and 
associated temperatures diminishes by late spring. However, it can modulate 
tropical cyclone (TC) development across the East Pacific and Atlantic basins. 
If the MJO continues to propagate eastward over the Western Hemisphere through 
late May into early June, that would provide a favorable large-scale 
environment for the genesis of an early season TC in the western Caribbean Sea. 
This was a factor in the June precipitation outlook for the Southeast. Since a 
transition from El Niño Southern Oscillation (ENSO)-neutral to El Niño is 
likely during the next couple of months, El Niño temperature and precipitation 
composites during May-June-July were also considered. 

A strong omega block has persisted over or in the vicinity of North America 
since late April. Model solutions depict a weakening of this blocking pattern 
during late May which lowers forecast confidence heading into June. During late 
May and early June, the Global Ensemble Forecast System (GEFS) and European 
Centre for Medium Range Weather Forecast (ECMWF) ensemble means maintain 
positive 500-hPa height anomalies over Alaska and the northern two-thirds of 
the contiguous U.S. (CONUS) with near to below normal heights across the 
southern tier. The prominent area of positive 500-hPa height anomalies at the 
middle to high latitudes of North America would favor a warm start to June 
throughout the northern CONUS. This likely warm start to June along with 
monthly dynamical and statistical tools support increased probabilities for 
above-normal temperatures from the Pacific Northwest east to the Northern Great 
Plains. This favored area of above-normal temperatures extends southward to the 
Central Great Plains and Middle Mississippi Valley where low soil moisture 
conditions are likely to warm surface temperatures. The week 3-4 GEFS and ECMWF 
models, C3S model, and recent daily CFSv2 model runs for June support to 
increased probabilities for above-normal temperatures across parts of the 
Northeast. Based on the NMME, C3S, and decadal trends, above-normal 
temperatures are favored for parts of the Southwest, Rio Grande Valley, Gulf 
Coast, and Florida. Increased probabilities for above-normal temperatures are 
forecast for nearly all of Alaska, consistent with dynamical and statistical 
tools. The one exception is the western coast of Alaska due to below-normal SST 
anomalies across the eastern Bering Sea. 

The week 3-4 GEFS and ECMWF, valid during early to mid-June, are in good 
agreement for elevated probabilities of above-normal precipitation across 
portions of the High Plains, Central Rockies, and Great Basin. This wet signal 
is also present in the monthly NMME and consistent among daily CFSv2 model runs 
for June. Therefore, above-normal precipitation is favored for those areas 
during June. The NMME along with an increased potential for an early season TC 
to emerge from the western Caribbean Sea favors above-normal precipitation for 
parts of the Southeast. Based on the NMME and El Niño precipitation composites, 
elevated probabilities for below-normal precipitation are forecast for 
southeastern Alaska and parts of the Pacific Northwest. A large area of EC was 
necessary in the June precipitation outlook due to weak or conflicting signals 
among the guidance and lower predictability associated with convective rainfall 
during the late spring and early summer. This large coverage of EC will be 
reevaluated with the updated June outlook, released on May 31. 

FORECASTER: Brad Pugh

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 Wed May 31 2023

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