May 31, 2023 2:00 PM

FXUS07 KWBC 311900
Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT Wed May 31 2023


The updated June temperature and precipitation outlooks are based on the latest 
dynamical models, WPC temperature and precipitation forecasts during the first 
week of the month, the CPC 6-10/8-14 day temperature and precipitation 
outlooks, and the week 3-4 dynamical models (valid June 14-27). Sea surface 
temperature (SST) anomalies and soil moisture conditions were used for the 
temperature outlook. The Madden-Julian Oscillation (MJO) eastward propagation 
recently slowed as its enhanced phase entered the Western Hemisphere. The MJO 
is expected to provide a favorable large-scale environment for tropical cyclone 
(TC) development across the East Pacific during early June. The National 
Hurricane Center is currently monitoring a trough of low pressure over the Gulf 
of Mexico. Regardless of development, this disturbance could result in heavy 
precipitation across the Florida Peninsula at the beginning of June. Later in 
the month, large uncertainty exists on the MJO evolution and its related 
influences as a transition to El Niño is well underway. 

Typhoon Mawar, currently located to the east of Taiwan, is forecast to recurve 
northeastward over the Northwest Pacific. This predicted model track of the 
extratropical low pressure system is likely to contribute to an amplified 
500-hPa trough (ridge) over the Aleutians (western North America) during early 
to mid-June. This predicted longwave pattern along with the latest model 
guidance favors below-normal temperatures across the Aleutians and Alaska 
Peninsula with above-normal temperatures more likely for southeastern Alaska 
and northern Mainland Alaska. Dynamical models generally depict a persistent, 
anomalous 500-hPa ridge over the higher latitudes of west-central North America 
into the latter half of June which supports increased probabilities for 
above-normal temperatures from the Pacific Northwest and Northern Rockies east 
to the Midwest. The largest probabilities (more than 60 percent) of 
above-normal temperatures are forecast across parts of the Pacific Northwest, 
North Dakota, and Minnesota where guidance favors above-normal temperatures 
throughout the month. 30-day precipitation deficits range from 2 to 5 inches 
across the Corn Belt where low topsoil is present. This low soil moisture is 
another factor supporting above-normal temperatures for this region. Although 
near to below-normal temperatures are forecast across the Northeast during 
early to mid-June, building heat upstream over west-central Canada is expected 
to eventually spread eastward with time, which is consistent with the week 3-4 
dynamical models. Therefore, the updated June outlook leans towards 
above-normal temperatures for much of this region. Equal chances (EC) of below, 
near, or above-normal temperatures are forecast for areas of New England where 
the signal for relatively cool temperatures is strongest early in the month. 
Positive SST anomalies over the Gulf of Mexico along with forecasted above 
normal temperatures in week 3-4 tools, tilts the forecast toward above normal 
across Florida and along the Gulf Coast. 

Based on the likelihood of below-normal temperatures associated with an early 
month southern stream trough and support from the week 3-4 European Centre for 
Medium Range Weather Forecast (ECMWF) and Climate Forecast System (CFS) models, 
increased probabilities for below-normal temperatures are forecast for the 
Central to Southern High Plains, Southwest, and southern California. During the 
past 30 days, more than 5 inches of precipitation occurred in northeast 
Colorado and the Texas Panhandle which has led to moist topsoil and further 
supports cooler-than-normal temperatures for these areas. The lowest forecast 
confidence in the temperature outlook exists across much of the interior 
Southeast due to uncertainty on the amplitude and placement of a 500-hPa trough 
near the East Coast during the second week of June. The ECMWF and Canadian 
ensemble means are less amplified with this trough and provide a warmer outcome 
for these areas, compared to the GEFS. Given these diverging model solutions 
early in the month, EC are forecast for a majority of the Southeast. 

A predicted anomalous 500-hPa ridge upstream over western to central Canada 
throughout much of June and little to no precipitation during the first week of 
the month favors below-normal precipitation across the Midwest. This favored 
dryness extends east to the Central Appalachians, based in part on WPC’s 7-day 
forecast. Through at least mid-June, model solutions remain consistent that 
shortwave troughs are likely to undercut the high-latitude ridging over 
west-central Canada, favoring wetter-than-normal conditions especially across 
the interior West, High Plains, and Southern Great Plains where increased 
probabilities for above-normal precipitation are forecast for the month. Daily 
CFS model runs, dating back to mid-May, have been very consistent with this wet 
signal during June. A wet start to the month is likely across the Florida 
Peninsula as a trough of low pressure shifts east from the Gulf of Mexico. 
Based on predicted heavy precipitation at the beginning of June and the lack of 
a dry signal among tools at later time scales, elevated probabilities for 
above-normal precipitation are forecast across the Florida Peninsula. The 
largest change in the revised precipitation outlook was made to Alaska as most 
recent model guidance has backed off the dry signal initially forecast for 
southeastern Alaska. A slight lean towards below-normal precipitation is 
maintained for interior eastern Alaska due to the nearby anomalous 500-hPa 
ridge. Conversely, an amplified 500-hPa trough early in the month favors 
above-normal precipitation across the Aleutians and Alaska Peninsula. 


********** Previous discussion, released on May 18, is below **********

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. 


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.

The next monthly outlook...for Jul ... will be issued on Thu Jun 15 2023

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