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Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT Mon May 31 2021
30-DAY OUTLOOK DISCUSSION FOR JUNE 2021
The update to the June 2021 temperature and precipitation outlooks are driven
primarily by the most recent short-, medium- and extended-range model guidance
as well as the most recently available subseasonal and monthly integrated
forecast products. The MJO has become less coherent in recent weeks and does
not play as much of a role in the updated outlook, while soil moisture
anomalies continued to inform the June temperature outlook.
Changes to the June temperature outlook are generally small overall. The
outlook continues to favor above-normal temperatures in an inverted horseshoe
pattern encompassing areas from the Southwest CONUS to the Pacific Northwest
across the northern Plains and Great Lakes to the Northeast and mid-Atlantic.
Strong ridging anticipated during much of the first half of June increases odds
for above-normal temperatures for the Northeast, Great Lakes and mid-Atlantic
compared to the mid-month outlook. Also, highest probabilities for above-normal
temperatures in the western CONUS have been shifted to the northwest and are
now focused in the central Great Basin and western Rockies where ridging and
warmer-than-normal temperatures (some potentially extreme) are likely during
the first week of June.
The most substantial change in the updated June outlook, is the inclusion of
favored below-normal temperatures for the southern Plains, lower Mississippi
Valley and western Gulf coast. The mid-month outlook did note the uncertainty
in this region and potential cooler temperatures with a forecast area of
Equal-Chances (EC) due to negative 500-hPa heights indicative of weakened
sub-tropical ridging and enhanced cloudiness and precipitation. Model guidance
through the end of May 2021 across time scales has become more clear and
increased the likelihood of the conditions described above. Substantial further
support for this addition is the recent heavy rainfall, especially for parts of
east Texas and Louisiana, which has maintained or increased anomalously wet
surface conditions across this region. Some minor changes are made in Alaska in
the update, but forecast confidence is low and only very slight tilts from
climatological odds are depicted for the state.
For precipitation, the updated June 2021 outlook illustrates some minor
adjustments in general from the mid-month outlook. Favored below-normal
precipitation remains for the northern Rockies and Pacific Northwest, but has
been removed from parts of the eastern Southwest and southern High Plains.
Model guidance favors some rainfall early in the month in this region where
normal precipitation totals are relatively low.
In addition to the potential MJO influence noted in the mid-month discussion
below, model guidance across time scales has increased confidence for
above-normal precipitation for a region from Texas to the lower Ohio Valley,
mid-South, Gulf coast, Southeast and lower mid-Atlantic. Greatest odds are for
parts of eastern Texas and Louisiana.
Other minor changes include the addition of a small region of favored
above-normal precipitation for parts of the northern Plains and upper
Mississippi Valley, but confidence is low. High uncertainty due to varying
signals in the available forecast tools across time scales in Alaska has led to
a forecast of EC for the state of Alaska in the updated June outlook.
****** Previous mid-month discussion below ******
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
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 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
FORECASTER: Jon Gottschalck
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 17 2021
These outlooks are based on departures from the 1981-2010 base period.