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Official 90-day Outlooks are issued once each month near mid-month at 8:30am Eastern Time. Please consult the schedule of 30 & 90-day outlooks for exact release dates.

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HOME> Outlook Maps>Seasonal Forecast Discussion
 
Prognostic Discussion for Monthly Outlook 
NWS Climate Prediction Center College Park MD
300 PM EDT Fri Mar 31 2023


30-DAY OUTLOOK DISCUSSION FOR APRIL 2023

The updated temperature and precipitation outlooks for April 2023 reflect
recent dynamical model guidance from the GEFS and CFSv2, as well as current WPC
week 1 outlooks and the CPC week 2 and week 3-4 outlooks. The Madden Julian
Oscillation (MJO) was recently active with convective activity over the
Maritime Continent, although the Real-time Multivariate MJO (RMM) index now
indicates a reduced MJO signal, as subseasonal variability interacts with the
background climate state. Dynamical models , such as the ECMWF and GEFS,
forecast a possible reemergence of the MJO signal over the tropical Pacific.
However, there is uncertainty in the timing and phase of a future MJO signal
and potential impacts to the temperature and precipitation patterns over North
America. While the recent La Niña event has ended, residual atmospheric
conditions similar to La Niña continue, such as suppressed convection near the
date line.

The updated April temperature outlook indicates an expansion of enhanced
probabilities for below normal temperatures for the western and north-central
contiguous U.S. (CONUS), due to recent dynamical model guidance and outlooks
for the beginning of the month. WPC temperature outlooks for the first week of
April indicate a very similar temperature pattern, as do recent CPC 6-10 day
period outlooks and dynamical model consolidation tools. The updated April
temperature outlook shows a reduction in the probabilities favoring above
normal temperatures for parts of the Southwest, while continuing to indicate
likely above normal temperatures for the Southern Plains, the Central and Lower
Mississippi Valley, the Ohio Valley, the Southeast, and the Mid-Atlantic
region. This pattern of below and above normal temperatures across this CONUS
is supported by the CFSv2 model guidance for the month, in addition to the WPC
and CPC outlooks for the beginning of the month. Above normal temperatures are
favored for a small coastal area of northwestern Alaska, while below normal
temperatures are favored for the south coast of the Alaska Mainland, supported
primarily by the most recent CFSv2 model forecasts. A considerable increase in
uncertainty leads to a forecast of equal chances (EC) of above, near and below
normal temperatures for much of Alaska, with conflicting signals among various
tools.

The updated April precipitation outlook indicates an increased probability of
above normal precipitation for the Pacific Northwest, supported by recent WPC
outlooks for the first week of the month, the CFSv2 April precipitation
forecast, and the CPC Week 3-4 Outlook. The area of enhanced probabilities of
below normal precipitation over parts of the Southwest has decreased in the
updated April Outlook, with increased chances of precipitation in both the CPC
8-14 day outlook and the Week 3-4 Outlook over eastern areas of the Southwest,
and over parts of Central California in the first week of April. The updated
April precipitation outlook indicates increased probabilities of above normal
precipitation from East Texas across the Lower Mississippi Valley into the Ohio
and Tennessee Valleys, as well as for eastern areas of the Northern Plains, the
Great Lakes region, and western New York state. Chances of above normal
precipitation for the month of April are increased over these areas by
precipitation forecasts for the first week of the month. Probabilities exceed
50 percent for parts of East Texas northeastward to the Mississippi, where
predicted precipitation in the first week approaches April climatological
precipitation amounts.

The April precipitation outlook favors above normal precipitation for
northwestern Alaska into parts of the Alaska interior and below normal
precipitation for the Alaska Peninsula and the southwestern coast, supported by
the most recent CFSv2 model forecasts and consistent with precipitation
outlooks for the start of the month. An area of enhanced probabilities for
below normal precipitation over the Alaska Panhandle has been removed in the
updated outlook, considering recent outlooks for week 2 and weeks 3 and 4.

*******************************************************************************
***** The previous discussion from mid-March is below *****
*******************************************************************************

The La Niña event has ended as of March, 2023. Sea surface temperature (SST)
anomalies have tended towards positive across most of the equatorial Pacific
Ocean in recent weeks, and the most recent Niño 3.4 region anomaly is
approaching zero degrees Celsius. The East Pacific is particularly warm with an
anomaly of +1.5 C in the Niño 1+2 region. Easterly equatorial wind anomalies
over the Pacific Ocean have weakened in the last month and are confined to a
small area of the central Pacific. Upper-level westerly wind anomalies
continued over the eastern equatorial Pacific. Positive subsurface temperature
anomalies observed in the western and central equatorial Pacific Ocean have
expanded eastward, while extending towards the surface in the eastern Pacific
Ocean. Negative subsurface temperature anomalies near the surface of the
central Pacific Ocean have weakened. Although ENSO-neutral conditions are
predicted in the official ENSO outlook to continue through the Northern
Hemisphere spring, a rapid warming of the Niño 3.4 region SST anomaly is
forecast by most statistical and dynamical models , with an increasing chance of
an El Niño from summer into autumn. Consolidated dynamical model forecasts from
the North America Multi-Model Ensemble (NMME) predict positive SST anomalies in
the Niño 3.4 region, bordering on El Niño conditions near the 0.5 degree C
threshold, from summer through autumn. The Madden-Julian Oscillation (MJO)
strengthened significantly in the beginning of March with convective activity
currently over the Western Hemisphere. Dynamical model forecasts of the
Real-time Multivariate MJO (RMM) index indicate a weakening MJO signal
propagating eastward into the Indian Ocean towards the end of March.

The ECMWF dynamical model forecasts for the beginning of April indicate likely
below-normal temperatures for much of the western contiguous U.S. (CONUS) and
parts of the northern Great Plains. Anomalous snowpack and snow cover over
parts of the West play a role in the temperature outlook for April. In addition
to surface boundary conditions, near-coastal sea surface temperature anomalies
were considered. Linear regression forecasts based on the RMM index indicate a
potential for below-normal temperatures across much of the CONUS at the
beginning of April, followed by warming, particularly in the East. The
temperature and precipitation outlooks for April are based primarily on a
skill-weighted consolidation of dynamical model forecasts from the North
America Multi-Model Ensemble (NMME). Statistical tools, such as the Canonical
Correlation Analysis (CCA), Constructed Analog (CA), and a linear regression
model based on the CPC SST Consolidation forecast of the Nino 3.4 index and
decadal trends were considered, but played a lesser role given the uncertainty
of ENSO-related signals given the rapid transition in the ENSO state. In
addition, skill-based consolidations of statistical and dynamical tools for
temperature and precipitation were consulted.

The April Monthly Outlook favors below-normal temperatures for southwestern
Alaska, as indicated by the NMME consolidation tool, with negative SST
anomalies along the coast contributing to cooler temperatures. Above-normal
temperatures are favored for northeastern Alaska, supported by the NMME
consolidation tool, as well as the statistical forecast tool consolidation. The
probability of below-normal temperatures is enhanced in the Pacific Northwest,
Northern Rockies, and parts of the Great Basin, supported by recent CFSv2 and
ECMWF dynamical model forecasts for April, and consistent with areas of
anomalous snow cover and deep snowpack. Negative SST anomalies near the Pacific
coast contribute to an increased likelihood of below-normal temperatures for
the coasts of California, Oregon and Washington. Above-normal temperatures are
favored from parts of the Southwest eastward across the Southern Plains, and
from the Gulf Coast region northward across the eastern CONUS, as indicated by
the NMME model forecasts. Strong positive SST anomalies along the Gulf Coast
increase the likelihood of above-normal temperatures. Conflicting signals in
the temperature forecast tools lead to equal chances of below, near and
above-normal temperatures in the April outlook over a large area of the
north-central CONUS.

Above-normal precipitation is favored for parts of the west coast of Alaska, as
indicated in the precipitation consolidation of dynamical and statistical tools
and the CFSv2 model forecasts. Below-normal precipitation is slightly favored
for parts of the south coast of Alaska, as predicted by the NMME precipitation
anomaly forecast. Below-normal precipitation is favored for a large area of the
western CONUS from California and southern Oregon to the Central and Southern
Rockies, as predicted by most dynamical and statistical model forecasts and
consistent with decadal precipitation trends for April. Above-normal
precipitation is favored from the western Gulf Coast region northward into
parts of Oklahoma and Arkansas, as predicted by the dynamical and statistical
model forecast consolidation. Above-normal precipitation is also favored for
parts of the Midwest and Great Lakes region, supported by recent dynamical
model forecasts such as the CFSv2 and ECMWF, and consistent with decadal
precipitation trends for April.

FORECASTER: Dan Collins

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 May ... will be issued on Thu Apr 20 2023

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

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