955
FXUS07 KWBC 161331
PMD30D
Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
830 AM EST Thu Jan 16 2025
30-DAY OUTLOOK DISCUSSION FOR FEBRUARY 2025
The long-awaited transition from a neutral El Nio Southern Oscillation (ENSO)
to a weak La Nia finally occurred during December 2024, with the latest weekly
value of the Oceanic Nio Index (ONI) of -0.7C for the Nio 3.4 region.
Below-average sea-surface temperatures (SSTs) now dominate the central and
east-central Pacific with significant subsurface cooling to a depth of 100-200
meters. Broad expanses of enhanced (suppressed) tropical convection are noted
over the vicinity of Indonesia (Date Line), with persistently enhanced
low-level trade winds over the western and central near-equatorial Pacific. La
Nia conditions are expected to persist through the Feb-Mar-Apr (FMA) 2025
season with odds of 59 percent, followed by a nearly equally likely transition
to ENSO-neutral starting in Mar-Apr-May (MAM) 2025.
In addition to La Nia being the expected primary driver of the atmospheric
circulation pattern in February, there is significant forcing associated with
the Arctic Oscillation (AO) and the Madden-Julian Oscillation (MJO). The AO
index has been negative during the past two weeks, which has likely contributed
to the current cold snap across the central and eastern contiguous U.S.
(CONUS). The AO index is forecast to transition toward its positive phase in
the next 2 weeks, which may signify at least a brief reprieve from the
persistent influence of Arctic air masses over this portion of the country. In
the tropics, the convectively enhanced phase of the MJO is currently in the
Western Hemisphere, near the interface of Realtime Multivariate MJO (RMM)
Phases 8 and 1. During the past 10-14 days, there has been a very significant
increase in amplitude of the MJO signal, though there has been little eastward
propagation. Most RMM-based MJO Index forecasts predict a high-amplitude MJO
accelerating to phase speeds more consistent of a convectively-coupled Kelvin
Wave, as the signal traverses the remainder of the Western Hemisphere, Africa,
the Indian Ocean, and reaches the Maritime Continent during the next two-week
period. Historically, an MJO signal propagating eastward across the Indian
Ocean and Maritime Continent favors a warm response downstream over the central
and eastern CONUS towards the end of January, but this is contradicted by most
dynamical model guidance which favors the continuation of below normal
temperatures across this region.
Other considerations for the February outlooks include coastal SSTs, sea and
lake ice, and snow cover. At the present time, near to primarily above normal
SSTs prevail near the West Coast of the CONUS, the western and central Gulf
Coast, and near the southwest coast of Alaska. Below normal SSTs are observed
near the coast of the Northeast CONUS. Most of the Alaska coast as far south as
Kuskokwim Bay (Southwest Alaska) is dominated by sea ice. Over the Lower 48
states, the Great Lakes remain mostly ice-free as of mid-January, with
relatively shallow Lake Erie being the most likely to freeze over during the
next few weeks. Current snow cover is widespread across the northern and
central CONUS, with associated radiational cooling helping to keep surface
temperatures lower over this area.
The monthly Temperature and Precipitation Outlooks for February are based on
historical La Nia composites and regressions and the secondary forcings
described above, as well as on dynamical and statistical model support.
Dynamical support is derived from dynamical model suites including the North
American Multi-Model Ensemble (NMME), Copernicus Climate Suite (C3S), and from
the Climate Forecast System version 2 (CFSv2) dynamical model. Statistical
support comes largely from a combined ENSO-OCN tool, and to a lesser degree the
Canonical Correlation Analysis (CCA). CPCs official outlooks for Weeks 3-4,
and monthly and submonthly temperature and precipitation guidance from the
Global Ensemble Forecast System (GEFS), CFSv2, and European Centre for
Medium-Range Weather Forecasts (ECMWF) models are also used in the preparation
of the February Outlooks, though it is important to note that these forecasts
only cover the first half of February.
The February 2025 Temperature Outlook features elevated odds of above normal
temperatures over the vicinity of the Four Corners states/Southwest, southern
Plains, Lower Mississippi and Tennessee Valleys, the Southeast, Upper Ohio
Valley, most of the Appalachians, Mid-Atlantic, and Northeast. Probabilities of
above normal temperatures reach 50 to 60 percent over parts of the southern
Rockies. This broad pattern is characteristic of part of the typical cold
season La Nia signature, and is supported by available models and tools such
as the dynamical consolidation (NMME CON), NMME Probability Anomaly Correlated
(PAC) calibrated forecasts, C3S, and recent runs of the CFSv2. Below normal
temperature chances are enhanced from the Pacific Northwest eastward across
much of Montana, the Northern and Central Plains, and the Upper Mississippi
Valley. This is supported by the statistical consolidation (Stat CON), recent
runs of the CFSv2, the ENSO-OCN tool which combines influences of ENSO and
trends, and the ECMWF and Deutscher Wetterdienst (DWD, German model) which are
constituents of the Copernicus model Suite (C3S). Other constituents such as
the United Kingdom Met Office (UKMO) and Meteo-France models appear to be too
warm overall. This broad area of favored anomalous cold is also very typical of
classic wintertime La Nia events. In Alaska, many tools support some variation
on the classic La Nia theme which is characterized by increased chances for
below normal mean temperatures across southcentral and southeast Alaska, and
increased chances for above normal mean temperatures confined to northwest
portions of the Mainland.
The February 2025 Precipitation Outlook features elevated odds for above normal
precipitation from the Pacific Northwest eastward across the Northern
Intermountain region and Northern Rockies to the northern High Plains. This is
generally associated with the Pacific jet stream as it traverses much of the
northern CONUS. One of the few dissenting opinions comes from the Stat CON
(specifically the CCA input) which favors below normal precipitation across the
Pacific Northwest and was discounted for this particular forecast. Above normal
precipitation chances are also increased for much of the Mississippi Valley,
Tennessee and Ohio Valleys, Great Lakes region, central and northern
Appalachians, and interior portions of the Mid-Atlantic and Northeast.
Probabilities of above normal precipitation reach 50 to 60 percent percent from
the central Great Lakes region southwestward towards the Missouri Bootheel.
This second region of favored anomalous storminess is associated with a typical
meandering of the jetstream across this region and the resulting mean storm
track, and is consistent with many of the precipitation tools. Approximately
half of the available tools forecast above normal precipitation reaching the
Northeast and Mid-Atlantic coasts, and while this is certainly reasonable with
individual cyclonic systems, the La Nia storm track on average tends to be
shifted farther inland. There are enhanced odds of below normal precipitation
from far southern California generally eastward across much of the Four Corners
region, the central and southern High Plains, much of Texas, far southern
Mississippi Valley, and a large portion of the Southeast as far north as the
Tidewater area of southeastern Virginia. Probabilities reach 50 to 60 percent
over the vicinity of the Rio Grande Valley, and also most of Florida,
southeastern Georgia, and nearby parts of South Carolina. This broad region of
favored drier than normal conditions is consistent with the typical La Nia
footprint, and is well supported by many tools, such as the Stat and NMME CONs
and the CFSv2 to name a few. Over Alaska, above normal precipitation chances
are elevated over most of the Mainland north of the Alaska Range, with a sliver
of slightly enhanced below normal precipitation chances over parts of
southcentral and southeastern Mainland Alaska. These predicted anomalies are
generally consistent with mean surface high pressure and mid-level ridging over
the Gulf of Alaska during La Nia events.
FORECASTER: Anthony Artusa
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 Feb will be issued on Fri January 31 2025
These outlooks are based on departures from the 1991-2020 base period.
$$
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