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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 EST Sun Feb 28 2021


30-DAY OUTLOOK DISCUSSION FOR MARCH 2021

The updated March 2021 temperature and precipitation outlooks are not too
significantly changed from the previous mid-month outlook. The updated outlooks
utilized the latest short-range, medium-range, extended-range and subseasonal
dynamical model forecast guidance for some adjustments. In addition, the most
recent assessment of boundary conditions (anomalous soil moisture and snow
cover), the MJO state and the AO state are also considered in making the
update.

The uncertainty whether short-range forecasts of a change to a positive AO
phase would persist and be supported by changes in stratosphere troposphere
interaction have been removed as the extended range forecasts of the AO support
continuation of the current positive AO phase through at least mid-month.

The MJO influence described at mid-month, however, remains in play as
predictions of the MJO signal (i.e., RMM) are forecast to shift from Phase 5/6
(Indonesia/far western Pacific) to potentially Phase 8/1 over the next two
weeks. This increases uncertainty in the temperature outlook some for the Great
Lakes, Ohio Valley and Northeast as the odds for below-normal temperatures
would increase for the 3rd and 4th weeks of March. This is strongly at adds
with the latest Week 3-4 dynamical model guidance which continues persistence
of favored above-normal temperatures for the eastern two-thirds of the CONUS
from Week-2.

Anomalous snow cover and depth remains strongly negative across the northern
plains as noted in the mid-month outlook. Soil moisture anomalies are likely to
become increasingly positive for areas in the lower Mississippi Valley, the
Tennessee Valley and lower Ohio Valley as a combination of antecedent
conditions from recent snowmelt and heavy rains in some areas prior to the
start of the month.

Based on the above factors, the updated March 2021 temperature outlook keeps
elevated odds for monthly mean below-normal temperatures for southern Alaska,
and the Far West - which is a more narrow area than the mid-month outlook
depiction. Above-normal monthly mean temperatures remain favored for the
eastern two-thirds of the CONUS, however, there are some changes. First,
above-normal temperatures in the Southwest were shifted eastward in the updated
outlook and probabilities across the northern Plains and Great Lakes are
increased. Lower probabilities are located in a zonal swath for the Tennessee
and lower Ohio Valley's due to possible impact from above-normal surface
wetness and also along the eastern seaboard due to cooler temperatures forecast
early in the month and also due to the potential impact from the MJO, albeit
highly uncertain.

For precipitation, the latest dynamical model guidance, especially in the short
term help better focus favored above-normal precipitation in the Tennessee
Valley at the start of the month of March. This region and areas northward to
the Great Lakes are slightly modified from the half month lead outlook.
Below-normal precipitation is highlighted from the interior West and Southwest
eastward to the central and southern Plains and along the Gulf Coast and
Florida. Changes in these regions from the earlier outlook include removal of
the slightly elevated odds for above-normal precipitation in the northern
Rockies, removal or reducing of chances for below normal precipitation for
parts of California and the central and southern Great Basin and Rockies. A
strong jet forecast to impinge western Alaska through at least the first half
of the month, favors elevated odds for above-normal precipitation for much of
Alaska with removal of the small region of elevated odds for below-normal
precipitation along the Alaska south coast in the mid-month outlook.

****************************************************************************
*** Previous mid-month discussion below ***
****************************************************************************

As we approach the month of March, the pattern across the greater North America
region appears to be in the process of changing from the last few weeks. Week 2
dynamical model forecast guidance supports a change to anomalous ridging over
the north central Pacific with the central North America mean trough shifted
westward and deepening over portions of western North America including into
western CONUS. Downstream of this, more amplified ridging and positive 500-hPa
height departures are forecast for much of the southeast U.S. favoring a more
southwesterly-westerly mean flow for the eastern half of the CONUS then in
recent weeks.

The most recent Week 3-4 guidance from the CFS, ECMWF and extended GEFS support
a continuation of this change, in the mean, for approximately the first two
weeks of March. March CFS forecasts as well as those from the majority of the
NMME and Copernicus model suites also favor this pattern and associated
anomalous temperature and precipitation patterns which are consistent with
typical La Nina conditions in many ways during this point in the seasonal
cycle.

Other factors to consider in addition to a review of the available dynamical
model guidance across time scales, is the state and forecast evolution of the
MJO, the AO and most recent anomalous snow cover.

The MJO has been active during January and February resulting in both
constructive and destructive interference with La Nina impacting anomalous
tropical rainfall, circulation and other variables in the Pacific basin.
Forecast information suggests that the MJO is likely to weaken or become less
coherent entering March and is not strongly utilized in the March outlook due
to this as well as indications that much of recent mid-latitude temperature and
precipitation anomalies have most likely been driven by high latitude
subseasonal variability.

Predictions in the short-term (next 10 days) indicate the phase of the AO
(which has returned to near zero) to remain near zero or weakly positive in the
mean as compared to the strongly negative phase of the last couple months. The
Sudden Stratospheric Warming (SSW) of early-mid January would continue to
elevate odds for a negative AO phase into the month of March resulting in the
continuation of potential cold air outbreaks into the mid-latitudes. There is
high uncertainty, however, in whether the negative phase of the AO will return
and persist and if so where troughing and so favored below-normal temperatures
are most likely to develop at forecast lead times well into the month of March.

Finally, substantially below-normal snow cover and snow depth exist across
parts of the northern Plains and upper Mississippi Valley. Although, early in
the seasonal cycle, taken alone, this is likely to favor above-normal
temperatures in these areas.

After consideration of the factors described above, the March temperature
outlook favors monthly mean below-normal temperatures for a region stretching
from south-central Alaska southeastward to include northern California, the
Pacific Northwest and the northern Rockies. This is strongly supported by
dynamical model guidance across time scales and is consistent with La Nina
conditions. Elevated probabilities for above-normal temperatures are depicted
for parts of the north and west coast of Alaska based on negative sea ice and
positive ocean surface temperature trends especially later in the month of
March.

Dynamical model guidance and in some cas es typical La Nina conditions and
positive temperature trends favor above-normal temperatures for a region from
the Southwest eastward to include the southern CONUS and northward to encompass
the central Mississippi Valley, eastern Great Lakes, Ohio Valley and eastern
seaboard. Only slightly tilted odds of above-normal temperatures or
Equal-Chances (EC) are depicted for the northern and central Plains, central
and upper Mississippi Valley and parts of the Ohio Valley, Great Lakes and
Tennessee Valley due to the uncertainty and conflicting indicators described
above with respect to the phase of the AO, anomalous snow cover and snow depth
and dynamical model guidance.

For precipitation, below-normal monthly total precipitation amounts are most
likely for the southern tier of the CONUS with some expansion of this
highlighted area to the central Great Plains, primarily based on dynamical
model guidance which is consistent with La Nina typical impacts. For similar
reasons, elevated odds for above-normal precipitation is forecast for a small
region in the northern Rockies and for the Ohio Valley and Great Lakes region.
For Alaska, elevated odds for above-normal precipitation is depicted for parts
of the north and west coasts associated with anticipated more open and warmer
waters in nearby areas as well as typical La Nina impacts. Below-normal
precipitation is most likely for the south-central coast and far northern
Alaska Panhandle.

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 Apr ... will be issued on Thu Mar 18 2021

These outlooks are based on departures from the 1981-2010 base period.
$$

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