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As of the May 19th, 2017, release, Week 3-4 outlooks precipitation outlooks are experimental, whereas the temperature outlooks are operational. Both are issued Friday between 3pm & 4pm Eastern Time.
HOME> Outlook Maps> Week 3-4 Outlooks

Week 3-4 Outlooks
Valid: 01 Dec 2018 to 14 Dec 2018
Updated: 16 Nov 2018

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Temperature Probability

Week 3-4 Outlooks - Temperature Probability
Precipitation Probability

Week 3-4 Outlooks - Precipitation Probability

Click HERE for information about how to read Week 3-4 outlook maps

Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EST Fri Nov 16 2018

Week 3-4 Forecast Discussion Valid Sat Dec 01 2018-Fri Dec 14 2018

CPC continues to maintain its El Nino watch for boreal winter, indicative of the lack of a sufficiently long, robust, coupled oceanic-atmospheric response to the anomalously warm sea surface temperatures (SSTs) in the west-central equatorial Pacific. Low frequency signals for enhanced convection exist, but are displaced fairly far westward (around 150E) from canonical Central Pacific ENSO events. This region is also presently being constructively interfered with by the active phase of the Madden-Julian Oscillation (MJO), which is forecast to convectively decouple as it propagates further eastward into the Pacific and also increase its phase speed, as is typical. For an active MJO over the eastern Maritime Continent this time of year, the typical lagged response for Weeks 3 and 4 sees odds increase for above-normal temperatures west of the Rockies, while below-normal probabilities are increased from the Upper Mississippi Valley through New England. The El Nino footprint generally supports destructive interference with the aforementioned cold signal, while also skewing the temperature distribution towards below-normal temperatures for the Southern Plains.

Dynamical model guidance for Weeks 3 and 4 are broadly consistent with each other and depict the Arctic Oscillation (AO) in its negative phase, reflected by positive 500-hPa height anomalies at the polar latitudes and anomalous troughing from the Great Plains through Northeast. The CFS is most extensive with this troughing, with the Weeks 3 and 4 ensemble mean height anomalies being negative for the near entirety of the CONUS. The ECMWF and JMA maintain weakly positive heights close to the Pacific coast. Subseasonal Experiment (SubX) guidance is broadly consistent with the ECMWF and JMA forecasts, although the SubX models also feature extensive anomalous ridging over Alaska that is absent in the other guidance. In that vein, the GEFS late in Week-2, and Week-3 CFS and ECMWF ensemble means each depict a robust negative North Pacific Oscillation-West Pacific (NPO-WP) mode. In this scenario, anomalous ridging over the Bering Sea would promote cross-polar transit of Siberian air into the Plains. Given the broad consistency among the model guidance, and their consistency with the typical MJO response for an event initially over eastern Maritime Continent, a blend of all available dynamical model guidance forms the baseline for the current forecast. This blend is then adjusted towards a statistical tool leveraging the canonical lagged impacts from MJO, ENSO, and decadal trends to produce the final outlook.

While the negative AO and NPO-WP modes each support cold air spilling into the Central U.S., there is limited cold air for each to work with as temperatures have been warm across Siberia since October and the Yukon cold pool has eroded some in recent weeks. Despite this, temperature advection arguments argue for enhanced below-normal temperature probabilities simply from the anticipated anomalous northerly flow, although chances for a severe cold-air outbreak may be limited due to the aforementioned source region arguments and below-normal temperature probabilities are similarly tempered. Highest confidence for below-normal temperatures is over the Northeast, in a continuation of the Week-2 pattern and consistent with the anomalous trough axis proximity. Equal chances are forecast across the South, where decadal trends may help offset any frontal intrusions over the two-week period. Above-normal temperatures are forecast for the West linked to positive 500-hPa height anomalies, and for Alaska where anomalous ridging, above-normal SSTs, and below-normal sea ice coverage all support increased chances of a warmer than usual start to December.

Forecast anomalous northerly flow over the central and eastern US supports increased chances of below-median precipitation with continental polar airmasses descending from Canada. The one potential exception for this scenario would be downstream of the Great Lakes where increased lake-effect snowfall is possible, although this is likely to be highly localized, and as such not shown on the forecast graphic. With a mean frontal zone shifted southward in the aforementioned scenario, above-median precipitation is forecast for the Southeast through Mid-Atlantic. Equal chances are favored for the West, given models exhibiting a tilt towards below-median precipitation, although the negative AO would support a wetter solution and more troughing. Dynamical models are more consistent with below-median precipitation favored for most of Alaska, tied to the anomalous ridge axis forecast to be over the Bering Sea.

Given persistent above-normal SSTs in the vicinity of Hawaii, above-normal temperatures are also favored across the islands. Dynamical models consistently forecast below-median rains. These outcomes are typical for El Nino events which are associated with above-normal temperatures across the islands, in addition to a wet start to the rainy season that becomes rapidly drier with time.

Temperature Precipitation
Hilo A70 B55
Kahului A70 B55
Honolulu A70 B60
Lihue A70 B60

Forecaster: Daniel Harnos

The next week 3-4 outlook will be issued on Friday, Nov 23, 2018

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

These are two category outlooks and differ from official current three category outlooks currently used for the monthly and seasonal forecasts.

The shading on the temperature map depicts the most favored category, either above-normal (A) or below-normal (B) with the solid lines giving the probability ( >50%) of this more likely category (above or below).

The shading on the precipitation map depicts the most favored category, either above-median (A) or below-median (B) with the solid lines giving the probability ( >50%) of this more likely category (above or below).

In areas where the likelihoods of 2-week mean temperatures and accumulated precipitation amounts are similar to climatological probabilities, equal chances (EC) is indicated.

As of May 19, 2017, the temperature outlook is operational, while the precipitation outlook is still experimental

An ASCII (w/ HTML markup tags) text version of the written forecast is available.

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