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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: 29 Sep 2018 to 12 Oct 2018
Updated: 14 Sep 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 EDT Fri Sep 14 2018

Week 3-4 Forecast Discussion Valid Sat Sep 29 2018-Fri Oct 12 2018

The doldrums of the forecasting season continue in terms of predictability for the mid-latitudes at the subseasonal scale. ENSO neutral conditions persist in the equatorial Pacific, while the Madden-Julian Oscillation index appears weak due to competing signals of the low frequency in the Pacific and a Kelvin wave over the Americas. The mid-latitude circulation pattern in recent weeks has been fairly persistent and amplified for the time of year, with anomalous ridging over Alaska and a downstream trough over the Yukon, but there are signs of this pattern starting to break down during the next two weeks. Dynamical model guidance for Week 3-4, the evolving extended range pattern, and long-term trends are the primary guidance used to inform the present Week 3-4 outlook. Among dynamical models used in the present outlook, the ECMWF is favored given its transition from Week-2 being the least drastic.

Model guidance overall shows low amplitude anomalies, typical of the relaxed vorticity gradients during late boreal summer. The CFS breaks down the ridge over Alaska by Week-2, in disagreement with the entire CPC model suite utilized during the extended range period, with negative height anomalies across the state during both Week-3 and Week-4. The ECMWF and JMA maintain this feature, as do most of the Subseasonal Experiment (SubX) models. The resulting downstream impacts are felt in the CFS, with amplified ridging along the Canadian border for Weeks 3-4, while the ECMWF appears to have a better handle with anomalous troughing extending from the Canadian prairies through Hudson Bay. The JMA model favors generally positive height anomalies across the CONUS, potentially tied to the model overplaying decadal trends. Both the ECMWF and JMA maintain anomalous ridging off the Eastern Seaboard in Week 3-4, along with much of the SubX guidance.

The favored pattern in line with the ECMWF solution would support a mean frontal zone extending from the Midwest through New England, with surface high pressure over much of the West and along the eastern seaboard. Given that pattern, the ECMWF anticipates substantial chances of below-normal temperatures from the Northern Plains through the Northeast, which may be overdone given the difficulties observed in recent weeks for cold air built up over Canada to push south into the CONUS. Similarly, the positive height anomalies from the JMA and discounted CFS are at odds with potential cold along the northern tier, resulting in a forecast of equal chances in the outlook. More consistency exists among forecasts for above-normal temperatures over the West and Southeast, given the positive height anomalies favored for these regions. Above-normal temperatures are also favored in Alaska, with southerly flow anticipated for much of the mainland, while well above-normal sea-surface temperatures (SSTs) in the Bering Sea may help to offset anomalous northerly flow across the Aleutians. Model guidance is consistent in indicating an increase in below-normal temperature chances across portions of the Southern Plains, tied to either increased precipitation or the mean front being east of the region, depending on the model.

Forecast ridging across the West Coast supports increased chances of anomalously dry conditions for many areas from the Plains westward. The exception to this is across Arizona, where above-median precipitation odds are increased due to model signals of a surge of moisture into the state from the Gulf of California associated with tropical cyclone activity off of the Baja Peninsula. The enhanced subtropical ridge forecast by model guidance also leads to increased above-median rainfall chances for much of the East, tied to amplified transport of moisture from the Gulf of Mexico, as has been observed in recent weeks. This area was extended slightly westward from what models indicated due to the forecast weakness in the model height fields across the central CONUS, suggesting any potential tropical cyclone activity could be focused towards the western or central Gulf of Mexico coastline. With anomalous ridging favored over the Western CONUS, the storm track appears likely to shift northward into southern Alaska, yielding increased odds of above-median precipitation for portions of the Aleutians, Kenai Peninsula vicinity, and Alaska Panhandle.

Persistent positive SST anomalies continue to surround Hawaii, supporting increased chances of above-normal temperatures and precipitation across the island chain. Dynamical model guidance is similarly unanimous in the increased chances of above-normal temperatures and above-median rainfall for the island chain.

Temperature Precipitation
Hilo A70 A70
Kahului A70 A70
Honolulu A70 A70
Lihue A70 A70

Forecaster: Daniel Harnos

The next week 3-4 outlook will be issued on Friday, Sep 21, 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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