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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: 02 Sep 2017 to 15 Sep 2017
Updated: 18 Aug 2017

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Temperature Probability


Week 3-4 Outlooks - Temperature Probability
Precipitation Probability
(Experimental)


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 Aug 18 2017

Week 3-4 Forecast Discussion Valid Sat Sep 02 2017-Fri Sep 15 2017

Influences on the extratropics from the tropics continue to be muted, with the exception of tropical cyclone activity. Sea surface temperature (SST) anomalies are largely neutral throughout the global tropics, with a slight cooling trend noted in the Central Pacific. Signals related to the Madden-Julian Oscillation are relatively generally out of phase with each other, while there is some consistency among dynamical models regarding a growing signal in the Indian Ocean during Week-2. Given the lack of overall tropical influences, the present Week 3-4 outlook is predominantly influenced by dynamical model ensemble guidance, long-term trends, observed SSTs and soil moisture, in addition to anticipated evolution from Week-2.

500-hPa height forecasts are in good agreement and relatively amplified for this time of year. In general, anomalous ridging is favored over the Pacific Northwest and off New England, with troughing focused over the Upper Midwest and south of the Aleutians. The CFS height pattern appears most consistent with Week-2 guidance and generally maintains each of the aforementioned features throughout the period. The ECMWF and JMA heights are markedly higher over Hudson Bay relative to the CFS and Week-2 guidance, while the ECMWF retrogrades the ridge across the Pacific Northwest in Week-2 to the North Pacific in Week-3 before returning it in Week-4. Given these discrepancies, the CFS solution is favored and its temperature and precipitation forecasts given slightly more weight relative to the other dynamical models. Experimental SubX model output is largely consistent with the CFS, giving further support for its predictions.

Calibrated temperature forecasts depict varied coverage and magnitudes of enhanced probabilities for below-normal temperatures across the Great Plains in association with the forecast troughing. The greatest consistency for cold signals in dynamical guidance appears to be across the Central Plains, with this also being the region of weakest warm signals in decadal variability across the CONUS. Above-normal temperatures are forecast across the Western U.S., with the highest probabilities in the Pacific Northwest due to the greatest height anomalies situated here. Smaller areas of above-normal temperatures are forecast in the Northeast, where anomalous ridging is supported by the CFS, and Southeast due to frontal boundaries typically not making it that far south. Above-normal temperatures are also forecast in Alaska due to anomalous southerly flow for the eastern part of the state; western areas may have a northerly component to the flow but SSTs in the Bering and Chukchi Seas exhibit large positive anomalies.

With ridging favored in the west and amplified troughing through the Central U.S., this circulation favors below-median precipitation for the Pacific Northwest along with suppression of any monsoonal activity in the Southwest. Ensemble guidance is broadly consistent with above-median rainfall along a frontal zone situated along and to the east of the Mississippi Valley. The best signal for above-median precipitation appears to be for southeastern Alaska and the Alaska Panhandle, given forecast anomalous southerly flow off the Gulf of Alaska among all dynamical model guidance. There was some indication of above-median precipitation for the Northern Plains, but this area is not highlighted on the map due to ongoing drought conditions and lack of a clear physical mechanism to yield the anomalous precipitation here.

Anomalously warm SSTs continue to persist around Hawaii, leading to a forecast of above-normal temperatures. Dynamical model precipitation forecasts for Week 3-4 on average predict an increased likelihood of below-median precipitation for Hawaii, with marginally elevated probabilities in the east.







Temperature Precipitation
FCST FCST
Hilo A60 B60
Kahului A60 B55
Honolulu A60 B55
Lihue A60 B55


Forecaster: Daniel Harnos

The next week 3-4 outlook will be issued on Friday, Aug 25, 2017

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




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6 to 10 Day Outlooks
8 to 14 Day Outlooks
30-day Outlooks
90-day Outlooks
 
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Page last modified: May 19 2017
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