Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EST Fri Jan 15 2021
Week 3-4 Forecast Discussion Valid Sat Jan 30 2021-Fri Feb 12 2021
This week's forecast is based on a blend of dynamical guidance and expected La Nina conditions. The Madden Julian Oscillation (MJO) is weak and most guidance predicts it to remain weak throughout the next couple of weeks. La Nina, however, remains strong. Persistent negative OLR anomalies, corresponding to anomalous convection, have been present over the Maritime Continent for months now. The anomalous convection has resulted in positive height anomalies to its northwest, which forms the basis of a Rossby wave that extends from southeastern Asia northeast over North America. This pattern resembles a typical La Nina, though isn't a direct match to a climatological La Nina composite, particularly since the anomalous trough and ridge couplet over central Pacific are more zonally oriented than in the composites. Still, dynamical model forecasts feature strong height anomalies over the Pacific and northwestern North America.
The CFS, ECMWF, JMA, and GEFSv12 operational models all forecast a wide swath of anomalous ridging centered over the Central Pacific, a relatively small anomalous trough over the northwestern U.S., and anomalous ridging over the southern U.S. and Northeast for both Weeks 3 and 4. The largest discrepancy lies in the anomalous ridge over the Northeast during Week-3. The CFS forecasts anomalous ridging along the East Coast, whereas the GEFSv12, ECMWF, and JMA both predict near-normal to negative height anomalies throughout Northeast. All three models are in agreement with anomalous ridging over the Northeast during Week-4.
Today's Week 3-4 forecast features below normal temperatures favored throughout most of Alaska and the Pacific Northwest and aligns well with the aforementioned predicted troughing. Increased chances for above normal temperatures are forecast throughout the Southwest and Southcentral U.S., which resembles a climatological La Nina pattern and matches the forecast anomalous ridging. The forecast throughout the Eastern U.S. is especially uncertain with significant model disagreement regarding the sign of temperature anomalies, leading to an equal chances forecast.
Negative precipitation anomalies are forecast over all of Alaska, with the highest probabilities found along the South Coast and Aleutians where nearly every piece of model guidance predicts anomalous dryness. Negative precipitation anomalies also extend from southern California throughout the southern third of the country to Florida. Anomalous precipitation is expected throughout the northern tier of the CONUS, with the highest probabilities over the Pacific Northwest and Great Lakes regions. There is some evidence in the SubX models that there will be an active storm track throughout the Eastern CONUS during Weeks 3-4, but there is not much support for this in our operational model suite. This was also the region that exhibited the most variance among 500-hPa height anomaly forecasts.
Sea surface temperature anomalies are above normal surrounding Hawaii, resulting in elevated probabilities of above-normal temperatures during the Week 3-4 period. Dynamical models also agree on a forecast of slightly above-median precipitation values.
| Temperature | Precipitation |
| FCST | FCST |
| Hilo | A60 | A55 |
| Kahului | A60 | A55 |
| Honolulu | A60 | A55 |
| Lihue | A60 | A55 |
Forecaster: Kyle MacRitchie
The next week 3-4 outlook will be issued on Friday, Jan 22, 2021
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