Climate Prediction Center - Week 3-4 Outlook

Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EDT Fri Jun 14 2019

Week 3-4 Forecast Discussion Valid Sat Jun 29 2019-Fri Jul 12 2019

The MJO remains active, with the enhanced convective phase now over the Maritime Continent, although other modes, including Rossby wave activity over the Indian Ocean possibly associated with TC Vayu, have interfered with the signal in recent days. Dynamical models favor continued eastward propagation of the MJO signal, with uncertainty increasing as the signal approaches the Pacific, where the low frequency weak El Nino signal persists. Teleconnections between these tropical signals and the midlatitude pattern are generally weak during the boreal summer months, but there is a weak statistical relationship favoring increased probabilities for below-normal temperatures across the U.S. northern tier and Great Lakes during the Week 3-4 outlook period. In addition to the statistical guidance, this outlook is based primarily on a consensus of recent runs of the CFS, ECMWF, and JMA dynamical models, with some consideration given to the multi-model ensemble built from the Subseasonal Experiment (SubX) suite of models.

Both the CFS and ECMWF depict a weak 500-hPa anomaly field during the Week 3-4 period, which is fairly common during the summer months. The JMA is an outlier, and builds a substantial trough over the north-central CONUS. The NAO and AO signals which have been persistently negative since late April are forecast to flip signs during Week-2, and should that pattern change persist beyond Week-2, it would support a shift towards a more northerly storm track across the U.S. than what has been observed during the late spring and early summer. Incipient conditions, including abundant to excessive soil moisture over the central Plains and Corn Belt, may also play a role in the broader temperature and precipitation outlooks during Weeks 3-4.

The highest confidence for below-normal temperatures exists over Michigan, where there is a strong consensus among dynamical and statistical model guidance. Below-normal temperatures are favored from the interior Northeast southwestward across the north-central U.S. to the Great Basin and southern California. Despite the predicted deamplified pattern, the large extent of below-normal temperatures indicated on the outlook is supported by the anticipated persistence of much above normal soil moisture over the north-central U.S. In contrast, the model guidance strongly favors above-normal temperatures across Alaska and the Northwest. Additionally, above-normal temperatures are favored across the south-central CONUS and parts of the Gulf Coast.

Consistent with the idea of a northerly storm track, above-normal precipitation is favored from the northern Intermountain West through parts of the Great Lakes region. Dynamical models generally favor below-normal precipitation across parts of the East, Southeast, and south-central U.S., although confidence is fairly low, particularly across the Gulf and South Atlantic coasts, where seabreeze thunderstorm activity and climatological potentials for tropical cyclone activity may result in localized areas of heavier rainfall. Equal chances for below- or above-normal precipitation are maintained across most of Alaska, with enhanced chances for above-normal precipitation over the southwestern part of the state.

Above-normal SSTs and dynamical model guidance supports above-normal temperatures during Weeks 3-4 across Hawaii. Dynamical models fairly consistently depict above-normal precipitation, with probabilities increasing from northwest to southeast.

Temperature Precipitation

FCST FCST

Hilo A70 A70

Kahului A70 A60

Honolulu A70 A55

Lihue A70 A55

Forecaster: Adam Allgood

The next week 3-4 outlook will be issued on Friday, Jun 21, 2019

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