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 28 2024

Week 3-4 Forecast Discussion Valid Sat Jul 13 2024-Fri Jul 26 2024

ENSO-neutral conditions continue across the tropical Pacific basin, though negative sea surface temperature (SST) anomalies are slowly increasing across the eastern Pacific. Intraseasonal activity has been largely incoherent during the past few weeks, with fast propagating Kelvin waves and equatorial Rossby wave activity providing most of the variability. Dynamical model forecasts show a gradual shift towards enhanced trade winds across the east-central Pacific, with enhanced westerlies over the Maritime Continent and far western Pacific. This signal may indicate the beginning of an atmospheric response to the cooling equatorial Pacific, which is necessary for a transition towards La Niña conditions. Given both the lack of a robust Madden-Julian Oscillation (MJO) and the time of year, it is difficult to prescribe specific midlatitude impacts from broad-scale intraseasonal tropical activity. Dynamical model forecasts generally depict an enhanced central American monsoonal pattern during the Weeks 3-4 time period. This active pattern may provide a source for monsoonal moisture surges into the southwestern US, and a potential for enhanced precipitation across the Gulf Coast or Southeast.

A manual blend of operational dynamical model guidance, including the GEFS, ECMWF, JMA, and CFS, depicts pronounced ridging near and south of the Aleutians, similar to the anticipated setup for Week-2. Troughing is favored to the north and downstream of this ridge, which would favor onshore flow from the Bering Sea across much of Alaska. For the CONUS, ridging is favored across the West, with the strongest positive height anomalies centered over the northern Rockies and northern High Plains. Across the East, the strong ridging favored during Week-2 de-amplifies, though positive height anomalies remain favored for most of the CONUS. This pattern favors enhanced monsoonal moisture across the Southwest and widespread warmth.

The Weeks 3-4 temperature outlook depicts enhanced chances for below-normal temperatures across much of Alaska due to the likelihood of enhanced onshore or northerly flow, though a slight tilt towards above-normal temperatures extends across the North Slope region due to adjacent above-average water temperatures. Across the CONUS, the outlook universally favors above-normal temperatures. The weakest probabilities extend across immediate coastal California, while the highest probabilities extend from the northern Rockies, where the mean ridge axis is centered, southeastward to the south-central CONUS, where rapidly drying soils may exacerbate the hot conditions. Slightly lower probabilities for above-normal temperatures extend across portions of the upper Midwest, due in part to above-average soil moisture conditions and a potential for convective activity during the period. Equal chances for above- or below-normal temperatures are maintained across Hawaii despite favored above-average 500mb height anomalies, as SSTs have recently trended towards near normal and dynamical model guidance is mixed.

The precipitation outlook for Weeks 3-4 contains higher uncertainty than the temperature outlook, which is typical during the Boreal summer months. Ridging may favor reduced onshore flow across the Northwest, so below-average precipitation is slightly favored for Washington and Oregon along and west of the Cascades. Equal chances for below- and above-average precipitation are maintained for the northern Intermountain West, due to a potential for isolated convection tied to monsoonal flow. Above-average precipitation is favored for the Southwest monsoon region given the favorable height pattern. Across the central and eastern CONUS, there is high variability among the dynamical model guidance, but most model systems depict an area of below-average precipitation across either the central Plains or the western Corn Belt. This region of below-average precipitation is extended into north-central Texas, based on rapidly drying soil moisture conditions and drier guidance from the skill-based model subsampling tool. In contrast, above-normal precipitation is favored for the upper-Midwest and Northeast due to a potential for periods of convection associated with shortwaves moving through the broader flow, and along the Gulf Coast and Southeast due to enhanced tropical moisture and above-average SSTs. Across Hawaii, the manual blend precipitation outlook slightly favors above-normal precipitation for the southeastern islands, due in large part to the GEFS and ECMWF solutions.

Temperature Precipitation

FCST FCST

Hilo EC A55

Kahului EC A55

Honolulu EC A55

Lihue EC EC

Forecaster: Adam Allgood

The next week 3-4 outlook will be issued on Friday, Jul 05, 2024

These outlooks are based on departures from the 1991-2020 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