Climate Prediction Center - Week 3-4 Outlook

Prognostic Discussion for Week 3-4 Temperature and Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EDT Fri Apr 18 2025

Week 3-4 Forecast Discussion Valid Sat May 03 2025-Fri May 16 2025

A Final La Niña Advisory was recently issued and El Niño Southern Oscillation (ENSO) neutral conditions are now present. The Madden Julian Oscillation (MJO) is also largely inactive, and while forecasts of the Realtime Multivariate MJO (RMM) index hint toward a possible re-emergence of the MJO signal in late April, it is uncertain and perhaps more related to a low frequency convective signal and a Convectively Coupled Kelvin Wave rather than MJO. Moreover, teleconnections to the extratropics weaken in the spring. Given the lack of ENSO and MJO forcing, the Weeks 3-4 Temperature and Precipitation Outlooks mainly rely on dynamical model output, trends, and some influence from soil moisture where appropriate. A manual blend of dynamical models including GEFSv12, CFSv2, JMA, and ECMWF, and the statistical Multiple Linear Regression (MLR) tool is utilized. Additionally, experimental predictions from CMCE are considered.

Dynamical models generally favor above normal heights over the Contiguous United States (CONUS), though GEFSv12 and ECMWF favor ridging that stretches at least coast-to-coast, while CFS and JMA forecast more neutral heights over the west coast. In Week 3, above normal heights are favored over the eastern CONUS, while in Week 4, the above normal heights shift westward. This leads to broad weakly above normal heights in the Weeks 3-4 period that stretch across the CONUS in GEFSv12 and ECMWF. Overall, taking into consideration the models and their differences, as well as the differences between weeks, we expect weak above normal heights over the East and West CONUS, and neutral to above normal heights over the central CONUS. Heights are mainly neutral over Alaska.

The Weeks 3-4 Temperature Outlook is quite similar to last week's Outlook. However, given the potential for shifting heights from week 3 to week 4 and some model discrepancies, probabilities are comparatively weaker. The Temperature Outlook is very reflective of an experimental manual blend of GEFSv12, CFSv2, JMA, ECMWF, and the MLR tool. Above normal temperatures are indicated over much of the CONUS, including the western two thirds, the southern tier, and parts of the East Coast. Probabilities are higher where dynamical models had good agreement, for instance, over the Northwest, parts of the Four Corners, southwestern Texas, and parts of the Southeast. Equal chances (EC) of above and below normal temperatures are favored over parts of the Northern and Central Plains, Upper Mississippi Valley, Upper and Lower Great Lakes, and the Northeast given weakness in model probabilities and the transitioning of the ridge from over the East to over the West during the period. Over Alaska, models are mixed, but trends in temperature lead to enhanced probabilities of above normal temperatures over the northern and southern coasts. Similar to last week, a small region of below normal temperatures is indicated for parts of western Alaska given model agreement.

Dynamical model forecasts of precipitation were more mixed than temperature. Models show a variety of possible precipitation patterns across the CONUS and Alaska, and calibrated vs. uncalibrated guidance show differences in the regions of highest probabilities. Following an overall above normal pattern in the 8-14 day Precipitation Outlooks, most models favor some broad regions of above median precipitation into the Weeks 3-4 period as well, though the positioning of strongest probabilities is model dependent. For example, CFSv2 has stronger above median precipitation probabilities over the western half of the CONUS and Great Lakes, ECMWF favors below median precipitation over the West, Southeast, and Mid-Atlantic, and above median precipitation over the central CONUS and Great Lakes, while JMA favors above median precipitation over a large portion of the CONUS excepting the West Coast and Southeast. Moreover, the region of strongest probabilities of above median precipitation in calibrated model output is shifted westward comparatively to much of the uncalibrated dynamical model guidance, increasing the uncertainty of this precipitation forecast. As such, probabilities are relatively lower than those in the Weeks 3-4 Temperature Outlook. A broad region of above median precipitation stretches across much of the central CONUS to the Northeast coast, including the Great Lakes and parts of the Mid-Atlantic. The area of enhanced precipitation probabilities, reaching 55 to 60%, is due to JMA, ECMWF, and GEFSv12 agreement on above median precipitation, as well as higher soil moisture over the Lower Mississippi and Ohio River Valleys. A weak tilt toward below median precipitation is favored over parts of the Southeast where models had more agreement. EC of above and below median precipitation is favored over much of the western half of CONUS where there was disagreement among calibrated vs. uncalibrated model guidance, dynamical models for the month of May as a whole tilt strongly below normal, and due to a tilt toward below normal soil moisture over the Southwest. Model guidance was weak and inconsistent over Alaska, but a weak tilt toward above median precipitation is indicated over the southeastern part of the state given model guidance and recent trends.

Probabilities for above normal temperatures remain elevated over Hawaii given above average sea surface temperatures and guidance from ECMWF. Slightly above median precipitation is indicated over Hawaii by dynamical models, with weaker probabilities over Hilo.

Temperature Precipitation

FCST FCST

Hilo A55 A55

Kahului A60 A60

Honolulu A55 A60

Lihue A55 A60

Forecaster: Johnna Infanti

The next week 3-4 outlook will be issued on Friday, Apr 25, 2025

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.