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Summary- There is a tendency for troughing near and just west of N California, before and after May 1st. The sea surface temperature anomaly (SSTA) pattern in the central N Pacific is strong and persistent enough to continue the tendency for troughing through May and possibly into early June near and over the Calif coast. Forcing for troughs over western Mexico will continue. A classic, moderate to strong El Niño anomaly pattern is expected to develop per the current SSTA pattern and the NMME (North American Multi-Model Ensemble): Time frame- later in the summer and in autumn.

Summary- The tendency for troughing near and west of N California continues, even as we approach the normal end of the season. The sea surface temperature anomaly (SSTA) pattern in the central N Pacific is strong and persistent enough to continue the tendency for troughing through May and possibly into June. Forcing for troughs over the southwestern US may still be related to the currently weak El Niño, although seasonal factors that affect El Niño’s influence decrease with approach of summer. A classic, moderate to strong El Niño anomaly pattern is starting to develop, as shown by the current SSTA pattern, and the forecast developments shown by the North American Multi-model Ensemble (NMME) in the early fall.

Summary- The brief break in the rains ends Thursday, April 6th. The tendency for troughing near and west of N California continues, even as we approach the normal end of the season. Forcing for troughs over the southwestern US may still be related to the currently weak El Niño, although seasonal factors that affect El Niño’s influence are decreasing with approach of summer.

Summary- We have a brief break in the wet pattern for a few days. The tendency for troughing near and west of N California continues, even as we approach the normal end of the season. Forcing for troughs occurring from the N and north-central coast and WSW-ward is from the sea surface temperature anomaly (SSTA) pattern W of north-central Calif. Forcing for troughs over SE Calif, NW Mexico and Arizona and S Great Basin may still be related to the currently weak El Niño, although the seasonal factors that affect El Niño’s influence are decreasing with the approach of summer.

Summary- We have the wetter pattern with a broad belt of westerlies across most of Calif. The troughing pattern is bi-modal. Most troughs develop near the coast of northcentral and N Calif, but a few develop into S Calif, coming down the coast and deepening over NW Mexico and into Arizona. Forcing for troughs occurring from the N and north-central coast and WSW-ward is from the sea surface temperature anomaly (SSTA) pattern W of north-central Calif. Forcing for troughs over SE Calif, NW Mexico and Arizona and S Great Basin is related to the currently weak El Niño. The combined effect is for wet in N and north-central California, and a drier regime, punctuated by an occasional rain in southcentral and S Calif. We still could see a late season southern storm track condition, usually appearing as an upper low over SOCAL, NW Mexico, or S Arizona in April.

Summary- Strong, stationary, warm upper high pressure continued across Calif on March 13, but will weaken on the 14th. We are seeing a shift to a wetter pattern with resumption of a broad belt of westerlies across most of Calif in by March 18-19. The troughing pattern is bi-modal. Most troughs develop near the coast of northcentral and N Calif, but a few develop in the Great Basin and Rockies area. Forcing for troughs occurring from the N and Calif coast and WSW-ward is from the sea surface temperature anomaly (SSTA) pattern W of Calif. Forcing for troughs over the Great Basin is related to the currently weak El Niño. The combined effect has been wet in N and northcentral California, and drier than normal in southcentral and S Calif, however this is changing to mostly wet in N and central Calif. We still expect occasional southern storm track conditions, with showers and low snow levels in the Sierras in late Mar and Apr.

Summary- Westerlies occur across most of Calif. The troughing pattern is bi-modal, with some troughs developing just off the coast of central and N Calif, and some focusing into the Great Basin. Forcing for troughs occurring from the N and Calif coast and WSW-ward is from the sea surface temperature anomaly (SSTA) pattern W of Calif. Forcing for troughs over the Great Basin is related to the currently weak El Niño. The combined effect will be wet in N and northcentral California, and drier than normal in southcentral and S Calif. Individual troughs contain moisture but their south portions weaken upon reaching the coast. This pattern of development, related to El Niño favors development of troughs in S and SE Calif, NW Mexico, and Arizona with occasional offshore flow at the southcentral Calif coast. We still expect occasional southern storm track conditions, with showers and low snow levels in the Sierras in late March and April.

Summary- Westerlies occur across most of Calif. The troughing pattern is bi-modal, with some troughs developing just off the coast of central and N Calif, and some focusing into the Great Basin. Forcing for troughs occurring from the Calif coast southwestward is from the sea surface temperature anomaly (SSTA) pattern W of Calif. Forcing for troughs over the Great Basin are related to the current new El Niño that has begun. Periods of WNW flow with troughing occur, bringing more occurrence of cold conditions with lower snow levels into N and central Calif, due to troughing over the Great Basin. Individual troughs contain moisture but lack strength as they reach the coast, but intensify while moving inland. This new pattern of development, related to El Niño favors development of troughs in S and SE Calif, NW Mexico, and Arizona, and a colder and occasionally showery pattern in central and N Calif. This maintains a colder than normal pattern with periods of snow showers thru the Sierras. As El Niño becomes more active during late March thru early May, the southern storm track continues. The southern storm track will induce showers and continued snowy conditions in the Sierras in late March thru April. The southern storm track will tend to support the development of severe weather events (thunderstorms and tornadoes), with above normal rainfall in Oklahoma, north Texas in April and Kansas-Nebraska in May.

Summary- High pressure builds into the N Pacific and southern Gulf of Alaska while a weak southern storm track persists along 30N to the W of SOCAL. Troughs are over the Rockies and off the Calif coast. In March, the dry, cold pattern with troughing and a few mountain showers dominates during the first week. Model guidance has shown support for low latitude westerlies and cool conditions during the first half of March, with NW flow from the Gulf of Alaska. This maintains a colder than normal pattern with periods of snow showers thru the Sierras. The developing El Niño anomaly in March will induce troughing into SOCAL and central Calif and abnormally cold weather with some SOCAL showers in early March. As El Niño becomes more active during late March – early May, the southern storm track continues. The southern storm track will induce showers in N and central Calif, and continued snowy conditions in the Sierras in late March thru April. The southern storm track will tend to support the development of severe weather events (thunderstorms and tornadoes), with above normal rainfall in Oklahoma, north Texas and Kansas.

Summary- Troughing continues to focus to the west of California between 130W and 145W. Troughing also increases into the southern deserts and SOCAL as the southern storm track becomes more active.Troughing occurs during Feb 16-23 with wet conditions.Troughing migrates slightly east, putting us in a cold pattern with snow showers in the Sierras and return of cold conditions through all of California, with some offshore flow mixed in during February 24 – March 1.For March, the dry, cold pattern with troughs and showers in the southern deserts dominates during the first week of March. Although northern California turns dry for a while in March, SOCAL and the southern deserts have a tendency for recurrent cold showery conditions.There is support for the next series of storms into all of California during March 19-23, after a long, drier than normal pattern.The La Niña period ends quickly, and the current trend for an El Niño anomaly to develop will continue thru March, to induce more troughing into SOCAL and central California with a continued trend of colder and wetter than normal.As El Niño becomes more active during the next two months (March and April), and the southern storm track continues, the incidence of severe thunderstorms (TSTMS) and tornadoes may shift to above normal, along with above normal rainfall for Oklahoma, Kansas, and north Texas.

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