####018006509#### AGUS76 KRSA 301456 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 800 AM PDT Sat Mar 30 2024 ...MODERATE/LOCALLY HEAVY PRECIP ACROSS COASTAL SOCAL THRU SUN AM... ...A LOW PRESSURE SYSTEM WILL CONTINUE TO TRAVEL SOUTH OFFSHORE OF CNTRL/SRN CA COAST THE REST OF THE WEEKEND BRINGING SCATTERED PRECIP/ISOLATED THUNDERSTORMS... ...DRYING FOR EARLY NEXT WEEK BEFORE ANOTHER SYSTEM RETURNS PRECIP CHANCES MID/LATE WEEK... .METEOROLOGICAL CONDITIONS (SAT AM - FRI AM)... The surface/upper low is currently just west of the central coast/Monterey Bay as a 0.75-1" PW plume of moisture funnels into srn CA around a cold front. Morning 12z sounding out of San Diego measured PW of 0.92" which is above the 90th percentile for the date. The low is generating showers across nrn/central CA as the moisture plume and cold front produce precip from Ventura County to San Diego. Overnight the highest precip amounts have been in the mountains of Santa Barbara/Ventura counties at 1.50-3.50" with 0.50- 1.50" for low lying areas along the coast. Rainfall rates of 0.50"/hr were observed overnight with rates locally nearing 1"/hr at times. The rest of the state has seen about 0.25-0.75" with locally 1-2" over parts of the Sierra and Big Sur coastal mountains. The low will continue to slowly head southward off the coast the rest of today as the moisture plume traverses the soCal coast. This will focus most of the precip this morning from LA to San Diego county as the moisture moves through. HREF exceedance probabilities show about a 20-50% or so chance of 0.50"/hr rates during this time. Models still show the plume exiting into Baja this afternoon allowing precip to diminish. The slow moving low pressure system, however, will continue to generate scattered showers across the region later today along with chances of isolated thunderstorms. Overnight, a secondary low will develop over NV as the offshore low slowly passes Point Conception. This will generate two main areas of precipitation, one across coastal srn CA and the other over NV. The same pattern will persist on Sunday as the offshore low passes by the soCal coast and the inland low moves from NV into UT. There is still some uncertainty regarding the precip along the soCal coast overnight tonight through Sunday morning. The ECMWF continues to show a heavier band of precip just offshore as the low passes. The differences amongst the ECMWF ensembles on the position of the surface low is causing higher QPF values to be forecast by the ECMWF members compared to the GFS which is not showing this feature. This is evident in the 24 hr QPF clusters ending Sunday afternoon. The clusters are split into 3 groups (39%, 34%, 27%) each corresponding to its parent model (72% ECMWF, 75% CMC, 83% GFS). Cluster 1 is the wettest and contains none of the GFS ensemble members. The 24 hr QPF spread at San Diego covering that time period, for example, is between 0.25" to 3.50" for the ECMWF while the GFS has 0.10-0.90". The current official forecast is about 0.75", but wanted to emphasize the range of possibilities. This will depend both on the amount of precip the low generates as it passes and how close to the coast it gets. For what it's worth, HREF exceedance probabilities showing again around a 20-50% or so chance of 0.50"/hr rain rates. The rest of Sunday, the region will be under a large positively tilted troughing pattern with the trough axis stretched offshore of Baja through ID/WY/MT. This will keep scattered showers in play for central/srn CA and NV the remainder of the weekend along with chances of thunderstorms over soCal and parts of NV. By Monday, an upper ridge will move into the eastern Pacific and begin to push inland across the PacNW suppressing the troughs influence over the nw part of the region. Troughing will remain over srn CA and part of NV on Monday allowing for some lingering shower potential as well as isolated thunderstorms over srn CA/NV. The majority of the precip for the rest of the current system is expected along coastal soCal and an area from the nrn Sierra through nrn NV. The morning forecast was a combination of WPC guidance and the latest NBM. Manually adjust some numbers for the current period to reflect precip that has already fallen. QPF 18z Sat through Monday: 0.75-1.50" coastal SoCal, 1.50-2.75" Transverse Range/mntns east of San Diego, 0.25-1" northern Sierra, 0.50-1.50" nrn NV mountains, 0.10-0.75" central coast/rest of Sierra, and a few hundredths to 0.50" the rest of CA. The ridge will take over entirely on Tuesday as the trough exits returning dry conditions and raising temperatures above normal for northern areas. This ridging will be short lived as another system approaches from the Gulf of Alaska mid-week. Initial showers expected to reach nw CA on Wednesday as the trough digs in offshore becoming a closed low near BC/WA by early Thursday morning. The troughing from the system will also expand to cover much of the region the rest of the forecast period. Not seeing any significant moisture with this system, which should limit precip amounts for mid to late next week. Precip for mid/late next week will mainly be across nrn CA/NV and across the Sierra. QPF 12z Tues-12z Fri: 0.10- 0.75" Sierra (locally closer to 1" for parts of the nrn Sierra), 0.30-1" Shasta, 0.10-0.75" along the CA/OR border through nrn NV, and a few hundredths to a couple tenths across the rest of nrn/cntrl CA. Some light showers possible for soCal. Freezing levels 4.5-7 kft over the weekend then rising from nw to se as a ridge builds in Monday. Expecting 8.5-10 kft for the nrn CA coast early Monday before higher levels spread across the region the rest of the day. By Tues am, expecting 9-11 kft north of Point Conception and 7-9 kft for s/e CA/NV. Freezing levels lowering again mid/late week as the next system moves in. Thus am, freezing levels 2-5.5 kft north of I-80 and 4-11.5 kft to the south. Lower levels spreading across the region into Friday down to 2-3.5 kft north of Point Conception across CA and 4-9.5 kft to the south/east. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php AS $$ ####018006510#### AGUS76 KRSA 301457 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 800 AM PDT Sat Mar 30 2024 ...MODERATE/LOCALLY HEAVY PRECIP ACROSS COASTAL SOCAL THRU SUN AM... ...A LOW PRESSURE SYSTEM WILL CONTINUE TO TRAVEL SOUTH OFFSHORE OF CNTRL/SRN CA COAST THE REST OF THE WEEKEND BRINGING SCATTERED PRECIP/ISOLATED THUNDERSTORMS... ...DRYING FOR EARLY NEXT WEEK BEFORE ANOTHER SYSTEM RETURNS PRECIP CHANCES MID/LATE WEEK... .METEOROLOGICAL CONDITIONS (SAT AM - FRI AM)... The surface/upper low is currently just west of the central coast/Monterey Bay as a 0.75-1" PW plume of moisture funnels into srn CA around a cold front. Morning 12z sounding out of San Diego measured PW of 0.92" which is above the 90th percentile for the date. The low is generating showers across nrn/central CA as the moisture plume and cold front produce precip from Ventura County to San Diego. Overnight the highest precip amounts have been in the mountains of Santa Barbara/Ventura counties at 1.50-3.50" with 0.50- 1.50" for low lying areas along the coast. Rainfall rates of 0.50"/hr were estimated overnight with rates locally nearing 1"/hr at times. The rest of the state has seen about 0.25-0.75" with locally 1-2" over parts of the Sierra and Big Sur coastal mountains. The low will continue to slowly head southward off the coast the rest of today as the moisture plume traverses the soCal coast. This will focus most of the precip this morning from LA to San Diego county as the moisture moves through. HREF exceedance probabilities show about a 20-50% or so chance of 0.50"/hr rates during this time. Models still show the plume exiting into Baja this afternoon allowing precip to diminish. The slow moving low pressure system, however, will continue to generate scattered showers across the region later today along with chances of isolated thunderstorms. Overnight, a secondary low will develop over NV as the offshore low slowly passes Point Conception. This will generate two main areas of precipitation, one across coastal srn CA and the other over NV. The same pattern will persist on Sunday as the offshore low passes by the soCal coast and the inland low moves from NV into UT. There is still some uncertainty regarding the precip along the soCal coast overnight tonight through Sunday morning. The ECMWF continues to show a heavier band of precip just offshore as the low passes. The differences amongst the ECMWF ensembles on the position of the surface low is causing higher QPF values to be forecast by the ECMWF members compared to the GFS which is not showing this feature. This is evident in the 24 hr QPF clusters ending Sunday afternoon. The clusters are split into 3 groups (39%, 34%, 27%) each corresponding to its parent model (72% ECMWF, 75% CMC, 83% GFS). Cluster 1 is the wettest and contains none of the GFS ensemble members. The 24 hr QPF spread at San Diego covering that time period, for example, is between 0.25" to 3.50" for the ECMWF while the GFS has 0.10-0.90". The current official forecast is about 0.75", but wanted to emphasize the range of possibilities. This will depend both on the amount of precip the low generates as it passes and how close to the coast it gets. For what it's worth, HREF exceedance probabilities showing again around a 20-50% or so chance of 0.50"/hr rain rates. The rest of Sunday, the region will be under a large positively tilted troughing pattern with the trough axis stretched offshore of Baja through ID/WY/MT. This will keep scattered showers in play for central/srn CA and NV the remainder of the weekend along with chances of thunderstorms over soCal and parts of NV. By Monday, an upper ridge will move into the eastern Pacific and begin to push inland across the PacNW suppressing the troughs influence over the nw part of the region. Troughing will remain over srn CA and part of NV on Monday allowing for some lingering shower potential as well as isolated thunderstorms over srn CA/NV. The majority of the precip for the rest of the current system is expected along coastal soCal and an area from the nrn Sierra through nrn NV. The morning forecast was a combination of WPC guidance and the latest NBM. Manually adjust some numbers for the current period to reflect precip that has already fallen. QPF 18z Sat through Monday: 0.75-1.50" coastal SoCal, 1.50-2.75" Transverse Range/mntns east of San Diego, 0.25-1" northern Sierra, 0.50-1.50" nrn NV mountains, 0.10-0.75" central coast/rest of Sierra, and a few hundredths to 0.50" the rest of CA. The ridge will take over entirely on Tuesday as the trough exits returning dry conditions and raising temperatures above normal for northern areas. This ridging will be short lived as another system approaches from the Gulf of Alaska mid-week. Initial showers expected to reach nw CA on Wednesday as the trough digs in offshore becoming a closed low near BC/WA by early Thursday morning. The troughing from the system will also expand to cover much of the region the rest of the forecast period. Not seeing any significant moisture with this system, which should limit precip amounts for mid to late next week. Precip for mid/late next week will mainly be across nrn CA/NV and across the Sierra. QPF 12z Tues-12z Fri: 0.10- 0.75" Sierra (locally closer to 1" for parts of the nrn Sierra), 0.30-1" Shasta, 0.10-0.75" along the CA/OR border through nrn NV, and a few hundredths to a couple tenths across the rest of nrn/cntrl CA. Some light showers possible for soCal. Freezing levels 4.5-7 kft over the weekend then rising from nw to se as a ridge builds in Monday. Expecting 8.5-10 kft for the nrn CA coast early Monday before higher levels spread across the region the rest of the day. By Tues am, expecting 9-11 kft north of Point Conception and 7-9 kft for s/e CA/NV. Freezing levels lowering again mid/late week as the next system moves in. Thus am, freezing levels 2-5.5 kft north of I-80 and 4-11.5 kft to the south. Lower levels spreading across the region into Friday down to 2-3.5 kft north of Point Conception across CA and 4-9.5 kft to the south/east. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php AS $$