One of the most active storm periods this Water Year is unfolding during the next 7 Day Forecast period. It possibly could be one of the biggest storm event series of the year with possible flood conditions in the far northern portions of the State by Saturday morning. A subtropical Atmospheric River (AR) attached to a cold frontal boundary will slowly spread into NORCAL today and tonight with steady, continuous warm air advection rains with high elevation snowfall. Even though the width of the precip shield is fairly narrow, the forward motion of the front is slow, which produces high precip accumulations due to the high PWAT moisture content values which increase rainfall efficiencies. Rapid rises in main stem rivers is expected for portions of NORCAL due to 4 inch rainfall accumulations within a 24hr period, producing possible flood conditions into the Siskiyou Mts. The rest of NORCAL rivers are expected to remain below Monitor Stage. NORCAL and a portion of CENCAL down to Madera Co are included in a SPC General Risk Category for Thunderstorms. Supercells are possible north of Modesto with a possible tornado around the Stockton/Delta region. Large hail is indicated from near Stockton to near Chico with small hail possibly as far south as Madera. The southern extent of Thunderstorms could be extended further south to Kings and Tulare Co, so an update on Convective Potential will be issued tomorrow.
The storm exits the region overnight on Saturday into early Sunday predawn. The next inbound storm quickly follows, and spreads into CA late Sunday into Monday. This storm is very cold, with a -34°C cold core approaching the OR coastline on Sunday night, with snowlevels plummeting down to near 3.5K near YNP and near 4.5k into the Tehachapi Mts. This storm could potentially risk travel over the Grapevine. Charts indicate a powerful cold front travels thru the State Monday afternoon, and cold air advection follows frontal passage with a -30°C isotherm digging into NORCAL to near SAC. The timing schedule for this FROPA is too late to allow for post frontal Thunderstorms to be in optimal conditions, but with the air this cold arriving they may occur into the evening hours. The potential for Thunderstorms on Monday/Tuesday should be monitored closely, due to the extreme cold nature of this disturbance, which could easily trigger Thunderstorms. Yet another storm system reaches into NORCAL on Thu, Apr 3rd and then into CENCAL on Fri, Apr 4th, departing CA on Sat, Apr 5th. The GFS Fantasyland Forecast realm shows another cold trough dipping into CA on TuePM Apr 8th, and stalling over CENCAL Wed, Apr 9th thru Fri, Apr 11th with a -30°C cold core over the SJV. If that verifies, watch out for a possible majorThunderstorm event. The end of the GFS Fantasyland Forecast at 384hrs on Day 16 shows yet ANOTHER cold core storm circulation diving into CA with a -32°C circulation approaching the NORCAL coastline! WOW..when was the last time we had 5 storms providing 8 rainy days for CENCAL to talk about in one 16 Day period! Let’s see if Mother Nature delivers the goods. If all of these progged storms do verify, this could help ease the drought situation.
Previous Storm Accumulated Total Highlights;
NORCAL; 5.11 Camp Six, 4.13 Gasquet, 3.44 Elk Valley, 3.38 Cooskie Mtn, 3.24 Four Trees, 3.13 La Porte, 3.12 Klamath River, 3.08 Bucks Lake, 2.84 Oak Mtn, 2.69 Jarbo Gap, 2.64 Seedorchard, 2.56 Strawberry Valley, 2.53 Blue Cyn, 2.52 Shasta Dam, 2.49 Manzanita Lake, 2.48 Honeydew, 2.47 Slate Crk, 2.40 Stouts Mdw, 2.39 Drum Powerhouse, 2.32 Greek Store, Sims, 2.28 Deer Crk, 2.20 Huysink, Hirz, 2.16 Shingletown, 2.10 DeSabla, 2.08 Laytonville, 2.04 Black Springs, 2.01 Brush Mtn, 2.00 Central Sierra Snow 1.99 Brush Crk, Beaver, Paradise, 1.89 Bloods Crk, 1.84 Forni Ridge, 1.67 Lassen, 1.63 Carpenter Ridge, 1.62 Bald Mtn, 1.61 Crescent City, 1.56 Taylor Ridge, 1.50 Tiger Crk Powerhouse, 1.48 Pacific House, 1.44 Middle Peak, 1.40 Calaveras, 1.30 Ebbetts Pass, 1.27 Stanislaus Mdw, 1.03 Placerville, 1.01 Ukiah, 0.80 OAK, Heavenly Valley, 0.79 New Hogan, 0.77 Travis AFB, 0.70 Carson Pass, 0.67 Redding, 0.60 Petaluma, 0.57 Oroville, 0.54 Auburn, 0.43 Concord, 0.41 Livermore, 0.39 Red Bluff, 0.38 SAC Exec, 0.32 Napa, 0.27 Marysville, 0.18 Alturas
CENCAL; 1.68 Eagle Crk, 1.67 Los Gatos, 1.59 Fish Camp, 1.49 Camp Nelson, 1.42 Ben Lomond, 1.40 Gianelli, 1.36 Big Sur, 1.28 Pascoes, 1.24 Mammoth Pass, 1.21 Hossack Mdw, 1.19 Wofford Heights, 1.16 Chilkoot Mdw, 1.07 Hetch Hetchy, 1.06 Oak Opening, 1.05 YNP, 1.00 Dinkey Crk, Rogers Camp, 0.99 Wawona, Three Pks, 0.94 Pinehurst, Wolverton, 0.93 Minarets, 0.88 Devils Postpile, 0.84 Shaver Lake, Peckinpah, 0.83 North Fork, Gem Pass, 0.77 Woody, 0.76 Graveyard, Stockton, 0.68 Nature Pt, Johnsondale, 0.64 New Melones, 0.62 Fence Mdw, Milo, 0.61 Cedar Grove, 0.53 Mt Tom, 0.52 High Sierra, 0.47 Balch Camp, 0.46 SFO, 0.45 Exchequer, 0.38 Monterey, 0.36 A.G. Wishon Powerhouse, Arroyo Grande, 0.35 Stratford, 0.31 Trimmer, Pacheco Pass, Porterville, 0.30 Fancher Crk, 0.29 Pine Flat, 0.27 Isabella, Visalia, 0.25 Lake Kaweah, 0.23 Clovis, 0.22 San Luis NWR, 0.18 FAT, 0.17 San Jose, 0.16 Eastman Lake, 0.14 Hurley, Salinas, Lake Success, 0.13 Walker Pass, Lompoc, 0.12 Gustine, 0.11 Merced, Selma, Lamont, Madera, Vandenberg, 0.10 SLO, 0.07 South Lake, Lemoore, Hensley Lake, 0.06 Hanford, Paso Robles, 0.03 Mettler, 0.02 Huron
SOCAL; 0.67 Tanbark, 0.61 Julian, 0.46 Alpine, 0.43 Mt Laguna, 0.23 Grass Mtn, 0.18 Camp 9, 0.15 Big Bear, 0.07 San Diego Brown Field, 0.04 Long Beach, 0.02 Mt Wilson, Malibu, Santa Monica, Corona, 0.01 Santa Barbara
NORTHERN SIERRA 8-Station Precip Index; update shows an increase of 1.3 inches since last week, which pushes the 7 inches for the month of March to 101% of average! This amt should increase dramatically by Tuesday, April 1st.
San Joaquin 5-Station Precip Index; update shows an increase of 1 inch since last week, which raises the 3.9 inches for the month of March to 64% of average! This amt should increasedramatically by Tuesday, April 1st.
Hydrologic Outlook; issued by NWS Medford, OR and by NWS Eureka, CA for a FLOOD POTENTIAL in the Siskiyou Mts, and for rapid rises in main stem rivers of Del Norte, Humboldt and Trinity Co due to expected heavy precip amts of up to 4 inches in a 24hr period with high snowlevels which may lead to rapid rises on area rivers, creeks and streams with potential flooding in the Siskiyou Mts. There is also the potential for rock and mud slides in the mts. Mainstem rivers in Del Norte, Humboldt and Trinity Co are expected to rapid rise but remain below Monitor Stage, however the Eel River at Fernbridge and the Mad River at Arcata are expected to peak just below Monitor Stage. Tributary streams will also rise but remain within their banks.
WINTER STORM WARNING; posted for the Northern Sierra from Friday night into Sunday morning for periods of heavy snowfall of up to 2 feet at the highest elevations, accompanied by strong winds of 55mph or higher. This will impact the Sierra from Lassen southward to Donner (I-80), Echo (Hwy 50) and Carson passes.
Winter Wx Advisory; posted for the Southern Sierra from YNP to the Tulare Co Sierra, for snowfall of up to 7 to 10 inches for the Southern Sierra from YNP into the Kings River basin above 6K, accompanied with gusty winds up to 55mph and up to 70mph near the Crest.
Hazardous Wx; Thunderstorms possible Saturday afternoon and evening, Mar 29th for the SAC Valley, capable of producing lightning, hail and possibly a tornado.
Special Notation; The GFS forecast charts continue a very interesting and important theme into the next 7 Day period with a very active storm period..which according to the past several. This storm series could produce the most significant precip event for NOR/CENCAL this Water Year. This is especially true with regards to NORCAL, with impressively high 5-10 inch QPF’s suggested during the 7-Day period into the most important region for CA Water Storage…the Shasta and Feather River basins! The QPF charts offer this significant amount of rainfall within a short time frame with expectations of high streamflow runoffs with possible flood conditions near the OR border region, due to the initial warm-type storm #1 which arrives on Friday/Saturday with high snowlevels and rainfall rates of up to 0.35 inch per hour for up to 6 hours, with total accumulations of up to 4 inches during the 24hr period reaching into the Feather River basin Saturday. There is good model agreement for this significant precip event for NORCAL. Another shortwave moves across NORCAL on Sunday with widespread rains and snow. After a brief break into Monday, another storm reaches into CA on Monday/Tuesday. The extended models are in good agreement with these storm systems bringing a significant amt of precip into at least the NORCAL watersheds.
Fri, Mar 28th The approaching frontal boundary warm sector is attached to a narrow subtropical Atmospheric River (AR) which spreads heavy rains thru NORCAL. The AR contains warm Hawaiian PWAT’s with up to 1.25 inch values which increase precip efficiencies sharply. 700mb lift is high as well as orographic lift from the SW alignment of the flow pattern…all favorable for heavy precip production. The forward directional speed of the front is very slow, which allows for high accumulations of liquid precip to high elevations of the NORCAL mts. Thunderstorms spread onshore over the coast from Ukiah northward. NORCAL main stem rivers are expected to respond in kind to the heavy runoff with possible flooding near the OR border region. Overnight the front slowly sags to a position near SFO to Tahoe with heavy rains continuing along the boundary. 700mb charts show top of the scale lift occurring along the front.
Sat, Mar 29th The weakening cold front continues to bring heavy rainfall on a line across the CENCAL region along a narrowing band of precip. Although the frontal boundary is narrow it does contain a shortening Atmospheric River (AR) attachment which originated from the Hawaiian Island region, but which has been severed. The broad trough axis remains stationary off the West Coast with a strong cyclonic SW flow aloft over CA with energy supplied by a robust 105kt upper Jet Stream, which should produce excellent orographic lift for the Sierra. The GFS forecast charts show the front rapidly weakening over CENCAL, but with good lift producing a shorter burst of mod/heavy precip for the Southern Sierra. Overnight as weak flat ridging moves over CA, another shortwave trough drops out of the GOA along 140W and heads east. Precip chart showing front moving thru CENCAL late Saturday;
Sun, Mar 30th As the flat High Pressure ridge kicks east into the Great Basin a new -30°C trough axis moves closer to the coast, with a strong cold front developing west of the CA/OR border which extends to the west. This is a much colder storm than the previous one. Overnight the trough shifts east, with the alignment of the frontal boundary extending north to south along the NORCAL coast. Charts show powerful upper level dynamics and cold air are associated with this storm system.
Mon, Mar 31st Forecast charts show a strong frontal passage thru CA early in the day with the -30°C cold core storm center near the CA/OR border and strong vort dynamics reaching southward to the Tehachapi Mts. This would place the SJV into the left front quadrant of the upper Jet Stream (Blue chart below), an optimum position for classic Thunderstorm development. If these charts do verify, then strong Thunderstorms, possibly SEVERE could be expected within the SJV. This should be closely monitored. Overnight the upper level Jet Stream moves back over CENCAL at 120kts, which keeps rainshowers going over most of NOR/CENCAL and the cold core Low Pressure center moves SE to a position near Cape Mendocino. Precip chart (green) and upper level Jet Stream chart (blue)
Tue, Apr 1st The cold core Low Pressure circulation moves near Pt Arenas with rainshowers and Thunderstorms moving thru CENCAL and the Southern Sierra. As the trough axis moves onshore the upper level Jet Stream kick east and the clouds and precip move into the Great Basin with a clearing trend for CA overnight. Precip chart below showing Thunderstorms moving thru CENCAL.
Wed, Apr 2nd A transitional day with weak High Pressure nosing inland over CA as the westerly zonal flow across the PAC basin continues with another cold front approaching NORCAL. Overnight the cold front reaches the NORCAL coast with moderate rains commencing from Ukiah northward.
Thu, Apr 3rd As a large Low Pressure circulation fills most of the GOA, the nearly stationary frontal boundary brings more continuous rains into NORCAL from SFO to Tahoe northward. Overnight at the trough axis nears the coast, and the front has stalled out, the rainfall rates increase over NORCAL to heavy.
Days 8-16, Long Range into Fantasyland Outlook; Day 8 begins;
Fri, Apr 4th shows the trough axis moves closer to the CA coast with the cold front dragging across CENCAL with moderate precip. Overnight the trough axis moves onshore with an onshore flow pattern over NORCAL keeping heavy rainshowers going throughout the night.
Sat, Apr 5th shows moderate rains continue over NORCAL, with lighter showers over CENCAL as the onshore flow pattern continues. Overnight the trough kicks east into the Great Basin with High Pressure moving onshore over the CA coast providing a dry NW flow pattern.
Sun, Apr 6th shows weak High Pressure over CA with a NNW flow pattern. A few showers continue to drop southward from OR into far NORCAL, with partly cloudy skies over most of CENCAL. Colder temps are indicated. The synoptic scale features show a long wave trough in the GOA extending southward to Hawaii, with a Kona Low Pressure circulation pulling a long-fetched Atmospheric River (AR) northward along 160W into the GOA trough.
Mon, Apr 7th shows High Pressure strengthening over CA, with the trough pattern in the GOA at 140W trailing back to the Kona Low Pressure cell.
Tue, Apr 8th shows High Pressure migrates to 160W and tucks the Kona Low beneath itself to produce a REX configuration High over Low. To the east the GOA trough is shifting east to 130W just west of the CA coast, and producing an increasing SW flow pattern into CA…which is attaching a long fetch Atmospheric River supplies by the Kona Low Pressure cell. Overnight the trough brings renewed rains back into NORCAL.
Wed, Apr 9th shows a large trough along the WCONUS with a cold front stretched from the Central coast NNE into NORCAL with heavy rains over portions of CENCAL.
Thu, Apr 10th shows the large Low Pressure trough over the WCONUS which is stalling out, with continued rainshowers over most of CA. Since the parent Low Pressure is centered over the PACNW, the moisture supply is limited.
Fri, Apr 11th shows High Pressure begins to nose into the PACNW while the Low Pressure trough lags over CA with continued rainshowers. Overnight the trough kicks rapidly east with a migratory High Pressure ridge moving onshore over the West Coast.
Sat, Apr 12th shows the High Pressure ridge shifting into the Great Basin as a new very cold storm drops SE from the GOA and is heading toward NORCAL. Overnight clouds move onshore from Cape Mendocino northward with rains not far behind.
NEW CA RECORDS
Station New Record Old Record__
Stockton 0.66 inch 0.64 inch set in 2011
Day 1 – 5 QPF:
At 12Z (9am) Thursday thru the period Monday night (Tuesday @4am); showing as much as 6 to 8+ inches of precip for the wet spots of the NW coastal region and up to 6 inches for the wet spots of the Feather River basin and portions of the North Coast of Del Norte and Humboldt Co, up to 4-6 inches for the North Coast of the Eel River basin northward and including a major portion of the Shasta River basin, and the Northern Sierra from Lassen to the I-80 corridor, up to 2-4 inches for the North Coast from the Golden Gate northward thru most of the Shasta River basin SE thru the Northern Sierra to the Tuolumne River basin, with 1-2 inches from the Central Coast NE to the Delta then SE thru the Southern Sierra, with 0.5 to 1 inch for most of the SJV. Up to 0.2 to 0.5 inch falls along the Westside SJV southward into most of Kern Co and the Tehachapi Mts, with 0.25 to 0.5 inch for the higher terrain of SOCAL and 0.2 inch for the coastal lowlands diminishing to >0.1 inch into the lower deserts.
7 Day QPF Chart; the 0Z Thursday evening WPC 7-Day QPF showing up to 7.8 inches of rainfall into the far NW coastal region into the Smith River basin with up to 9.1 inches falling into the Northern Sierra/Lassen to Feather River basin region. Amts over NORCAL diminish to 5-7 inches of precip from Del Norte Co to northern Mendocino Co along the North Coast and into the Northern Sierra down to near Donner Pass and up to 4-5 inches from near Ukiah northward along the coast and into the Shasta River basin region, then SE into the Northern Sierra to near the Hwy 50 corridor, with up to 3-4 inches from near the Russian River basin northward along the coast thru the northern SAC Valley, then SE into the Sierra to near YNP, with up to 2-3 inch from near Santa Cruz NE into the SAC region and then southward into the Sierra to the Kings/Kaweah River basins, with up to 1-2 inches from the Central Coast region to the Northern SJV and up to 1 inch from near Santa Maria northward along the coast and Kings and Tulare Co in the SJV northward, diminishing to 0.25 to 0.5 inch into the Southern SJV/Kern Co and into the coastal region of SOCAL. The lower CA desert region remains dry.
The Latest 12Z Friday morning WPC 7-Day QPF showing up to 10.8 inches of rainfall into the Northern Sierra, an increase of 1.7 inches from 12 hours earlier. This is a nice trend! This chart also showing an increased amt of precip falling into the Southern Sierra as well, with up to 4-5 inches depicted to extend southward to near YNP!
16-Day QPF estimates (from the 0Z GFS model) for;
Days 1-7; shows up to 7.8 inches of rainfall into the far NW coastal region into the Smith River basin with up to 9.1 inches falling into the Northern Sierra/Lassen to Feather River basin region. Amts over NORCAL diminish to 5-7 inches of precip from Del Norte Co to northern Mendocino Co along the North Coast and into the Northern Sierra down to near Donner Pass and up to 4-5 inches from near Ukiah northward along the coast and into the Shasta River basin region, then SE into the Northern Sierra to near the Hwy 50 corridor, with up to 3-4 inches from near the Russian River basin northward along the coast thru the northern SAC Valley, then SE into the Sierra to near YNP, with up to 2-3 inch from near Santa Cruz NE into the SAC region and then southward into the Sierra to the Kings/Kaweah River basins, with up to 1-2 inches from the Central Coast region to the Northern SJV and up to 1 inch from near Santa Maria northward along the coast and Kings and Tulare Co in the SJV northward, diminishing to 0.25 to 0.5 inch into the Southern SJV/Kern Co and into the coastal region of SOCAL. The lower CA desert region remains dry.
Days 8-16; depicts a flip back into a dry mode with only 0.25 inch suggested for the NW Coastal region. This solution is much drier than previous models which showed additional storms reaching into CA. Therefore the Week #2 time frame is highly uncertain and with a low confidence forecast.
GFS 384hr, 16Day QPF Chart showing precip total accumulations of up to 5-10 inches for a large portion of NORCAL including the Shasta and Feather River basins, diminishing to 2-3 inches from near Monterey to near the San Joaquin River basin, diminishing down to 1 inch from near San Diego northward to near Barstow, diminishing to 0.5 inch reaching into portions of interior SOCAL, and the lower Colorado River desert region with >0.1 inch.
Weekly Evapotranspiration rates for the local 7 Counties shows up to 0.85 near Merced to 1.13 inches near Lost Hills and Taft for the SJV during the next 7 Days. The Sierra Crest evaporation loss is 0.49 inch in the upper Tuolumne River basin up to 1.12 inch near Isabella.
Water Vapor 4KM Image of the West Coast Friday, March 28th, 2014, shows increasing high level cloudiness moving over CENCAL from the SW as a disturbance travels toward the PACNW carrying an Atmospheric River full of subtropical moisture.
Visible Satellite Image of the CA Friday, March 28th, 2014, shows increasing cloudiness over NORCAL, with CENCAL under mostly clear skies along with all of SOCAL.
If you have any questions please call or text at any time of day or night.
Comments and suggestions always welcome.
Atmospherics Group International
Dan Gudgel Steve Johnson