CW3E AR Update: 13-15 October 2016 Outlook

CW3E AR Update: 13-15 October 2016 Outlook

October 12, 2016

A series of ARs are expected to make landfall over the Northwest U.S., including Northern CA. The first AR is expected to make landfall on 13 October 2016 followed by a second AR on 15 October 2016. These systems have R-Cat 2 rainfall potential as some areas could see >12 inches of precipitation in 72 hours. For up to date AR forecasts visit the CW3E AR Portal.

Click here for a pdf file of this information.


 

 

Publication Notice: Extreme Daily Precipitation in the Northern California Upper Sacramento River Watershed Requires a Combination of a Landfalling Atmospheric River and a Sierra Barrier Jet

CW3E Publication Notice

Extreme Daily Precipitation in the Northern California Upper Sacramento River Watershed Requires a Combination of a Landfalling Atmospheric River and a Sierra Barrier Jet

July 18, 2016

Ralph, F.M., J.M. Cordeira, P.J. Neiman and M. Hughes, 2016: Extreme Daily Precipitation in the Northern California Upper Sacramento River Watershed Requires a Combination of a Landfalling Atmospheric River and a Sierra Barrier Jet. J. Hydrometeor., 17, 1904-1915.

The top 0.3% most extreme daily precipitation events in the key Sacramento River watershed all involved both a landfalling atmospheric river and a Sierra Barrier Jet. Thus, forecasts of extreme precipitation are related to the skill of forecasts of each of these key phenomena, and can be enhanced by evaluation of, and enhancement of, skill in predicting each of these key processes. This study was led by the CW3E Director, was supported by the California Department of Water Resources, used data from NOAA’s Hydrometeorology Testbed collected over a decade, and epitomizes the focus of the “Center for Western Weather and Water Extremes,” and its partnership with NOAA Research’s Physical Sciences Division and Plymouth State University.

Contact: F. Martin Ralph (mralph@ucsd.edu)

Abstract

The upper Sacramento River watershed is vital to California’s water supply and is susceptible to major floods. Orographic precipitation in this complex terrain involves both atmospheric rivers (ARs) and the Sierra barrier jet (SBJ). The south-southeasterly SBJ induces orographic precipitation along south-facing slopes in the Mt. Shasta–Trinity Alps, whereas landfalling ARs ascend up and over the statically stable SBJ and induce orographic precipitation along west-facing slopes in the northern Sierra Nevada. This paper explores the occurrence of extreme daily precipitation (EDP) in this region in association with landfalling ARs and the SBJ. The 50 wettest days (i.e., days with EDP) for water years (WYs) 2002–11 based on the average of daily precipitation from eight rain gauges known as the Northern Sierra 8-Station Index (NS8I) are compared to dates from an SSM/I satellite-based landfalling AR-detection method and dates with SBJ events identified from nearby wind profiler data. These 50 days with EDP accounted for 20% of all precipitation during the 10-WY period, or 5 days with EDP per year on average account for one-fifth of WY precipitation. In summary, 46 of 50 (92%) days with EDP are associated with landfalling ARs on either the day before or the day of precipitation, whereas 45 of 50 (90%) days with EDP are associated with SBJ conditions on the day of EDP. Forty-one of 50 (82%) days with EDP are associated with both a landfalling AR and an SBJ. The top 10 days with EDP were all associated with both a landfalling AR and an SBJ.

Mesoscale Frontal Wave AR during CalWater-2014

CW3E Publication Notice

An Airborne and Ground-Based Study of a Long-Lived and Intense Atmospheric River with Mesoscale Frontal Waves Impacting California during CalWater-2014

May 10, 2016

Neiman, P.J., B.J. Moore, A.B. White, G.A. Wick, J. Aikins, D.L. Jackson, J.R Spackman, and F.M. Ralph, 2016: An Airborne and Ground-Based Study of a Long-Lived and Intense Atmospheric River with Mesoscale Frontal Waves Impacting California during CalWater-2014. Mon. Wea. Rev., 144, 1115-1144.

This study provides the most comprehensive observations to date of a mesoscale frontal wave associated with an atmospheric river, including its structure offshore, landfall characteristics and impacts on precipitation. It utilizes research aircraft, a unique array of coastal hydrometeorological measurements and inland data. This paper reflects the broader scientific collaboration between CW3E and NOAA/PSD, and adds to the knowledge of phenomena that are critical to creating extreme precipitation on the U.S. West Coast – a major thrust of CW3E. Dr. Ralph contributed to this paper by proposing the experiment (Ralph et al. 2016 BAMS), identifying the science objective for the flights (i.e., mapping out the structure of a mesoscale frontal wave with dropsondes and airborne radar), laying out the flight tracks, guiding the mission onboard, having been the PI of the major projects that created the unique land-based observing network (NOAA HMT- Ralph et al. 2013 BAMS, and the DWR-sponsored EFREP mesonet – White et al. 2013 JTech) used in the study and contributing to the analysis and interpretation of the measurements in this paper.

Contacts: Paul Neiman (paul.j.neiman@noaa.gov) and F. Martin Ralph (mralph@ucsd.edu)

Abstract

The wettest period during the CalWater-2014 winter field campaign occurred with a long-lived, intense atmospheric river (AR) that impacted California on 7–10 February. The AR was maintained in conjunction with the development and propagation of three successive mesoscale frontal waves. Based on Lagrangian trajectory analysis, moist air of tropical origin was tapped by the AR and was subsequently transported into California. Widespread heavy precipitation (200–400 mm) fell across the coastal mountain ranges northwest of San Francisco and across the northern Sierra Nevada, although only modest flooding ensued due to anomalously dry antecedent conditions. A NOAA G-IV aircraft flew through two of the frontal waves in the AR environment offshore during a ;24-h period. Parallel dropsonde curtains documented key three dimensional thermodynamic and kinematic characteristics across the AR and the frontal waves prior to landfall. The AR characteristics varied, depending on the location of the cross section through the frontal waves. A newly implemented tail-mounted Doppler radar on the G-IV simultaneously captured coherent precipitation features. Along the coast, a 449-MHz wind profiler and collocated global positioning system (GPS) receiver documented prolonged AR conditions linked to the propagation of the three frontal waves and highlighted the orographic character of the coastal-mountain rainfall with the waves’ landfall. Avertically pointing S-PROF radar in the coastal mountains provided detailed information on the bulk microphysical characteristics of the rainfall. Farther inland, a pair of 915-MHz wind profilers and GPS receivers quantified the orographic precipitation forcing as the AR ascended the Sierra Nevada, and as the terrain-induced Sierra barrier jet ascended the northern terminus of California’s Central Valley.

CW3E AR Update:Post-Event Summary: 7-10 April 2016

CW3E AR Update: 7-10 April 2016 Post Event Summary

April 13, 2016

CW3E and WRCC give a post-event storm summary about two cutoff lows that made landfall over Southern California during 7-10 April 2016. Precipitation was widespread throughout the Southeastern United States with 72-hr accumulations generally ~0.5-3 inches. While the low pressure system entrained moisture from the tropics, spatial characteristics of IWV >20 mm and IVT >250 kg m-1 s-1 did not meet the necesarry requirements to be considered an Atmospheric River.

Click here for a pdf file of this information.


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CW3E AR Update: 7-10 April 2016 Outlook

CW3E AR Update: 7-10 April 2016 Outlook

April 7, 2016

A weak low pressure system and high Integrated Water Vapor (IWV) values have brought light-to-moderate precipitation over Southern California this morning. A closed low is expected to develop off the coast over the next two days and will produce moderate precipitation over Southern California on 8-10 April 2016. IWV and Integrated Water Vapor Transport (IVT) values will be above AR thresholds but spatial characteristics of IWV/IVT will not meet the requirements of an AR. Coastal Southern California will experience AR conditions (IWV >20 mm and IVT >250 kg m-1 s-1) and light-to-moderate precipitaton, but this event is not considered an AR. For up to date AR forecasts visit the CW3E AR Portal.

Click here for a pdf file of this information.


 

 

CW3E AR Update: Post-Event Summary: 5-6 March 2016

CW3E AR Update: 5-6 March 2016 Post-Event Summary

March 10, 2016

CW3E gives a post-event storm summary about a moderate strength Atmospheric River that made landfall over Northern California on 5 March 2016. The AR was an R-Cat 1 event and produced over 10 inches of 72-hour precipitation.

Click here for a pdf file of this information.


 

 

 

 

Northern Sierra Precipitaiton: 8-Station Index

~7.5 inches of precipitation measured by the 8-Station Index

Increased water-year-to-date accummulation from average to ~115% of average

Lake Mendocino Storage

Increase in storage of ~8000 af

Storage remains above the Target Water Supply Storage Curve

SSMI Integrated Water Vapor: 0000 UTC 3 March – 0000 UTC 7 March

  • AR developed over the Central North Pacific and made landfall over Northern California
  • AR entrained moisture from previous decaying AR off California coast prior to landfall

GFS IVT Analysis: 0000 UTC 3 March – 1200 UTC 7 March 2016

Cazadero, Ca Snow Level Radar

Heavy bright-band precipitation began ~0600 UTC 5 March

Large drop in snow level post-frontal

Bodega Bay 0200 UTC Sounding

  • Saturated atmosphere up to ~550 hPa
  • IWV = 31.9 mm
  • IVT = 878.3 kg m-1s-1
  • Winds >50 knots throughout the troposphere
  • Majority of water vapor flux between 950-700 hPa

Event Summary

  • A moderate strength Atmospheric River made landfall over Northern California during 5-6 March 2016
  • Maximum 48-h precipitation of >10 inches occurred over the Sierra Nevada
  • Widespread precipitation >6 inches occurred over the Coastaland Sierra Nevada Ranges
  • Several rivers reached above flood stage in Northern California

CW3E R-Cat Alerts

CW3E R-Cat Alerts: Automated Notification of Heavy Precipitation Events

March 10, 2016

The Center for Western Weather and Water Extremes (CW3E) has set up an automated e-mail notification service that informs users of heavy precipitation events in near real-time. Along the West Coast, such events are often the result of land-falling atmospheric rivers, which transport substantial moisture into the area. Tracking, analyzing, improving the forecasting, and anticipating the impacts of such extreme events are a core element of CW3E’s mission.

The “Rainfall Category” or “R-Cat” 3-day precipitation classification of Ralph and Dettinger (2012) is a simple, effective measure of strong precipitation events, which can have a large impact on the Western U.S.:

R-Cat 1: 200-299 mm (roughly 8-12 inches) / 3 days

R-Cat 2: 300-399 mm (roughly 12-16 inches) / 3 days

R-Cat 3: 400-499 mm (roughly 16-20 inches) / 3 days

R-Cat 4: more than 500 mm (more than roughly 20 inches) / 3 days

An R-cat email alert includes a short summary of the 3-day total precipitation, location of the event (based on sources such as the Global Historical Climatology Network [GHCN] and the National Weather Service’s co-op precipitation stations), and a map showing the location of the event(s). Here is a recent example:

————————————————————————————————————
Station: BRUSH CREEK RS USC00041130
Location: (39.695, -121.345)
Date: 2016/03/07 (third day of event)
Event strength: R-Cat 1
3-day total precip (mm): 206.3
Individual days precip (mm): 76.5 102.1 27.7
 
————————————————————————————————————
Station: QUINCY USC00047195
Location: (39.937, -120.948)
Date: 2016/03/07 (third day of event)
Event strength: R-Cat 1
3-day total precip (mm): 202.7
Individual days precip (mm): 59.7 119.9 23.1

The email R-Cat alert service can be subscribed to by sending a message with the subject line “subscribe” to rcatalert@cirrus.ucsd.edu.

For more information, please contact David Pierce, dpierce@ucsd.edu.

CW3E AR Update: 10-11 March 2016 Outlook

CW3E AR Update – 10-11 March 2016 Outlook

March 10, 2016

A storm predicted to make landfall over northern California on 10 March 2016 has characteristics of an Atmospheric River. The AR is showing weak-to-moderate strength with an average landfall duration of 12-24 hours. This AR is about 75% as strong as the last significant AR landfall over northern California (March 5-6, 2016). The storm has the slight potential for R-Cat 1 rainfall in favored mountain areas. For up to date AR forecasts visit the CW3E AR Portal.



CW3E AR Update: 5-7 March 2016 Outlook

CW3E AR Update – 5-7 March 2016 Outlook

March 4, 2016

A storm predicted to make landfall over northern California on 5 March 2016 has characteristics of an Atmospheric River. The AR is showing moderate strength with an average landfall duration of 12-24 hours. The storm has the potential for R-Cat 1 rainfall in favored mountain areas. For up to date AR forecasts visit the CW3E AR Portal.


CW3E AR Update: 3 March 2016 Outlook

CW3E AR Update: 3 March 2016 Outlook

March 3, 2016

CW3E gives an outlook on current and upcoming Atmospheric River (AR) events along the U.S. West Coast. A moderate AR is currently impacting central California producing light precipitation over the northern Sierra Nevada and Central Valley. Two ARs are expected to make landfall over the Pacific Northwest in the next seven days, with both propagating south over California prior to dissipation. Long range forecasts also show the potential for another strong AR to make landfall in the Pacific Northwest next week.

For the latest river and precipitation forecasts and observations visit the California Nevada River Forecast Center (CNRFC) or the U.S. Geological Survey (USGS). For the latest AR forecasts visit the CW3E AR Portal.

Click here for a pdf file of this information.


 

Current Conditions: 3/3/2016
Northeast Pacific SSMI IWV: 1400 UTC 29 Feb 2016 – 1400 UTC 3 March 2016


 
GPS Integrated Water Vapor: 1515 UTC 3 March 2016
 
 
 
   
IWV values greater than 2 cm
throughout central California
-Current AR conditions

Current California Precipitation Conditions
The North Sierra 8-Station and Tulare Basin 6-Station Precipitation Indices are average for this time of year.


 

 
Forecasts
AR Landfall Probability Tool: Initialized 0000 UTC 3 March 2016
Hover mouse over description below to see forecast product or click to open. Images courtesy Jason Cordeira; Plymouth State University

IVT >250 kg m-1 s-1
IVT >500 kg m-1 s-1
Inland IVT >250 kg m-1 s-1
Inland IVT >500 kg m-1 s-1

  • Periods of AR conditions forecasted along most the U.S. West Coast on forecast days 0-1, 1-2, 2-5 and 4-5
  • Strong probability of AR event on forecast days 7-8
  • All forecasted ARs are expected to penetrate inland over Oregon and northern California


 


 
CNRFC River Forecasts
2000 UTC 3 March 2016
 
 

  • 1 river forecasted above flood stage
     -Navarro River
  • 7 rivers forecasted above monitor stage

    Russian River CNRFC Forecast


     
    GFS Ensemble MJO Index Forecast; 3 March 2016 – 17 March 2016

     

    • A continuation of MJO activity is expected
    • Propagation through Phases 8 and 1 and possibly 2
    • Significant decrease in amplitude

    GFS IWV: 0600 UTC 3 March 2016 – 1800 UTC 10 March 2016
     
      >

    • AR currently impacting northern and central California
    • AR to make landfall at 1800 UTC 4 March 2016 over NW Pacific
    • AR to make landfall at 0600 UTC 9 March 2016 over NW Pacific
    • All three ARs propagate south over California prior to dissipation

    GFS IVT: 0600 UTC 3 March 2016 – 1800 UTC 10 March 2016
     



     
    CNFRC Precipitation Forecasts: Produced 3 March 2016

    Max 72-h precip >6 inches over Northern Sierra Nevada and California Coastal Range
    Max 6-day precip ~11 inches over Northern Sierra Nevada and California Coastal Range

     
    7-day Precipitation Forecasts: Ending 4:00 am PST 10 March 2016

    Max 7-day precip ~290 mm over Northern Sierra Nevada, Olympic Mountains and Vancouver Island
    Max 7-day precip ~270 mm over Northern Sierra Nevada, Olympic Mountains and Vancouver Island


     

     
     

    Summary

    • Current dissipating AR impacting central California
    • Two moderate strength ARs expected to make landfall along the U.S. West Coast over the next five days
    • Another AR may potentially make landfall late next week
    • 7-day precipitation totals up to 300 mm in multiple locations over the U.S. West Coast


    For more information about AR updates or forecast products visit the CW3E Home Page or contact Brian Kawzenuk, Marty Ralph, or Scott Sellars at CW3E.