CW3E AR Update: 17 February 2017 Outlook

CW3E AR Update: 17 February 2017 Outlook

February 17, 2017

Click here for a pdf of this information.

Update on ARs Currently Impacting and Forecast to Impact West Coast

  • Precipitation continues to fall over a majority of California
  • The Transverse Mountains (north of Santa Barbara) have received over 3.5 inches in the last 24-hours
  • SoCal is forecast to receive another 2 – 6 inches in the next 24-hours, raising concerns for flooding and landslides
  • Forecast confidence for this weekends landfalling AR has increased over Northern California

NOAA NWS NEXRAD Pacific Southwest Radar Loop

Valid 10:08 AM – 11:18 AM PST 17 Feb 2017




 

 

 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 1 PM PT Fri 17 Feb. 2017

CW3E AR Update: 16 February 2017 Outlook

CW3E AR Update: 16 February 2017 Outlook

February 16, 2017

Click here for a pdf of this information.

Update on ARs Currently Impacting and Forecast to Impact West Coast

  • As much as 6 inches of precipitation has fallen over the past 24-hrs over the high elevations of Northern CA, OR, and WA
  • The second AR, which develops in conjunction with a mesoscale frontal wave, is forecast to impact Southern CA
  • Over 12 inches of precipitation is forecast to fall over the Transverse Ranges, raising concern for flooding and landslides
  • The lower elevations of Los Angeles and San Diego are forecast to receive 1–4.5 inches over the next 72 hours


 

 

Click IVT or IWV image to see loop of 0-126 hour GFS forecast

Valid 1200 UTC 16 Feb – 1800 UTC 21 Feb 2017

  • A mesoscale frontal wave is forecast to develop off of the current AR which will bring AR conditions to Southern CA.
  • The proximity and propagation of the low-pressure system will bring non-AR related precipitation the North/Central CA
  • Another AR is forecast to make landfall over Northern CA from 20 – 22 Feb.


 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 1 PM PT Thurs 16 Feb. 2017

CW3E AR Update: 15 February 2017 Outlook

CW3E AR Update: 15 February 2017 Outlook

February 15, 2017

Click here for a pdf of this information.

Update on Multiple ARs Forecast to Impact West Coast

  • Precipitation has begun to fall over portions of WA, OR, and Northern CA in association with first AR
  • A second AR, which develops with a mesoscale frontal wave, is forecast to propagate southward and impact Southern CA
  • A third AR could impact portions of Northern CA on 20–22 February, but forecast certainty is currently low
  • Maximum 7-day precipitation forecasts are over 12 inches over the high elevations of Northern CA, OR, and WA
  • Southern CA could see as much as 8 inches over the Transverse ranges, which could be a concern for flooding and landslides

Click IVT or IWV image to see loop of 0-180 hour GFS forecast

Valid 1200 UTC 15 Feb – 0000 UTC 20 Feb 2017


 

 

 

 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 12 PM PT Wed 15 Feb. 2017

CW3E AR Update: 13 February 2017 Outlook

CW3E AR Update: 13 February 2017 Outlook

February 13, 2017

Click here for a pdf of this information.

Two ARs Forecast to Impact the West Coast

  • Potentially moderate AR conditions to impact the Pacific Northwest and Northern CA on 15–16 Feb.
  • Up to 5 inches of precipitation could fall over the next 72-hrs over the Coastal Ranges
  • Although forecasts are more uncertain, a second AR is likely to impact most of CA from late 16 Feb through early 18 Feb
  • 7-day precipitation forecasts are as high as 7.6 inches over Northern CA and 6.5 inches over Southern CA

Click IVT or IWV image to see loop of 0-132 hour GFS forecast

Valid 1200 UTC 13 Feb – 0000 UTC 19 Feb 2017


 

 

 

 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 3 PM PT Mon 13 Feb. 2017

CW3E AR Update: 9 February 2017 Outlook

CW3E AR Update: 9 February 2017 Outlook

February 9, 2017

Click here for a pdf of this information.

Update on AR Currently Impacting CA, OR, and WA

  • Precipitation continues to fall over portions of Northern California, Washington, and Oregon
  • Another 3–5 inches of precipitation has fallen over some locations over the last 24-hrs
  • AR conditions will last for several more hours over Northern CA before the AR propagates southward over Southern CA
  • Up to 5 more inches could fall over the High Sierra’s and 1–2 inches forecast at lower elevations and portions of Southern CA


Click IVT or IWV image to see loop of 0-84 hour GFS forecast

Valid 1200 UTC 8 Feb – 0000 UTC 12 Feb 2017

The AR will continue to impact Central and Northern CA, OR, and WA before weakening and propagating southward over Southern California


 

 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 1 PM PT Thurs 09 Feb. 2017

Odds of Reaching 100% Water Year Precipitation – Feb Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2017 (February Update)

February 9, 2017

Contribution from Dr. M.D. Dettinger, USGS

The odds shown here are the odds of precipitation in the rest of the water year (after January 2017) totaling a large enough amount to bring the water-year total to equal or exceed the percentage of normal listed. “All Yrs” odds based on monthly divisional precipitation totals from water year 1896-2015. Numbers in parenthesis are the corresponding odds if precipitation through January had been precisely normal (1981-2010 baseline).

Click here for a pdf file of this information.
 

 

 

How these probabilities were estimated:

At the end of a given month, if we know how much precipitation has fallen to date (in the water year), the amount of precipitation that will be required to close out the water year (on Sept 30) with a water-year total equal to the long-term normal is just that normal amount minus the amount received to date. Thus the odds of reaching normal by the end of the water year are just the odds of precipitation during the remaining of the year equaling or exceeding that remaining amount.

To arrive at the probabilities shown, the precipitation totals for the remaining months of the water year were tabulated in the long-term historical record and the number of years in which that precipitation total equaled or exceeded the amount still needed to reach normal were counted. The fraction of years that at least reached that threshold is the probability estimate. This simple calculation was performed for a full range of possible starting months (from November thru September) and for a wide range of initial (year-to-date) precipitation conditions. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, and 150%, to ensure that the resulting tables of probabilities cover almost the full range of situations that will come up in the future.

[One key simplifying assumption goes into estimating the probabilities this way: The assumption that the amount of precipitation that will fall in the remainder of a water year does not depend on the amount that has already fallen in that water year to date. This assumption was tested for each month of the year by correlating historical year-to-date amounts with the remainder-of-the-year amounts, and the resulting correlations were never statistically significantly different from zero, except possibly when the beginning month is March, for which there is a small positive correlation between Oct-Mar and Apr-Sept precipitation historically.]

Contact: Michael Dettinger (USGS)

CW3E AR Update: 8 February 2017 Outlook

CW3E AR Update: 8 February 2017 Outlook

February 8, 2017

Click here for a pdf of this information.

Update on AR Currently Impacting CA, OR, and WA

  • Precipitation continues to fall over portions of Northern California, Washington, and Oregon
  • 6–10 inches of precipitation has fallen over some locations over the last 72-hrs
  • AR conditions continue to persist over Northern CA, OR, and WA as the second AR made landfall this morning
  • Another 5–8 inches are forecast for the higher elevations of Northern CA, OR, and WA as flooding remains a concern


 

 

Click IVT or IWV image to see loop of 0-128 hour GFS forecast

Valid 1200 UTC 8 Feb – 0000 UTC 12 Feb 2017

The southwesterly oriented AR is forecast to bring IVT magnitudes as high as 1000 kg m–1 s–1 and IWV values as high as 28 mm to the West


 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 5 PM PT Wed 08 Feb. 2017

CW3E AR Update: 7 February 2017 Outlook

CW3E AR Update: 7 February 2017 Outlook

February 7, 2017

Click here for a pdf of this information.

Two ARs to Impact the West CoastUpdate on ARs Currently Impacting and Forecast to Impact West Coast

  • As much as 6.5 inches of precipitation has fallen over the high elevations of CA over the previous 48 hours
  • Several rivers and streams are currently experiencing flooding in the San Francisco Bay Area
  • The second AR is forecast to make landfall at ~4 AM on Wednesday 8 February
  • An additional 5–10 inches of precipitation could fall over already wet soils, raising concern for additional flooding


 

 

 

Click IVT or IWV image to see loop of 0-127 hour GFS forecast

Valid 1200 UTC 7 Feb – 1800 UTC 11 Feb 2017

The next AR is currently forecast to make landfall at ~4 AM on 8 February 2017 with maximum IVT ~1000 and IWV ~34 mm


 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 2 PM PT Mon 07 Feb. 2017

CW3E AR Update: 6 February 2017 Outlook

CW3E AR Update: 6 February 2017 Outlook

February 6, 2017

Click here for a pdf of this information.

Two ARs to Impact the West Coast

  • Two moderate to strong ARs are forecasted to make landfall in Northern CA and the Pacific Northwest
  • Due to the timing of both ARs, AR conditions could last over 90 hours in some locations
  • Weather Prediction Center forecast shows 1-5 Day precipitation amounts up to 17.5 inches over higher elevations in Sierras
  • 15 river gauges are currently forecast to rise above flood stage by the California Nevada River Forecast Center

Click IVT or IWV image to see loop of 0-126 hour GFS forecast

Valid 1200 UTC 6 Feb – 1800 UTC 11 Feb 2017


 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 3 PM PT Mon 06 Feb. 2017

CW3E AR Update: 1 February 2017 Outlook

CW3E AR Update: 1 February 2017 Outlook

February 1, 2017

Click here for a pdf of this information.

Precipitation forecast for Northern CA Pacific Northwest

  • A low pressure system is forecast to propagate toward Northern CA and Oregon
  • Up to 6 inches of precipitation are forecast to fall over higher elevations, while low elevations of N. CA could see as much as 2.5 inches
  • This event is not representative of an AR structure (long and narrow plumes IVT and IWV), though the IVT and IWV thresholds associated with an AR will be met at certain locations
  • Extended forecasts indicate the potential for an AR to make landfall in the next 5–7 days

Click IVT or IWV image to see loop of 0-126 hour GFS forecast

Valid 1200 UTC 6 Feb – 1800 UTC 11 Feb 2017


 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 12 PM PT Wed 01 Feb. 2017