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NOAA,NWS,CBRFC www.cbrfc.noaa.gov B.Bernard 2014 Today’s Presentation

January weather – Mild and dry pattern continued

Current snowpack conditions – Near record low snowpack in many areas

2018 water supply forecasts – February update

Select forecast site review – Evolution Plots

February forecast – Much improvement over January?

Upcoming weather – Below average precipitation again in February?

Contacts & Questions

Phone: 1-877-929-0660 Passcode: 1706374

* Please mute your phone until ready to ask questions * Early January Storm System brought widespread (but light) precipitation amounts

Jan 8th 2018 Early January Precipitation January Weather

Mean Atmospheric Pattern Strong January 2018 persistent Low in the east

Mean high pressure in the west Winter Weather

Much below average precipitation in both December and January…

Bear 70% Bear 75%

Weber 60% Weber 65%

Six Creeks 65% Six Creeks 65%

Provo 40% Provo 70% Winter Weather

…combined with much above average temperatures Water Year Precipitation

Entire CBRFC forecast area Great Basin (primary contributing areas)

Greatest impacts

Bear 80% Missing out on storms Weber 65%

Six Creeks 55%

Provo 50% Snow Conditions SNOTEL Snow Water Equivalent (% 1981-2010 median)

January 8, 2018 February 5, 2018 Snow Conditions SNOTEL SWE Historical Rankings (period of record 30-40 years) (**earliest year 1978+) January 8, 2018 February 5, 2018

Red: Lowest on record Orange: Many in bottom 3 of record Dry seasons have happened in the past

How does this year compare? Atmospheric Pattern Atmospheric Pattern December 1976 December 2017

Blocking high Strong Hudson pressure ridge Bay low

Previously 1976/77 winter was referenced because it stands out as one of the lowest snow years. There were also some similarities in the late fall / early winter atmospheric pattern. Many record low flows were established in 1977. Comparing the January patterns

Mean Atmospheric Pattern Mean Atmospheric Pattern January 1977 January 2018

Similarities in large scale features but some subtle differences as well Location of ridge axis – strength of ridge – Pacific Ocean features Comparing the January patterns

Mean Atmospheric Pattern Mean Atmospheric Pattern January 1977 January 2018

January 1977: Greater amplified ridge/trough developed the 2nd half of January and persisted through February.

January 2018: High pressure ridge remains dominant player but the pattern has recently become more progressive in a northwest flow. Snow Conditions Snow Course SWE Historical Rankings (minimum years of record = 45)

Beginning of February 1977 Beginning of February 2018 CBRFC Model States Current SWE (% median) / Fall Soil Moisture February 1st Water Supply Forecasts – Bear River Basin

Median Basin Stewart Dam Smiths Fork Forecast:

Jan – 85% 82% Feb – 75% 46%

April-July Logan River 88% Forecast Streamflow Volumes (% of 1981-2010 average)

74% Blacksmiths Fork Little Bear 45% Bear Above Woodruff 71% Narrows

88% Bear Stateline February 1st Water Supply Forecasts – Weber River Basin

South Fork Ogden Median Basin 50% Forecast: Pineview Inflow 61% 46% Jan – 65% Lost Creek Feb – 50% Inflow

44%

April-July Forecast Weber-Gateway Streamflow Volumes (% of 1981-2010 average)

Echo 50% 51% 44% East Canyon Weber Inflow Chalk Creek Coalville 49%

64%

Rockport Weber-Oakley Inflow 51% February 1st Water Supply Forecasts – Six Creeks

Median Basin City Creek 53% Forecast: 30% 32% 49% Red Butte Jan – 55% Emigration Little Dell Inflow Feb – 45%

45% Parleys April-July Creek 45% Forecast Lambs Streamflow Volumes Creek (% of 1981-2010 average) 47% Mill Creek

58% Big Cottonwood

63% Little Cottonwood February 1st Water Supply Forecasts – Provo River/Utah Lake

Median American Fork Provo Hailstone West Canyon Basin Creek Forecast: 75% 39% 75% 24% Provo Woodland Jan – 50% 67% Feb – 45% Deer Creek Inflow

April-July Forecast Streamflow Volumes (% of 1981-2010 average)

53%

Utah Lake Inflow

35%

Spanish Fork January to February Change in Runoff Forecast % change in volume

-10-15%

-20-25%

-10-20%

-15-20% Forecast Evolution Plot Bear – UT/WY Stateline: 99 kaf / 88%

Official Jan 1 Fcst Official Cursor is on 2/1/2018 Feb 1 Fcst 10%

Raw ESP 50%

90%

Available on CBRFC web page by selecting sites from map: https://www.cbrfc.noaa.gov/lmap/lmap.php?interface=wsup list: https://www.cbrfc.noaa.gov/rmap/wsup/wsuplist.php Forecast Evolution Plot Weber – Oakley: 76 kaf / 64%

Model calibration period is 1981-2015 ESP: - Start from today’s model conditions (snow and soil moisture) - Use precipitation and temperature from each of those 35 years going forward à 35 possible runoff scenarios - Median of those 35 scenarios is the 50% exceedance value à basis of Official 50% Forecast Less than 10% chance of average runoff Forecast Evolution Plot Provo – Hailstone (Jordanelle Inflow) – 82 kaf / 75%

Future weather

Wetter scenario

“Average” scenario

Drier scenario Forecast Evolution Plot Little Cottonwood Creek: 24 kaf / 63%

~3% (1/35) chance of average runoff Additional ESP levels shown plus Maximum (~3% probability) and Minimum (~97% probability) traces

Greater than 10% chance of record low runoff

Select “Probability Traces” option Forecast Validation: How good are forecasts in February ?

Historical Water Supply Verification - February Historical Model Error % Model Error for February 1981-2010 April-July Forecast

February forecast error a general improvement over Logan River: January Jan: 27% Feb: 22% significant snow accumulation period remains Little Bear River: Forecasts are better than just going with average Jan: 36% Feb: 28%

Error tends to decrease each month into the spring

Where We Do Better: Bear River: Headwaters Jan: 21% Feb: 20% Primarily snow melt basins Known diversions / demands Weber River: Where We Do Worse: Jan: 23% Feb: 19% Lower elevations (rain or early melt) Downstream of diversions / irrigation Little Cottonwood: Jan: 20% Feb: 17% Little is known about diversions / demands Provo River: Jan: 25% Feb: 20%

Map is available at: https://www.cbrfc.noaa.gov/arc/verif/verif.php

From Water Supply drop down menu à select Historical Verification Map February Precipitation First 7 days Entire CBRFC forecast area Great Basin Upcoming Weather: Current Pattern as of Today à Weak storms in a northwest flow may impact the upper Green River Basin and possibly parts of the Bear River Basin. This Morning Feb 7th 2018

Strong High Pressure

Northwest Flow Upcoming Weather: Next Week à A possible storm system drops southward. The model splits and weakens the storm system. Precipitation amounts likely to be light in the north. Tue Feb 13th

Weakening and splitting storm system in northwest flow Upcoming Weather: Next Week à Models are struggling; if a closed low develops over southern California precipitation will remain south of Great Basin. Low confidence. Wed Feb 14th

This scenario would result in a very weak system with light precipitation amounts possible over the southwest Upcoming Weather NWS Weather Prediction Center: Precipitation Forecast Feb 7 – Feb 14

Greatest precipitation impacts are likely over the same areas that have seen it all winter Upcoming Weather and Impacts to Water Supply Forecasts NWS Climate Prediction Center: Temperatures & Precipitation probability Feb 14- Feb 20

Temperature Probabilities Precipitation Probabilities Long Range Weather Outlook: Storm systems appear weak at best as they encounter and move around the high pressure ridge. Models are inconsistent so confidence is low. Fri Feb 23rd 2017

Weak storms and light precipitation in this scenario Key Points

The dry fall and early winter continued into January with below average precipitation.

Outside of the Bear River Basin, the snowpack is near record low for this time of year.

Forecasts decreased everywhere from those issued in January. Largest decreases as a percent of volume were in the Weber River Basin.

Our official 50% forecast is based on ‘average’ conditions (1981-2015 climatology) going forward. A wet month in the future mix would result in some rebound in water supply forecasts but reaching near average runoff would take abnormally wet spring conditions in many areas. 2018 water supply briefing schedule

2018 monthly water supply briefings for the Great Basin:

Wednesday Mar 7th @ 1:30 pm MT

Thursday Apr 5th @ 1:30 pm MT

Monday May 7th @ 1:30 pm MT

Colorado River Basin webinars are same dates at 11 am MT

Peak flow briefing early March. Additional briefings scheduled as needed.

Date/Times are subject to change. All registration information has been posted to the CBRFC web page. CBRFC Water Supply Contacts Please contact us with any questions Michelle Stokes – Hydrologist In Charge [email protected]

Paul Miller– Service Coordination Hydrologist [email protected]

Basin Focal Points (Forecasters)

Greg Smith – San Juan, Gunnison, Dolores Focal Point [email protected]

Ashley Nielson – Green River Basin, Lake Powell Focal Point [email protected]

Cody Moser – Upper Colorado Mainstem Focal Point [email protected]

Tracy Cox and Zach Finch – Lower Colorado Basin, VirginFocal Point [email protected] [email protected]

Brent Bernard – Six Creeks, Provo , Sevier Focal Point [email protected]

Patrick Kormos – Bear, Weber Focal Point [email protected]