spring

Spring 2022 Season in Review

For the three-month period, temperatures were mainly below normal. Precipitation was above normal in Baker County Oregon and near to below normal elsewhere.

MARCH

March precipitation anomalyMarch temperature anomaly

March was unusually dry. Much of our area received less than half normal precipitation.  Temperatures averaged near normal in the valleys, but above normal at higher elevations.

The month began with an upper level high pressure ridge over the region, resulting in above normal temperatures for the first three days of the month.

A cooling trend commenced when the ridge exited to the east on the 3rd and a ridge off the coast amplified northward into Alaska. This pattern brought cold dry air under northerly flow aloft.

By the 8th Arctic air had pushed south of the Canadian border into Montana, northern Idaho, and Washington. the Arctic front arrived in southern Idaho early on the morning of the 9th, leaving only light snowfalls. By that night the front was on its way south across Utah and Nevada.  Northwest winds which had gusted over 25 mph died down and skies cleared, allowing temperatures to dip into the teens and single digits by sunrise on the 10th. McCall’s low of minus 4 was not a record, but the lows of 14 at Boise and 9 at Twin Falls where previous records were 15 in 1948 at Boise and17 in 2006 at Twin Falls.

Temperatures quickly recovered on the 11th as a high pressure ridge moved inland, bringing warmer Pacific air. A weak upper level low pressure trough followed the ridge on the 13th.

On the 15th a stronger moister trough arrived from the Pacific. Precipitation was mainly less than two-tenths of an inch, but .41 inch was measured at McCall and .34 inch at Boise.

Westerly flow aloft continued to support near normal temperatures through the 18th. On the 19th the next trough brought light precipitation and cooler air.

The 20th was 10-15 degrees cooler behind the cold front, but the ridge which followed brought more spring like temperatures, with highs in the lower to mid 70s in the lower valleys from the 23rd through the 26th.  The ridge kept temperatures 5-10 degrees above normal through the 29th. The 75 at Burns on the 23rd tied the record set in 1940.

On the 30th another Pacific cold front was followed by gusty northwest winds, but little if any precipitation.  Temperatures cooled from normal on the 30th to below normal on the 31st as breezy northwest winds resumed.

APRIL

April precipitation anomalyApril temperature anomaly

April was a cold, stormy, and windy month. All of our area as well as the entire northwestern U.S. averaged cooler than normal. Here are some of the record lows…

aprrecs

In contrast to the cold, Twin Falls set a record high of 80 on  April 8, eclipsing the old record for the date of 77 set in 2016.

Precipitation was generally above normal in southeast Oregon, southwest Owyhee County, and the central Idaho mountains. Elsewhere totals were near or slightly below normal.

At Boise, snowfall totaled 1.5 inches. That exceeds the April normal of 0.1 inch. The .3 inch on the 13th set a record for the date.

During the first 6 days of the month, strong westerly flow aloft carried weather systems from the Gulf of Alaska across the Pacific Northwest states.  On the 2nd the first of these systems brought no precipitation.

The next system on the 4th was stronger, but most locations received little or no precipitation. Exceptions were a quarter inch at Boise and half an inch at McCall. Strong winds followed the cold front, with gusts mainly in the 40-50 mph range. But there were several reports of gusts exceeding 60 mph.

An upper level high pressure ridge warmed temperatures to 10-20 degrees above normal on the 7th and 8th ahead of the next Pacific system.

On the 9th the ridge was replaced by an upper level trough, following another very windy cold front. Gusts of 40-50 mph were common, and there were a few reports of gusts exceeding 60 mph.

By the 10th the trough had expanded to cover much of central and western North America.  Unseasonably cold air kept temperatures in our area 10-15 degrees below normal.

Rain and snow fell daily from the 10th through the 14th as disturbances from the Gulf of Alaska dropped into the trough. Snowfall amounts were mostly under half an inch in the valleys, but 2.5 inches was measured near Twin Falls on the 11th, and 2.5 inches in Boise’s north end on the 12th. Also on the 12th 4.5 inches fell north of Donnelly. On the 14th 5.9 inches blanketed the ground near New Meadows.

https://twitter.com/NWSBoise/status/1513683580236435457?s=20&t=NMwydGu9khBfHvz75UnWMQ

More gusty northwest winds, mainly under 50 mph, followed a cold front on the 16th. A weak upper level ridge built over the region on the 17th, and on the 18th temperatures had warmed to around 10 degrees above normal. Cooler unsettled weather resumed on the 19th as an upper level trough off the coast sent impulses across our area.

The trough moved inland on the 22nd with another round of 40-50 mph winds. But most of its energy concentrated over southern California and the four-corners states, so most of our area was denied precipitation.  The high pressure ridge following the trough gave us the last warm weather of the month on the 25th ahead of another Pacific cold front.

The unsettled pattern redeveloped on the 26th as an upper level trough in  the Gulf of Alaska sent a series of disturbances inland across the Northwest. The first two systems dropped scarcely more than traces of precipitation.

On the 28th a cold front formed over Nevada and southwest Idaho, resulting in another episode of 40-50 mph winds.

On the 30th, showers and thunderstorms associated with an upper level trough brought generally light precipitation.

MAY

May precipitation anomaliesMay temperture anomaly

Unrelenting unseasonably cold and unsettled weather continued through much of May, but the latter half of the month brought long-awaited but brief hints of summer.

Precipitation was above or much above normal across most of our area.

The month began under an upper level low pressure trough which produced only light precipitation. A second stronger trough originating in the Gulf of Alaska brought more copious precipitation in the form of rain and snow, including .70 inch at Boise, .58 inch at McCall, .38 inch at Jerome, and .28 inch at Baker.

Here are a few snowfall reports on the 3rd…

9 inches 11 NE Garden City (Boise County) and 20 SSW of Silver City (Owyhee County)

7 inches 5 SW Donnelly (Valley County) and 15 W of Cambridge (Washington County)

6 inches 6 WSW Atlanta (Elmore County), 9 ESE Pioneerville (Boise County), 9 W Featherville (Elmore County), 16 E Rogerson (Twin Falls County), and 8 SE Three Creek (Twin Falls County)

5 inches 20 NNE McCall (Valley County)

4 inches 9 NNW Halfway (Baker County)

Precipitation started again on the evening of the 6th following a cold front which preceded a deepening trough from the Gulf of Alaska. Northwest winds in the 40-50 mph range were reported at many locations. Gusts of 69 mph were measured near Wagontire in Harney County and 62 mph near Kuna in Ada County.

As the trough took up residence over the Western Region on the 7th, it cooled highs by around 15 degrees and generated more rain and snow. McCall received .55 inch of precipitation, but amounts were generally light elsewhere.

A trough from the Bering Sea arrived over the coast on the 8th with even colder air. Snow began that night, and by the morning of the 9th the ground was white at many locations.

Here are a few reports…

11 Inches in Avimor (north Boise)

8 inches 6 N Boise (Ada County)

7 inches at Boise (Ada County)(totals ranged from 2 to 7 inches around Boise, but only half an inch at the airport, and a lot of tree damage in north Boise) and Cascade (Valley County)

https://twitter.com/CoachRittsD/status/1523735766412660736?s=20&t=s_JO4cOPlqcjHV84-ogwuA

4 inches at Centerville (Boise County), 4ENE Boise (Ada County), and 2E Emmett (Gem County)

3 inches at Garden City (Ada County)

2 inches at Mountain Home (Elmore County)

Generally light precipitation fell on the 12th and 13th as yet another trough from the Gulf of Alaska pushed inland along the Canadian border. A high pressure ridge building northward prevented most of the weather from penetrating very far south.

Temperatures rose steadily under the ridge, reaching the 80s at several locations on the 15th. Highs included 88 at Ontario and Rome, 85 at Boise and Mountain Home, 83 at Burns, 82 at Jerome, and 81 at Twin Falls.

Temperatures cooled to near normal from the 16th through the 18th as the ridge departed to the east and our area came under westerly flow aloft.

A cold front which passed late on the 18th brought gusts of 40-50 mph at many locations. Gusts exceeded 60 mph in the Twin Falls area.

The 19th were as much as 20 degrees cooler than the previous day.  The trough hung around through the 22nd.

Temperatures stayed below normal but gradually moderated as a high pressure ridge began to build inland. By the 25th highs were in the 80s again at lower elevations. Highs on the 25th and 26th included 82 and 91 at Jerome, 88 and 89 at Rome, 88 and 86 at Ontario, 85 and 89 at Mountain Home, 82 and 88 at Boise, 80 and 88 at Twin Falls, 82 and 81 at Burns, and 79 and 84 at Baker.

On the 26th a Pacific cold front was followed by another round of gusty northwest winds gusting to 40-50 mph.

On the 27th the trough following the cold front ushered in a wet period. And on the 28th a deeper, wetter, and colder trough, which originated in eastern Siberia, moved inland over the Pacific Northwest states. Finally on the 30th, a trough from southeast Alaska reinforced the main trough. Temperatures that day averaged as much at 20 degrees below normal.

Here are Precipitation totals(inches) for the 26th through the 31st…

Baker 1.41
Boise .85
Burns .31
Jerome 1.07
McCall .76
Mountain Home .97
Ontario .53
Rome .30
Twin Falls 1.04

As the trough began to exit southward over the Great Basin on the 31st, weak high pressure and partly cloudy skies started a warming trend.

2022 Idaho Spring Flood and Water Resources Outlook

Spring Flood PotentialSEWApr622

The risk for spring flooding due to snowmelt is low across Idaho. Snowpack in the lower valleys has melted out and the remaining mid and high elevation snowpack is well below normal for this time of year with the exception of northern Idaho where snowpack percentages are near normal. Snowpack in most basins peaked early and is on pace to melt out several weeks earlier than normal. 

The primary factors in the development of spring flooding are the occurrence of persistent above normal temperatures, and rain on snow precipitation events. Even if mainstem rivers do not reach flood stage, smaller creeks and streams can still overflow their banks. Under the right scenario, spring flooding is possible even for areas that have low snowpack. 

 

Water Supply 

NWSFApr622ational Weather Service water supply forecasts for April through September 2022 call for near normal runoff volumes for northern Idaho watersheds. Meanwhile, forecasts vary considerably across central and southern Idaho and are generally well below normal. Forecasts for the Snake River Headwaters near the Wyoming border and the Bear River in far southeast Idaho are generally 50 to 70 percent of normal. Volume forecasts for the Lost River Basins and Salmon River Basin are 60 to 80 percent of normal while forecasts for the Wood River Basins are 35 to 55 percent of normal. Forecasts for the Middle Snake River and the    Boise, Payette, and Weiser Basins range from 50 to 75 percent of normal. Across south central and southwest Idaho near the Nevada border runoff volumes are only expected to be 40 to 45 percent of normal. 

 

Temperature and Precipitation

In October, southern Idaho and the Panhandle Region had average to well above average precipitation while the Clearwater and Salmon River Basins in central Idaho were below average.  November precipitation was average to above average across the north while southern Idaho received well below average precipitation. Autumn was relatively warm statewide, especially in November when temperatures were 3 to 6 degrees (F) above average. December moisture varied considerably across Idaho but the majority of the state received average or above average precipitation. December temperatures were on the cool side across northern Idaho and a little above average across southern Idaho. 

AnoApr622

January precipitation was below average across most of the state while temperatures were near average across northern Idaho and below average across the south. Northern regions of Idaho were a mix of below average and above average precipitation in February while record dryness occurred across central and southern Idaho. February was a cold month with below average temperatures throughout the state.  March precipitation was below average with the exception of some of the Idaho Panhandle where precipitation was near average. March temperatures were average to below average across northern and eastern Idaho and a little above average elsewhere across the state.  The three month period from January through March, 2022 was one of the driest on record for many locations across central and southern Idaho. 

Snowpack

Mountain snowpack was well above normal across most of the state in early January. However, snowpack percentages trended down afterward and by the end of February had decreased by 50 to 60 percentage points across much of central and southern Idaho. As of April 6, mountain snowpack was well below normal with the exception of northern Idaho where snowpack percentages are near normal. April 6 snowpack percentages were the highest in the Spokane and Clearwater Basins at 99 and 91 percent of median, while the lowest was in the Owyhee Basin at only 48 percent of median. Idaho snowpack as a whole typically builds through March and peaks in early April.

SWEApr622

Reservoirs

April 1 reservoir storage in northern Idaho, far southeast Idaho, on the Henrys Fork arm of the Upper Snake, the Payette Basin, and on the main stem Snake River was generally around normal. Elsewhere across central and southern Idaho, reservoir system storage ranged from 39 to 88 percent of normal. Reservoirs on the Snake River above Heise were at a combined 57 percent of normal. Magic Reservoir in south central Idaho was only at 39 percent of normal while Owyhee Reservoir was only 63 percent of normal. Weather patterns and irrigation demand will drive reservoir operations over the next several months. Wet spring weather or extended periods of above normal temperatures resulting in rapid snowmelt and large reservoir inflows could result in significant fluctuations in reservoir discharge and downstream river levels.

Drought

Drought continues to plague much of Idaho. Very dry conditions across much of central and southern Idaho from January through March have led to intensification of drought in some areas. Temperature and precipitation patterns for the remainder of spring and this summer will determine whether or not drought conditions improve or deteriorate. The U.S. Seasonal Drought Outlook indicates that drought is likely to persist across central and southern Idaho at least through the end of June. 

DRApr622

Long Range Outlook

The outlook for April through June favors below normal temperatures across the Idaho Panhandle and above normal temperatures for most of southern Idaho, and equal chances of either below, above, or normal temperatures elsewhere. The precipitation outlook favors below normal precipitation across central and southern Idaho, and equal chances for either below, above, or normal precipitation across the Idaho Panhandle.

SEAApr622

Online Resources

Water Supply Volume Forecasts…
National Weather Service-Northwest River Forecast Center www.nwrfc.noaa.gov/ws/

National Weather Service-Colorado Basin River Forecast Center
www.cbrfc.noaa.gov/

USDA-Natural Resources Conservation Service
www.nrcs.usda.gov/wps/portal/nrcs/main/id/snow/

Snowpack Information…
National Weather Service-Northwest River Forecast Center
www.nwrfc.noaa.gov/snow/

National Weather Service-National Operational Hydrologic Remote Sensing Center
www.nohrsc.noaa.gov/

USDA-Natural Resources Conservation Service
www.nrcs.usda.gov/wps/portal/nrcs/main/id/snow/

Reservoir Storage…
Bureau of Reclamation Reservoir Storage
www.usbr.gov/pn/hydromet/select.html

USDA-Natural Resources Conservation Service
www.wcc.nrcs.usda.gov/basin.html

Drought Information…
U.S. Drought Portal
www.drought.gov

Peak Flow Forecasts…
Northwest River Forecast Center
www.nwrfc.noaa.gov/peak/

Colorado Basin River Forecast Center
www.cbrfc.noaa.gov/rmap/peak/peaklist.php

Temperature and Precipitation Outlook…
Climate Prediction Center
www.cpc.ncep.noaa.gov/

 

2021 Idaho Spring Flood and Water Resources Outlook

Spring Flood Potential

Screen Shot 2021-03-23 at 10.28.21 AMThe risk for spring flooding due to snowmelt is near average across most of Idaho. The exceptions are the Big Lost Basin and Little Wood Basin, and the Medicine Lodge, Beaver, and Camas Basin in central and east-central Idaho where the risk is slightly below average due to well below normal snowpack and low soil moisture. Above normal
temperatures in December and January helped limit the snowpack in the low elevations which significantly reduces the snowmelt flood risk during late winter and early spring.

The primary factors in the development of spring flooding are the occurrence of persistent above normal temperatures, and rain on snow precipitation events. Even if mainstem rivers do not reach flood stage, smaller creeks and streams can still overflow their banks. Under the right scenario, spring flooding is possible even for areas that have low snowpack. Additionally, wildfire burn scars can have a significant impact on local flood potential during spring snowmelt.Screen Shot 2021-03-23 at 10.28.15 AM

Water Supply

National Weather Service water supply volume forecasts for the spring and summer of 2021 are near normal for northern Idaho watersheds. Meanwhile, forecasts vary considerably across central and southern Idaho with subpar snowpack and longer term hydrologic drought leading to well below normal forecasts in some areas. Forecasts for the Snake River headwaters region along the Wyoming border and the West Central Mountains are generally 75 to 85 percent of normal. Volume forecasts for the rest of the Central Mountains and southern Idaho watersheds are well below normal ranging from 25 percent to 70 percent of normal. The lowest forecasts are for the Big Wood and Little Wood Basins, and the Big Lost River Basin. Low snowpack and poor streamflows in these areas could lead to water supply concerns, especially for those relying on natural flows. These forecasts may change considerably over the next couple of months since seasonal snow accumulation and rainfall typically occur during March and April.

Temperature and Precipitation

The 2021 Water Year started out well across northern Idaho with above normal precipitation in October, while rather dry conditions prevailed across southern Idaho. Most of the state received near normal or above normal precipitation in November with the exception being near the Canadian border and portions of central Idaho where only 50 to 70 percent of normal occurred. December was a very dry month for the state as a whole. Precipitation in January was improved for some areas but dry conditions continued for the majority of Idaho. A favorable storm track in February brought normal or well above normal precipitation to the majority of the state except for the Northern Panhandle and the Central Mountains east of the Sawtooths which received less than normal precipitation. Temperatures were around normal in October and November with warmer than normal conditions prevailing in December and January. February temperatures were near normal across far southern Idaho and below normal across the remainder of the state.

Screen Shot 2021-03-23 at 10.28.08 AM

Snowpack

As of March 3, mountain snowpack was near normal for most of Idaho. The Clearwater Basin led the way with 113 percent of normal while the Little Wood and Big Lost River Basins were lagging at 66 and 69 percent of normal. Idaho snowpack as a whole typically builds through March and peaks in early April.Screen Shot 2021-03-23 at 10.28.00 AM

Reservoirs

Reservoir storage across Idaho was in good shape as of early March with major reservoir systems holding near average water with the exception of the Wood and Lost River Basins. Across southern Idaho, basin-wide total storage in the Bear River Basin was near 136 percent of average while Southside Snake Basins were near 81 percent of average. Storage in West Central Basins was near 103 percent of average while the Wood and Lost Basins were only 59 percent of average. The Upper Snake River Basin was at 120 percent of average, the Clearwater Basin at 103 percent of average and Panhandle Region was 106 percent of average. Weather patterns, irrigation demand, and flood control needs will drive reservoir operations over the next several months. Wet spring weather or extended periods of above normal temperatures resulting in rapid snowmelt and large reservoir inflows could result in significant fluctuations in reservoir discharge and downstream river levels.

Drought

Drought conditions continue to plague portions of southern Idaho. The Wood River Basins and Big Lost River Basin of south central Idaho are the focus for drought due to subpar snowpack and precipitation dating back to the winter of 2019-2020. Meanwhile, long-term dryness along the Utah and Nevada border is resulting in drought conditions as well. Weather and precipitation for the remainder of winter and this spring will determine whether or not drought conditions improve or deteriorate.

Screen Shot 2021-03-23 at 10.27.52 AM

Long Range Outlook

The outlook for March through May favors below normal temperatures across the Idaho Panhandle and above normal temperatures along the Utah and Nevada border. Elsewhere across the state, the chances for either below, above, or normal temperatures are equal. The precipitation outlook slightly favors above normal precipitation across the Panhandle Region. Elsewhere the precipitation outlook is equal chances for either below, above, or normal precipitation.

Screen Shot 2021-03-23 at 10.27.43 AM

On-line Resources

Water Supply Volume Forecasts…
National Weather Service-Northwest River Forecast Center www.nwrfc.noaa.gov/ws/

National Weather Service-Colorado Basin River Forecast Center
www.cbrfc.noaa.gov/

USDA-Natural Resources Conservation Service
www.nrcs.usda.gov/wps/portal/nrcs/main/id/snow/

Snowpack Information…
National Weather Service-Northwest River Forecast Center
www.nwrfc.noaa.gov/snow/

National Weather Service-National Operational Hydrologic Remote Sensing Center
www.nohrsc.noaa.gov/

USDA-Natural Resources Conservation Service
www.nrcs.usda.gov/wps/portal/nrcs/main/id/snow/

Reservoir Storage…
Bureau of Reclamation Reservoir Storage
www.usbr.gov/pn/hydromet/select.html

USDA-Natural Resources Conservation Service
www.wcc.nrcs.usda.gov/basin.html

Drought Information…
U.S. Drought Portal
www.drought.gov

Peak Flow Forecasts…
Northwest River Forecast Center
www.nwrfc.noaa.gov/peak/

Colorado Basin River Forecast Center
www.cbrfc.noaa.gov/rmap/peak/peaklist.php

Temperature and Precipitation Outlook…
Climate Prediction Center
www.cpc.ncep.noaa.gov/

Winter 2016 and Spring 2017 Flood Summary

This past winter and spring had its share of flooding across southeast Oregon and southwest Idaho.  Not only did spring runoff bring flooding to rivers and streams, but ice jams and snow melt caused flooding during the winter as well.  The stage was being set for an active spring flood season as far back as October 2016, when 150 to 400 percent of normal precipitation occurred across much of the region which moistened the soil profile.  The winter storm track brought well above average snowfall to most of southeast Oregon and southwest Idaho, with extreme snowfall across lower valleys.  A relatively cool and wet early spring was the final piece of the puzzle to ensure abundant spring runoff.  An indicator of how wet this past winter and spring have been, water supply forecasts for the April through September period rank in the top 10 for most of southeast Oregon and southwest Idaho, dating back to 1970.  Additionally, all major reservoir systems either have filled or are expected to fill.  Record high precipitation was seen across many areas from December 2016 through June 2017, shown in the figures below.

pnw_cl (3) pnw_cl (4)

The map below shows March 1 snow pack along with areas where flooding had a significant impact.

flood

Although the threat of snow melt flooding has diminished, summertime thunderstorms can pose a serious flood risk.  Areas of steep terrain and areas burned by wildfire are at particular risk for flash flooding due to thunderstorms.  For flood safety information, visit http://www.floodsafety.noaa.gov/.  For the latest river conditions, see http://water.weather.gov/ahps2/index.php?wfo=boi.