Showing posts from April, 2017

Weather Forecast Accuracy

FYI: I was asked to clarify a statement that was made on the last weather report about forecast accuracy being +- 2%.  Dan and Jack (avalanche forecasters) record the forecasted snow totals along with their daily weather observations.  The goal for this was to statistically provide an accuracy % for our internal forecasts. The scientific method was a simple record of snow totals forecasted (see example below) and then compare that spread with what actually fell.   So if the forecast was for 3-5” and what fell was within that spread, that was a score of 100%.  Plus or minus percentages correlates with how far off from the forecasted spread the actual snowfall was.
Example: 24hr Precipitation ending at 4 am: Today 24hr water = .25-.5 snow = 3-5   - actual = 4”  100%
As stated in the last forecast of the season with the seasonal stats, the accuracy was +-2%.  Another way to look at this is:  The forecast for snow totals was 98% accurate – or 98% of the time, the actual snowfall fell within for…

Seattle Wettest Winter on Record

Even though the mountains  got a relatively normal amount of snow this year, Seattle had its wettest period on record.   Seattle has soaked up 44.67 inches of rain since October 1, according to the National Weather Service.
That makes this October-through-April the wettest such period since record-keeping began in the city in 1895.

The normal amount of rainfall for the October-through-April period in Seattle is 30.9 inches, according to the service...

Full story:

9:00 Start for Teardown, Monday April 24

Sleep in a little bit and take it easy out there.


Time and Day:  Sunday 0700  (Last day of this great season) 
The Snapshot:   Dan V says it is mostly cloudy and 35degrees this morning.  Rain this afternoon with mixed rain and snow on the upper ridges.   Another short dry period tomorrow morning with rain expected on Tuesday.
The Science:  Some weak upper-level ridging has provided a short period of dry but cloudy conditions over Stevens Pass.   Radar shows more precipitation to the west which should reach the mountains around noon or so.   A similar pattern emerges tomorrow with weak upper-level ridging providing a dry and partly cloudy morning with rain moving in tomorrow night and Tuesday.   
What a great winter:  Some seasonal stats to add to your memory of the great powder we all enjoyed:
443” of snow fell   Nov        40 Dec        133 Jan         42 Feb         90 March   105 April      18 (thru 4/22)
Best storm/powder cycles: December 1-6 we got 51”, February 26-March 9 we got 88”.
Forecast accuracy for snow totals  had an error of +-2…

8:00 Sunday April 23rd no ABS


Time and Day: 0700 Saturday
The Snapshot:  Increasing clouds today with light rain reaching Stevens Pass by mid-afternoon or so.  Cooler tonight with mixed rain and snow showers tomorrow.  
The Science:  It’s a balmy 400f  this morning with high clouds moving in.  Moisture ahead of an approaching cold front will bring light rain to Stevens Pass this afternoon with freezing levels +- 7000’.  Once the front passes east of the crest, freezing levels will drop to around 4500’ with light snow possible overnight.  A weak ridge forms behind the front which will produce some partial clearing tomorrow morning with mixed rain and snow showers re-developing through the day.  
The Long Range:   A steady stream of precipitation takes aim at the PNW next week.
24hr Precipitation ending at 4am: Today 24hr water = lt .25  snow = trace Tomorrow’s 24hr water = .5  snow = 1-3
Trend and Timing: Light rain develops this afternoon with light mixed rain and snow tomorrow.  

24hr temperature ending at 4 am:…


Time and Day: 1100 Friday
The Snapshot:  A beautiful sunny day today with high clouds developing tonight.  Dry for most of tomorrow with light rain developing late afternoon.   Sun breaks with light passing rain/snow showers can be expected for the final day of the season.
The Science:  A high pressure ridge has produced a beautiful clear day over the North Central Cascades.   The eastern basin is heating up with Wenatchee temperatures possibly reaching into the 70’s today and tomorrow.   The warm air will also make its way west with freezing levels over Steven Pass peaking +7000’ during the heat of the day tomorrow.  Good pond skimming.
A cold front will move through late tomorrow, lowering temperatures and bringing light mixed snow and rain with it.  The atmosphere will remain unstable under WSW flow through Monday with light mixed rain and snow showers persisting.
The Long Range:  The wet spring weather pattern will continue through at least the middle of next week.
24hr Precipitati…


Time and Day: 1000 Thursday
The Snapshot:  Looking ahead to the weekend, tomorrow and the second half of Saturday will be mostly dry, warm and partly sunny.  Light rain enters the scene on Saturday afternoon with light mixed rain and snow persisting through the final weekend of the season.  
The Science:  These light snow showers will taper off today as high pressure ridge moves in.  A low-pressure system developing way out in the Pacific will pull warm and dry air up from the south with the moisture eventually making its way into the region on Saturday.   Light showers with sun breaks will continue through Sunday.   

The Long Range:   This active weather wet weather pattern will persist through most of next week.

8:00 Start Monday April 17 for Backside Teardown


Time and Day: 0700  Sunday
The Snapshot:   Warm and dry with increasing high clouds on this Easter Day.  Rain returns tomorrow with a soggy start to the new week.   
The Science:  A dry atmosphere with high cirrus clouds are being reported throughout the state this morning.  Offshore/easterly winds will be a bit gusty today as pressure gradients tighten over the mountains.  This feature will allow warm air to filter in from the east. We may see the warmest temperatures of the season today with surface temperature peaking +50f late this afternoon. Enjoy.  
The Long Range:  A weak low pressure system tracks in tomorrow with light rain expected.   More rain is expected on Tuesday as several weak frontal systems prepare to embark on the region.  Temperatures will begin to be seasonally average with freezing levels trending above 4000’.   
24hr Precipitation ending at 4am: Today 24hr water =0  snow =0 Tomorrow’s 24hr water = .25  snow = 0
Trend and Timing: Dry today with light rain tomorrow …

8:00 Sunday April 16th no ABS


Time and Day: 0630 Saturday
The Snapshot:  300 f with morning fog this morning. The weekend will trend dry, warmer and sunny.   
The Science:  The barometer has begun to rise with 1026hPa values beginning to clear and dry out the region.  A typical early morning cloud layers over Stevens Pass should begin to thin and break up as the morning progresses.   A real taste of spring should be felt tomorrow as a warm stable airmass settles in overnight.    
The Long Range:  Next week will start out dry with light rain developing Tuesday and Wednesday.    
24hr Precipitation ending at 4am: Today 24hr water = .10  snow = Trace Tomorrow’s 24hr water = 0 snow = 0
Trend and Timing: With the exception of a few light snow showers, it will be mostly dry into Monday morning.

24hr temperature ending at 4am:  Low: 28   High: 40 Freezing level: 4500’ -7000’
Trend and Timing:    Surface temps are expected to peak late this afternoon with good nighttime cooling expected.   Freezing level rise to +-70…

8:00 Start Saturday April 15, No ABS


Time and Day: 0700 Friday
The Snapshot:   Partly sunny with passing snow showers today.  The weekend is beginning to look pretty good with dry and warmer weather developing.
The Science: This morning's satellite imagery has spotty showers and partly cloudy skies over the region.  The atmosphere will remain unstable under weak westerly flow with slowly rising pressure gradients taking shape late tonight. Dry and warmer weather is expected to begin tomorrow as the pressure continues to rise and the atmosphere stabilizes.
The Long Range:  Next week will start out dry and warm with light rain expected on Tuesday.  There are early signs in the long range weather models of a trend to drier, typical PNW spring weather.  It's about time.
24hr Precipitation ending at 4am: Today 24hr water = .25 snow = 0-2 Tomorrow’s 24hr water = .10 snow = 0-1
Trend and Timing: Light passing snow showers will continue into early tomorrow morning.

24hr temperature ending at 4 am:  Low:   26  High: 36

8am Start Friday April 14, No ABS

Morgan Miller killed in Avalanche at Snoqualmie Pass

Morgan Miller, 36, an experienced ski mountaineer from Snoqualmie, was killed Tuesday in an avalanche on Red Mountain in the Snoqualmie Pass area.

sad. jM


Time and Day:  0830 Thursday
The Snapshot:   More mixed rain and snow showers with a sun break or two today and tomorrow.  The weekend is trending dry and partly sunny.  
The Science:  .5” of water equates to 3” of new snow in the base area with +-5” on the upper mountain this morning.  We will take it.   
Pressure gradients have eased a bit this morning with cool weak west/southwest flow filling in behind the front that passed earlier this morning.  This pattern will persist into early Saturday morning with the weekend trending dry and partly sunny.  
The Long Range:   Saturday will start out with light showers and then begin to dry out through the day.  Sunday will be dry and warm under weak high pressure.  The wet weather returns early next week.   
24hr Precipitation ending at 4am: Today 24hr water = .25  snow = 0-2 Tomorrow’s 24hr water = .25 -.5  snow = 1-3
Trend and Timing: Light intermittent showers today and tomorrow.

24hr temperature ending at 4am:  Low: 28    High: 34 Freezi…


Time and Day:  0800 Wednesday
The Snapshot:   This wet weather with periods of rain and snow will extend into the upcoming weekend.  There is a good chance of some snow accumulation early tomorrow morning.     
The Science:  A complex low-pressure system centered off the PNW coast will produce a mixed bag of snow and rain for the next few days.  A cold front associated with a deep trough could produce a period of heavy snow early tomorrow morning.   Cooler air aloft appears to fill in behind this feature allowing freezing levels to drop below 4000’ tomorrow and Friday.    
The Long Range:  Active weather continues through Saturday.  At the moment, Sunday is trending dry with temperatures returning to seasonal norms.
24hr Precipitation ending at 4am: Today 24hr water = .5-.75  snow = 3-6 Tomorrow’s 24hr water =.25-.5  snow = 2-4
Trend and Timing: Rain today shifting to snow tonight.   A burst of heavy snow will be possible between midnight and 7 am tomorrow morning. 

24hr temperat…

April 10-13

Have a good mid-week off. Check Thursday afternoon for Friday's start time.


Time and Day: 0700 Sunday
This is how today’s national weather service forecast discussion started: “Here I sit looking model to model, seeking a solution that won't make me hit the bottle. Though I must admit perpetual sogginess makes forecasting a breeze.Debating whether or not Seattle is under a curse…”  Funny. The Snapshot: The broken record continues. Dry today, light snow tomorrow, dry on Tuesday,  rain Wednesday and Thursday.
The Science:  A rising barometer has cleared the skies over the mountains with partly sunny conditions expected for most of today.  Clouds will increase tonight as the next weak system begins its approach.  Therefore, expect another day of light precipitation tomorrow.     
The Long Range:  Tuesday will be another dry interim day with rain expected on Wednesday/ Thursday.
Note: Next forecast will be posted on Wednesday morning.
24hr Precipitation ending at 4am: Today 24hr water = .10 snow = trace Tomorrow’s 24hr water = .25 snow = 1-2
Trend and Timin…

8:00am Start Sunday April 9, No ABS


Time and Day: 0630 Saturday
The Snapshot:   Light snow is falling this morning with an inch of new to play on.   Snow today with drying late tonight and tomorrow.  More of the same mixed bag of weather next week.
The Science:   Temperatures cooled off nicely overnight with the temperature dropping to around 21f on the upper mountain.  This morning’s satellite imagery has isolated snow showers along the cascade crest, clear skies to the east and more moisture to the west rotating around a parent low.  As the low-pressure cell makes its way north, the flow will shift westerly which will allow some orographic snow showers to move into the mountains.   Hopefully, we will squeeze a few more inches of snow out of these passing showers before it tapers off tonight.  A high pressure ridge develops tonight which will cut off the moisture and begin to break up the clouds for a partly sunny and mostly dry day tomorrow.
The Long Range:   Next week will start out with another light rain and snow ev…