COEUR D`ALENE AREA-SPOKANE AREA- INCLUDING THE CITIES OF...COEUR D`ALENE...POST FALLS...HAYDEN... WORLEY...SPOKANE...CHENEY...DAVENPORT...ROCKFORD 309 PM PST SUN FEB 23 2014 ...WINTER WEATHER ADVISORY IN EFFECT UNTIL 11 PM PST THIS EVENING... .TONIGHT...SNOW IN THE EVENING. SNOW ACCUMULATION OF 1 TO 2 INCHES. LOWS 19 TO 21. NORTHEAST WIND 5 TO 15 MPH WITH GUSTS TO AROUND 25 MPH. CHANCE OF PRECIPITATION NEAR 100 PERCENT. .MONDAY...MOSTLY CLOUDY. HIGHS IN THE LOWER 30S. NORTHEAST WIND 5 TO 15 MPH. .MONDAY NIGHT...MOSTLY CLOUDY. A 20 PERCENT CHANCE OF SNOW IN THE EVENING. LOWS 18 TO 21. NORTHEAST WIND 5 TO 10 MPH.
After Sunday's snow wound down, we expected that Monday would be dry, with just a 20% chance of snow on Monday evening.
We updated the forecast at 338am Monday morning.
COEUR D`ALENE AREA-SPOKANE AREA- INCLUDING THE CITIES OF...COEUR D`ALENE...POST FALLS...HAYDEN... WORLEY...SPOKANE...CHENEY...DAVENPORT...ROCKFORD 338 AM PST MON FEB 24 2014 .TODAY...MOSTLY CLOUDY WITH A 20 PERCENT CHANCE OF SNOW. HIGHS IN THE LOWER 30S. NORTHEAST WIND 5 TO 15 MPH. .TONIGHT...MOSTLY CLOUDY WITH A 20 PERCENT CHANCE OF SNOW. LOWS 18 TO 21. NORTHEAST WIND 5 TO 15 MPH.
We now had a 20% chance of snow for Monday and Monday night. But still, when we have probabilities that low, we don't even include the expected snow amounts. Even if we had, it wouldn't have been anywhere near what actually happened.
Most people understand that a forecast a few days into the future is a bit iffy and subject to change. But a forecast only a few hours into the future? Surely we can get those right. So how could we bust a forecast less than 8 hours into the future?
First, let's take a look at the weather pattern. Here's the surface analysis at 4am Monday:
The red and blue line south of Washington is called a stationary front. This front moved down from Canada through Spokane on Sunday, bringing us our Sunday snow. But it stalled over northern Oregon. Note that there's no big areas of low pressure off the Washington/Oregon coast.
Next, we'll look at the satellite image at this time:
We realize that this may not mean a great deal to most of you. But trust us, the satellite doesn't show any big storm over the ocean, headed our way. In fact, the satellite shows a rather disorganized atmosphere.
But perhaps the radar was showing something. Here's a image from 330am
The radar doesn't show any big areas of precipitation headed our way. There is a couple of bands of precipitation north of Seattle, and some snow showers over the southern Idaho Panhandle.
So what did the computer models show? Here's the forecast 6-hour precipitation for Monday afternoon from 3 of our models.
 |
| NAM Forecast Precipitation 1-7pm |
 |
| GFS Forecast Precipitation 10am-4pm |
 |
| HRRR Forecast Precipitation 9am-3pm |
As you can see, 3 different computer forecasts all put an west-to-east band of precipitation over southeast Washington into the southern Idaho panhandle, well south of the Spokane area. And this made sense, given how far south the stationary front was.
Bu 830am, surely we knew the forecast wasn't panning out, right? Here's the radar image at that time.
 |
| 830am Radar |
There's definitely more precipitation west of the Cascades than a few hours ago. And a band of very light precipitation has begun to form south and west of Spokane. But still, we expected the precipitation to stay south of Spokane, and so far it's looking good.
 |
| 930am Radar |
COEUR D`ALENE AREA-SPOKANE AREA- INCLUDING THE CITIES OF...COEUR D`ALENE...POST FALLS...HAYDEN... WORLEY...SPOKANE...CHENEY...DAVENPORT...ROCKFORD 946 AM PST MON FEB 24 2014 .REST OF TODAY...SNOW. SNOW ACCUMULATION UP TO 1 INCH. HIGHS AROUND 30. NORTHEAST WIND 5 TO 15 MPH. CHANCE OF PRECIPITATION 90 PERCENT. .TONIGHT...MOSTLY CLOUDY. SNOW LIKELY IN THE EVENING. SNOW ACCUMULATION UP TO 1 INCH. LOWS 18 TO 21. NORTHEAST WIND 5 TO 15 MPH. CHANCE OF PRECIPITATION 60 PERCENT.
 |
| 1230pm Radar |
The forecast is updated yet again, this time issuing a Winter Weather Advisory for the metro area.
COEUR D`ALENE AREA-SPOKANE AREA- INCLUDING THE CITIES OF...COEUR D`ALENE...POST FALLS...HAYDEN... WORLEY...SPOKANE...CHENEY...DAVENPORT...ROCKFORD 1249 PM PST MON FEB 24 2014 ...WINTER WEATHER ADVISORY IN EFFECT UNTIL 10 PM PST THIS EVENING... .REST OF TODAY...SNOW. SNOW ACCUMULATION NEAR 2 INCHES FROM SPOKANE SOUTH...WITH UP TO AN INCH ELSEWHERE. HIGHS IN THE UPPER 20S TO LOWER 30S. NORTHEAST WIND 5 TO 15 MPH. CHANCE OF PRECIPITATION NEAR 100 PERCENT. .TONIGHT...MOSTLY CLOUDY. SNOW LIKELY IN THE EVENING. SNOW ACCUMULATION UP TO 1 INCH. LOWS 18 TO 21. NORTHEAST WIND 5 TO 15 MPH. CHANCE OF PRECIPITATION 60 PERCENT.
Even at this stage, the forecast was only for 2-3 inches at best.
So how much snow actually fell?
You can see that the metro area received the most snowfall. Locations to the north (e.g. Deer Park, Athol) as well as to the south (e.g. Palouse, Ritzville) received about half of what the Spokane and Coeur d'Alene area picked up.
In summary, this was not a typical snowfall event for our area. A typical event is one characterized by a large storm moving in from the Pacific, bringing widespread precipitation to the area. And that's the other aspect of this event: it was localized. Those two attributes (atypical and localized) are the most difficult to forecast. And they have the largest potential to be wrong. Instead of the snow hitting the Palouse, it winds up 50 miles to the north, over the Spokane metro area.
Additionally, none of our computer guidance saw it coming either. Add all of these factors together, and you get a busted forecast.
Thank you for all of your hard work! Things happen...
ReplyDeleteGreat write-up! Post mortems are interesting. Going back and looking at SPC's mesoscale archive page, there was an area of 850mb frontogenesis over eastern WA starting around 17Z Monday, just prior to the event: http://www.spc.noaa.gov/exper/mesoanalysis/s11/8fnt/8fnt_14022417.gif
ReplyDeleteNot sure if it would have made a difference in the forecast snow totals given the model data you had to work with.