Wednesday, November 4, 2015

Official 2015-2016 Winter Outlook

I'll give you the quick outline of how I think this winter turns out and then do some "splaining" about why and how I got there.

Winter snow totals: Lynchburg 20-25 inches.  Roanoke 25-30 inches, Blacksburg 30-40 inches, Danville 10-20 inches. 

Month Temps:  December Normal to +1, January +2  February -2 to -4
Seasonal Average 0 to +1

Summary :Winter temps slightly above normal, snowfall above normal. 

If I use a term and you don't know what it is, GOOGLE it.

The "Godzilla El Nino" as labeled has behaved as expected and it makes for somewhat of challenging forecast. There are honestly quite a few good reasons why going warmer and less snow is not a bad call including the QBO and some calculated risks about what the El Nino will do.

Remember.. Western Based El Nino's are usually colder with more snow, while eastern based tend to be much warmer with less snow. Basin wide events are less frequent and have mixed results. We currently have a basin wide el nino, stronger in the west but not much stronger. The overall belief seems to be that it will trend more west based and then weaken, but not sure exactly when. This is a key factor to a later winter surge of cold and snow.

As a result, hedging on things that we are not certain about is always a risk and needs to be treated that way.

The QBO is measurement of winds in the tropical stratosphere and a negative reading favors high latitude blocking while positive is usually more associated with less blocking. The number is strongly positive currently. On the flip side, certain snap shots of the AO from the summer reflect a likely hood of a negative AO in the winter.

I've mentioned the topic before of Snow cover in Eurasia and it grew quickly in October-- the second best advance on record. This DOES support high latitude blocking. High latitude blocking is associated with longer lasting cold snaps AKA, ways to get cold and keep it cold so we can snow. (-EPO, -AO and or -WPO)

The General feel for winter :
December starts off warm but trends colder later in the month. A week either side of Christmas has a shot at a snow/ice event.  The El Nino of 09-10 had a big event December 18th. 02-03 had a Dec 5th event PLUS a big Nor Easter on Christmas Eve/Day (That was north of here, but close enough to consider) 97-98 had a small event on Dec 27 and then 4-8 incher on December 30. 86-87 had a 4-8 inch snow ending as rain in early January.

Early January trends warmer and this will last most of the month. By mid to late month we see the pattern change clearly and we know it's on the way. By late month, we are back in a colder regime and should get 1-2 small to moderate events and ONE big event that helps us reach above normal snow during February.

March - some Data supports some risks for additional snow/cold but I'm going to punt that off and avoid it as of now predicting a benign weather month.

I'm not to jazzed about basing my forecast on the hopes that we get ONE big snowfall to push us above normal. Talking with Kevin Myatt from the Roanoke Times, he cited that El Nino's winters push our likely hood for a 12 + event snowfall from 20% to 40% . I'd like to add that we could end in a near perfect pattern, storm track is a little off or cold air isn't deep enough and we end up with ice rather than snow.

Another factor is that often if we get ONE 10+ event, we see another. 09-10, 86-87 and 65-66 are prime examples of this. So, I could be too low too..

Some clunker winters with El Nino's are : 06-07 but it was east based little snow, one ice event. 91-92, least snowiest winter on record, the Eruption of Mt Pinatubo has been offered as a reason why.  72-73 in many areas to our north had NO snow, but we managed 10 inches down here so not  horrible winter here. 41-42 winter had only 5 inches, but if you look at the bigger pattern you'd think we had a snowy winter. 97-98 wasn't horrible here with a few snows east of the appalachians and 2 near misses, one that crushed those west of the Blue Ridge.

Some snow el nino winters: 09-10, big snow in December then a pretty brutal stretch from late January till Mid February. We missed the worst with 20-30 inches in a 10 day stretch but places up from DC to Philly had 40-60 inches in 10 days. 02-03 Pretty cold and snowy all winter, with the BIG event being a sleet storm. 86-87- One snow to rain just after new years then back to back events Late January, a few more events in February. 65-66- one of my favorite winters where from Mid January till  early Febryary 40-60 inches fell in a 3 week period.

So, outside of a cold snap and possible snow/ice  near Christmas- We wait for the pattern to develop in the second half of winter and should have some decent snow to enjoy. If you recall last winter, we had literally nothing then for 2 weeks it snowed 3 times, including a 6-10 inch snowfall and schools were out the most past of 2 weeks. This winter may reflect that in our "sensible" weather.

If you want my confidence level:
50% we end up within a reasonable range of this forecast.
30% we end up warmer/less snow
20% we wend up colder/ more snow and ice.

I'm using 82-83 as my top analog. We had a December snow, but a warmer month. January was warm and basically snowless, February flipped colder and had a decent event on 6 of 3-6 inches then a NICE storm of 15-20 inches region wide on February 10-11.