A mild winter that is morphing into spring.
Climatology tells us that we can expect six out of 10 winters when temperatures at the Portland Airport fail to dip below 20ºF. I call these Pelargonium winters because they will generally survive. Our lowest temperature this winter at the airport was 21ºF on December 31st. January was above normal with a striking 17 days with temperatures in the 50ºs and two days of 60ºF. That is more typical of March than January and it answers the question why so many plants are ahead of schedule
The forecast for the next month looks toasty.
Below is our forecast of temperatures for the next month and I have to say that the NOAA has been right on with their forecast of this winter. This gives me hope that we are out of the woods for any truly arctic weather. As we all know in the PNW spring is a whole different animal. Modified polar air from the Gulf of Alaska almost always makes its presence known. Thats 45ºF and frequent showers with small hail through March and April. Our spring is so cool and unsettled it often amazes me that plants can even wake up and grow. For that we have in part the longer days to nudge things along.
The warm west and the cold east.
One very broad way of describing the weather which is made up of troughs and ridges is that when there is a ridge in the west there is a trough in the east. That by no means is 100% true but its likely. This year we have seen that repeatedly another reason why winter didn’t really show up. The midwest and northeast are having completely normal winters in terms of temperature. With blizzards striking both New England and the Chicago area and some near historic snowfall totals.
Is this winter normal?
Yes and no. In terms of average temperatures it has been above normal on a day to day basis. As I said before though mild winters are just as expected as colder than normal winters- thats just how the planet rolls. In many ways the mild El Nino has given us a textbook winter. And not all El Nino winters escape without at least a dose of wintery conditions- but not this year. Precipitation has been just slightly below normal- a hallmark of ENSO. But for the most part this has been a typical mild PNW winter. (Remember 6 out of 10).
Zone 8b and Zone 9a Winter.
A good example of the urban heat island occurs during our coldest weather. The city with concrete and glass absorbs heat during the day and loses it at night. This keeps the low temperatures in the core of the city quite a bit warmer than the rural areas. Also- proximity to the Columbia River Gorge in times of high pressure leads to an east wind drifting over the city. That stirs up the atmosphere and rather than stratifying with cold at the surface and warm air rising temperatures become moderated. In the suburbs and down the Valley temperatures dropped into the upper teens during our coldest episode. A typical zone 8b winter- so in that things have been perfectly on schedule with averages. Our average annual low in PDX is 20.3ºF and the lowest so far of 21ºF is right where it should be To be honest I only become concerned when temperatures drop below 15ºF. That seems to be a magic number for the hardiness of a LOT of plants. Phormium, Abutilon for instance are massively damaged below that temperature. A reason why they and many plants we designate borderline hardy. Pair that with high temperatures in the 20ºs and strong east wind and that is the recipe for real damage. True arctic conditions that we can expect 4 out of 10 winters. We were due for a mild winter- its just part of the law of averages.
There is March to get through
In 2011 we had one of the coldest March’s ever. There was frequent snow and surges of cold- though not arctic air. It culminated in a large snowstorm on the 23rd of March. This caused a lot of damage to trees that were already in bloom or leafing out. This just proves that winter can wait until the end to throw us a curve ball. So far, there is no indication that it will happen this year, but I always keep that in mind. Knowing how good it can be is not nearly as important as remembering how bad it can be. I’m a nursery owner and I have to be prepared for contingencies. As a gardener I plan for the worst and almost always am pleasantly surprised with the results.
Bummer ski year dude
The most dramatic thing about this winter has been the lack of snow at higher elevations. Not to mention that we had one brief snow flurry down here in November. People tend to panic when there are low snow packs. And there is a reason why- but its not often as dire as reported. Our water supplies are very well managed by a series of reservoirs and the Army Core of Engineers know what they are doing. One dry year doesn’t necessarily mean disaster. And March is typically a huge snow month in the mountains. So, if there was just a complete lack of precipitation and snow pack for several years- then you can worry. To be honest our annual summer drought (June-September) would be considered dire in the summer rainfall areas of the eastern United States. We are used to it and so are our plants- they are not.
Screw it, I’m planting.
So, with an eye to the weather and relying on the law of averages I have already begun planting in my garden. I’ve even plunked in some relatively tender things (Desfontaina spinosa Zn8a) and I’m trusting that the goddess flora will see mild weather. This is by the way a great time to plant hardy plants. The mild winter has resulted in warmer than normal soil temperatures and getting plants in the ground in February means that you will have a good long following of rain into late spring to establish the plants before the summer dry. So, in this mild winter you can take advantage of the conditions and make them work for you. Just be careful not to compact the sodden soil- that is the real danger of winter planting.
As of February 6 I have Camellias, Hellebores, Cyclamen, Heather, Grevilleas, Crocus and Snowdrops all in full bloom. I’m going to enjoy it and watch the weather closely. We trust the forecasts so much that we opened our shop 2 weeks early this year. We have a huge selection of plants just waiting to be shipped to the shop. Drop in and introduce yourself to the plants. Both they and we will be thrilled.