Wednesday, February 22, 2017

A February Like No Other?

This week of unseasonably and crazy warm weather is like kryptonite to a winter fan like myself. It paralyzes me from doing much at all. The calendar says February, but outside it's all April. It's not just one day which you briefly enjoy before the reality of winter sets in again. It's been a whole week, and we have two more days to go here (at least in the Midwest). Outdoor projects that were suspended in late fall are trying to pull me outside but I'm still in winter mode and trying to resist. Fortunately, or unfortunately depending on your viewpoint, it's all coming to an end soon.

This stretch of warm weather has been unusual not just in its intensity and duration. For a large portion of the central U.S. to have warm and sunny days in winter is very unusual. Typical warm-ups in winter tend to occur in advance of large weather systems moving out of the Rockies. Strong southerly winds will pull warm air well northward at times, but it is often moisture-laden and we end up with mild but  cloudy or partly cloudy days. Combine that with stiff winds and yes, it's mild, but not the kind of days we have enjoyed this week. This week of late fall-like (or spring-like, if you prefer) is clearly something most of us have never experienced in February.

Earlier this month it was downright hot in the southern Plains. High temperatures in northern Texas and southwestern Oklahoma were in the 90s, and it was confirmed one location topped out at 99°F! In February!

Maximum temperatures across Oklahoma on February 11, 2017.
Credit: Oklahoma Mesonet

Record high temperatures were recorded from New Mexico to the southeast coast. While that was occurring, New England was digging out of another snowstorm.

The exceptional warmth is not limited to the central part of the country, of course. Even Florida has been relatively warm. Miami, FL has not yet recorded a single day below 50° since December 1. This has never happened in the Miami period of record which dates back to 1896. (Thanks to John Morales, Chief Meteorologist at WTVJ NBC-6 in Miami for tweeting this fact.)

This current warm spell began late last week in the central and southern Plains and then expanded east  over the weekend and this week. The animation below shows the temperature map at 2:00 p..m CST starting on Friday, February 16 through today.  The area of green (55°F contour) was associated with the upper level system that moved across the southern U.S. last weekend.

 Here is the temperature map for 2:00 p.m. CST today. Note that it was warmer in Milwaukee, WI (69°F) than in Miami, FL (67°F)!

This map shows where record highs had occurred or were close to occurring today as of 2:00 p.m. CST.

While the warm weather is most welcome by many people, it's not without some problems. The very early warmth and its duration is coaxing plants to respond well before we are out of the danger for freezing weather.

The USA National Phenology Network, which like CoCoRaHS utilizes volunteers observers, tracks the start of the spring season across the country using models called the Spring Leaf and Bloom Indices. The Spring Leaf Index is a synthetic measure of these early season events in plants, based on recent temperature conditions. The index allows the NPN to track the progress of spring across the country.

The latest Spring Leaf Index map shows that the changes seen with the warm weather are about two to three weeks ahead of normal. It's still February, and much of the country is a long way from seeing the last freezing temperatures.

This maps below shows the distribution of the date of the earliest last freeze in the spring, and the median date of the last freeze in the spring.

Ten years ago, in the spring of 2007, much of the central U.S. experienced a very warm end to March and first days of April, with numerous record high temperatures and record high minimum temperatures recorded. High temperatures in the low to mid 80s were measured as far north as central Wisconsin. Unfortunately a major winter storm the first week of April pulled in cold air that resulted in a hard freeze across most of the Midwest. Subzero readings occurred in northern Minnesota. Many plants and fruit trees had budded in the warm March weather, and the hard freeze ended up extensively damaging fruit trees, grapes, and other plants. You can read more about the weather the first week of April 2007 here.

Enjoy this unusual warm weather while it lasts.

Meanwhile, noon temperatures today in west-central Alaska ranged from -10°F to -40°F.

Wednesday, February 1, 2017

Winter? What Winter?

Today marks the start of the last third of winter, climatologically speaking. The winter statistics will be calculated over the months of December through February, even though in many areas winter weather can continue through March and into April. So, where are we at with a month go go in official winter?

One quick way to look at the status of the winter season is to look at a map of the Accumulated Winter Season Severity Index (AWSSI). The AWSSI (pronounced "aww-see") is an index that scores the impact of cold and snow (both snowfall and snow depth) occurring during the winter season. The index was developed by Barbara Mayes-Boustead with the National Weather Service in Omaha, NE, and yours truly. Scores fall into one of five categories ranging from Mild to Extreme. Here is the map as of January 31 showing how winter is progressing across the country.

The categories of the Accumulated Winter Season Severity Index as of January 31, 2017

As you can see from this map, this winter has been particularly severe in the northwestern quarter of the nation from the Pacific Northwest down through the northern Rockies and into the Northern Plains. Over the rest of the country, winter so far has been mild.

Here are the temperature departures for the period from December 1 through January 31. The areas of the country that have experienced warmer than normal temperatures also tend to have below normal snowfall.

Snowfall, as you no doubt have heard, is heavy across the western U.S. More snow is expected over the next several days as another storm slams into the coast.

As of this morning, snow cover is extensive over the western U.S. and across the northern tier of states into New England.

We can look at the progress of the AWSSI though the season by plotting the score for each day through thee season. Individual storms or snowy periods and cold periods can be seen by the sharp changes in the AWSSI plot, The shading on the chart shows the envelope of all AWSSI scores for that location and the five categories for that station. For example, here is the plot for Redmond, OR.

Redmond's normal seasonal snowfall is around 16 inches and annual precipitation is 8.90 inches. Oregon State CoCoRaHS Co-Coordinator Jim Jones, who lives in Redmond, reports that he has measured a total of 47.9 inches of snow since December 1, and 4.39 inches of precipitation, about half the annual total..

In contrast to the extreme winter weather in Redmond, let's take a look at the AWSSI this winter in Utqiaġvik (formerly Barrow), Alaska. The AWSSI is at a record mild level in Utqiaġvik. As of today the score was 1570, and the previous record low on February 1 was 1965. At the rate the winter is going it is not likely to climb out of record mild territory.

You an follow the AWSSI through the rest of the winter and learn more about it at the Midwestern Regional Climate Center's AWSSI page.

Tuesday is Groundhog Day, so Punxsutawney Phil will allegedly tell us how much winter is left (but you get a better forecast just flipping a coin). Four to six weeks more of potential winter weather (i.e. until the beginning or middle of March) is a pretty good bet in almost any year. Sorry, Phil.