Does this weather picture mean anything to you?
To most of us it doesn't. And most of the time during the year it doesn't either. But now it does. It's a pattern that is prime for the spread of wildfires in our area.
This image is courtesy the National Weather Service in Burlington, Vermont. Welcome to the last and final day of this week's blog topic about the threat for wildfires this year and bumping up your knowledge regarding what to do/what not to do this fire season.
So here we are on this last day of the topic, talking about weather patterns that contribute to high fire dangers. This is a classic weather pattern above. In fact so far this year, we've had two Red Flag Warnings in our area (for high fire threats) and this was the weather pattern both times.
So what's going on here? The capital 'H' stands for high pressure. On the filp side the capital 'L' stands for low pressure. The flow around a high is clockwise and the flow around low pressure systems are counter-clockwise. When you get down to the nitty gritty details friction comes into play and the winds are never fully as perfect as this drawing, but this gets the point across very easily.
When we have an exiting low pressure to our east and an approaching high pressure to our west, this creates a strong pressure gradient. Gradient=the amount of change in a certain distance. So the stronger both of these air masses are, the stronger the gradient will be, and the stronger your winds will be.
This is a prime set up for a couple of reasons.
One: The wind.
When low pressure exits and high pressure builds in, we generally see winds sustained anywhere from 5 to 20 mph, but gusts can reach to 40 mph depending on how strong the gradient (all based on the strength of these air masses at that time).
Wind is one of the major fuels for these fires. They can spread easily under these situations when winds can get gusty. It makes it very tough for firefighters to battle and contain it.
Two: The dry air.
When high pressure builds in from the west/northwest, it generally brings a drier air mass into the picture. Low relative humidity levels also fuel the fire threat. Humidity is an important factor because the drier it is out there, the more likely fires will start and fires will spread.
This is a picture from a couple of years ago courtesy the NWS in Burlington.
I'm not urging you to go study weather maps and memorize weather patterns to heart (although if you want to, be my guest I love the weather!) But recognizing a pattern on our weather maps and also hearing the words "High pressure building in" should perk your ear if you're planning a burn.
So does that weather pattern look familiar here?
This is the surface analysis courtesy NOAA from TODAY! (Friday, March 30). High pressure to our west is building in and low pressure is meandering off to our east. Now you say, 'Is it a high fire danger today?' The answer technically is no. Here's why.
The wind will not be strong enough from this event. While the ingredients are there, high pressure building in, low pressure exiting, and dry relative humidity levels, the winds are dying down as time goes on this Friday. Here's an excerpt from the daily fire report from the National Weather Service in Burlington:
...LOWER HUMIDITIES AND MORE SUN EXPECTED TODAY AND SATURDAY...
CLOUDS WILL CONTINUE TO DECREASE IN AREAL COVERAGE THROUGH THE
MORNING HOURS TODAY AND A GOOD DEAL OF SUN IS EXPECTED. THIS WILL
ALLOW FOR FINE FUELS TO DRY OUT. AFTERNOON RELATIVE HUMIDITIES
WILL FALL INTO THE 26 TO 32 PERCENT RANGE...BUT WINDS WILL REMAIN
BELOW CRITICAL LEVELS. EXPECT TEMPERATURES ON SATURDAY TO BE
SEVERAL DEGREES WARMER THAN TODAY AND THIS WILL HELP KEEP
AFTERNOON RELATIVE HUMIDITIES DOWN INTO THE 20 PERCENT RANGE.
DESPITE EVEN WEAKEN WINDS ON SATURDAY...PLENTY OF SUN IS EXPECTED
THROUGHOUT THE DAY TO HELP DRY THE FINE FUELS EVEN FURTHER. AN
UPPER LEVEL TROUGH OF LOW PRESSURE WILL MOVE TOWARD THE REGION ON
SUNDAY...THUS LOOKING AT INCREASING CLOUDS...HUMIDITIES...AND
PRECIPITATION CHANCES AS THE DAY WEARS ON.
But it's close. Hope you've enjoyed the fire blogs and have a safe season! Remember peaks for fires come in April and May. This year is no exception, with the area running around (-2") for precipitation on the year so far and no majorly heavy precip storms on the way. Have a great weekend!
-Meteorologist Steve Glazier