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It is 6:00 AM. The sun is just on the horizon, the sky is clear
and the air is cool…a little too cool for mid May. However,
there is no room to complain because the sun is out and
it is shaping up to be a pretty pleasant day weather-wise. I
walk to my car, unlock it and get inside. As has been a common
theme since November, I see my breath float aimlessly in my car
because of the cold night the night before. I put the key in the
ignition and get ready to drive off, except there’s one thing—dew
has blanketed my windshield and I need to use the wipers in order
to see the road ahead of me.
No problem.
I twist the little knob on the side of my steering wheel and the
wipers go back and forth once, making a horrible scratching noise.
I shut them off and stare horrified at my windshield.
The dew is frozen. The Killing Frost has arrived
unexpectedly.
Indeed, I sat stunned in my car for several seconds staring at
my windshield, thinking frustratingly, “How in the world am I
sitting in my car with a frozen winshield in the middle of May?
FROST SEASON IS OVER! It’s not even technically freezing out! It
can’t frost above 32 degrees!” But I quickly stopped myself. How
foolish of me! Frost can definitley occur above freezing, and has
done it several times this season without a lot of us even knowing
it. But how can that be? How can the late-season Killing Frost be
active?
Have you ever heard weather anchors use the term “surface
temperature?” Surface temperature is the
temperature of the air 4-6 feet above the surface which is what
most weather observatories use for the surface temperature
forecast, so it is a little misleading. The closer to the ground
the cooler the temperature, making sense because cold air sinks and
is heavier than the air above it. The radiation of heat away
from the ground causes the temperature to drop.
So here’s what I THINK happened: it was a still, calm night (1st
ingredient for a frost) and the clouds steadily increased through
the night hours helping keep most of the moisture from the day
previous still intact by the time the clouds parted early this
morning. It is important to note the coldest time of day is
typically between 4-6 AM, so the clouds couldn’t have parted at a
better time to allow quick cooling and a brief glaze of frost on
some surfaces. In fact, between midnight and 3 am the low
tempertaure was only at 46 degrees. But by 4 am the temperature
plummeted to 41. So, even though last night’s official low surface
temperature was 41 degrees, the ground temperature (though not
official considering I don’t have a ground thermometer) was likely
at freezing or below, resulting in an unexpected frost. And WHY the
ground temperature was so cold I don’t know. I’m still dumbfounded
by that myself!
Now on to the next question…was it the dreaded Killing Frost? I
think it would be safe to say no. First of all, the frost wasn’t
widespread or heavy. It didn’t take much to scrape the ice of my
windshield, though it was enough to prevent my windshield wipers
from wiping it off clean in the first place. A heavy widespread
frost in mid-late May is not impossible, but is very much unlikely
especially over here west of the cascades. So should you plant your
vegetables and flowers now? I’d say go ahead. But if Jack Frost
startled you this morning with a brief glaze, then by all means
wait until after Memorial Day 🙂
Speaking of which, Memorial Day weekend looks absolutely
splendid…and frost free! Highs tomorrow will likely get close to 70
with Saturday looking like a cooler day in the mid to upper 60s. I
know, I know, I said Friday would be the cooler day but the models
have flip-flopped on that idea. Bottom line, it’ll be dry. Sunday
through most (if not all) of next week will be partly to mostly
sunny and positively, absolutely, no question BEAUTIFUL with highs
in the low to mid 70s and a slight sea breeze to keep things from
getting too warm.
I have to say, May is one of my favorite months not just because
it’s my birthday month but because typically the most
comfortable spring (and summer) temperatures of the whole year
occur during this time. And you know what else is awesome? We may
actually have a full 7 days of dry, sunny and pleasant weather for
once without the obnoxious cloudy, rainy intermissions we’ve
been experiencing lately.
Have a fantastic day and before you go to bed, make sure you can
locate your ice scraper easily just in case 😉
Matthew Leach
Forecasting Kitsap
forecastingkitsap@live.com
7 DAY
FORECAST
