Light but persistent southerly wind
with a bit of Lake Ontario influence, combined with increasing clouds, led to
temperatures not really dropping last night, with a low of 15F. This is much
warmer than consensus and pretty much the warmest it could have possibly been.
It seems like a subtle surface trough centered just to the north extending across
the Great Lakes was stronger than modeled, evident by the widespread light snow
showers across eastern Ontario, northern New York, and northern Vermont this
morning that were not modeled, with not even a chance of snow mentioned. This
meant that the southerly flow just to the south, including over Watertown, was
stronger than expected, and also that clouds were more widespread than expected.
Some of the moisture appears to have originated from Lake Huron. Since then, the
clouds have cleared out with mostly sunny skies, allowing for a warmup to 35F despite
snow cover, but it likely would have been even warmer without the snow cover. The
maximum wind was 11 kt earlier today, though it has since calmed down.
Tonight will feature another tricky low
temperature forecast. Skies will be clear tonight through at least 08z or so (with a few mid-level clouds afterward), and winds will temporarily calm
down a bit this evening, but they will increase later in the night. The low
will likely be achieved at the beginning (Wednesday 06z) as winds increase
above the 5 kt threshold for good radiational cooling around that time. If the
winds increase before that, it will warm up before 06z, making for a warmer low,
and if they increase later, it will warm up after 06z, making for a colder low.
It’s not clear which scenario will occur, but high resolution models like the HRRR show the quick radiational cooling and low-level inversion formation keeping KART protected from the stronger southerlies until just after 06z, though it is close. Also, the winds will initially be
more south-southeasterly, without the westerly component off Lake Ontario,
leading to less lake moderation and it cooling down a bit more easily before
the winds get too strong. The high is more certain, with almost full sunshine and
stronger southerly winds and warm advection leading to a significantly warmer
high temperature than today, with snow cover melting, aging, and becoming less
reflective.
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