Hmmm Ice...

10:30 UPDATE:
The NWS came out with their ice map. The .25 inch line, which is the warning criteria level, is in  Moco.

ORIGINAL TEXT:
Today was a forecaster's nightmare come true. The temps failed to drop like expected and as a result, rain prevailed, with only a few wet snowflakes to remind us that we are at the mercy of Mother Nature. tonight should be quite cold though, with lows in the low 20s. On Wednesday, temps will only rise into the low to mid 30s, keeping the ground cool, which is better for accumulation. At night, temps drop into the upper 20s as an low pressure system approaches from the south. High pressure to the northeast will force cold air against the mountains, keeping us below freezing as the upper levels rise above freezing. depending on how much cold air is in place, precip can range from snow, to sleet, to freezing rain ,to even plain rain. The most recent NAM model runs have come in colder and wetter and as a result, the NWS has extended the Winter storm watch to cover Moco.

THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS
ISSUED A WINTER STORM WATCH...WHICH IS IN EFFECT FROM TUESDAY
EVENING THROUGH WEDNESDAY AFTERNOON.

* PRECIPITATION TYPE...SLEET AND FREEZING RAIN

* ACCUMULATIONS...A COATING TO ONE INCH OF SLEET ACCUMULATION.
  POTENTIAL FOR A QUARTER INCH OR MORE OF ICE ACCUMULATION FROM
  FREEZING RAIN.

* TIMING...FREEZING RAIN AND SLEET WILL BEGIN TUESDAY EVENING.
  PRECIPITATION WILL CHANGE TO ALL FREEZING RAIN LATE TUESDAY
  NIGHT AND IT WILL CONTINUE THROUGH WEDNESDAY MORNING.
  PRECIPITATION WILL END WEDNESDAY AFTERNOON.

Once again, a few degrees difference can affect the precipitation type. However, cold air damming has a tendency to be colder and stay colder than what models predict. Sleet and freezing rain, falling on roads that are devoid of salt, can turn it into a skating rink. Not something fun to drive on. School closures, if we are upgraded to a warning, are likely. Otherwise, a delay is likely and closing possible.

Since the NWS has not issued an accumulation map, I will make one based off of their totals:

Freezing rain accretion

Sleet

The sleet and ice accumulation may be a little high but the ranges are generally accurate, just don't expect the high side of the estimates. Temps will rise above freezing on wednesday morning progressing from SE to NW. When it will rise is tricky and will depend on how far the high leaves and how strong our easterly winds off the ocean are. In any case, cold air can be very stubborn and areas to the north may deal with an extended period of freezing precipitation.

Thanks for reading!

-Alex