Wednesday, February 15, 2017

Weather It Is (Winter Weather Advisory)

Good Morning:

After a lot of talk, and even more than that, it comes down to a degree or two -- but for snow lovers a degree or two too warm.

Temperatures at 850 mb will fall until evening, but middle and upper level temperatures will warm.

Then, when the cold air and heavy precipitation arrives towards Thursday morning with an extremely cold upper level trough, temperatures will be steady or rise a bit in the middle and lower levels.

This is response to the arrival of a really moist layer (from the sea).  It has also been pointed out that the height of the 500 mb level is higher than usual in storms that bring snow.  This means that cold air descending in convective storms has more time to diabatically warm (with increasing pressure).  Hence, any snow/ice would just become wet snow or rain tomorrow morning as the cold air moves in.

The lower levels will start to cool down in the afternoon, but the upper trough will be moving through, reducing the air parcel ascent required for precipitation formation.

Yet, there is a middle atmospheric disturbance (at 700 mb) shown to arrive in the evening with the coldest air at lower levels, and our high resolution model shows some precipitation at this time.

For this reason, we'll issue a "Winter Weather Advisory" for the possibility of some snow/ice in the afternoon and evening on Thursday.

Very cold nighttime temperatures could lead to slippery conditions on Friday morning.

There are some lower level temperature differences between the different global models, but it is hard to see how the initial burst of very heavy precipitation tomorrow morning will be anything but rain.

If you like snow, then hope that your trusted weatherman will be wrong.

Barry Lynn

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