.. Possible Winter Precipitation with the Possibility of  Some Snow Accumulations Thursday Night …

.. Synoptic / Forecast Discussion …
By late tomorrow into tomorrow night, a southward moving cold front.. the leading edge of much
colder arctic air.. will advance southward across our area. As this colder air continues to advance
southward over the area, a series of west-to-east moving upper air disturbances  will move overhead..
riding up and over the much colder surface air.. beginning Thursday morning and continuing into
Thursday night and into the early morning hours Friday.

The latest computer and manual forecast guidance suggests that “overrunning” light precipitation will
develop over our local area during the mid and late morning hours Thursday and continue through Thursday
afternoon and Thursday night before ending with the departure of the upper air disturbances by the
early morning hours Friday morning. The key to this forecast and the forecast precipitation type will
be surface and upper air temperature profiles and actually how cold the atmosphere becomes Thursday
into Friday.

The latest guidance now suggests that surface temperatures locally will fall and hold in the 30s to near 40 for
much of the day Thursday before falling below freezing around sunset Thursday evening and then into the mid and
upper 20s for the overnight hours Thursday night into Friday morning. Temperatures will only rise into
the 30s for highs Friday because of lingering cloud cover. With the slow rise in temperatures Friday, it may
be late morning into midday hours before we get above freezing.

Earlier guidance had suggested that precipitation would be mostly in liquid form.. freezing rain.. but the
latest guidance has now gone for a more substantial deeper layer of subfreezing air and therefore, much
more favorable for frozen precipitation.. i.e., ice pellets/sleet and snow. Given this and the fact that we
could see liquid equivalent precipitation amounts of up to one to two tenths of an inch (0.10-0.20″), it now
seems possible that some areas of south central Texas and the adjacent Texas Hill Country could see
up to 1/2 to 1 inch of snow/sleet accumulations especially in the Thursday night time period when surface
air temperatures are well below freezing. This could cause hazardous driving conditions locally in the
Thursday night into midday Friday time period.

Please note.. as I mention every time we encounter this type of winter weather episode.. the difficulty in
forecasting winter precipitation types at 30 degrees north latitude (the Austin area).  A relatively thin
warmer than expected layer of temperatures aloft could easily cause this to be more of a freezing rain
event (ice).. just as a layer of much drier air aloft than expected can reduce the amount of precipitation
that reaches the surface.

Please consider this update as a “heads up” regarding the potential for a Thursday into Friday morning
winter weather event. I will continue to monitor this situation carefully and will issue another update
tomorrow (Wednesday). As usual, please continue to be weather aware  and listen for later statements.