…. Very Low Probability Winter Weather Event Possible Thursday into Early Friday ….
…. A Slim Chance of Freezing Rain and Freezing Drizzle ….
…. Little Change in my Forecast Thought Other Than to Add Very Slim Chances Tomorrow Morning ….

Another strong cold front.. with modified arctic air.. has moved through our area in the early
morning hours on this Wednesday.

While we are seeing some sunshine right now, a series of weak low pressure disturbances
will trek overhead west-to-east late by late tonight into tomorrow and Friday.

As they do, it will result in an “overrunning” pattern with an extensive cloud layer
moving in and  over the top of the fairly shallow layer surface based cold air with enough
atmospheric lift to give us some very slim rain chances. However, based on the latest computer
guidance and manual data, I am seeing a very “moisture starved” atmosphere, especially
initially, and I wonder how efficiently the system will have enough available moisture to produce
much in the way of precipitation. There are signatures in the guidance today that suggest a
very slim precipitation chance early tomorrow (Thursday) so we need to watch this possibility.
If this system does produce precipitation, the chances are, I think, a tad better on Thursday
afternoon when temperatures rise to slightly above freezing.

However, with below freezing temperatures after sunset Thursday night into the morning hours on
Friday and with the possibility of a more moist atmospheric column, the slim rain/freezing rain
chances look possible but, again, there shouldn’t be much precipitation. Even so, with what we’ve
seen over the past two months, we all know what a sprinkle or even several hundredths of an inch of
rain, in the Austin metro area and the IH35 corridor,  can produce in a freezing/subfreezing
surface environment. As a result, we must continue to monitor model precipitation trends over
the next 12 to 24 hours and then monitor the disturbances in real time as they pass overhead.

As far as current (late Wednesday morning) precipitation forecast probabilities, I’ve introduced a
less than 20% chance of precipitation for tomorrow morning.. and dropped back to a 20% chance of
precipitation Thursday night and Friday. You can compare this to NWS Austin forecasts showing
a “slight”/20% chance beginning tomorrow morning and continuing into Friday.. local broadcast
meteorologists have lowering their probabilities slightly back to near 20% for the same period.
Private sector weather forecast companies’ probabilities are very slim tomorrow morning but are
up a bit for Friday morning with one showing a 47% probability for Friday morning (TWC).. another
carrying probabilities of near 30% for Friday morning (AccuWx).
All of the major atmospheric computer models suggest, if precipitation occurs (given the very slim
probabilities), amount would be, at most, several hundredths of an inch. To really indicate the low
probability of this event, all of the latest atmospheric model output, as of this moment, show less
than 20% precipitation probabilities through midday Friday.

Bottom line.. my forecast thought, with only minor changes, is that this is a very low to
low probability event with, if it materializes, a high potential impact for the Austin metro area and
the IH35 corridor.

—

A reminder.. winter weather episodes are difficult to predict at 30 degrees north latitude.. the latitude
of the Austin metro area and the IH35 corridor. Precipitation types.. i.e., sleet, snow, freezing rain..
are even more difficult to predict. You should be prepared in case the forecast or the on going weather
conditions change expectantly at the last minute. I will do the best I can to keep you informed during
this potential weather event.