…. Low Probability Winter Weather Event Again Possible Tonight into Friday Morning ….
…. WINTER WEATHER ADVISORY for all of our local area from 6am to 12 noon Friday ….
…. Little Changes in my Forecast Thought ….

A massive arctic high pressure area continues across our area.

Later tonight into tomorrow, another upper air low pressure disturbance will move overhead over
the top of the surface based arctic air mass with enough atmospheric lift to give us renewed low
precipitation chances. At this point, we could see freezing drizzle, freezing rain, sleet and snow
as far as precipitation types are concerned which could start as early as 3am tomorrow and
continue on and off into the midday and even early afternoon.  Temperatures have already
fallen to below freezing  (after reaching highs today of 31/32 F).. this will continue into
midday tomorrow so any precipitation that does occur could easily create icy conditions.

Remember, 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 6 to 9 hours and then, like early this morning, monitor the
disturbance in real time as it passes overhead.

As far as current (Thursday evening) precipitation forecast probabilities, I’m raising my precipitation
chances slightly to 30% for late tonight into midday tomorrow. You can compare this to NWS Austin
forecasts also showing a 30% chance of precipitation.. local broadcast meteorologists have made
changes in their raising their probabilities to average between 20% to 50% for the same period.
Private sector weather forecast companies’ probabilities are generally slim (around 20%) for late
tonight  into tomorrow with the exception of AccuWeather which still shows a 50% probability locally
for Friday morning.
All of the major atmospheric computer models (through the 6am/12noon data) suggest.. through
their output statistics.. relatively slim probabilities (around or less than 20%)  late tonight into
Friday. Guidance amounts in that output are only a few hundredths of an inch with no model
showing more than .05″ to .10″ of liquid precipitation.

Bottom line.. my forecast thought.. for the event tonight into early Friday, is that this is still a 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.

…. Wave of Precipitation Moves East of Area This Morning ….
…. Low Probability Winter Weather Event Again Possible Tonight into Friday Morning ….
…. Little Change in my Forecast Thought ….

Another arctic high pressure area has now settled southward through our area.

The first in a series of weak low pressure disturbances has trekked overhead of the area this
morning with some light snow/sleet accumulations to our immediate south.. southeast and east.
No major problems have been reported in the Austin Metro area or in the majority of Travis
County (or areas to our immediate north or west of the local area) with this event.

Even though precipitation chances have decreased over the area as of this moment, the ongoing
“overrunning” pattern with an extensive cloud layer continuing midday through the afternoon hours
as temperatures climb a few degrees above freezing by afternoon.

Tonight into Friday, another upper air low pressure disturbance will move overhead over the top of the
surface based cold air with enough atmospheric lift to give us renewed slim precipitation chances.
At this point, freezing drizzle and freezing rain seems to be the forecast precipitation type for this
event which could start after sunset tonight and continue into the day Friday. Temperatures will
likely be below freezing from just after sunset tonight through mid and late morning tomorrow so
any precipitation that does occur could create icy conditions.

Remember, 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 18 hours and then, like this morning, monitor the disturbance
in real time as it passes overhead.

As far as current (early Thursday morning) precipitation forecast probabilities, I’m keeping my 20%
chance of precipitation tonight and Friday. You can compare this to NWS Austin forecasts showing
a “slight”/20% chance of precipitation.. local broadcast meteorologists have made minor changes
in their raising their probabilities to average between 20% to 30% for the same period.
Private sector weather forecast companies’ probabilities are generally slim (around 20%) tonight
into tomorrow with the exception of AccuWeather which shows a 55% probability locally for Friday
morning.
All of the major atmospheric computer models (through the 12 midnight data) suggest.. through their
output statistics.. very slim probabilities (less than 20%)  tonight into early Friday. Guidance amounts
in that output are only a few hundredths of an inch with no model showing more than .05” of liquid
precipitation.

Bottom line.. my forecast thought.. for the event tonight into early Friday, is that this is still a 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.