Austin / Travis County and South Central Texas Weather Update #7
Prepared by Incident Meteorologist Troy Kimmel (www.troykimmelweather.com)
430pm CT – Friday / 6  December 2013

.. Weather Update #7 ..

… Good News …
There are NO current NWS watches/advisories/warnings for counties in our immediate
area from the following NWS offices…

NWS/Austin-San Antonio…
NWS/Fort Worth…

It is possible that new NWS issuances may be necessary by late tomorrow through
tomorrow night into early Sunday. I will continue.. as will the NWS/Austin-San Antonio
office.. to keep you advised reference this possibility.

DISCUSSION

…. Our First Upper Air Disturbance has Passed …
…. Another Weak Disturbance Due Tomorrow Night into Early Sunday …
…. Perhaps Other Passing Disturbances Again Early Next Week ….

Assisted by a massive area of counterclockwise rotating upper air low pressure over southern Canada
and the western USA.. the unseasonably cold arctic surface air mass continues to slide southward out of
Canada into the western two thirds of the USA. The heart of this arctic air is still centered over northern
Alberta (Canada) with mid day temperatures today under a surface high pressure area- north of Edmonton –
as cold as -31 degrees F. As this cold  air continues to surge south southeastward into the southern plains,
it is still in a relative shallow layer close to the ground over our area. This is combining with an active
subtropical jet stream.. from the Pacific Ocean to our southwest… to cause moisture to overrun the cold air
overhead. In that upper air flow, weak northeastward moving upper air disturbances are expected to move
overhead between now and Sunday and perhaps even early next week, create lift in the atmosphere and, as
a result, cause precipitation at times.

With the unseasonably cold arctic surface air in place outside, the first of those disturbances passed over our
area last night into this morning with the dangerous icy conditions on bridges and overpasses in the northern
and western Austin metro area and the northern part of the IH35 corridor. With that system having passed off
to the northeast now, there is no longer precipitation across the area. In fact, we’ve actually seen some breaks
in the overcast in some areas this afternoon in the wake of the disturbance. However, clouds will continue, for
the most part, to hold in through the weekend.

We’ll continue this precipitation lull until midday and early afternoon tomorrow. After about 3pm tomorrow and
continuing through tomorrow night and into Sunday morning, another weak upper air low pressure disturbance
traverses the area southwest to northeast. With additional cold surface air advecting into the area.. I expect
that we will see freezing temperatures tonight with temperatures struggling to get to near freezing tomorrow.
Temperatures will then fall to well below freezing areawide tomorrow night. Even with lower precipitation
probabilities (around 30% for the Austin area) as the next disturbance passes, we must still consider that even
a light freezing rain or drizzle could cause problems especially on bridges and overpasses tomorrow night into
early Sunday. At this point, guidance suggests that rainfall equivalents for tomorrow night should be somewhere
in the trace to 0.10″ range.. with ice accumulations expected to be light but still potentially a factor. Precipitation
from this disturbance should shut off by midday Sunday as the disturbances passes to our northeast.

By late in the weekend and into next week,  numerical computer and manual forecast guidance is now suggesting
that we might deal again with the possibility of freezing/frozen precipitation.. although with slim chances.. Sunday
night into Monday morning and again, perhaps, Monday night into Tuesday. Sorry to bring you this news, but I’d
rather you be aware and proactive rather than us having to be reactive. >From my standpoint, I’ll “fight one battle
at a time”.. and I’ll do my best to keep you informed from one event to potentially another (anyone care to take a
guess how high my weather update numbers – in the reference line – will become before the end of next week????).

As mentioned in earlier updates, this cold arctic air will continue to be reinforced from the north through the
weekend and into next week. The surface air is dense and heavy will be hard to dislodge. Based on the guidance
I’m seeing now, I would be surprised if we’re back above 50 degrees F for high temperatures until about next
Thursday or Friday.

I’ll continue to monitor this situation.

Bundle up and have a good, safe and warm weekend..
tk