re: Louisiana Ice Storm Thread *Winter Storm Warning*

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Chances of driving from Shreveport to Baton Rouge on Tuesday?

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Uri

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Ice accumulations up to 0.50" possible.

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DISCUSSION...
As one of my colleagues would say woo wee! This forecast looks
more like one I would make will working at the NWS Detroit some 27
years ago than one for down here.

Rather cold and cloudy currently across the forecast area as
polar high pressure system builds down from the Canadian border
toward the Gulf of Mexico. Good news is that a few light returns
showing up on radar are not producing any significant accumulating
precipitation. A weak disturbance will help increase this activity
through the morning. However, rainfall amounts look to be very
light so at this point we will handle the situation for any frozen
stuff over northern portions of the forecast area with short fuse
special weather statements.

Trends from guidance continue to show a potentially significant
winter weather event for tonight into Monday as a rather potent
upper level trough and jet dynamics should bring plenty of lift to
work with abundant moisture to get widespread precipitation
going. Changes are that the precipitation may start earlier across
southeast Texas with intensity increasing into southwest Louisiana
and west central Louisiana before daybreak.

Forecast soundings still show a very warm layer above the cold
surface, and therefore, freezing rain will be the predominate
weather to start at with. However, cooling brought about by strong
lift looks to bring about a cooler profile than what was seen
yesterday, so the snow potential looks to increase for northwest
sections of the forecast area.

Around this part of the country winter weather events are quite a
headache to figure at and always have a degree of uncertainty
right up until it begins. Also, there will gradients of different
weather types that will play with accumulations of ice versus
snow/sleet. However, either situation will still be significant.

The most concerning is the potential for ice accumulation with
amounts from the most likely scenario from 0.20 to 0.40 inches a
good estimate as probs show greater than 50 percent of 1/4 inch.
However, looking at the probs, there is a 10 to 30 percent chance
of greater than 1/2 inch roughly between the 1-10 and Highway 190
corridor in Louisiana with reasonably worse case scenario between
1/2 and 3/4 of an inch.

Winter storm criteria with accumulations over 0.25 inches will
cause significant travel problems along with power outages. Also
local criteria for snow is over 2 inches of accumulation. So with
increasing probabilities and confidence have decided to issue a
Winter Storm Warning for the entire forecast area that will end 6
pm Monday.

After the precipitation ends Monday night and Tuesday morning look
to have bitter cold conditions with a biting wind chill. Low
temperatures were derived from consensus means, which shows almost
the entire forecast area experiencing hard freeze conditions with
lows in the teens. Meanwhile, winds will not be calm, so speeds
around 5 to 10 mph will produce wind chill values in the single
digits and with confidence growing in these scenarios, it was time
for hard freeze warnings and wind chill advisories to be issued
from 6 pm Monday to noon Tuesday.

It should be noted that melting of any ice/sleet/snow accumulation
will not take place until some time Tuesday afternoon.

The next disturbance will come across on Wednesday, give or take a
period. Details are still uncertain with this system, but it looks
like some type of winter precipitation may occur as it begins and
near the end of it. However, trends show the surface low tracking
further north which may lead to a low level warming that will
hopefully limit frozen accumulation amounts.

Everyone be smart, be prepared and be safe during this event.

Rua

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