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3/12 Severe Storms & Snow Threat


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This one must have taken some extra time to write


A northern-stream and southern-stream shortwave will phase over the
MS Valley on Friday night, with an associated surface cyclone moving
northeast from the Deep South, deepening to 990-995 mb by the time
it reaches north-central NC early Saturday morning. Deep southerly
flow from this system will help draw plenty of low-level moisture
from the Atlantic, with PW values of 1.25-1.75 inches. Thus bands of
WAA-induced showers will move in from the south on Friday evening
and Friday night, when POPs increase to likely and then categorical
over much of the area. Not expecting any thunder during this period
given a complete lack of instability with a low-level inversion in
place. However, this changes in the late overnight hours into early
Saturday morning, when southerly low-level flow really starts to
increase as the surface low approaches and deepens. Thus outside of
the far NW, temperatures and dew points will start to rise through
the 50s and even lower-to-mid-60s, with MLCAPE reaching as high as
300-500 J/kg. Meanwhile a squall line associated with a strong cold
front will be moving through the area around 09z to 15z. While
instability will not be too impressive due to the time of day and
widespread precipitation, some damaging winds and isolated tornadoes
are still possible with the squall line given the very strong
low/mid level wind fields and rich low-level moisture. The one
exception is across the Triad region, where the cold front should
probably arrive early enough to shut off any instability and threat
of storms. The most favorable location for severe weather is in the
eastern Sandhills and southern Coastal Plain, which will have the
longest opportunity for WAA and daytime heating before the cold
front moves through. This is also where 0-1 km shear and 0-6 km
shear look to be at least 40-50 kts and 60-80 kts, respectively,
which is more than enough to support supercells and tornadoes. Thus
the SPC has introduced an enhanced risk for severe storms in the far
SE, and has expanded the slight risk to include the US-1 corridor
and points east. The slower the frontal timing the better the severe
threat as it would give these areas more time to destabilize. Total
rainfall of around 0.75-1.25 inches is expected on average across
central NC. This isn`t enough to cause any significant flooding
concerns, but some localized urban and poor drainage flooding can`t
be ruled out.

Widespread precipitation will come to an end from west to east with
the passage of the cold front on Saturday morning. However, our
region will be in a strong pressure gradient between the rapidly-
deepening 970-980 mb surface cyclone just off the coast New England
and high pressure building over eastern TX and the lower MS Valley.
Thus strong NW winds gusting as high as 30-40+ mph are expected
during the day and into the evening. This will result in
temperatures initially in the 50s and 60s early Friday morning
falling into the 30s and 40s through the day. As the mid/upper
trough swings through on Saturday afternoon, models show potential
for a few wet snowflakes to fall across the NE Piedmont and
especially the northern Coastal Plain, as temperatures aloft will be
falling to well below freezing. However, with surface temperatures
still above freezing during the afternoon and having been well above
freezing over the past week, ground temperatures should be too warm
for any accumulations to take place
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19 minutes ago, Brick Tamland said:

I didn't realize the Triangle was in the mountains.

FB-IMG-1647002212974.jpg

It is classic cold chasing the moisture. It won't result in any real accumulation if it happens at all. This is what I am getting at.

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1 minute ago, eyewall said:

It is classic cold chasing the moisture. It won't result in any real accumulation if it happens at all. This is what I am getting at.

Do you not think this is a ana frontal system? 

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4 minutes ago, eyewall said:

It is classic cold chasing the moisture. It won't result in any real accumulation if it happens at all. This is what I am getting at.

Who said anything about accumulations? There's still a chance we can see severe storms and snow in the same day. This is a very dynamic system and something that we rarely see here. 

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The GEFS is showing snow all the way into Atlanta between midnight and 7am on Saturday but it appears to be an outlier compared to other models. How reliable is it in predictions this close to an event?

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1 hour ago, BornAgain13 said:

The totals have actually increased the closer we get to this. Could be a few surprises for some outside of the mountains. The Euro and RAP are very similar 

Rap and the derpy derp look super interesting up this way. Any further southeast and you could be in for a pleasant surprise.

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The winds are definitely strong as soon as the front passes. We will see if any flakes make it here but it looks like any chance at accums is northeast of the Triangle (story of the year).

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