Severe weather threat Wednesday 

Posted: 6:00 am Tuesday, April 4th, 2017

By Kirk Mellish

(UPDATED 9am WEDNESDAY):

No need to panic or be hysterical, it is after all severe weather season. April is a peak month here in Georgia. Most of the country has been in a relatively quiet tornado cycle for the past 5-6 years, especially here in the Southeast U.S.

The risk today has the potential to be worse than Monday. Storms will be possible anytime of the day or evening, but there may be two focused rounds one mid morning to early afternoon then another late afternoon and evening will a lull in-between. The second and third rounds are more likely to be the most robust, but we can’t let our guard down before Noon either. Listen to the radio and follow for updates and frequent changes throughout the day.

There is always the possibility that something will happen to lessen the threat or coverage of severe weather Wednesday. BUT, as of now the threat of severe weather looks significant in much of Georgia, including the potential for a strong tornado.

Not every thunderstorm will be severe, but its worth noting that at least for now, the Storm Prediction Center has the threat level higher for the system today than they did with Monday’s! It is a LEVEL 4 on a scale of 5.

Rainfall amounts of 1-2 inches are also expected for possible flooding in spots, with large hail possible in some storms along with active lightning and the possibility of damaging strait-line winds or a tornado in some storms. The risk for power outages is obvious.

Make sure you have a way of getting warnings, have an action plan, and have a good readiness kit in that safe place and we will be just fine. A tornado watch will be no surprise later in the day.

As I said, there is always the chance this could be a “busted forecast”… a situation with storms not as severe as expected or not widespread. It takes many (meso-scale) things coming together at a single place and time for severe storms to form.

WEDNESDAY MORNING SURFACE WEATHER MAP:

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WEDNESDAY MID-DAY SURFACE WEATHER MAP:

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WEDNESDAY EVENING SURFACE WEATHER MAP:

94fndfd_init_2017040500

WEDNESDAY SEVERE WEATHER OUTLOOK:

GA_swody1

understanding_categories

Windy and much colder weather follows Thursday and Friday. Snowflakes are not out of the question in the NE Georgia mountains by Friday, and frost will be possible by Saturday morning even in Atlanta with a freeze possible for the mountains.

NWS discussion concerning Wednesday:

A very vigorous storm system will impact the CWFA today. There
could be several rounds of severe thunderstorms today, so don`t
let your guard down if you experience relatively quiet conditions
for a period of time. The first round of severe weather is
currently impacting portions of southern Alabama and the Florida
panhandle. This activity is associated with a northward moving
warm front. This warm front is expected to move into SW GA early
this morning and keep moving to near the I-20 corridor by
daybreak. South of the warm front, the airmass is very unstable
and lapse rates are very steep for this time of the morning.
Reports of up to half dollar sized hail have been reported across
portions of SE AL. With this first round of thunderstorms, expect
the primary modes of severe weather to be large hail (up to 2
inches possible) and damaging wind gusts in excess of 60 MPH. An
isolated tornado cannot be ruled out either, as the front will
provide an excellent source of low level shear.

The warm front may end up settling somewhere in the vicinity of
the northern `burbs of Atlanta by mid morning. This means that
most of the CWFA will be in the warm sector for the afternoon. The
atmosphere should have enough time to recuperate from the morning
storms, and become very unstable during the peak heating of the
afternoon - especially if the clouds begin to break. All the
ingredients for severe weather will be present: strong mid and
upper level forcing, strong surface instability, plenty of deep
level shear, a 40-50kt 850mb jet, etc. This will be the time that
discreet cells ahead of the front are expected to develop and
supercells will be likely. (Prime time for tornado development.)

The actual cold front isn`t expected to move through until later
in the evening and into the overnight hours. The actual front will
provide enough focus for additional storms well into the evening
and overnight. However, the atmosphere *may* be worked over enough
by the time the front moves through that the coverage and
*possibly* severity of the storms may decrease. However, not
entirely confident on this situation - so continue to stay weather
aware even after the sun sets.

 

The model forecast sounding profiles Wednesday afternoon concerns me:

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It’s not very often that we get this kind of upper-level trough and jet stream dynamics crashing into an unstable air mass with both long-wave and short-wave (vorticity) energy and the kinematics of jet streaks 500mb and above:

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IMG_0114

Tornado Safety Tips

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Follow me on Twitter @MellishMeterWSB.

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