Jump to content
  • Forum Image

Recommended Posts

Good morning!

Two nice days in store before the severe weather makes a return on Thursday. There is nothing on the map this morning to talk about, and the sun will be shining brightly today and tomorrow, but don't let the nice weather fool you or lull you into complacency. 

Snap346064896.thumb.png.d555527058987ff26c78a39cfd74121b.png

 

We are looking at what may become a significant severe weather event for Thursday. 

Snap346064895.thumb.png.416dfcf64dbb89363fd763427bff9e6e.png

Snap346064897.thumb.png.bc69ecbd68916ef6f3648ea0e6bfb8d7.png

Quote

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 AM CDT Tue Apr 21 2020

   Valid 231200Z - 241200Z

  •    ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS MAINLY OVER ALABAMA...GEORGIA...AND NORTHERN FLORIDA INCLUDING THE PANHANDLE...

   ...SUMMARY...
   Significant severe storms are expected over parts of the Southeast on Thursday, including the potential for strong tornadoes.

   ...Synopsis...
   A positive-tilt upper trough with 70-80 kt midlevel speed max will move from the lower MS Valley Thursday morning toward the Appalachians by 00Z, with a 50-60 kt low-level jet core shifting from AL to the Mid Atlantic during the day.

   At the surface, low pressure will move from northeast AR into KY through 00Z, and toward the Delmarva by 12Z Friday. A dryline will extend southwestward from the low, and will move across AL, MS and LA during the peak heating hours. East of this boundary, 65-70 F dewpoints will be common, beneath cooling temperatures aloft.

   Models differ with how quickly the dryline will move, and early day storms may dictate where the quasi-stationary warm front sets up latitudinally. Regardless, the warm sector will become very unstable, with shear favoring tornadic supercells along the dryline and warm front/outflow boundary. At this time, it appears the bulk of the activity will occur over AL, GA, and the FL Panhandle into northern FL.

   The NAM solution, if taken literally, suggests strong and perhaps violent tornadoes will be possible over parts of MS, AL, and GAHowever, this solution is much slower with the dryline than other models, and may be overdone with instability and low-level shear. Using the preferred ECWMF solution, the dryline will extend from southern MS into central AL Thursday afternoon, with early day storms reinforcing a warm front roughly from Birmingham AL to Atlanta GA. Outflow could potentially push the warm front farther south. Supercells will be possible both along the dryline and along the warm front, with strong tornadoes possible. The strongest lift will occur early in the period related to warm advection, and this will lift northeast during the day. However, subtle lift along the dryline will favor supercells, as opposed to a linear storm mode. MUCAPE of 2000-3000 J/kg is possible, with midlevel lapse rates of 6.5 to 7.0 C/km aiding updraft vigor. Regardless of preferred model, this event will be adjusted with time as predictability increases, with categorical upgrades possible.

I do NOT like the way this sounds and we will need to watch this very closely. 

 

Rainfall with this system will be heavy and falling on top of saturated soils. The WPC has north Georgia in an elevated risk of excessive rainfall, and my guess is this will become Moderate Risk tomorrow.
1679392131_99ewbg(1).gif.765fdae0c733b8f0f8023d712802c5b7.gif

 

Quote

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
448 AM EDT Tue Apr 21 2020
 
Day 3
Valid 12Z Thu Apr 23 2020 - 12Z Fri Apr 24 2020 

  • ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PARTS OF ALABAMA, GEORGIA, SOUTH CAROLINA AND NORTH CAROLINA...

...Southeast, Tennessee Valley and Mid-Atlantic Region...

The surface cyclone mentioned in the Day 2 discussion will move trough the Tennessee Valley and Mid-Atlantic regions. Also, there will be a cold front pushing south through the Ohio Valley and northern Mid-Atlantic. An axis of 1-1.25 inches is forecast to fall along and north of the low track-- over an area that is 150% of normal for precipitation. As the low lifts north-northeast, it will bring a fairly quick cold front through the Tennessee Valley and into the Southeast and Mid-Atlantic region. PW values of 1.5 inches will be transported northward of ahead of the advancing cold front within the 30 to 50 kt low-level flow. CAPE values up to 2500 J/kg will be present across the Southeast. While the storm motion is expected to be progressive, brief periods of intense rainfall will be possible, especially near the terrain of Georgia and South Carolina. Soils within this region are near saturation from heavy rains in the past week or so. Rainfall near or exceeding 1 to 3 inches could easily lead to rapid runoff, urban ponding or flash flooding conditions. A Slight Risk area was introduced for parts of eastern Alabama, northern Georgia, South Carolina and extreme southern North Carolina. A Marginal Risk spans from the Southeast to the Ohio/Tennessee Valley and the northern Mid-Atlantic. 

Quote

Hydrologic Outlook issued April 20 at 4:40PM EDT by NWS Peachtree City GA

Alert
.SYNOPSIS...

A deepening surface low will track across the Tennessee Valley late Wednesday through Thursday, lifting a warm front through Georgia. Above normal amounts of moisture are expected to stream into the region, and even with dry conditions expected Tuesday and Wednesday, this additional rainfall will increase the risk for flooding on Thursday.


.RAINFALL EXPECTED...
Highest rainfall amounts expected on Thursday are concentrated across middle Georgia, generally an area one to two counties on either side of a line extending from Columbus, to Macon, to Swainsboro. In this area, 1.5 to 2 inches are expected, with locally higher amounts possible. This same general area received 3 to 8 inches in a 24-hour period ending this morning, April 20th. Outside of this region, rainfall amounts will range from 0.5 to
1.5 inches, with the lowest amounts most likely over far north and northwest Georgia.


.ANTECEDENT CONDITIONS...
Recent heavy rainfall has kept soils moist and stream flows much above normal to high across the state. In spite of the dry conditions expected Tuesday and Wednesday, these antecedent conditions will impact the ability for rivers to handle the increased runoff from Thursday's heavy rainfall, and could result in flooding.


.IMPACTS...
With the expected rainfall amounts, isolated flash flooding is possible, particularly south of the I-20 corridor where the rain is expected to be the heaviest. Periods of heavy rain can overwhelm or clog storm drains and ditches with debris. Take time ahead of the rain to clear leaves and debris from drainage systems.

Minor flooding of some of the larger creeks or rivers is possible with the forecast storm total rainfall, especially as some of these channels are already high from the weekend rain. A few rivers may experience a period of moderate flooding as well. Quickly accumulating rainfall can also produce widespread flooding of smaller, fast-responding creeks. Again, at this time, the highest threat for flooding remains over middle Georgia.


.ACTIONS...
Stay alert to changing forecasts. A Flash Flood or Flood Watch may be issued for parts of the area. Know what county you are in and the names of rivers and creeks in your area. Do not be caught off guard. Know what to do if a Flash Flood Warning is issued, particularly if you live or are visiting an area near a creek or river.

For additional hydrologic information, visit our website at weather.gov/atlanta. Click on the Rivers and Lakes tab under current weather to access the latest river and precipitation information.

 

The low level jet will be ripping again... these are 850 mb winds

nam-218-all-georgia-z850_speed-7686400.thumb.png.2f2e2712ba3e5aed02cb85c9fa4a6837.png

 

And the thunderstorm potential is very high

nam-218-all-georgia-kindex-7675600.thumb.png.bc3379c93ba049df844a0588728379c0.png

 

We have several days to see how this is going to evolve but now would be a good time to revisit your severe weather plan.

In the meantime, enjoy the next several days of weather!
Have a great day!

ffc-21.png.9acdfbd66a7fb62b2c02614c55ee1611.png

mrx-21.thumb.png.ff2fc8d5e9501c8b464b77d65d6aeada.png

bmx-21.thumb.png.3a553c7cb39859a1ef5528df4210fde9.png

  • Like 1

Share this post


Link to post
Share on other sites
5 minutes ago, TinaTrivett said:

Are any of the models showing it moving further South? Thanks so much.

Not right now, we'll just need to watch, wait, and see.

  • Thanks 1

Share this post


Link to post
Share on other sites
1 hour ago, Lori said:

What time of the day on Thursday? 

Right now, and this will change as we get closer, between noon and midnight. Could be a little later for some people.

Share this post


Link to post
Share on other sites
2 hours ago, NorthGeorgiaWX said:

Right now, and this will change as we get closer, between noon and midnight. Could be a little later for some people.

That's not a good sign. We've been "lucky" to miss peak heating for the last few severe events, this one finally looks to get us during the day instead of 2am. At least for my location.

  • Like 2

Share this post


Link to post
Share on other sites
Posted (edited)

The NWS out of Peachtree City is typically fairly "tame" in regards to the language they use with events two to three days away. However, their afternoon discussion was quite lengthy and eye opening in my opinion.

 

Edited by Shannon

Share this post


Link to post
Share on other sites
3 minutes ago, Nic said:

That's not a good sign. We've been "lucky" to miss peak heating for the last few severe events, this one finally looks to get us during the day instead of 2am. At least for my location.

Yep... 

 

13 minutes ago, CaptainTraunt said:

What are the 2 images on the right? The captions are cut off. 

Analogs for the setup of this event.

Share this post


Link to post
Share on other sites
Quote

So what DO we know?
Severe parameters for discrete supercellular convection will be in place and abundant sometime through the day and evening on Thursday. Instability will be higher than in several of our past severe weather days this year. MUCAPE values at projected to be up to 2000-3000 J/kg, with similar SBCAPE values in the warm sector. Low level shear will also be abundant with 0-6km Bulk shear between 50-70 knts and low-level 0-1 km storm relative helicity values well over 300m2/s2. the combination of these values with minimal if any CIN is projecting EHI and SigTor values over 4 for several areas of central Georgia. Furthermore, modeled hodographs look very favorable for rotating tornadic supercells with nearly all the horizontal vorticity being streamwise versus crosswise making storms efficient in turning environmental shear into rotating storms. With all this combined threats for large hail, damaging wind gust, and tornadoes all look possible, with a few tornadoes having the potential to be long- track, strong tornadoes. Furthermore, with several rounds of heavy rain possible with the storms and central Georgia being saturated from previous rains, flash flooding will also be a concern with an areal average of 1.5 to 2.5 inches forecast and higher local values likely where stronger storms develop for prolonged periods of time.
 

 

Share this post


Link to post
Share on other sites
Posted (edited)
8 minutes ago, NorthGeorgiaWX said:

 

Sounds ominous?  Do we have agreement on the models about placement and timing?  How much certainty are we looking at.  And if you had to guess based on current info where would the best chances for the worse weather be in Ga?

Edited by RickyD
  • Like 1

Share this post


Link to post
Share on other sites
21 minutes ago, NorthGeorgiaWX said:

 

This is what I was talking about. Strong wording. 

Share this post


Link to post
Share on other sites

Reading through this portion of the GSP forecast discussion and I suppose for now the threat up in this area is down to whether or not the NAM stays an outlier. 

... rain is expected to
shift east by late aftn/early evening, with the warm front lifting
north across central GA and SC. the question is how far north will
the front get before the occluded front passes by Thu evening. The
NAM is an outlier with a faster surge north and bringing the warm
sector of the system into the entire area by 00z Fri. Within this
warm sector, 1000-2000+ j/kg of sbCAPE and bulk shear of 70 kts or
more (with curved hodographs of various soundings). Even the GFS and
ECMWF do hint that the warm sector will creep into at least the
southern fringes of the forecast area, and so the Day 3 slight risk
for severe weather looks well placed. A threat of supercells with
possibly some violent tornadoes will be possible, if the NAM is
right. 

Share this post


Link to post
Share on other sites
47 minutes ago, NorthGeorgiaWX said:

 

Yikes. How does this compare to 2 weeks ago? I believe there was already a moderate on day 3. Is this looking as bad as that? Sorry, I’m not super well versed on these graphics. Weather is just a hobby for me and I’m still learning 😁

Share this post


Link to post
Share on other sites
3 hours ago, RickyD said:

Sounds ominous?  Do we have agreement on the models about placement and timing?  How much certainty are we looking at.  And if you had to guess based on current info where would the best chances for the worse weather be in Ga?

Not yet

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Who's Online   0 Members, 0 Anonymous, 15 Guests (See full list)

    There are no registered users currently online



×
×
  • Create New...