Jump to content
  • Forum Image
NorthGeorgiaWX

Wednesday, April 22

Recommended Posts

Good morning!

Let's just jump right in to the severe weather forecast for Thursday. First, the Storm Prediction Center. The next update to this will be around 1:30 pm.

1369034908_SPC_CO_Day2State(3).thumb.png.36a63830ee60c9c73d3bbada2b8f9d15.png

Quote

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1257 AM CDT Wed Apr 22 2020

   Valid 231200Z - 241200Z

  •    ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE SOUTHEAST...

   ...SUMMARY...
   Significant severe storms are possible over parts of the Southeast on Thursday, including the potential for a few strong tornadoes and damaging winds.

   ...Synopsis...
   A positive-tilt shortwave trough will move from the lower MS Valley toward the Appalachians by evening, with gradual cooling aloft across the region. A surface low is forecast to move northeast across KY during the day and toward the coastal Mid Atlantic by 12Z Friday. A warm front will lift north across AL, GA and SC during the day, with mid 60's F dewpoints surging north. Farther south, dewpoints near 70 F will be common along the Gulf Coast. The 850 mb jet is forecast to be maximized over AL/GA/SC during the day at around 50 kt, and will lift rapidly north across the Carolinas after 21Z. Meanwhile, a dryline will surge east across the lower MS valley early, then into AL and northern GA during the afternoon. Given the positive tilt to this system, the dryline will move slower over southern AL, MS and LA, where heating may occur. The combination of a moist and unstable airmass and favorable shear suggest a corridor of tornado and severe wind potential, although there is significant uncertainty with this forecast.

   ...Southeast...
   Model consensus is for storms to be ongoing roughly across northern AL and GA near the warm front. These will likely be elevated initially, but localized wind damage or a tornado is possible along the southern fringe. Given little if any capping extending southwestward ahead of the dryline, other storms may form by 18Z across AL, southern MS and LA. Some models develop a significant amount of storms along the Gulf Coast, which may inhibit destabilization to the north. 

   Low-level shear for tornadoes will be most favorable early in the day across LA/MS/AL, and later in the day across GA and SC near the warm front. Adding uncertainty to this forecast is potential outflow boundaries from the early day storms, and questions regarding airmass recovery in those areas (northern GA and SC). Tornado and wind risk will largely depend on storm mode. If midday heating occurs along the dryline, and the air mass has not been overturned, supercells and tornadoes will be possible. A few strong tornadoes might occur should sufficient SRH (200-300+ m2/s2) remain prior to 850 mb winds veering. Tornadoes will also be possible along the warm front into GA/SC, assuming it is not reinforced with too much outflow. Otherwise, a general upscale growth of storms is expected for the remainder of the area including FL. Damaging winds are most likely should the storm mode be linear. Given such large model variability, large changes in area are possible in later updates.

 

1015181495_SPC_TP2_Day2State(4).thumb.png.6c09eaec4cd0f0075724bdeb8318f414.png1602149349_SPC_WP2_Day2State(3).thumb.png.5624f1a607c158d2075dc09490b680a5.png1866397331_SPC_HP2_Day2State(3).thumb.png.3914aef4544351a2b42b8a3911a5576a.png

 

One thing you may or may not notice is that the Enhanced Risk area shifted just a little bit south which of course is good news for north Georgia.

More local detail from the Atlanta NWS

Quote

An Enhanced Risk of severe storms is in effect for Thursday for central and portions of north GA Thursday. The models appear to be coming into much better agreement especially with the timing and intensity of this next system. The models currently show this system pushing precip into the state tonight with the cold front sweeping through Thursday into Thursday night. The models do differ a bit in the placement of this system. Things are trending towards the best locations for severe storms to be mainly across central GA as the warm front pushes NE through the state Thursday. This warm front will act as a catalyst for tornadic activity and strong gusty winds so its eventual location is very important.

Severe parameters for discrete supercellular convection will be in place Thursday.  MUCAPE values are projected to be in the 1500-3000 J/kg, with similar SBCAPE values in the warm sector. Low level shear will also be abundant with 0-6km Bulk shear between 50-80 kts 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 most of central Georgia. Modeled hodographs look very favorable for rotating tornadic storms with nearly all the horizontal vorticity being streamwise versus crosswise. Things also look favorable for large hail and damaging wind gust. Also...with several rounds of heavy rain possible 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. This system finally sweeps through the area by  Thursday night into Friday morning.
 

 

The latest NAM run keeps the bulk of the severe well to our south so we'll see how this plays out. Of course that would be good new for north Georgia. 
nam-nest-conus-georgia-supercell_comp-7682800.thumb.png.9e5f4801b59b0c178ed09f8a371fbf88.png

 

Since the exact location has not been pinned down yet, we'll keep watching the trends to give us clues. We're in range of most of the short range models now, so that will aid in determining that location.

I'll have more information as the day goes on and we'll watching for changes on the location of the main axis of severe weather. 
Have a great Wednesday!
ffc-22.png.d081937cd3af7b6cf56d90c835db6d0a.png

mrx-22.thumb.png.480c531327edbbf797fd8c775f85dc97.png

bmx-22.thumb.png.d8e6277aa1d246d11d41382e7d7a3813.png

  • Like 2

Share this post


Link to post
Share on other sites

Looking at the 12z models as they role in and they do not look impressive at all for tomorrow. 

  • Like 1

Share this post


Link to post
Share on other sites
2 minutes ago, Shannon said:

Looking at the 12z models as they role in and they do not look impressive at all for tomorrow. 

No, the warm air never gets too far north.

Share this post


Link to post
Share on other sites

Did I see a wedge  of colder air in N  Georgia for tomorrow?  Looks like some will not get out of the 50's.  Set up similar to Sunday.  Unfortunately , it looks like this time the warm front will get past us here at Metter.

Share this post


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

At this point, I'm not seeing a big severe threat for north Georgia tomorrow.

?  It the level 3 risk moved north and the Tornado threat moved north also?

  • Like 1

Share this post


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

Looking at the 12z models as they role in and they do not look impressive at all for tomorrow. 

Sorry to be this person but it’s roll in* not role in 

  • Like 1

Share this post


Link to post
Share on other sites

Snap346064930.thumb.png.2b81587cdbb7794a7700a0c032be608c.png

Snap346064932.thumb.png.cbdc252ed5b82443f8c820c864c30e16.png

Snap346064933.thumb.png.319f39f33ee3490c66907ca004319725.png

Snap346064934.thumb.png.f7b92f5fd9c74415af9c413fa3c7af66.png

Quote

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1229 PM CDT Wed Apr 22 2020

   Valid 231200Z - 241200Z

  •    ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THURSDAY THROUGH THURSDAY NIGHT ACROSS SOUTHEASTERN MISSISSIPPI...CENTRAL AND SOUTHERN ALABAMA...MUCH OF NORTHERN FLORIDA AND GEORGIA THROUGH THE CAROLINAS...

   ...SUMMARY...
   Severe thunderstorms are expected to develop and impact much of the  Southeast Thursday through Thursday night, including the potential for a few strong tornadoes and damaging winds, as well as large hail.

   ...Synopsis...
   A strong, amplified short wave trough, within a distinct northern branch of mid-latitude westerlies, appears likely to continue gradually pivoting across the Canadian Maritimes, and away from the U.S. Atlantic Seaboard through this period.  In its wake, models indicate that broad, low amplitude mid-level troughing will continue to evolve within a southern branch of mid-latitude westerlies, across the southern Rockies through the middle and southern Atlantic Coast states by the end of the period.

   Within the latter regime, a significant lead short wave trough is forecast to progress east of the Ozark Plateau, toward the central
and southern Appalachians, Thursday through Thursday night.  This likely will be accompanied by the east-northeastward migration of a fairly deep (sub-1000 mb) surface cyclone across the Mid South into the western slopes of the central Appalachians.  Although little substantive further deepening is forecast, there may be secondary surface wave development along a frontal zone from the lee of the southern Appalachians into the Mid Atlantic coast by the end of the period.

   Although relatively cool/dry, stable boundary-layer conditions may still be entrenched across much of the eastern Gulf into South Atlantic Coast region early Thursday, models indicate that rapid boundary-layer moistening will occur through the day.  By Thursday evening, this is forecast to be sufficient to contribute to moderate boundary layer destabilization as far east as the Carolina piedmont and coastal plain.

   ...Southeast...
   Considerable spread exists, particularly within convection allowing model output, concerning possible ongoing early morning convection across parts of Mississippi into Alabama, and subsequent development through the period.  However 60-80 kt west-southwesterly flow at 500 mb is forecast to overspread much of the warm sector, contributing to strong vertical shear supportive of organized severe thunderstorm development, in the presence of CAPE on the order of 1000-2000+ J/kg.

   Models also suggest that west-southwesterly 850 mb flow will strengthen from 50-70+ kt, in association with the developing wave along the stalling surface frontal zone across the piedmont of Georgia into the Carolinas.  And, there is increasing concern that this could become the focus for organized severe thunderstorm development, including supercells and an upscale growing convective system by Thursday evening, if not earlier.  Given strong to extreme low-level shear, it appears that the environment will become potentially conducive to the risk for damaging wind gusts and a few tornadoes, some of which could become strong. 

   Otherwise, although mid-level capping may be an issue, at least initially, within the warm sector to the south and west, south-southwesterly 850 mb flow on the order of 30-50+ kt across western Georgia and eastern Alabama through late afternoon will  contribute to an environment conducive to organized severe convection.  This may include discrete supercells, with potential to  produce a few tornadoes, some possible strong, before convection probably tends to grow upscale into a line or cluster as mid-levels cool and inhibition weakens.  This will spread toward Georgia/South Carolina coastal areas, and perhaps across portions of northern Florida, through Thursday evening.

 

Share this post


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

Snap346064930.thumb.png.2b81587cdbb7794a7700a0c032be608c.png

Snap346064932.thumb.png.cbdc252ed5b82443f8c820c864c30e16.png

Snap346064933.thumb.png.319f39f33ee3490c66907ca004319725.png

Snap346064934.thumb.png.f7b92f5fd9c74415af9c413fa3c7af66.png

 

Well I guess there is still enough uncertainty in the models to warrant this risk. 

Edited by Shannon

Share this post


Link to post
Share on other sites
Quote

Considerable spread remains within the hi-res and the synoptic models for tomorrow's system. Have tried to take a blend for timing, but multiple systems/scenarios are still presenting an issue. Models are progging an overnight MCS type system approaching western portions of GA towards 12Z. This system looks to weaken as it approaches the AL/GA border, but strong to severe storms will still be possible. Do think the main threats with this system would be damaging wind gusts and large hail. Most of the convection should remain elevated with this system. The MCS will most likely leave behind a boundary...outflow/differential heating. A brief lull in convection is likely during the late morning/early afternoon before firing again during the mid-late part of the afternoon.

In addition to any left over boundaries from the MCS, the warm front should be lurking across central portions of the state/CWA.
Conditions will become favorable for discrete convection that may eventually morph into another strong line/QLCS during the evening hours. The afternoon convection will have 60+ dewpoints to work with, contributing to CAPE values 1500-200 J/kg. The mid and upper levels will also be favorable with a 60-70kt 850 jet, strong shortwave energy and broad/strong upper divergence. Forecast hodographs also show good potential for tornadoes along with damaging wind gusts.

Even with all of this said, timing of any severe weather remains an issue, but multiple rounds are anticipated at this time. The
forecast will be highly dependent upon any early morning convection tomorrow and where it weakens/stabilizes areas. Models are typically not great at handling the specifics (timing/weakening) of MCS activity. The MCS could also potentially end up stabilizing quite a bit of the CWA (like last Sunday) with the stronger afternoon convection firing a bit further south than anticipated.

 

NWS Atlanta

  • Thanks 1

Share this post


Link to post
Share on other sites

Looking at the 18z HRRR I get the concern. You can see the discrete cells develop after the MCS later in the day.

Share this post


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

Round 1 looks to be your normal thunderstorms, cool air over the area will keep those from being too strong.

hrrr-conus-georgia-refc-7639600.thumb.png.b04990b56e6e3d42ec0ab9514138ee51.png

989929482_hrrr-conus-georgia-t2m_f-7639600(1).thumb.png.4f6453d333b07259ab341575f292eb0a.png

We subtract 4, or add 4 for real time? I forget which

Share this post


Link to post
Share on other sites

So, to me, while not completely unscathed, North Georgia still seems like it will get less than more southern areas. Please correct me if I am wrong Steve.

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, 11 Guests (See full list)

    There are no registered users currently online



×
×
  • Create New...