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High-Impact Mid-Atl/Northeast Ida-related Weather Event


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Here's an email I just sent out to all of our mets here...slightly re-purposed but not much because I'm too tired to:   Just wanted to comment on a trend I'm noticing on guidance with Ida's

I had to walk home from work.  There were no ubers, taxis, buses, etc, running, and I didn't drive today. On my walk home, I literally almost got swept away by waters.  I lost textbooks, my watch

convection wins. the models routinely show too little activity near the warm front 

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2 hours ago, forkyfork said:

it shows the max amounts along the warm front which i completely agree with 

It makes sense to agree with what makes the most meteorological sense.

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8 minutes ago, Snowman11 said:

Gfs further north 

gfs_apcpn_neus_7.png

Yep, can't deny its steadfast trend. Though it does extend the 2"+ line a little further S in the same breath. 

264f75d4-c6d1-4415-b1d0-3df6205a5f1f.gif

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I am starting to wonder if we may get the "best" of both worlds here in Middlesex County NJ. While the heaviest rain amounts may fall just to our northwest we may also have more of a severe threat here as well. So the warm front may hover around this area. We'll see.

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Also some of these north/south adjustments with the heaviest rains may be just "noise" which was something that was mentioned in Mt. Holly's discussion. 

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5 minutes ago, Rtd208 said:

fill_94qwbg.gif

94ewbg.gif

wow what a nice picture lol, funny when you look at the radar it does not look impressive, however that will change with the enhancement due to the stalled front and overrunning

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Mt.Hoily:

 

.NEAR TERM /THROUGH TONIGHT/... 
  ...Significant flash flood and severe weather event likely to  
  occur in much of the area today and tonight... 
   
  First concern to address is precipitation/convection this morning,  
  with long-lived storms continuing to affect northern Virginia, the  
  DC area, and adjacent portions of central Maryland. Although the  
  environment appears less favorable for our area, could see some  
  strong/severe slow-moving storms move into Delmarva and adjacent  
  portions of far southeast Pennsylvania and southern New Jersey this  
  morning. Will be monitoring this potential closely the next few  
  hours. 
   
  The remnants of Ida will be affecting the region today and tonight,  
  with significant impacts expected for the area. Model trends early  
  this morning continued a slight northward nudge of the highest QPF  
  axis, with the GFS/NAM/ECMWF in good agreement that 3+ inches of  
  rainfall will occur near/northwest of the Fall Line (with embedded  
  totals 6+ inches somewhere in the southern Poconos and/or Lehigh  
  Valley and vicinity). The CMC remains farther south (almost to  
  outlier status), with the main axis generally between I-76 and I-80.  
  The convection-allowing models (CAMs) are in between, and these are  
  generally in line with our current thinking this morning. 
   
  There are a few reasons for favoring a slightly farther south  
  solution to the main QPF axis. For one thing, models tend to shunt  
  warm sectors too far northward in advance of these systems,  
  particularly ones that are in the process of intensifying via large- 
  scale baroclinic processes. Additionally, models tend to bias  
  convective precipitation too far north, in association with the  
  synoptic forcing, rather than with the ambient/pooling instability  
  (which tends to win out with convectively-enhanced events like  
  these). Finally, suspect upslope contributions to precipitation are  
  being underrepresented farther southeast near the Fall Line to the I- 
  95 corridor. For these reasons, our latest QPF forecast did not  
  adjust totals as far north as the consensus of the coarser NWP  
  models. However, these discrepancies do lead to higher uncertainty  
  with forecast totals along the I-95 corridor. For example,  
  Philadelphia may end up anywhere between 1 and 5 inches of rain  
  based on the array of guidance available. 
   
  However, the risk of flash flooding is not only tied to total  
  rainfall but also duration, and the CAM solutions would suggest that  
  much of the rainfall south of the high-QPF axis will be occurring in  
  a relatively short period of time. Excessive rainfall rates (via PWs  
  well north of 2 inches) are likely with the main convective show  
  late this afternoon into the early overnight hours, and will likely  
  lead to several instances of flash flooding near the urban corridor.  
  Therefore, despite somewhat lowered QPF for the I-95 corridor  
  southeastward, the risk of flash flooding remains quite elevated  
  because of the rainfall rates. The HREF guidance provides some  
  insight here, with the 00z ensembles indicating probabilities of 1-h  
  rainfall accumulations exceeding flash flood guidance (FFG) above 50  
  percent in virtually all areas northwest of I-95 in our CWA during  
  the evening hours, despite a range of 3-5 inches in total QPF.  
  Notably, the probabilities of 6-h rainfall accumulations exceeding  
  FFG are above 90 percent in much of the same area, which conveys the  
  seriousness of the flooding threat for our area quite well. 
   
  Of course, that is not all. With the warm sector expected to shift  
  northward into at least the southern half of the CWA, the ambient  
  preconvective environment will be quite favorable for severe  
  weather. Model soundings indicate MLCAPE 1000-2000 J/kg (closer to  
  500-1000 J/kg near the warm front), 0-6 km bulk shear nearing 40 kt,  
  and SRH > 200 J/kg in the late afternoon and early evening hours.  
  This is an environment supportive of rotating storms, with CAM  
  simulations suggesting a mixed mode of short line segments and  
  cellular storms. Damaging wind gusts and tornadoes are the main  
  threats, and the SPC has nudged the enhanced risk slightly farther  
  north given model trends this morning. Given the coverage of  
  convection expected, the favorable environment is quite concerning,  
  with the severe potential continuing to look more and more  
  impressive. The main time window for severe weather is likely in the  
  20z to 06z time frame from west to east. Individual cells will  
  likely move quickly north-northeast, but the overall system will  
  move only slowly eastward, so training convection poses a flash  
  flood risk in the southern half of the CWA. 
   
  Models continue to trend faster with precipitation moving out of the  
  region, with most areas likely drying out by daybreak Thursday. 
   
  && 
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