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may 10-16 convection


forkyfork

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18 minutes ago, forkyfork said:

i really like saturday. models point to an east/west boundary overhead with a wave of low pressure riding it

 

6 minutes ago, Rjay said:

Yup. Looks legit. 

Yeah Saturday could be a really interesting day for severe/heavy rain. Even Earthlight mentioned the potential earlier today on social media.

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Mt.Holly:

.LONG TERM /SATURDAY THROUGH THURSDAY/... 
  Active pattern in the long term, with several chances for  
  showers/storms as a surface front wavers back and forth in the Mid- 
  Atlantic through the period. 
   
  The large-scale setup is rather stagnant, with broad cyclonic flow  
  in eastern Canada and the adjacent northern fringes of the U.S.,  
  while high-latitude ridging poleward of an upper low dominates  
  western North America. In the quasi-zonal to slightly northwesterly  
  midlevel flow east of the upper low, several low-amplitude  
  perturbations will progress through the northeastern U.S.,  
  along/north of a waffling surface front. To the south, warm/humid  
  air will dominate, while much cooler conditions will exist to the  
  north. This sets up a long-term temperature/dew point forecast  
  subject to large errors, especially this weekend (when the front  
  will likely be within the CWA) and later next week (when model  
  discrepancies begin to increase in the large scale). 
   
  Additionally, the large-scale pattern remains favorable for at least  
  locally heavy rain. However, operational models look fairly muted in  
  this respect through Sunday night, likely a combination of three  
  factors: (1) progressive nature of the perturbations in the quasi- 
  zonal flow, (2) somewhat hampered moist advection via developing  
  upper low in the Gulf region, and (3) sufficiently large meridional  
  movement of the front during the period. Most models have 0.5-2 inch  
  output north of the Mason-Dixon Line this weekend, with the NAM/NAM  
  Nest somewhat on the aggressive side. Think that the narrow  
  corridors of higher QPF are plausible, but the geography is open to  
  question (with the CMC/GFS farther north and the ECMWF somewhat  
  farther south through Saturday night). Bottom line is that the  
  potential remains (WPC maintains a marginal risk north of Mason- 
  Dixon Line Saturday and Sunday), but given the aforementioned  
  inhibiting factors, think this threat is lower than it has appeared  
  to me in past forecasts. 
   
  Of greater concern, perhaps, is the potential for severe storms on  
  Saturday afternoon/evening. High-resolution output suggests  
  anomalously large instability developing south of the front (which  
  should be lifting into/through the CWA on Saturday). Potential for  
  MLCAPE of 1000-1500 J/kg to exist by afternoon combined with several  
  sources of smaller-scale lift (differential heating, terrain  
  effects, presence of a surface boundary, and residual outflow from  
  early day precipitation in the northern CWA) suggests convection  
  will readily develop in much of the northern Mid-Atlantic during the  
  afternoon. Additionally, larger-scale lift aided by a passing low- 
  amplitude vort max will likely contribute to the organization of  
  convection. With deep-layer shear of 35-50 kts, storms should  
  readily become strong to severe. Environment is reminiscent of warm- 
  season regional wind-damage events, with high-octane air impinging  
  upon a quasi-zonal surface boundary downstream of the aforementioned  
  midlevel perturbation with strong/fairly unidirectional low- to  
  midlevel flow. There are indications of a fast-moving squall line or  
  large-scale bow echo in the latest NAM Nest and WRF-ARW/NMM  
  simulations. Should these simulations remain consistent, will need  
  to ramp up the severe wording in subsequent forecasts. SPC has  
  upgraded much of the region to a slight risk during this period. 
   
  The convection Saturday afternoon/evening looks to permit the front  
  to sag southward Sunday and Sunday night, with most of the CWA  
  considerably cooler to the north of the boundary. Lowered  
  temperatures even more (by about 5 degrees across the area) during  
  this period, with more chances of showers as upstream perturbations  
  move through the region. There is at least some chance for elevated  
  instability to persist, especially south of the Mason-Dixon Line, so  
  cannot completely rule out a storm or two. 
   
  The front may move far enough southward to bring a period of  
  relatively dry conditions to the area Monday and Tuesday, but there  
  are enough signals with the CMC/ECMWF to maintain continued PoPs for  
  showers/storms, especially in the southern CWA. Did lower them in  
  the northern CWA to unmentionable Monday afternoon/night.  
  Temperatures will begin to warm as large-scale southerly flow  
  commences (and the front makes progress back northward). 
   
  By midweek, there are indications a northern-stream vort max will  
  dig southeastward into the northern/northeastern U.S. as an upper  
  low in the Southeast begins to lift northeastward. Increasing moist  
  advection downstream of the upper low in a region of enhanced low- 
  level convergence along the remnant surface boundary could aid in  
  the development of widespread and/or several rounds of convection  
  Wednesday through the following weekend. Upper-level divergence via  
  the right-rear entrance region of a 250-mb jet streak in New England  
  and the Canadian Maritimes may aid in the heavy rain threat. Models  
  have signaled for several days widespread moderate to heavy rainfall  
  totals during this period, with the GFS/CMC/ECMWF continuing to  
  indicate this with the most recent (00Z) simulations. Though  
  spatiotemporal discrepancies remain (and should be expected at these  
  time ranges), the large-scale pattern is strongly suggestive of this  
  threat. 
   
  Latest forecast Tuesday night onward keeps PoPs for the entire  
  period with above-seasonal temperatures in the long-duration  
  southerly (moist) boundary-layer flow. 
   
  && 
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You can clearly see it here on the SPC day 2, slight/enhanced risk just off to our south which seems to happen more often then not. Looks like anyone from Monmouth/Mercer county on south has a good chance of seeing severe weather not so much north of there but heavy rain is still a threat. We will have to see how things play out tomorrow with the movement of the front.

 

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Mt.Holly:

.NEAR TERM /UNTIL 6 PM THIS EVENING/... 
  515 am update: Showers and storms are moving through the area 
  this morning, with the hi-res models quite poorly simulating the 
  ongoing event. Lightning is generally confined to the south and 
  west portions of the precipitation shield, in proximity to 
  elevated instability as low-level flow ascends poleward of a 
  warm front situated near or just south of the CWA at this time. 
   
  Precipitation appears closely tied to the area just downstream 
  of a weak midlevel perturbation as evidenced on moisture-channel 
  imagery this morning. This will be advancing eastward to the 
  coast this morning, with chances diminishing south of I-76 in 
  the next few hours. However, upstream precipitation continues to 
  develop and progress east-southeast into southwestern New York 
  and northern Pennsylvania. This will likely keep precipitation 
  chances going much of the morning north of I-78. 
   
  Rainfall totals have been much higher than advertised...a  
  testament to the NAM simulations from the past couple of days  
  (anomalously wet and farther south than the coarser operational  
  models). Several 6-hr totals of 0.5-0.75 inches have been  
  received so far in southeastern PA and adjacent southwest NJ. 
   
  Made several adjustments to PoPs/Wx grids this morning, mainly 
  to boost them to likely/categorical for the next few hours, with 
  a diminishing trend near/after 12Z south of I-78. 
   
  Latest simulations from NAM Nest (06Z)/HRRR (06Z-08Z) continue  
  to show intense convection developing between 3 and 10 pm in  
  much of the area south of an Allentown to Belmar line. The NAM  
  Nest has trended southward and is in pretty good agreement with  
  the HRRR simulations at the moment. Fairly widespread severe 
  potential with this event, so best to keep tabs on the weather 
  this afternoon/evening. 
   
  Previous discussion... 
   
  Several forecast concerns exist today, with the biggest being a 
  chance of a fairly significant severe-wind event late this  
  afternoon into this evening. 
   
  Showers and embedded/elevated storms have developed in much of  
  central Pennsylvania overnight, and these are beginning to enter 
  portions of the Poconos and Lehigh Valley. So far, lightning  
  has not occurred in our CWA, but several strikes have occurred  
  on the western fringe of the precipitation shield, likely on the 
  nose of elevated instability advecting into the northern Mid- 
  Atlantic this morning. Precipitation through the morning hours  
  should generally be light, but local downpours are expected with 
  the stronger convective cores. Increased PoPs markedly north of 
  I-76 through the early morning hours, with hi- res models  
  generally too far north with the precipitation so far. This band 
  of precipitation should move out late this morning, with  
  residual cloud cover/outflow likely keeping temperatures cool  
  north of the I-276/I-195 corridors. 
   
  This precipitation has implications on the northward push of  
  the warm front, which will be critical in pinpointing locations  
  at greatest risk of severe storms today. Guidance is fairly  
  aggressive in allowing the front to move north of a Reading to  
  Trenton to Belmar line by mid-afternoon (though some  
  discrepancies in model simulations remain). Notably, with the  
  precipitation early this morning farther south than anticipated, 
  not overly convinced in the northward push the hi-res models  
  are indicating. Frontal position will wreak havoc with temp/dew  
  point/sky cover/wind forecasts today; expect several updates  
  through the morning as the progress of the front becomes  
  clearer. Max temperatures are a blend of hi-res guidance, with  
  temps likely below 60 in the Poconos and far northwest NJ and  
  near 90 in southern Delmarva. Temp forecast is of lowest  
  confidence between I-76 and I-78, where the front is expected to 
  traverse this afternoon. 
   
  A potent vort max will be moving through the Ohio Valley and  
  lower Great Lakes today. Large-scale ascent should aid in  
  developing sufficient instability to the south of the front to  
  initiate convection (aided by a plethora of smaller-scale  
  processes, including differential heating from the leftover  
  clouds/precip to the north of the front, orographic effects, and 
  lake breezes to the lee of Lakes Erie/Ontario). With  
  strong/fairly unidirectional shear of 35-50 kts through the  
  lowest 6 km of the troposphere, current thinking is that there  
  will be quick organization of the storms into lines/bands.  
  However, some hi-res models exhibit more semi-discrete  
  characteristics to the convection (WRF-NMM and very recent HRRR  
  simulations).  
   
  With steepening midlevel lapse rates and sufficient boundary-  
  layer heating, expect an environment favorable for  
  strong/damaging wind gusts downstream of the developing  
  convection. The overall pattern and anticipated primary  
  convective mode is quite favorable for swaths of wind damage,  
  but model soundings continue to exhibit substantial midlevel  
  buoyancy/shear favorable for large hail. In addition, low-level  
  shear looks adequate for an isolated tornado threat should  
  mesovortices develop within the bands of convection or the  
  convection remain somewhat discrete. SPC has maintained the  
  enhanced risk for southeast PA/northern MD and DE/southwest NJ.  
  However, should the front progress farther north, the increased  
  threat will move north with it. 
   
  Main threat appears to be after 4 pm and should continue  
  through the evening hours. Heavy downpours are likely with the  
  strongest convection, and given the slow movement of the front,  
  there are indications that training may occur on the southwest  
  side of the line(s) of storms that develop. As such, cannot rule 
  out an isolated instance of flash flooding. 
   
  && 
   
  .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... 
  Band(s) of storms will be moving through this evening, with  
  good chances of severe weather occurring near/south of I-76.  
  Convection may redevelop on the southwest side of the line(s),  
  which would permit some training of storms. This may produce  
  locally heavy rainfall, with the greatest threat of this in  
  southern NJ and Delmarva. The bigger threat will be damaging  
  winds and isolated instances of hail, however. 
   
  The convection should force the meandering front southward  
  through much/all of the CWA. Northeast flow on the poleward side 
  of the front will allow the low clouds to move in. Could be  
  some fog/drizzle after the storms move out late this evening  
  into the overnight hours. 
   
  Any precip lull will be short-lived, as an upstream  
  perturbation is expected to approach the area late tonight. Hi-  
  res models are showing another round of convection for much of  
  the area after 3 am (and likely closer to daybreak). There is  
  considerable disagreement regarding the corridor of highest QPF, 
  with the NAM Nest considerably farther south than the WRF-  
  ARW/NMM. The farther south solution seems more likely given the  
  strength of the antecedent convection during the evening.  
  Trended PoPs upward for much of the area late tonight.  
  Instability will be marginal but not negligible. As such, kept  
  slight chances of thunder around/south of the Mason- Dixon Line  
  through the night. 
   
  Temperature forecast is a blend of hi-res guidance, which  
  generally lowered minimum temps by about 2-4 degrees from the  
  previous forecast. 
   
  && 
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2 hours ago, Rtd208 said:

Main severe threat has been shifted a little further south so wouldn't expect much here but we should still keep an eye on exactly how far north the front gets before shifting back south. Heavy rain and strong storms still remain a threat for the area today and tonight.

 

day1otlk_1200.gif

Heavy rain, yes.  Storms let alone strong, no we are marine cool and stable

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3 hours ago, Rtd208 said:

Main severe threat has been shifted a little further south so wouldn't expect much here but we should still keep an eye on exactly how far north the front gets before shifting back south. Heavy rain and strong storms still remain a threat for the area today and tonight.

 

day1otlk_1200.gif

I think that the front won't get much farther north than I-195. I've been watching TWC since 6 AM and they barely even mentioned this threat today.

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