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forkyfork

may 10-16 convection

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I haven't looked into the actual potential too deeply but I do know that the forest floor is dry and dusty already. As everything leafed out it drank the surface water right up, even down a few inches is getting sandy and the creeks have come down to summer levels. A few days of wetness will be good to saturate things and bring the soil moisture up a bit. It doesn't have to rain all that much just enough and frequently enough to soak in nicely.

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This was Mt.Holly's discussion from this morning which I thought laid things out pretty well. 

.LONG TERM /THURSDAY THROUGH TUESDAY/... 
  The long-term period looks active, with a setup that looks 
  favorable for an east-west axis of heavy rainfall that has at  
  least some potential to affect portions of the CWA Saturday  
  onward. 
   
  Positively-tilted trough is anticipated to move through the 
  Northeast/Mid-Atlantic on Thursday with a cold front sagging 
  southeastward from the lower Great Lakes and adjacent southeast 
  Canada upstream of a prefrontal trough crossing New 
  York/Pennsylvania during the day. Sufficient diabatic heating 
  will allow for some surface-based instability to develop and 
  focused lift via differential heating, topographic  
  effects, and boundary confluence/convergence should be  
  sufficient to develop scattered convection to our west by late  
  morning. Just how far east this convection makes it before  
  nocturnal cooling Thursday evening is the main forecast concern, 
  with the ECMWF/ICON keeping most precipitation west of the  
  Delaware River and the GFS more progressive, allowing scattered  
  convection to reach the coast. High-resolution/convection- 
  allowing models indicate at least some potential for storms  
  reaching the coast (e.g., the 00Z NAM Nest), but higher  
  potential is certainly northwest of the I-95 corridor. Did not  
  change inherited PoPs much, keeping chance-to-likely PoPs from  
  the urban corridor northwestward but at least slight-chance PoPs 
  all the way to the coast. 
   
  The environment is supportive of strong to severe storms, with  
  deep-layer bulk shear 35-45 knots and CAPEs approaching 1000  
  J/kg during peak heating...especially west of the Philly area  
  (one caveat to this discussed below). Forecast hodographs show  
  some curvature, and high-resolution models indicate potential  
  for a combination of discrete storms and line segments along  
  initiating boundaries. Would not be surprised to see some  
  rotating storms during the afternoon with potential for some  
  marginally severe hail in addition to strong downdraft gusts.  
  Again, one of the main question marks is how far east the  
  convection makes it before the window closes on the severe  
  potential. Will definitely need to keep an eye on this. 
   
  A potential complication to the above is residual morning  
  clouds (low stratus and/or fog), with the NAM showing its usual  
  soup hanging on in much of the area for a few hours after  
  sunrise. This may have implications on how much instability can  
  develop, should this materialize overnight. 
   
  Convection should dissipate fairly rapidly after dark Thursday 
  evening, with the lagging cold front set to move through 
  overnight into Friday morning. Skies are expected to become 
  clear(er) upstream of the front, with temperatures a few degrees 
  cooler than the very warm conditions expected Thursday. Forecast 
  temperatures Thursday through Friday are a blend of bias- 
  corrected statistical guidance. 
   
  The challenge then becomes what happens to the front as upstream 
  perturbations move eastward through the quasi-zonal midlevel 
  flow. This should result in a waffling (back-and-forth) of the 
  front in the Mid-Atlantic/Northeast upstream into the Ohio 
  Valley for the rest of the forecast period. Unfortunately, 
  accurate depiction of the timing/strength of these perturbations 
  (likely convectively reinforced) is quite challenging, and 
  operational models are showing quite a bit of spread in the 
  associated convective precipitation. Several rounds of 
  convection appear possible through the weekend north/west of the 
  CWA, but there are indications that we will get in on the action 
  by Saturday night (if not sooner).  
   
  One perturbation appears to initiate convection to our north  
  Friday night and Saturday, which may affect northern portions of 
  the CWA. This perturbation should draw the front northward  
  through much of the area by Saturday, allowing for warm max  
  temps. Convection may develop in the warm sector Saturday  
  afternoon, with another round of showers/storms Saturday night  
  in close proximity to the front. Convection and associated  
  mesoscale phenomena should drive the frontal placement  
  thereafter, and models are unsurprisingly in large disagreement 
  by Sunday as to where the front is located. The GFS appears to  
  be the most aggressive in the southward push, with the  
  ECMWF/CMC/ICON somewhat slower (to varying degrees). Generally  
  used a consensus blend for now, and kept chance PoPs through  
  Monday morning in much of the area. Best chances appear to be  
  Saturday night through Sunday night, but this will likely need  
  some geographic and temporal fine-tuning as the event  
  approaches. 
   
  Given the oscillating position of the front and the series of 
  perturbations moving along it Saturday to Monday, there is 
  potential for an axis of heavy rainfall. All operational models 
  show a swath of 1-3 inches in a lengthy corridor from the 
  northern/central plains to the Mid-Atlantic, but this corridor 
  has displacement of 150-300 miles model to model. The ICON  
  blasts the Mid-Atlantic with a 2-4 inch soaking by early next  
  week, with the GFS/ECMWF keeping the heavier precipitation to  
  our west and the CMC keeping it to our north (though all show  
  potential of 1+ inch of rain in the CWA during this time  
  window). Antecedent dry conditions suggest the flooding  
  potential is on the lower side compared to similar setups in the 
  past. Nevertheless, will need to keep a close eye on this  
  period, as pattern recognition suggests the ingredients are  
  available for heavy rainfall. 
   
  Severe potential is also non-negligible during this time frame, 
  with regionally maximized bulk shear in proximity to the 
  perturbations and near the front. In combination with diurnal  
  heating, sufficiently cool midlevels, and storm organization 
  (as suggested by model QPF/vertical motion fields), the 
  ingredients may be available for some strong to severe storms 
  during this time frame as well. 
   
  Models appear to show the front sagging to the southern CWA or 
  farther south early next week but also indicate potential for 
  upstream perturbations to allow for its return as the week 
  progresses. Timing discrepancies and the stagnant pattern that 
  develops necessitate keeping PoPs for the rest of the long term 
  (though capped at low chance) and maintaining fairly seasonal  
  temperatures during this period. 
   
  && 

 

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Another good write up by Mt.Holly for today's severe potential and the severe/heavy rain potential over the next several days. Upton's write up not as detailed so won't bother posting.

.NEAR TERM /UNTIL 6 PM THIS EVENING/... 
  As of 3 AM, very weak surface ridging trying to develop over the  
  area with low pressure located well off the coast. The low level  
  flow has had an onshore component and this has resulted in a marine  
  layer with coastal fog once again this morning, especially along the  
  NJ coast where a Dense Fog Advisory remains in effect until 9  
  AM. Otherwise, a fairly quiet morning across the area.  
   
  Heading into the day Thursday, weak surface ridge quickly gives way  
  to a SW flow ahead of an approaching frontal system so expect fog to  
  mix out by mid morning. The main concern will then shift to  
  shower/thunderstorm potential with approaching front. At this point,  
  expect an initial area of some showers with possible embedded thunder  
  to move through mid to late morning as activity currently over Ohio  
  moving into western PA moves east and weakens with time. Don`t  
  expect this to produce any severe weather. Beyond this time there  
  should be a break before additional showers and storms re-develop  
  along an approaching pre-frontal trough and move through the area  
  west to east during the latter part of the afternoon. Forecast  
  models generally indicate 500-1000+ J/kg of ML CAPE over the  
  area by this time with the exact amounts depending on how much  
  sun breaks out between the two rounds of precip. In addition,  
  mid level flow looks to be around 40+ knots in the 700-500 mb  
  layer with 30+ knots near the top of the boundary layer. This,  
  along with a relatively dry layer in the mid levels suggests  
  damaging winds may be able to be brought down to the surface in  
  any storms...especially along and N/W of the I-95 corridor. In  
  fact, the Storm Prediction Center has upgraded most of our  
  forecast areas except the coast to a Slight Risk for severe  
  storms. Again, biggest threat looks to be damaging winds though  
  large hail also a possibility in any stronger updrafts. Highs  
  today will generally be in the 70s to around 80  
  degrees...coolest along the coast and over the southern Poconos. 
   
  &&  
   
  .LONG TERM /FRIDAY THROUGH WEDNESDAY/... 
  Main concern for the long-term forecast remains the evolution of a  
  meandering front across the northern Mid-Atlantic this weekend into  
  next week, with several rounds of convection potentially affecting  
  the area. 
   
  On Friday, the cold front will have progressed through much of the  
  CWA, with dry and somewhat cooler conditions expected. Used a  
  consensus blend of bias-corrected statistical guidance, which has  
  performed well in recent days. Not expecting significantly cooler  
  temperatures, as there will likely be ample sun and some warming via  
  downsloping. 
   
  Forecast becomes tricky starting Friday night, as weak midlevel  
  perturbations begin to progress eastward via quasi-zonal midlevel  
  flow. In advance of the first vort max, the cold front should begin  
  to return northward as pressure falls occur downstream. How far  
  north the front advances is somewhat uncertain, with models already  
  exhibiting some discrepancies by this point. Thinking is that the  
  front`s retreat northward is probably overdone (typical model bias),  
  with the 00Z ECMWF favored given its relative consistency with this  
  first event over the past several days. The heaviest precipitation  
  looks to be north and west of the area, but areas north of I-78 may  
  see some decent amounts by Saturday morning. The NAM and NAM Nest,  
  notably, bring a swath of 1+ inch rains in this area, but the  
  GFS/CMC are much farther north (New York). The ECMWF is slightly  
  farther south than the GFS/CMC, but not much, so kept QPF generally  
  a half inch or below in this area for now. Confidence in this  
  portion of the event is on the low side. 
   
  The second round of precipitation may come as early as Saturday  
  afternoon and evening, as combination of diabatic heating and  
  enhanced convergence around the lingering front may initiate  
  convection. There are reasonably strong hints of this in all of the  
  operational models, with subtle depictions of vorticity maxima  
  continuing through the region during this time. CAPE-shear parameter  
  space is suggestive of an environment favorable for some strong to  
  severe storms, though antecedent precipitation and lingering effects  
  on destabilization do not have me sold on the potential yet.  
  Nevertheless, the potential is there, with organizing processes  
  associated with the front likely to generate some increasingly  
  widespread showers/storms by Saturday night (with potentially  
  locally heavy rainfall). Aside from the somewhat dry GFS, the  
  NAM/CMC/ECMWF all depict 0.5-2 inch rainfall totals by Sunday  
  morning in much of the area (including the QPF from Friday  
  night/Saturday morning). My forecast is on the conservative side  
  (given the uncertainty in frontal placement, along with the drier  
  looking GFS), but with the potential for multiple rounds of  
  convection affecting the area by this point, I am a little concerned  
  about potential impacts by this point. 
   
  Sunday looks wet, with all models depicting more convection  
  affecting the area as the front begins to sag southward. Instability  
  looks to be more marginal by this point, with widespread  
  clouds/precipitation ultimately hindering development of more  
  substantial CAPE. Nevertheless, plentiful moisture will be available  
  (PWs 1.25-1.75 inches), and the frontal progression southward will  
  be slow. Heavy rainfall potential continues to be a concern through  
  this time, though the axis of maximum QPF becomes more uncertain.  
  The GFS looks most aggressive in the southward progression of the  
  front, which continues to look like an outlier. Nevertheless,  
  convective/mesoscale processes (poorly modeled in general) will  
  ultimately dictate the front`s evolution. So a broad-brush of chance  
  to likely PoPs looks prudent for most of the area at this time.  
  Trend has been for much lower temperatures Sunday compared to  
  Saturday, which makes sense given the anticipated  
  clouds/precipitation coverage. 
   
  There does seem to be a precip lull in most of the model output for  
  Monday and Monday night, so kept a relative minimum in PoPs for the  
  area during this time. The front may progress far enough southward  
  to keep the best chances out of the CWA. This also coincides with  
  trough passage to the north Sunday night, with upstream synoptic- 
  scale descent likely hindering much precipitation coverage during  
  this period. However, did keep mentionable PoPs given remaining  
  uncertainty and the front`s continued proximity to the area. 
   
  However, there are indications that precipitation chances will  
  increase again for much of the rest of the week (at least at times)  
  as more perturbations pass the area in the quasi-zonal midlevel  
  flow. Furthermore, an upper-level low in the Southeast is expected  
  to drift northward east of the Appalachians Tuesday through  
  Thursday. A lengthy southerly (moist) fetch will develop and extend  
  into the northern Mid-Atlantic, and the lingering boundary along  
  with a reinforcing cold front and attendant vort max mid-to-late  
  week will provide ample lift for widespread showers/storms. It is  
  during this period that flood potential will likely increase  
  markedly. Stay tuned. 
   
  && 

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I think that the earlier the squall line comes through, the better chance of getting stronger thunderstorms. I always get hit right around 8-9 PM. Also another factor is how quick the sun will burn through the fog this morning. 

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7 minutes ago, LIWeatherGuy29 said:

Are those storms going to hold together and hit Long Island or are they going to weaken?

Currently 57 degrees here.  

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Seems focused north of the stadium for the moment, running closer to the Bx westchester border. Its pouring here

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Some great lightning here in Queens is visible to the north and west. CGs and in cloud. Had an isolated cell out in front of main line just move through with some downpours and nice wind gusts. 

More impressive storm than all of last season already 

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