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Rtd208

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  1. @wdrag Current Mt. Holly discussion for the late week storm. Still not hitting the wind potential to hard but coming around to the heavy rain idea. Upton has similar thoughts.

    .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... 
      A mid and upper level short wave ridge briefly builds over our 
      region on Thursday, resulting in tranquil and dry conditions. An 
      onshore northeasterly/easterly flow through the day will mean 
      temperatures may be a degree or two lower than today, but still 
      near normal with highs from the mid 50s to mid 60s.  
       
      After Thursday, our attention turns to the next closed low. This 
      low will be taking an inland track from the lower Mississippi 
      Valley to the northeastern U.S. from Thursday into Saturday. 
      Compared to the model runs 24 hours ago, there are some stark 
      differences with the latest runs. For one, most guidance is a 
      bit slower with the precip entering our region, as much of the 
      region may stay dry through Thursday night. The most notable 
      change though was that many of the operational models now show  
      a brief period of cyclogenesis on Friday as the low is centered  
      to the SW of our region (with yesterday`s run, the low was  
      filling/weakening as it approached our region). This could set  
      the stage for a low level southeasterly jet on the order of 40  
      to 60 kt progressing over our region from Friday afternoon to  
      Friday evening.  
       
      If this happens, that would result in significant moisture  
      transport coincident with the best synoptic scale lift,  
      resulting in an increased risk for heavy rain and flash  
      flooding. Not surprisingly, model soundings show precipitable 
      water values well above normal and mean RH values close to 100 
      percent through this time. If this solution develops, the area 
      most at risk for heavy rain would likely be the 95 corridor, and 
      locations just south and east of the fall line (as the low level 
      jet impacting the fall line could result in additional lift due 
      to orographic lift). Thus, I have added in a mention of heavy  
      rain in the grids generally along and SE of the 95 corridor. If 
      there is a silver lining in this solution it is that the area 
      most at risk with this event should be south and east of areas 
      that were the most impacted with the Monday night/Tuesday rain. 
       
      The other thing to watch for in these patterns is the potential 
      for the winds in the low level jet to mix down to the surface 
      resulting in strong winds. At this point, momentum transfer 
      during this period looks poor, so even if this solution were to 
      develop, it appears unlikely that there would be widespread wind 
      gusts of 45 mph+ (wind advisory criteria) on land. 
       
      All that being said, I have hesitation going completely with  
      this solution. In addition to this being a new trend, it is also 
      highly dependent on the location of the entire vertical profile 
      of the low. Small changes in the position, even in just one  
      level of the atmosphere could result in big changes of the net 
      impacts. Thus, will hold off on any flood watches or additional 
      messaging for at least another model run cycle to see if this 
      trend continues. 
       
      && 

     

  2. @wdrag Mt. Holly doesn't seem to be overly impressed with the next system per their morning discussion. 

    .LONG TERM /FRIDAY THROUGH MONDAY/... 
      The main focus through this period is on the closed low that will be  
      progressing from the lower Mississippi Valley into the northeastern  
      U.S.. This should bring a round of rain starting possibly as early  
      as Thursday night and continuing until the dry slot arrives on  
      Saturday or Saturday night. At this point it doesn`t appear to be as  
      high impact as our current coastal low since this low will not only  
      be taking an inland track, but should also be weakening and filling  
      as it crosses the Mid Atlantic. Once this system lifts away, a cold  
      front could approach our region early next week, though it may not  
      arrive until Tuesday or Tuesday night of next week. 
       
      && 
  3. 4 minutes ago, wdrag said:

    Wont change title numb ens despite being close to that for just the first storm.  I think I want to see what we have on the ground by 8P Tue before I 2" to the weekly total.  I think we have our hands pretty full with Tuesday-Tuesday night. 

    @wdrag any additional thoughts on the Friday/Saturday storm?

  4. Upton also hitting the late week/weekend system hard in their Hydrology Discussion.

    Rainfall of at least 1 to 3 inches, and possibly as high as 2 to 4
    inches, will accompany a slow moving low pressure system late
    Thursday night through Saturday night. The potential for the
    heaviest rainfall looks to be Friday night into Saturday afternoon.
    Impacts will depend greatly on antecedent conditions from the storm
    impacting the region early this week. At least minor impacts can be
    expected.
    • Like 1
  5. Discussions from Mt. Holly and Upton.

    Mt. Holly:

     

    .NEAR TERM /THROUGH TUESDAY/... 
      This remains a low confidence but potentially high impact forecast.  
      The main features to watch over the next 24 to 36 hours are the  
      closed low currently over the mid Mississippi Valley, the warm front  
      currently bisecting our region, and a mid level short wave trough  
      which was over AL/GA as of the 00Z soundings. The interaction of  
      these features is what is expected to result in cyclogenesis later  
      today off the GA/SC coast which will become the coastal storm to  
      impact our region tonight continuing through Tuesday. 
       
      As mentioned above, this is a low confidence forecast. The warm  
      front is much slower than any of the models had depicted even with  
      the 00Z runs. I am also concerned that at least some models appear  
      to have initialized with the center of the mid level low too far  
      south and east compared to what 00Z soundings and satellite trends  
      would suggest. If there is in fact more separation (distance wise)  
      between the mid level short wave trough and the closed low, then it  
      is possible the coastal low will develop further off shore.  
      Cyclogenesis occuring entirely off the coast is already a  
      notoriously high uncertainty pattern, and the previously mentioned  
      trends just add to my uncertainty with this forecast. 
       
      That being said, this has the potential to be high impact for our  
      region, so here is a summary of the potential hazards through  
      Tuesday: 
       
      Heavy rain: Heavy rain at this point is my biggest concern, and the  
      area of concern hasn`t changed much, generally favoring coastal NJ.  
      There is potential that the axis of heaviest rain could be slightly  
      further south along the southern NJ shore, so Cape May and Atlantic  
      counties were added in to the watch. Additionally, based on guidance  
      trends, increased the QPF slightly.  
       
      Severe Thunderstorms: Limited instability, but significant shear  
      (both speed and directional shear) means that there is potential if  
      any thunderstorms (or even just showers with a stronger updraft)  
      develop, that stronger winds could mix down to the surface.  
       
      As far as timing, expect most of today to be dry, but some initial  
      showers could move in or develop (especially if the warm front is  
      still in the area) by late in the afternoon. The bulk of the rain  
      should be from late this evening through much of the day on 
      Tuesday. 
       
      && 
       
      .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... 
      Major storm just off the coast will be in the process of pivoting  
      eastward Tuesday night and Wednesday as a digging vort max reaches  
      the Mid-Atlantic. As it reaches the base of the longer-wave trough  
      around 12z Wednesday, the orientation of the vorticity maximum will  
      allow for the increase in eastward momentum of the main upper low by  
      Wednesday afternoon. Of course, a number of questions remain about  
      this process, since the interactions among the various perturbations  
      and the predecessor impacts of widespread precipitation/convection  
      in tandem with the rapidly deepening low are generally low- 
      predictability phenomena. Nevertheless, with the notable model  
      trends on keeping the low closer to the coast and for a little while  
      longer, suspect stronger winds will linger near the coast for a time  
      Tuesday night and Wednesday morning, with gusts exceeding 35 to 40  
      mph probable along the immediate coast. Not out of the question a  
      wind advisory will be needed for these areas. Additionally, showers  
      will likely rotate south-southeastward on the west side of the low  
      in much of the area Tuesday evening, slowly shifting eastward as the  
      low begins its inevitable acceleration offshore. By Wednesday, most  
      if not all of the precipitation should be done for the region, with  
      breezy north winds also gradually declining during the day. Highs on  
      Wednesday should range from the mid 50s in the Poconos to the mid  
      60s in Delmarva. 
       
      Sky cover may diminish Wednesday night as north to northeast winds  
      slowly decrease, which may be favorable for some stronger cooling  
      than on the previous night. Still, think winds will not completely  
      decouple, so forecast lows are mainly in the mid 40s to around 
      50. 
       
      && 

    Upton:

     

    .NEAR TERM /THROUGH TONIGHT/...
    With a warm front north of the area for today, some mid level
    ridging will be allowed to momentarily take place. A deep layered
    southwesterly flow regime sets up for today allowing temperatures to
    warm. As a result dew points readings will get into the lower and
    even a few middle 60s, which is rather humid for late October. There
    will be some instability into the afternoon and early evening,
    however due to an overall lack of forcing not expecting really
    anything impactful in terms of sensible weather through the day.
    
    By this evening the jet axis begins to round the base of the upper
    level trough off to our west as it swings east. As this occurs the
    stronger mid and upper level forcing will begin to get underway.
    This should result in moderate to heavy rain to develop towards and
    after midnight across the area. Much of the guidance has a potent
    mid level shortwave pivoting through during the the overnight
    period, followed quickly by strong PVA at 500 mb into Tuesday
    morning. The winds at 850 mb also begin to back from the south to
    more out of the east. A strong LLJ gets into the region into the day
    on Tuesday with a double barrel low type structure. The exact
    placement and interactions of the low(s) will determine the
    intensity of the LLJ, thus determining where the axis of heavier
    rainfall will take place. Also there is the potential for strong
    winds. With the low levels becoming more stabilized it will be
    difficult to get the stronger winds down to the surface, at least
    initially. With some elevated instability and a strong LLJ
    developing into Tuesday morning expect more organized heavy rainfall
    along with embedded convective elements, a few rumbles of thunder
    are possible, if not likely. Over an inch of rain widespread across
    the area is looking increasingly likely from midnight to the Tuesday
    morning commute.
    
    &&
    
    .SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
    Strong forcing due to a strong WAA pattern and the potential for 50
    kt or greater easterly winds at 850 mb, along with strong PVA as the
    upper level trough axis and 500 mb low gets just south of the area.
    This should keep the best lift over the area with periods of heavy
    rain throughout much of the day on Tuesday. Some guidance does have
    some drying occurring in the mid levels late Tuesday into Tuesday
    evening. This will depend on the exact placement of the area of low
    pressure. If the low gets further north then some dry slotting may
    occur which could bring some of the heavier rain to an end maybe a
    few hours earlier than expected. In any event, a significant
    rainfall event looks like a proverbial lock due to the deep and
    strong WAA / Carlson conveyer belt set up. A strong LLJ gets going
    during the day on Tuesday, with the model guidance of the LLJ
    placement and intensity varying. Have issued a Wind Advisory for far
    eastern sections of CT and LI for late Tuesday and Tuesday night.
    There is the potential as the low deepens further and one low begins
    to take over that the winds could peak at 45 to 50 mph across far
    eastern sections with the winds more out of the northeast and north.
    The mostly likely time for this would be during Tuesday evening and
    into the first half of the overnight as the low may get slightly
    further to the east. The heavier rain would then end from west to
    east based on the latest timing. With the center of circulation
    potentially getting further east as the low gets more vertically
    stacked the storm should get to its peak in terms of intensity and
    lower surface pressure readings. Rainfall totals as this time look
    to be on the order of 2 to 4 inches. HREF 24 hr. PMM QPF has
    localized amounts of 5 to 7 inches which is tough to come by.
    Hopefully this scenario does not come to fruition as this would lead
    to widespread flooding issues. Thus continuing with the Flood Watch
    across the entire area for tonight into the day on Tuesday.
    
    On Wednesday the low will gradually get further offshore, especially
    by the afternoon. The current thinking has chance POPs giving way to
    slight chance POPs from west to east through the day as the back
    edge of any rainfall begins to pivot off to the east. With
    completely dry conditions returning by the late day and evening with
    mostly cloudy skies giving way to some clearing during this time
    frame. A gusty northerly flow will have temperatures running near
    normal with mainly lower 60s for afternoon highs.
    
    &&
  6. The NYC metro should see a widespread 1-3" rainfall w/locally higher amounts especially as you head further north and east. Severe weather also possible tomorrow night into the first half of Tuesday. I think the SPC may eventually go with a slight risk for the area. We'll see. Wednesday could be a windy day behind the system. 

    Storm #2 Friday into Saturday details TBD but potentially stronger and more impactful then storm #1??

    The fuse was light and the active pattern has now exploded after an extended break post Ida.

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