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E PA/NJ/DE Spring 2019 OBS Thread


Rtd208
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Mt.Holly and Upton ref Sunday/Monday.

Mt.Holly:

 

  .SHORT TERM /SUNDAY/... 
   
  For Sunday,  major low pressure system continues to lift northward  
  to our west reaching Lake Erie by late day. This will continue to  
  draw the warm front north through the area with the most 
  noticeable affect by afternoon being the increased dew points  
  as they will be in the 60s making it feel quite humid. Due to  
  the winds being more S/SE as opposed to SW this will tend to  
  keep low level moisture locked in through the boundary layer so  
  not expecting much sunshine. Conditions should be mainly cloudy  
  with lingering areas of drizzle and mist along with some  
  scattered showers as weak impulses aloft move through. It  
  shouldn`t be raining all day though and heavier showers and  
  storms should stay to our west through the daytime hours. Highs  
  will be mainly in the low to mid 70s except 60s across the  
  southern Poconos and NW NJ.  
   
  && 
   
  .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... 
   
  Overview... A mid-lvl trough and associated surface low will  
  lift just north of the area at the start of the long term  
  period, with the system`s cold front passing through the area  
  Monday morning. Behind this system low-amplitude (mid-lvl)  
  ridging will begin to develop by the middle of the week,  
  although the presence of a stationary front near the area will  
  result in a least a chance of precipitation during this period.  
  The next amplified trough/closed low will begin to make its way  
  towards the area towards the end of the workweek.  
   
  Dailies:  
   
  Sunday night-Monday morning: This will be an active period as  
  the mid-lvl trough currently over Texas progresses towards the  
  area, and the attendant surface low passes in the vicinity of  
  Lakes Eerie/Ontario. Expect that most of the action will be  
  centered around the passage of the system`s cold front Sunday  
  night into Monday morning. The combination of deep layer  
  moisture (PWATS near 1.5 inches) ahead of the front, modest mid- 
  lvl lapse rates, and impressive kinematic profiles (60 + kts of  
  bulk shear, > 50 kts of 0-3 km shear) will result in a severe  
  threat with the frontal precipitation band. Much will be  
  dependent upon how much surface-based instability can be  
  manifested along and slightly ahead of the convective line, as  
  this is always questionable in these nocturnal events. There is  
  some isolated tornado threat given 0-1 SRH values approaching  
  300 m2/s2 and sub 1000m LCLs, however, given the linear  
  convective mode the main threat will be straight-line winds. The 
  GFS is the fastest with advancing the cold front (bringing it  
  through in the 00-06Z time frame), however, leaned towards the  
  slower high-res consensus solution this forecast package, which  
  brings the bulk of the line into the area between 06-12Z (from  
  west to east).  
   
  In addition to the severe threat, given the high  
  PWATs/sfc.dewpoints can`t rule out a flooding rain threat  
  particularly in areas of eastern PA/NW NJ that received  
  significant rain with the Friday night-Saturday morning system.  
  The mitigating factor for hydro concerns will be the fast  
  forward motion of the system.  
   
  Monday: Drier air will filter in behind the cold front with  
  precipitation tapering off over most of the area by late  
  morning. The potential exception will be the Poconos/NW NJ where 
  some light backside precip may develop Monday afternoon as the  
  mid-lvl trough axis slides by. The main story during the day  
  Monday will be gusty west-northwest winds behind the cold front. 
  Given solid cold advection in the 925-850 layer, combined with  
  40-45 kts of flow at 850 expect fairly widesperad wind gusts of  
  30-35 kts Monday afternoon with gusts 35-40 kts also possible.  
  Temperatures will be a bit cooler than Sunday but good mixing  
  along with scattering clouds should keep maxes near if not  
  slightly above normal. 

Upton:

 

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/...
East coast upper ridging will exist, ahead of a strong southern
upper low over Texas shearing ne and interacting with a PAC
shortwave moving towards the Great Lakes. The associated
amplified shortwave trough will slide towards the east coast
Sunday Night and then negatively tilt through the region Monday.
Its resultant strengthening low pressure system will lift into
the Ohio Valley Sunday and the eastern Great Lakes and
Adirondacks Monday, with cold front approaching the region
Sunday Night and pushing through the region Monday morning.

On Sunday, a Canadian maritime airmass will be in place, with e
flow and a strong inversion promoting stratus maintenance and
areas of drizzle ahead of an approaching warm front. Temps will
likely remain near seasonable, generally around 60 se coastal
sections to mid 60s interior.

LLJ strengthens late Sunday into Sunday Night with warm front
most likely pushing north of the region in the aft/eve.
Scattered showers possible with warm frontal passage, and then iso-
sct showers and possibly a tstm in warm sector in the evening.
Main action may be with band/s of heavy rain showers and
embedded thunderstorm late Sunday Night into Monday morning in
response to deep layered lift and convergence of a +3-4 std pwat
subtropical moisture plume ahead/along the approaching cold
front. A general 3/4 to 1 1/2 inches of rain is likely, with
locally higher amounts where any training occurs. See hydrology
sections for impacts.

Additionally, potential exists for isolated strong
thunderstorms to be able to mix down the strong winds aloft to
the ground, particularly west of the Hudson River where some
weak surface instability is indicated ahead of the cold front.
If any stronger storms develop in this high shear/low cape
scenario, there is potential for rotation, but the potential is
very low. Further east, a stronger low-level inversion will
likely limit potential for downdrafts to mix to surface. If SPC
HREF mean elevated instability is correct though, indicating
borderline moderate elevated instability, the threat for strong
thunderstorms would increase.

Cold front and frontal rain band moves east Thursday morning,
with shortwave axis and secondary cold front moving through in
the afternoon. Scattered shower potential will likely continue
in cyclonic flow until trough passage. Otherwise, windy
conditions developing Monday afternoon and continue into Monday
Night with NW winds of 20 to 30 mph and gusts of 40 to 45 mph
likely, with isolated gusts to 50 mph possible.

&&
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31 minutes ago, hazwoper said:

You don’t need clear skies in this setup.  Just ask the folks in N Nc and S Va currently under TOR warnings and been socked in with clouds

Look at the batch that's actually going to hit us. Looks like maybe a rumble of thunder, let alone severe. Sticking with some rain but overall NBD.

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16 minutes ago, The Iceman said:

Look at the batch that's actually going to hit us. Looks like maybe a rumble of thunder, let alone severe. Sticking with some rain but overall NBD.

The SPC severe threat isn’t until overnight here. Guess we’ll see.  It’s about wind and isolated tornadoes anyway, not typical summer severe/fropa 

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2 hours ago, hazwoper said:

The SPC severe threat isn’t until overnight here. Guess we’ll see.  It’s about wind and isolated tornadoes anyway, not typical summer severe/fropa 

SPC going all out with tornado watches south of the Mason Dixon line. I wonder if the trend will continue into our neck of the woods, now that we're going to start losing the diurnal heat. Tricky setup, but yeah it also appears to me that they're being overly cautious given what's on the radar and the marginal CAPE and LI values.

 

*Edit: However, nearly every meso model has us under the gun from like 3-6am.

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Pretty interesting discussions from Mt.Holly and Upton for late week/next weekend.

Mt.Holly:

 

 .LONG TERM /TUESDAY THROUGH SUNDAY/... 
  An unsettled period of weather is set for midweek as we have a warm  
  front draped across the region. The warm front lifts into the area  
  on Tuesday but starts to stall, leaving it draped across the region.  
  The front is likely to wobble a bit north and south before it  
  finally starts to move northward on Thursday. A strong cold front  
  will then approach from the west and cross the region as we  
  head into the weekend.  
   
  Tuesday looks to be the driest day of the period as the front starts  
  to develop to our west. As the front starts to push east and into  
  our area, we may see some showers develop later in the day, mainly  
  over the northwestern areas, before starting to spread across much  
  of eastern Pennsylvania and northern and central New Jersey. Even as  
  we head through Wednesday, best chances for rain will exist north  
  and west of the I-95 corridor as the front remains nearly stationary  
  and multiple shortwaves track along the boundary. The airmass  
  appears to remain fairly stable so no thunderstorms are expected at  
  this time. Areas across Delmarva and southern New Jersey are  
  expected to remain mostly dry through Tuesday and Wednesday as high  
  pressure to our south should be strong enough to continue to  
  influence their weather.  
   
  The front finally lifts to the north later Thursday into Friday as  
  low pressure over the midwest starts to move to the east. This low  
  will track up through the Great Lakes region and then into eastern  
  Canada by late Friday. The associated cold front will start to move  
  into our area on Friday. Showers and thunderstorms will be possible  
  ahead of the fronts arrival on Friday night, and then will continue  
  with the frontal passage into Saturday. The front looks to be strong  
  as it arrives just after peak heating and conditions are expected to  
  be fairly unstable. A very tight gradient will exist on Friday so  
  expect rather gusty southerly winds to occur through the day.  
   
  The cold front exits offshore on Saturday morning but a secondary  
  cold front follows behind along with the deep upper low/trough. This  
  may result in more showers and thunderstorms through Saturday. We  
  may not clear out that quickly on Sunday as the upper low/trough  
  moves through the area and then moves offshore Sunday night into  
  Monday. 
   
  && 

Upton:

 

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Upper flow briefly flattens out to start the period with an
upper low departing from the Canadian Maritimes. At the same
time, a trough moves into the desert southwest. Later in the
week, this feature will interact with northern branch energy,
sending a frontal system into the area for the end of the week
into the weekend. There is very good agreement with the 12Z
ECMWF and GFS with the extent of phasing of the two branches and
the progression of the aforementioned frontal system. The GGEM
is a bit more progressive, especially with the lead frontal band
precipitation Friday night into Saturday morning.

A consensus forecast approach brings high pressure into the
region Tuesday into Wednesday with a warm front approaching from
the southwest. Prior to that time, gusty W winds will follow on
the heels of deepening low pressure tracking northeast across
the Canadian Maritimes. There could be some gusts up 30 kt
through early Tuesday afternoon as winds gradually subside with
high pressure building in from the west.

There is a low chance of rain working in from the southwest
Tuesday night. However, unlike 24 hours ago, it appears
Wednesday will be dry as ridging builds in both aloft and at the
surface. The northward progress of the warm front will likely
be very slow due to an amplified ridge building along the
eastern seaboard as the upper trough amplifies across the mid
section of the country.

Warm frontal passage has trended faster in the global guidance,
lifting north of the region by daybreak Friday. A deep-layered
southerly flow develops along the east coast as the upper ridge
slowly translates east Thursday into Friday. A strong low-level
jet ahead of the approaching cold front supports moderate to
heavy warm conveyor belt rains with embedded thunderstorms late
Friday night into the first half of Saturday. There will likely
be timing changes through the week as the Pac jet energy has yet
to move onshore. Additionally, a strong onshore flow Friday
into Saturday will likely result in areas of stratus and fog,
especially east of the Hudson River. Dew points are forecast to
be in the 50s, but this may be conservative.

Scattered showers may linger into Sunday depending on how
quickly the upper trough/low passes through the area.

As for temperatures, daytime highs will be near seasonable
levels through Thursday before a warm frontal passage Friday
morning. Lows will be several degrees above normal due to
onshore flow and potential for stratus/fog. Following the warm
front, warmer, humid conditions are likely with areas away from
the coast getting into the 70s.

&&

 

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