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Rtd208

Eastern US May 2019 Observations and Discussions

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Mt.Holly & Upton ref late week/weekend Temps, heavy rain/storms. Really excellent discussion from Mt.Holly

Mt.Holly:

 

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... 
  In "short," what a mess. 
   
  Starting with the convection ongoing in the central/southern 
  plains into the Midwest, the models performed noticeably  
  better than with the prior day`s convection, but there were  
  still some issues (mostly with convection allowing for  
  front/outflow boundary propagation displaced southeastward from  
  previous progs). Additionally, the models (hi-res and coarser  
  operational) whiffed on the long-lasting weak mesoscale  
  convective system moving from the Ohio Valley through much of PA 
  before dissipating in MD/DE and adjacent areas this evening. 
   
  I start with the above because, as discussed last night, the 
  relatively poor verification of convection (on Monday) has  
  wreaked havoc with the model forecasts (and trends) during the  
  past 24 hours and will likely continue today. For example, the  
  NAM surface pressure trends the past 24 hours have been for much 
  higher pressure in the Great Lakes/Northeast Thursday and  
  Friday (with implications of this to be discussed at length  
  below), and the GFS has trended with slightly lower pressure in  
  much of the Southeast through the period. The GFS has also  
  trended slightly weaker and faster with the ridging in the  
  eastern U.S. All of these trends make sense to me to some degree 
  given the delayed onset of widespread convection in the central 
  U.S. and the somewhat more progressive nature of the mesoscale  
  phenomena associated with the storms (and upscale effects on  
  larger-scale features). 
   
  There continues to be a sizable amount of disagreement of 
  timing/location of convection downstream in the eastern U.S. 
  associated with the plethora of perturbations convectively  
  generated or attendant to the widespread storms in the central  
  U.S. However, there appears to be some model convergence for  
  Thursday. Two perturbations appear to eject from the larger- 
  scale trough in the central U.S. The first comes Thursday  
  morning, with some showers/storms expected to initiate in  
  portions of the Northeast/Mid-Atlantic during the afternoon. The 
  00z NAM Nest develops some rather vigorous convection (with  
  hints of this in the 00z RGEM as well), and the environment is  
  certainly appearing increasingly favorable thermodynamically  
  (MLCAPE/SBCAPE approaching 1000 J/kg during the afternoon). With 
  deep-layer vertical shear of 30-40 kts, could at least see some 
  strong (perhaps a few severe) storms during peak heating. Exact 
  placement needs to be worked out, with some indications that  
  areas south of Interstate 78 appear most at risk. Notably, the  
  00z GFS/ECMWF develop convection in the northern Mid-Atlantic  
  during the afternoon as well, with precipitation lingering for  
  much of the night as the second perturbation approaches. 
   
  The big wild card will be what transpires upstream of these 
  perturbations. The 00z NAM blasts the region with onshore flow 
  and much cooler and more stable air by Friday (differences of 
  20+ degrees in surface temps; note the implications of higher  
  pressure in the northern U.S. mentioned above). Meanwhile, the  
  GFS and ECMWF are much warmer, inducing southerly flow as a  
  third perturbation approaches the region on Friday. Should these 
  latter solutions materialize, another line of loosely-  
  organized convection is expected to develop and move through the 
  area. However, the NAM solution would suggest more substantial  
  convection is in question and may be displaced south/west of the 
  area. Given what has transpired the past 24 hours, it is quite  
  difficult to discount the colder NAM solution and have at least  
  incorporated it into the temp/dew point forecast Thursday and  
  Friday. I also capped PoPs on Friday to chance given the large  
  discrepancies that have developed with the surface pattern among 
  the models. It is worthy of noting the NAM looks suspiciously  
  dry in the Northeast for much of this period and appears to be  
  an outlier with the convective evolution upstream as well. 
   
  For the weekend...the front appears to linger close enough to 
  the area to allow a potentially significant storm to affect the 
  area. The 00z GFS/ECMWF eject a southern-stream vort max from an 
  upstream/amplified trough in the plains (around 18z Friday) and 
  rapidly intensify it as it phases with a northern-stream 
  perturbation on Saturday and Saturday night. Rapid cyclogenesis 
  occurs in the Mid-South and Ohio Valley during this period, with 
  widespread convection expected to develop in its vicinity. This 
  system approaches the area Saturday night, so have increased 
  PoPs during this period substantially. 
   
  As could probably be deduced already, the temperature forecast 
  is subject to large errors given the huge uncertainty with the 
  surface pattern, especially Thursday night and Friday. Errors of 
  10 or more degrees are possible for much of the period. 
   
  && 
   
  .LONG TERM /SUNDAY THROUGH TUESDAY/... 
  The developing low to our southwest on Saturday appears to move 
  through or near our area on Sunday. Though the low remains 
  fairly weak from a sea-level pressure magnitude standpoint,  
  there will be a rather impressive setup for high QPF should the  
  00z GFS/ECMWF verify. With right-entrance region dynamics  
  provided by a retreating anticyclonic 250-mb jet streak in New  
  England and intensifying differential cyclonic vorticity  
  advection in the midlevels, the high-octane air provided by the  
  slowly retreating subtropical ridge in the eastern U.S. will  
  provide a highly favorable environment for heavy rainfall. The  
  QPF from the 00z GFS and ECMWF is quite impressive, with 1-2+  
  inch amounts in a 6-12 hour period in most of the CWA. That  
  spells flooding potential, and I have highlighted this in the  
  Hazardous Weather Outlook. There may also be potential for warm- 
  sector convection in portions of the CWA, but this is quite  
  uncertain since models are just beginning to converge on a  
  solution here. Notably, the CMC was discounted owing to its  
  suspiciously high influence of tropical convection in the  
  Bahamas. 
   
  Of course, a lot of uncertainty remains with the above scenario. 
  This involves phasing systems, a highly unpredictable 
  predecessor front, and antecedent convection allowing for the 
  synoptic-scale players to materialize. 
   
  There appears to be a brief break in the action Monday and 
  possibly Tuesday before another cold front approaches, perhaps 
  reloading a very similar pattern thereafter. 
   
  && 
   

Upton:

 

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Chances for light rain will increase tonight as a sfc warm
front approaches. Areas of fog should also develop mainly in
coastal sections and mainly after midnight as the warm front
nears, and this fog could become locally dense.

After dog burns off thu morning, big questions as to how far
north and east the warm front will lift through for a time on
Thu before a back door cold front pushes to the south and west.
There is about 20 degrees of spread between the coolest and
warmest model guidance, from the lower 60s to lower 80s across
NE NJ, and lower 50s to lower 70s across SE CT. Forecast takes
more of a middle ground approach between the NAM and ECMWF,
ranging from the mid 50s across eastern areas to near 70 in NE
NJ.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
A cloudy and wet pattern will persist across the area as deep layer
ridging remains firm over the western Atlantic and a long wave
trough lingers across the western U.S. The ridge axis then
retrogrades and rebuilds across the Central U.S. by early next week.
Initially the extended period will be dominated by southwesterly
flow aloft, advecting Gulf moisture into the region, with periods of
rain possible. Thereafter, troughing becomes more prevalent across
the Northeast as a result of the ridge building upstream.

For Thursday night, confluent flow aloft will shift offshore, with
the associated surface high following, allowing a back door cold
front to move through the area quite quickly overnight. The boundary
then stalls slightly to the west during the day time, through may
begin to return northward as a warm front as flow shifts to a more
southerly direction ahead of the next approaching front. There is
some uncertainty as to potential destabilization, depending on how
far the warm front can progress, but with height falls and the
quickly following cold front, there is potential for a rumble of
thunder across the interior. Expect temperatures to be coolest
across the coastal areas for Friday. Should the warmer guidance pan
out across the interior, temps over western zones could end up about
10-15 warmer than currently forecast.

The cold front then stalls offshore Saturday with a wave of low
pressure developing along it to our SW. The low eventually passes to
our south at some point Sunday into Sunday evening. This keeps the
threat of more rain through the entire period, but will cap PoPs at
50% this far out. If the low passes farther to the south on Sunday,
similar to the Canadian solution, then rainfall chances will be
lower than currently forecast.

A cold front then brings low chances of showers and Monday, then
will go with a dry forecast for Tuesday into Tuesday night as weak
high pressure builds in behind the front.

&&
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hoping for some nice warm weather this weekend...

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Wow the forums are really dead nowadays or is it just me.

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A warm front will push slowly northward tonight, bringing some drizzle, fog, and even showers to the region. In its wake, tomorrow will be variably cloudy with a risk of showers or even a thundershower. Readings will be much warmer than they were today. Some of the guidance suggests that temperatures in the mid-70s could extend as far north as New York City. The 80° isotherm could approach or reach Newark.

 

Farther south, temperatures could rise into the middle 80s in Washington, Baltimore, and even Philadelphia. Richmond could approach or reach 90°.

 

A strong backdoor cold front will then erase the warmth in the northern Middle Atlantic region, including Newark and New York City. Much above normal readings will persist in the greater Washington, DC area.

 

The ENSO Region 1+2 anomaly was 0.1°C and the Region 3.4 anomaly was +0.9°C for the week centered around April 24. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.05°C and the ENSO Region 3.4 anomaly has averaged +0.93°C. Conditions consistent with El Niño appear likely to persist through May in Region 3.4.

 

The continuation of El Niño conditions increases prospects for warm anomalies in the Middle Atlantic and southern New England areas.

 

During the 1981-2018 period, monthly mean temperature differences between cases when the ENSO Region 3.4 anomaly was +0.50°C or above and climatology were as follows:

 

Boston: 59.0° vs. 58.5° for climatology

New York City: 63.9° vs. 63.1° for climatology

Philadelphia: 65.2° vs. 64.3° for climatology

Washington, DC: 67.5° vs. 66.6° for climatology

 

The SOI was +9.06 today.

 

Today's preliminary value of the Arctic Oscillation (AO) was +0.096.

 

On April 30, the MJO was in Phase 4 at an amplitude of 1.829 (RMM). The amplitude was somewhat higher than the April 29-adjusted figure of 1.787.

 

Since 1974, there were four cases when the MJO reached an amplitude of 1.750 or above during Phase 2 during the April 20-30 period. The mean May 1-10 temperature was 58.8° vs. the 1981-2018 average of 60.2°. 75% of those cases were cooler than the 1981-2018 average. However, during May cases when the ENSO Region 3.4 anomaly was +0.50°C or above for the month, the May 1-10 temperature averaged 60.8°. Therefore, it is likely that the first 10 days of May will probably wind up with a mean temperature of 59.2°-61.2°. The latest guidance suggests a mean temperature around 59.4°.

 

Overall, May looks to be warmer than normal and wetter than normal.

 

Finally, from late yesterday into today, Detroit picked up 3.27" rain. That was Detroit's highest two-day precipitation total since September 28-29, 2016 when 3.34" rain fell.

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6 hours ago, Wxoutlooksblog said:

The weather here in the NYC Metro Region is so depressing I think few people even here would care to discuss it. If we do not briefly (I mean for like an hour or two) get into the warm sector tomorrow, we may not see the sun until sometime the middle of next week! Keep those umbrellas handy!

WX/PT

 

It's also depressing and miserable here. Seabreeze diarrhea all day yesterday and I'm just barely into the low 50s while 20 miles to the south is almost 70.

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I can see the weather turning on a dime by mid month from the cooler/wet conditions we are seeing now to warmer and more humid weather with the wet pattern continuing.

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4 hours ago, Rtd208 said:

I can see the weather turning on a dime by mid month from the cooler/wet conditions we are seeing now to warmer and more humid weather with the wet pattern continuing.

That would be climo but we'll see if it happens that soon. I'm not as optimistic.

WX/PT

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At 12 pm, temperatures in the Middle Atlantic region had warmed into the upper 60s and 70s in areas immediately away from the coastline.


Temperatures included:


Baltimore: 67°
New York City: 69°
Newark: 68°
Philadelphia: 60°
Richmond:78°
Washington, DC: 78°
Wilmington, DE: 68°


At present, it continues to look as if high temperatures could reach the mid-70s as far north as New York City and that the 80° isotherm could approach or reach Newark. Baltimore, Richmond, and Washington should see high temperatures in the 80s. The mercury could still make a run at 90° in Richmond.

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Current temp is 78 here.

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Current temp 79/DP 64/RH 54%

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Back door front working its way through, temp down to 64 here.

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Earlier today, the temperature surged well into the 70s from New York City southward and into the 80s across southern parts of the Mid-Atlantic region. High temperatures included:

 

Baltimore: 88°; Islip: 71°; New York City: 78°; Newark: 78°; Philadelphia: 83°; Richmond: 88°; and, Washington, DC: 87°.

 

With the frontal boundary's having pushed southward, a cooler day with readings in the upper 50s and lower 60s is likely across the northern Mid-Atlantic region tomorrow. However, readings in the 80s are still likely from Baltimore southward.

 

The ENSO Region 1+2 anomaly was 0.1°C and the Region 3.4 anomaly was +0.9°C for the week centered around April 24. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.05°C and the ENSO Region 3.4 anomaly has averaged +0.93°C. Conditions consistent with El Niño appear likely to persist through May in Region 3.4.

 

The continuation of El Niño conditions increases prospects for warm anomalies in the Middle Atlantic and southern New England areas.

 

During the 1981-2018 period, monthly mean temperature differences between cases when the ENSO Region 3.4 anomaly was +0.50°C or above and climatology were as follows:

 

Boston: 59.0° vs. 58.5° for climatology

New York City: 63.9° vs. 63.1° for climatology

Philadelphia: 65.2° vs. 64.3° for climatology

Washington, DC: 67.5° vs. 66.6° for climatology

 

The SOI was +11.74 today.

 

Today's preliminary value of the Arctic Oscillation (AO) was -0.107.

 

On May 1, the MJO moved into Phase 5 at an amplitude of 1.900 (RMM). The amplitude was somewhat higher than the April 30-adjusted figure of 1.843.

 

Since 1974, there were four cases when the MJO reached an amplitude of 1.750 or above during Phase 2 during the April 20-30 period. The mean May 1-10 temperature was 58.8° vs. the 1981-2018 average of 60.2°. 75% of those cases were cooler than the 1981-2018 average. However, during May cases when the ENSO Region 3.4 anomaly was +0.50°C or above for the month, the May 1-10 temperature averaged 60.8°. Therefore, it is likely that the first 10 days of May will probably wind up with a mean temperature of 59.2°-61.2°. The latest guidance has turned much warmer than the recent guidance. It now shows a mean temperature around 61.9°. That's somewhat above the range suggested by historical experience, so some cooling in the subsequent guidance is possible.

 

Overall, May looks to be warmer than normal and wetter than normal. Based on sensitivity analysis applied to the latest guidance, the implied probability of a warmer than normal month is currently 54%.

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Jet extension around mid-month should flip the PNA to positive and set up a trough in the east towards the 15th me thinks.

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Cooler conditions with some drizzle returned today as a front sagged south of the region. A few showers are likely tonight into tomorrow morning as a front pushes across the area. Afterward, partial sunshine could return for a time with readings rising into the middle and upper 60s.

 

A storm will likely track south of the region tomorrow night and Sunday. As a result, the New York City area and nearby suburbs will likely pick up 0.25"-0.75" rain with some locally higher amounts. A swath of 0.50"-1.00" rainfall with some higher amounts is likely farther south, including Atlantic City, Baltimore, Philadelphia, and Washington, DC. The implied probability of New York City's picking up 1.00" or more rain from this system are just under 30%.

 

The ENSO Region 1+2 anomaly was 0.1°C and the Region 3.4 anomaly was +0.9°C for the week centered around April 24. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.05°C and the ENSO Region 3.4 anomaly has averaged +0.93°C. Conditions consistent with El Niño appear likely to persist through May in Region 3.4.

 

The SOI was +0.02 today.

 

Today's preliminary value of the Arctic Oscillation (AO) was -0.417.

 

On May 2, the MJO was in Phase 5 at an amplitude of 1.666 (RMM). The amplitude was somewhat lower than the May 1-adjusted figure of 1.898.

 

Since 1974, there were four cases when the MJO reached an amplitude of 1.750 or above during Phase 2 during the April 20-30 period. The mean May 1-10 temperature was 58.8° vs. the 1981-2018 average of 60.2°. 75% of those cases were cooler than the 1981-2018 average. However, during May cases when the ENSO Region 3.4 anomaly was +0.50°C or above for the month, the May 1-10 temperature averaged 60.8°. Therefore, it is likely that the first 10 days of May will probably wind up with a mean temperature of 59.2°-61.2°.

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