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Subtropical Moisture Heavy Rain Potential 5/16-5/17


bluewave

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I shouldn't be ridiculed when I make a post about cool 850mb temps on day 6.

All the models have it and it's well advertised.

That's my main point. It always seems as if every single one of my posts is heavily scrutinized.

Now later Bluewave will post a day 7 map of the Euro ensemble mean and nobody will bat an eyelash.

It's pretty simple..bluewave is very well respected and you are not

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.HYDROLOGY...
THE PW VALUES ARE FORECAST TO SURGE INTO THE 1.5 TO 1.8 INCH RANGE
FRIDAY AHEAD OF A COLD FRONT GRADUALLY SHIFTING ACROSS OUR AREA AS A POTENT 850-925 MB SOUTHERLY JET MOVES THROUGH. THE MODEL GUIDANCE
INDICATES A RAPID INCREASE IN 850 MB THETA-E ADVECTION, HOWEVER THIS
IS GENERALLY WITHIN IN A NARROW CORRIDOR. IN ADDITION THE 850 MB
TEMPERATURES ARE FORECAST TO INCREASE TO ABOUT +10C AHEAD OF THE
FRONT, WHICH IS TYPICALLY A SIGNAL FOR VERY HEAVY RAIN. THE ENHANCED
LIFT WITHIN THE LOW-LEVEL JET, THETA-E AND THERMAL RIDGES SHOULD
RESULT IN A BAND OF HEAVY SHOWERS AND POTENTIALLY SOME EMBEDDED
THUNDER. IT IS PROBABLY IN THIS ZONE WHERE THE HEAVIER RAIN OCCURS
OVER A SHORTER PERIOD OF TIME.

IT STILL LOOKS LIKE THE MAIN AXIS OF MODERATE TO HEAVY RAIN OCCURS
BETWEEN 12Z FRIDAY AND 00Z SATURDAY. THE FLASH FLOOD GUIDANCE IS
BETWEEN 1 AND 2 INCHES FOR A 3 AND 6 HOUR PERIOD ACROSS MUCH OF
SOUTHEASTERN PENNSYLVANIA, NORTHERN DELAWARE AND EXTENDING
NORTHEASTWARD INTO CENTRAL AND NORTHERN NEW JERSEY. AS OF NOW, A
GENERAL 1 TO 2 INCHES OF RAIN IS EXPECTED WITH THIS SYSTEM ACROSS
THE REGION. LOCALLY HIGHER AMOUNTS ARE CERTAINLY POSSIBLE, WITH THE
BEST CHC FOR HIGHER TOTALS ACROSS THE WEST AND NORTHWEST PART OF THE
CWA DUE TO SOME ASSISTANCE BY OROGRAPHIC LIFT /SOUTHEASTERLY
INFLOW/. THE MAIN STEM RIVERS ARE EXPECTED TO HAVE NO ISSUES,
HOWEVER SOME SMALL STREAM /ESPECIALLY THE FAST RESPONDERS/ AND URBAN
RELATED FLOODING IS POSSIBLE. THIS WOULD BECOME LOCALLY ENHANCED IF
BURSTS OF RAIN OCCUR IN A SHORTER PERIOD OF TIME. WHILE THE
THREAT FOR WIDESPREAD FLOODING IS LOW, A FLASH FLOOD WATCH MAY BE
NEEDED FOR PORTIONS OF THE REGION ESPECIALLY IF ENHANCED RAINFALL
AMOUNTS/RATES LOOK TO OCCUR IN AN EVEN SHORTER PERIOD OF TIME. AS
OF NOW, WE OPTED TO HOLD OFF ON A FLASH FLOOD WATCH.

 

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There might be quite a bit of rain in some of the upslope areas in central and eastern PA, even N NJ and NY. The SE flow out ahead of the front will ride up the slopes of the mountains and aid in heavy rain amounts. I think 2-4" of rain if not more is a good bet in these areas.

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WPC was discounting the lower EURO totals just 24 hours ago BUT now they definetly have to be considered

If what's going on today over the Carolina's is any indication of what we can expect we're in for a deluge. 06z NAM only had 1.50"-2.00" and many areas are already at 2"+ as estimated by radar. One hour estimates are 2-4" per hour in spots east of Columbia this morning. This has flash flooding potential written all over it. Hence why Mt. Holly has issued a flash flood watch for most of its zones away from the coast.

 

Flash Flood Watch
FLOOD WATCHNATIONAL WEATHER SERVICE MOUNT HOLLY NJ356 AM EDT THU MAY 15 2014DEZ001-MDZ008-NJZ008>010-012-015>019-PAZ070-071-101>106-152030-/O.NEW.KPHI.FF.A.0002.140516T1200Z-140517T0600Z//00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/NEW CASTLE-CECIL-MORRIS-HUNTERDON-SOMERSET-MIDDLESEX-MERCER-SALEM-GLOUCESTER-CAMDEN-NORTHWESTERN BURLINGTON-DELAWARE-PHILADELPHIA-WESTERN CHESTER-EASTERN CHESTER-WESTERN MONTGOMERY-EASTERN MONTGOMERY-UPPER BUCKS-LOWER BUCKS-INCLUDING THE CITIES OF...WILMINGTON...ELKTON...MORRISTOWN...FLEMINGTON...SOMERVILLE...NEW BRUNSWICK...TRENTON...PENNSVILLE...GLASSBORO...CAMDEN...CHERRY HILL...MOORESTOWN...MOUNT HOLLY...MEDIA...PHILADELPHIA...HONEY BROOK...OXFORD...WEST CHESTER...KENNET SQUARE...COLLEGEVILLE...POTTSTOWN...NORRISTOWN...LANSDALE...CHALFONT...PERKASIE...MORRISVILLE...DOYLESTOWN356 AM EDT THU MAY 15 2014...FLASH FLOOD WATCH IN EFFECT FROM FRIDAY MORNING THROUGH LATEFRIDAY NIGHT...THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY HAS ISSUED A* FLASH FLOOD WATCH FOR PORTIONS OF NORTHERN DELAWARE...  NORTHEAST MARYLAND...NEW JERSEY AND SOUTHEAST PENNSYLVANIA...  INCLUDING THE FOLLOWING AREAS...IN NORTHERN DELAWARE...NEW  CASTLE. IN NORTHEAST MARYLAND...CECIL. IN NEW JERSEY...  CAMDEN...GLOUCESTER...HUNTERDON...MERCER...MIDDLESEX...  MORRIS...NORTHWESTERN BURLINGTON...SALEM AND SOMERSET. IN  SOUTHEAST PENNSYLVANIA...DELAWARE...EASTERN CHESTER...EASTERN  MONTGOMERY...LOWER BUCKS...PHILADELPHIA...UPPER BUCKS...  WESTERN CHESTER AND WESTERN MONTGOMERY.* FROM FRIDAY MORNING THROUGH LATE FRIDAY NIGHT* PERIODS OF HEAVY RAIN WITH POSSIBLE EMBEDDED THUNDERSTORMS ARE  EXPECTED TO DEVELOP FRIDAY MORNING AND CONTINUE INTO FRIDAY  NIGHT. A GENERAL 1 TO 2 INCHES OF RAINFALL IS EXPECTED...WITH  LOCALLY HIGHER AMOUNTS. FLASH FLOODING IS POSSIBLE ALONG SMALL  RIVERS AND STREAMS AND ALSO IN URBAN AREAS, ESPECIALLY IF THESE  RAINFALL AMOUNTS ARE MET OR EXCEEDED IN A 6 HOUR PERIOD OR LESS.PRECAUTIONARY/PREPAREDNESS ACTIONS...A FLASH FLOOD WATCH MEANS THAT CONDITIONS MAY DEVELOP THAT LEADTO FLASH FLOODING. FLASH FLOODING IS A VERY DANGEROUS SITUATION.YOU SHOULD MONITOR LATER FORECASTS AND BE PREPARED TO TAKE ACTIONSHOULD FLASH FLOOD WARNINGS BE ISSUED.
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09z SREF's are fairly dry now south and east of NYC

 

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I would be careful of using the SREF beyond 48 hours, it is like a clown car full of NAM models and how much do people trust the NAM beyond 48hr. Furthermore at this range the individual models within the SREF are susceptible to being overly convective.

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Beyond 48 hours?

He posted a QPF map through 75 hours and yes the majority falls before 48 hours but there is add on after 48 hours and with a large upper low the individual SREF members are going to have a hard time picking up on what locations might see enhanced rainfall with it.

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Yes but all of the rain falls in the first 48 hours or less. I thought that was understood.

Yeah I edited my post to clarify, as it stands though the individual members still tend to be overly convective in situations like this as you can see some are showing 4-6" over the mountains for example.

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Yeah I edited my post to clarify, as it stands though the individual members still tend to be overly convective in situations like this as you can see some are showing 4-6" over the mountains for example.

Understood.

 

What I don't understand is why just about all the models are weakening the convection as it approaches the region.

 

RH and VVEL are through the roof so to speak and the LLJ looks favorable for moisture transport.

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Understood.

 

What I don't understand is why just about all the models are weakening the convection as it approaches the region.

 

RH and VVEL are through the roof so to speak and the LLJ looks favorable for moisture transport.

BC it runs into the ridge in the Atlantic which is pushin west

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