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february 25 rain storm


earthlight

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Also from Mt. Holly

HYDROLOGY...

-- Changed Discussion --WHILE A FLOOD WATCH MAY EVENTUALLY BE NEEDED FOR THE UPCOMING

EVENT...WE WILL FORGO THE WATCH WITH THIS PACKAGE...AND WATCH MODEL

TRENDS FOR THE PLACEMENT OF THE AXIS OF HEAVIEST RAIN.

MODEL CONSENSUS AND HPC QPF FORECASTS SUGGEST THAT 1 TO 2 INCHES OF

RAIN IS POSSIBLE WITH THE WARM AIR ADVECTION RAIN THURSDAY NIGHT AND

FRIDAY MORNING...AND CONVECTIVE ACTIVITY FRIDAY AFTERNOON. THE SNOW

COVER IS RAPIDLY DISAPPEARING ACROSS MUCH OF THE SOUTHERN PORTION OF

THE AREA...AND SETTLING TO THE NORTH. NOT SURE HOW MUCH THIS WILL

PLAY INTO THE FLOODING POTENTIAL JUST YET.

THE POSITION OF THE AXIS OF HEAVIEST RAIN WILL MORE LIKELY BE THE

DECIDING FACTOR FOR WHETHER FLOODING OCCURS OR NOT. A GENERAL

RAINFALL OF 1 TO 2 INCHES (ASSUMING IT FALLS OVER A 12 TO 18 HOUR

PERIOD) WOULD BE CLOSE TO THE HEADWATER GUIDANCE NUMBERS FOR SOME OF

OUR FASTER RESPONDERS (SUCH AS THE ASSUNPINK AND RARITAN). THE MODEL

CONSENSUS (AS WELL AS HPC) IS STARTING TO LEAN TO A HIGHER QPF ACROSS

NORTHERN AREAS. 0900 UTC SREF PRECIPITATION PLUMES SHOW BETWEEN 1.35

AND 1.70 INCHES IN THESE AREAS.

THE GREATEST THREAT COULD BE FROM NORTHERN DELAWARE THROUGH

SOUTHEAST PENNSYLVANIA INTO NORTH CENTRAL NEW JERSEY. THESE AREAS

WOULD BE MOST PRONE TO FLOOD...IF THE AXIS OF HEAVIEST RAIN FALLS IN

THESE AREAS. SINCE THERE IS STILL SOME DOUBT TO THE POSITION OF THE

HEAVIEST RAIN...WE WILL FORGO THE WATCH THIS TIME...AND REEVALUATE

THE POTENTIAL THURSDAY.

-- End Changed Discussion --

pretty good consensus with Upton (below)

.HYDROLOGY...

-- Changed Discussion --THERE IS THE POTENTIAL FOR MODERATE TO HEAVY RAIN ACROSS THE

ENTIRE CWA THURDSAY NIGHT INTO FRIDAY. RIGHT NOW WE ARE EXPECTING

RAINFALL AMOUNTS OF ONE TO POSSIBLY TWO INCHES RESULTING IN AT

LEAST MODERATE RISES ON AREA RIVERS AND STREAMS.

HOWEVER...THE CONCERN EXISTS FOR POOR DRAINAGE FLOODING ACROSS

URBAN AREAS AS WELL AS BASEMENT FLOODING DUE TO THE COMBINATION OF

SNOWMELT AND HEAVY RAIN. IF THE AREA WERE TO RECEIVE HIGHER

RAINFALL AMOUNTS...IT IS NOT OUT OF THE QUESTION TO SEE SOME OF

THE SMALLER STREAMS AND EVEN MAINSTEM RIVERS ACROSS THE AREA

APPROACH FLOOD STAGE.-- End Changed Discussion --

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We can blame the the positive phase of the NAO...

actually, blame the PNA. The concept that you need a -NAO around here to get snow is simply not true. It helps, but its not the end all. HOWEVER, if your PNA looks like the current one, you are up a river without a paddle without the -NAO. Fact of the matter is this is the raging nina pattern and the NAO would help mitigate this and without it you need luck like two days ago or a different PAC.

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actually, blame the PNA. The concept that you need a -NAO around here to get snow is simply not true. It helps, but its not the end all. HOWEVER, if your PNA looks like the current one, you are up a river without a paddle without the -NAO. Fact of the matter is this is the raging nina pattern and the NAO would help mitigate this and without it you need luck like two days ago or a different PAC.

The west coast is the place to be for snow right now. Up to 8" in Seattle and Portland-- the latest theyve had significant snow since 1989! And it might even snow all the way down to San Fran! We know Feb 1989 sucked around here and was great on the West Coast, but what happened in March 1989?

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the 18z nam has a 70+kt low level jet over long island during the height of the storm. with tremendous isentropic lifting and upglide there is the potential for very heavy precipitation within the warm sector. its also moved the warm front a bit further north and west which allows the area to clear more into the warm sector. with strong southerly winds and the warm front to the north--most of the area gets into the mid 50's in this setup.

i wouldn't at all be surprised to see low topped convection in the area which could be a significant problem nearer to the low level jet with the very strong winds aloft. the nam has 20-30kt 10m winds in the city and near 40 kt 10m winds on the east end of long island.

f48.gif

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SPC has a small 5% risk area that extends into Southern New Jersey on the Day 3 Outlooks

...SYNOPSIS/DISCUSSION...

A FAST MOVING UPPER SHORTWAVE TROUGH WILL BE LOCATED OVER THE UPPER

OH VALLEY FRI MORNING WITH A SURFACE LOW CENTERED NEAR WV. VERY

STRONG SHEAR PROFILES WILL BE IN PLACE ACROSS THE MID ATLANTIC AHEAD

OF A COLD FRONT WHICH WILL MOVE TO THE COAST BY LATE AFTERNOON...BUT

LOW LEVEL MOISTURE FOR INSTABILITY WILL BE MINIMAL. STILL...STRONG

PRESSURE RISES WITH THE COLD FRONT...AS WELL AS THE PRESENCE OF

STEEPER LAPSE RATES IN THE DRIER AIR TO THE W...MAY RESULT IN

ISOLATED STRONG TO SEVERE WIND GUSTS MAINLY ACROSS VA...MD AND DE AS

THE COLD FRONT PASSES. THE COVERAGE OF SEVERE WIND WILL DEPEND

HEAVILY ON HOW MUCH HEATING AND DESTABILIZATION TAKE PLACE...WHICH

WILL BECOME BETTER KNOWN IN LATER OUTLOOKS.

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the 18z nam has a 70+kt low level jet over long island during the height of the storm. with tremendous isentropic lifting and upglide there is the potential for very heavy precipitation within the warm sector. it's also moved the warm front a bit further north and west which allows the area to clear more into the warm sector. with strong southerly winds and the warm front to the north--most of the area gets into the mid 50's in this setup.

i wouldn't at all be surprised to see low topped convection in the area which could be a significant problem nearer to the low level jet with the very strong winds aloft. the nam has 20-30kt 10m winds in the city and near 40 kt 10m winds on the east end of long island.

f48.gif

Yep with a strong low cutting to our west and and winds ripping out of the south winds should be strong. Wonder if a more southerly component wind keeps coastal sections of S LI cooler. Will see how that works out.

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Yep with a strong low cutting to our west and and winds ripping out of the south winds should be strong. Wonder if a more southerly component wind keeps coastal sections of S LI cooler. Will see how that works out.

the juxtaposition of some key features is also important to note. the 18z nam at 48 hours has a 989mb surface low in upstate new york. more importantly, the dynamics are through the roof at that time. there's a small area of 110+kt 300mb winds in the warm sector and the exit region of the upper level jet. the warm front is already over southern new england at this hour. the 500mb trough and associated forcing/ascent is still back to the west..this could be a wind producer especially further to the south where there is better low level moisture and temperatures are even into the 60's over the mid atlantic. for our area...we have to watch the more synoptic wind potential which will come with the heavy rain and insane isentropic lifting.

cool synoptic event being advertised by the 18z nam. we will have to wait and see if it has the right idea, or if it's overly dynamic.

post-6-0-32769900-1298501074.png

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The west coast is the place to be for snow right now.  Up to 8" in Seattle and Portland-- the latest theyve had significant snow since 1989!  And it might even snow all the way down to San Fran!  We know Feb 1989 sucked around here and was great on the West Coast, but what happened in March 1989?

NYC had a snowstorm and temps in the teens during the first week of 1989,a rain changed to snow situation.The rest of the month was cool with a heavy rainstorm with thunder near the first day of spring.

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the juxtaposition of some key features is also important to note. the 18z nam at 48 hours has a 989mb surface low in upstate new york. more importantly, the dynamics are through the roof at that time. there's a small area of 110+kt 300mb winds in the warm sector and the exit region of the upper level jet. the warm front is already over southern new england at this hour. the 500mb trough and associated forcing/ascent is still back to the west..this could be a wind producer especially further to the south where there is better low level moisture and temperatures are even into the 60's over the mid atlantic. for our area...we have to watch the more synoptic wind potential which will come with the heavy rain and insane isentropic lifting.

cool synoptic event being advertised by the 18z nam. we will have to wait and see if it has the right idea, or if it's overly dynamic.

post-6-0-32769900-1298501074.png

It will be interesting to see how things play out.Back on 3/5/08 we got a pre dawn squall line to race through a day after a MDT Risk to our south.

We'll have to watch for later runs to see the specifics.Sometimes the best LLJ runs just out ahead of developing warm sector convection.The

models are obviously hitting the heavy rain with the warm front but we'll have to see what kind of warm sector development there will be.

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