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Jan 23/24 Major Coastal Storm Discussion


Zelocita Weather

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6-12 is a terrible forecast in NYC. Storms like this generally have a tight gradient of higher totals; almost nothing on one end, 12-18 on the other, with a tiny zone in between. The odds of guessing where that zone falls, especially 2 days out, is basically nil; well more than half the potential outcomes for NYC fall outside that range. It may be guess as to the MEAN outcome but the distribution isn't normal.

Basically, 6-12 is someone who is scared to be wrong. Cant really miss with that one! If we get 2", the 6-12" was under much of the guidance and on the right path. Get 18", a slight bust high. But that doesn't make it a good forecast, since it predicts the exact amount of snow we're least likely to get.

As long as forecasts are expressed with the same, unscientific standard increments (6-12, 4-8, 12-18, etc) we're going to run into these issues.

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6-12 is a terrible forecast in NYC. Storms like this generally have a tight gradient of higher totals; almost nothing on one end, 12-18 on the other, with a tiny zone in between. The odds of guessing where that zone falls, especially 2 days out, is basically nil; well more than half the potential outcomes for NYC fall outside that range. It may be guess as to the MEAN outcome but the distribution isn't normal.

Basically, 6-12 is someone who is scared to be wrong. Cant really miss with that one! If we get 2", the 6-12" was under much of the guidance and on the right path. Get 18", a slight bust high. But that doesn't make it a good forecast, since it predicts the exact amount of snow we're least likely to get.

As long as forecasts are expressed with the same, unscientific standard increments (6-12, 4-8, 12-18, etc) we're going to run into these issues.

From the point of view of weather buffs you're right' but the function of a three-day out forecast is to put the public on notice of when they'll be able to go about their business and when that may be a problem. 6-12" does that job just fine since it alerts the public that a disruptive storm is on the way.

 

What was wrong was last January where the forecasts included snow of Biblical proportions and 8" was a bust.

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6-12 is a terrible forecast in NYC. Storms like this generally have a tight gradient of higher totals; almost nothing on one end, 12-18 on the other, with a tiny zone in between. The odds of guessing where that zone falls, especially 2 days out, is basically nil; well more than half the potential outcomes for NYC fall outside that range. It may be guess as to the MEAN outcome but the distribution isn't normal.

Basically, 6-12 is someone who is scared to be wrong. Cant really miss with that one! If we get 2", the 6-12" was under much of the guidance and on the right path. Get 18", a slight bust high. But that doesn't make it a good forecast, since it predicts the exact amount of snow we're least likely to get.

As long as forecasts are expressed with the same, unscientific standard increments (6-12, 4-8, 12-18, etc) we're going to run into these issues.

 

Upton is currently saying 6-8" for the NYC area. Ensemble guidance shows that we will either get plastered with over a foot or almost nothing. They are giving themselves flexibility so they can adjust accordingly tomorrow. It's pretty smart move. Notice how they kept the totals in the AFD.

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Upton updated flood potential

.TIDES/COASTAL FLOODING...

A POTENTIAL NOR`EASTER COULD PRODUCE MULTIPLE EPISODES OF COASTAL

FLOODING AROUND THE TIMES OF HIGH TIDE SAT INTO SUN. THE TIDES OF

PRIMARY CONCERN WILL BE SAT MORNING AND SAT NIGHT...WITH POTENTIAL

GALE TO STORM FORCE NE WINDS PILING WATER ALONG THE COAST.

POSITIVE TIDAL DEPARTURES OF 1 1/2 TO 2 FT ARE NEEDED FOR MINOR

COASTAL FLOODING AND 2 1/4 TO 3 FT FOR MODERATE COASTAL FLOODING

WITH THE SAT MORNING HIGH TIDE. AVAILABLE TIDAL GUIDANCE (BASED ON

GFS) IS INDICATING POTENTIAL FOR 2 TO 3 1/2 FT OF SURGE DURING THIS

TIME PERIOD...WHICH WOULD SIGNAL POTENTIAL FOR MODERATE COASTAL

FLOODING. FOR THE SAT EVENING HIGH TIDE...POSITIVE TIDAL DEPARTURES

OF 2 TO 2 1/2 FT OR SURGE ARE NEEDED FOR MINOR COASTAL FLOODING AND

3 TO 4 FT FOR MODERATE COASTAL FLOODING. IF NE GALE TO STORM FORCE

WINDS CONTINUE UNTIL THE TIME OF HIGH TIDE...POTENTIAL EXISTS FOR

MODERATE COASTAL FLOOD ONCE AGAIN. THE MOST VULNERABLE TO

MODERATE COASTAL FLOODING WOULD BE ALONG WESTERN/CENTRAL HALF OF

LI SOUND AND SOUTHERN BAYS OF WESTERN LI AND NYC...AND

TRADITIONALLY VULNERABLE PORTIONS OF NY HARBOR. FOR THE SUNDAY

MORNING HIGH TIDE THE SURGE SHOULD BE LOWERING DUE TO WINDS

TURNING NORTHERLY...BUT POTENTIAL FOR ANOTHER ROUND OF AT LEAST

MINOR COASTAL FLOODING EXISTS.

BASED ON SPREAD IN MODEL GUIDANCE ON TRACK AND INTENSITY OF THIS

COMPLEX NOR`EASTER...AND THEREFORE STRENGTH AND DIRECTION OF WIND

FIELDS...CONFIDENCE IS ONLY MODERATE IN THE SURGE RANGE AT THIS

TIME. SOME THINGS TO KEEP IN MIND...THE TENDENCY IS FOR MODELS TO

UNDERESTIMATE THE NORTHWARD BACKING OF WINDS OF INTENSIFYING

NOR`EASTERS TRACKING TO THE SE OF LI...WHICH IN TURN ACTS TO

REDUCE SURGE ALONG THE TRI-STATE AREA. ALSO...LOOKING BACK AT

SURGE FROM THE TOP 3 STORM ANALOGS AS ANALYZED BY SAINT LOUIS

UNIVERSITY CIPS PAGE (JAN 7-8 1996, MAR 3 1994, AND DEC

2010)...BETWEEN 2 1/2 TO 4 FT OF SURGE WERE EXPERIENCED WITH THOSE

PARTICULAR STORMS. THIS SURGE RANGE MATCHES FAIRLY WELL WITH

CURRENT SURGE FORECASTS...BUT PAST RESULTS DO NOT GUARANTEE FUTURE

FORECASTS...SO MONITOR THE LATEST FORECASTS.

IN ADDITION TO SURGE POTENTIAL...AN EASTERLY SWEEP OF 8 TO 12 FT

SURF WILL BRING POTENTIAL FOR DUNE TOE EROSION ALONG ALL ATLANTIC

OCEAN BEACHES AND POTENTIAL FOR LOCALIZED DUNE OVERWASHES FOR THE

BARRIER BEACHES FROM FIRE ISLAND AND POINTS WEST ON SATURDAY. THIS

IS BASED ON USGS COASTAL CHANGE HAZARDS MODELING FOR A GALE FORCE

NOR-EASTER.

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Upton is currently saying 6-8" for the NYC area. Ensemble guidance shows that we will either get plastered with over a foot or almost nothing. They are giving themselves flexibility so they can adjust accordingly tomorrow. It's pretty smart move. Notice how they kept the totals in the AFD.

I know the NWS does this, but I think it's stupid / patronizing. They assume the public can't understand the actual forecast so they make up a fake one with the least chance of verifying. IIRC the research on this shows that the public can understand a more accurate forecast. What they're doing is CYA - forecasting to avoid a fiasco - rather than presenting the public with the best information for people to make independent judgments about preparation.

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This is a bad sign IMO. The OP is increasingly by itself in showing a major snowstorm for NYC.

 

 

We're at the range where the OP's are becoming more useful than the ensembles. I'm not saying they should be ignored, but the mean is still 4-6" which really isn't bad at this range. Ensembles aren't going to pick up things like mesoscale banding.

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It was similiar on the 0z run and then it continued on the 6z run. We have already been burned this winter by the ensembles.

I'm I the only one that finds it completely off that every Ens is off from the OP... My opinions, models do NOT have a Handle on this.. Room to move, hate to use the same thing, but his could have 96' repeat written all over the it ( fingers crossed)

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We're at the range where the OP's are becoming more useful than the ensembles. I'm not saying they should be ignored, but the mean is still 4-6" which really isn't bad at this range. Ensembles aren't going to pick up things like mesoscale banding.

Also, see the BOX AFD. They argue that the lower-res ensembles are too far south because they can't see the impact of anomalously warm SSTs.

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It looks like the highest storm surge may now come at the Saturday evening high tide.

The morning has the highest astronomical of the day and the evening a little lower.

GFS guidance is indicating that there could be a surge of 4 feet or more Saturday

evening. The current run is close to a March 93 or March 10 level. A surge closing

in on 5 feet would approach Hurricane Irene coastal flooding levels. Major tidal

flooding begins at 8.7 feet at Sandy Hook.

njsand.gif

Is there a link for this?

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Cobb Snow Algorithm (LGA) which last night(00Z)  increased precip. to 2"+ but wasted half of it as rain, leaving 8" snow total with a minimal ratio of 8:1  is now (06Z) down to about 1.6" but has it as an all 10:1 ratio snow event,  or 16" total, in line with most of yesterday's outputs.

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I'm I the only one that finds it completely off that every Ens is off from the OP... My opinions, models do NOT have a Handle on this.. Room to move, hate to use the same thing, but his could have 96' repeat written all over the it ( fingers crossed)

 

No. It's deffinitly becoming concerning and has become the norm tracking this storm. Leaves gray area.

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