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Saint Patrick's Day Snow Event


stormtracker

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Think I'll just go with the HPC

 

Just saw their update after reading what you said.  Yeah, they've got us in the high prob. category for 4"+, moderate for 8"+, and...dare I say...low for 12"+.  Definitely more bullish than the earlier morning probabilities.  Also the experimental probabilistic/percentile forecasts have upped the 50th percentile amount to the 6-8" range, with over 8" heading toward the Blue Ridge.

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Just saw their update after reading what you said. Yeah, they've got us in the high prob. category for 4"+, moderate for 8"+, and...dare I say...low for 12"+. Definitely more bullish than the earlier morning probabilities. Also the experimental probabilistic/percentile forecasts have upped the 50th percentile amount to the 6-8" range, with over 8" heading toward the Blue Ridge.

People who work at HPC probably know more than most. Not going out on a limb when you trust them.

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Well also on the totally wrong 18z NAM... looks like we would get hit/scraped with the ULL at 84

 

Finally, I can see the full run!  And yes, I see what you're talking about, it's got a secondary surface low with that and if you (gasp!) extrapolate (argh!) the NAM looks like it would just scrape us.  And the silly NAM has us in the upper 20s or something through Monday.  A  chill for the green beer!

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http://www.hpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=qpfhsd

 

Afternoon Snow Discussion

 


..MIDDLE MS VALLEY/OH VALLEY/CENTRALAPPALACHIANS/MID-ATLANTIC/SRN NEW YORK/SRN NEW ENGLAND...THE MODELS/ENSEMBLE MEANS SHOW A SOUTHERN STREAM WAVE MOVING OUTOF THE SOUTHERN PLAINS TOWARDS THE MS VALLEY SAT NIGHT-SUN...WITHA CLOSED 700 MB LOW POSSIBLY FORMING NEAR THE AR/MO BORDER.  THE12Z NAM SHOWED A DEEPER 700 MB LOW THAN THE REMAININGMODELS/ENSEMBLE MEANS...RESULTING IN HEAVIER QPF AND RESULTANTSNOW AMOUNTS IN SOUTHERN MO ACROSS TO SOUTHERN IL/IN/OH. THE06Z-12Z GFS AND 00-12Z ECMWF/12Z UKMET SHOW LESS SNOW POTENTIAL INTHE OH VALLEY NORTH OF THE OH RIVER THAN THE 12Z NAM/09Z SREFMEAN.  THE LOW TRACKS AND THEIR RESPECTIVE LIQUID EQUIVALENTS ANDPRECIP-TYPES OF THE 12-00Z ECMWF/12Z UKMET/12Z GFS/12Z GEFS MEANWERE GIVEN THE MOST WEIGHT.THE DIRECT MODEL OUTPUT FROM THE GFS/ECMWF SUPPORT 4 TO EVEN 8INCHES OF SNOW ACROSS PART OF SOUTHERN TO CENTRAL MISSOURI.  ON DAY 3 IN THE MID ATLANTIC/SOUTHEAST NY/SRN NEW ENGLAND...MODELSAPPEAR TO BE COMING INTO BETTER AGREEMENT WITH HIGHER SNOW TOTALSDEVELOPING ACROSS THE CENTRAL APPALACHIANS...WHERE 6 TO 12 INCHESIS EXPECTED.  WHERE THE HEAVY SNOW OCCURS EAST OF THE APPALACHIANSARE LESS CLEAR DUE TO THE UNCERTAIN PHASING OF THENORTHERN/SOUTHERN STREAMS AND SUBSEQUENT SPREAD OF SOLUTIONS. A BAND OF 6-10 INCHES IS EXPECTED IN THE MID ATLANTIC EAST OF THEMOUNTAINS WITH MODEL RUN TO RUN DIFFERENCES SHOWING NORTH-SOUTHOSCILLATIONS ON THE AXIS OF HEAVIEST SNOW.  THIS IS REFLECTED IN ASIGNIFICANT DROP IN 12Z GEFS MEAN QPF ACROSS NORTHERN PA/NORTHERNNJ/NYC/LONG ISLAND/SRN NEW ENGLAND.  THE SOUTH TREND ON THE 12ZGEFS/GFS/ECMWF/CANADIAN GLOBAL LEADS TO AN INCREASED THREAT OFSNOW IN NORTHERN AND CENTRAL VA...AND EVEN FREEZING RAIN INSOUTHWEST VA.  THE 09Z SREF MEAN AND 12Z NAM EXTEND HIGHERQPF/RESULTANT HEAVY SNOW AMOUNTS FURTHER NORTH INTO NORTHERNPA/NJ/NY/SRN NEW ENGLAND...SO ONE CAMP OR THE OTHER WILLEVENTUALLY MAKE SIGNIFICANT ADJUSTMENTS.  THE 15Z SREF HAS ALREADYMADE A MAJOR REDUCTION IN QPF AND RESULTANT SNOW TOTALS INSOUTHERN NEW ENGLAND/SOUTHERN NY/NORTHERN PA FROM ITS 09Z RUN.PETERSEN
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LOL, the NAM is wrong (with no other rationale than it sucks). I guess the crystal balls are money? Magic eight balls? Why even look at models if you already know what's gonna happen?

To be fair, there is a legitimate rationale to doubt the NAM, it doesn't match any other guidance, and it is out of its best range.

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When the NAM shows 20" in Pittsburgh in late march, you know its wrong. I hope we can find a medium between south and north, because the bullseye needs to be right over nova!

Also, if you think about it, the NAM wasn't right with the early March storm because the heaviest snow wasn't south of dc, it was in eastern loudoun and western fairfax.

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To be fair, there is a legitimate rationale to doubt the NAM, it doesn't match any other guidance, and it is out of its best range.

I am not going to comment on the accuracy of the NAM, as I have not been keeping track. However, the NAM will be in its ideal range by tonight (48 hrs), assuming the event starts Sunday night.

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Per the 18z 4km NAM, precip doesn't get in here till around dinner time... 6pm or so on Sunday

 

If you wish to accept the 2mT, which we don't, DCA is ~32 by 11pm... I-81 corridor in the 20s... precip type claims its snow in N VA/DC/MD at 11pm Sun night... EZF sleety.. states prob of frozen precip is 100% at 11pm for DCA

 

And tries for 3"+ snow for BWI to DCA to EZFish and to the N and W of that by 2am Monday morning :lol:

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Serious question: What was it that LWX saw that made them want to just about double potential accumulations?

This is the MAX possible... 95th percentile! Worst case scenario. Based off 32 member ensemble members. The MIN and the MAX make up the goal post of possible scenarios. Higher the goal posts equals the more uncertainty! There are members giving those amounts as well as the lower amounts within the min scenario. Most Likely scenario comes out within 36 hours of the event.

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This is the MAX possible... 95th percentile! Worst case scenario. Based off 32 member ensemble members. The MIN and the MAX make up the goal post of possible scenarios. Higher the goal posts equals the more uncertainty! There are members giving those amounts as well as the lower amounts within the min scenario. Most Likely scenario comes out within 36 hours of the event.

I said potential, I meant to say max.

 

Thanks!

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