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PHL CWA Feb 1-2 Storm OBS and Discussion


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Wow, the freezing rain bullseye could be PA Turnpike to I-78 in PA, with more snow/sleet north of I-78 and more plain rain south of the PA Turnpike.

Yeah, most of Montgomery, Bucks, and all of Berks, Lehigh, and Northampton seem to be in the ice zone. With parts of Carbon, Schulkyll and Monroe, too.

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per NAM?

GFS looks much warmer

GFS is warmer than the NAM but colder than its 00z run. GFS is faster and weaker and the low is about 150 miles NE of the NAM. High pressure is also noticably weaker on the GFS vs the NAM. The NAM probably is the better way to go in terms of temperature profiles. GFS is probably a tad more accurate with QPF. A general comprimise gives areas north of TTN > 1.25" QPF and southern areas between 0.75" & 1.25" QPF. At least 80% of that is proably frozen or freezing north of I-80.

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From HPC...throw out the NAM? ( if I'm reading this correctly)

...LOW PRESSURE FORMING ALONG THE MID-ATLANTIC/NORTHEAST COAST

THROUGH TUESDAY...

PREFERENCE: EQUAL BLEND GFS/00Z ECMWF

FORECASTS AT THE SURFACE ARE SIMILAR. HOWEVER...THE NAM LIES NEAR

THE STRONG EDGE OF THE GUIDANCE WITH ITS ASCENT FORMING WITHIN THE

STRENGTHENING BAROCLINIC ZONE NORTH OF THE LOW INCLUDING AREAS

BETWEEN ALBANY AND BOSTON...WHILE THE GFS/00Z ECMWF SHOW SIMILAR

LARGER-SCALE STRUCTURE WHICH IS WEAKER THAN THE NAM. THUS...DUE TO

CONSENSUS RECOMMEND DISCOUNTING THE STRONGER NAM AND RELYING UPON

AN INTERMEDIATE SOLUTION BETWEEN THE GFS/00Z ECMWF TO ACCOUNT FOR

SOME LINGERING MODEL UNCERTAINTY.

http://www.hpc.ncep.noaa.gov/discussions/pmdhmd.html

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I suspect Southern areas of the watch zone will be changed to a WWA with the afternoon package. The NW burbs of philly will switch to WWA for the snow but keep the watches up for the impending ice to follow. Poconos and Sussex, Warren, Morris, Somerset, Mercer & Middlesex counties in NJ probably go with blanket winter storm warnings. If the precip does look to shut off for a period, could get the WSW over the NW changed to ISW with the second system. Then again who knows. Either way I don't think a blanket WSW acknowledges the sevarity of the situation in the NW zones.

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GFS is warmer than the NAM but colder than its 00z run. GFS is faster and weaker and the low is about 150 miles NE of the NAM. High pressure is also noticably weaker on the GFS vs the NAM. The NAM probably is the better way to go in terms of temperature profiles. GFS is probably a tad more accurate with QPF. A general comprimise gives areas north of TTN > 1.25" QPF and southern areas between 0.75" & 1.25" QPF. At least 80% of that is proably frozen or freezing north of I-80.

thanks - so probably 20 to 25% (max) frozen / freezing qpf in metro Philly, inconvience but not a dire icing situation

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Sounds like they feel the NAM is progging the system as too strong. That's a lifesaver here...sounds like we may be spared a major ice event and get plain rain instead.

One of the few times I will cheer for plain rain this winter. HPC FTW!!

actually it would be vica vs imho. A stronger system would limit the amount of frozen do to the stronger southerly flow. A weaker storm would create less southerly push thus a colder system, atleast thats how i would take it.

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Sounds like they feel the NAM is progging the system as too strong. That's a lifesaver here...sounds like we may be spared a major ice event and get plain rain instead.

One of the few times I will cheer for plain rain this winter. HPC FTW!!

check out what I and some of the mets wrote in the Upton thread. HPC didn't throw out the NAM at all. Just covered themselves by saying it lacked some data over the west coast and that could have led to downstream effects. In other words, just take the NAM solution with caution.

Overall trends have been colder and colder with each consecutive 00z & 12z runs of most of the guidance. Forget the off hour runs which have been making large swings. In the end, colder is likely the way to go.

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I guess its all based on what model you go with, a place like ABE could luck out with more snow/sleet than freezing rain...while areas just south.......Berks/northern Mont./Bucks deal with a period of light snow initially (maybe an inch or so) then a little sleet, but primarily freezing rain and drizzle until the heavier precip. moves through on Wednesday and temperatures try to budge above freezing. That would be my concern in places like RDG, PTW, UKT.

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OK now I'm more confused with the responses since I posted the HPC discussion :lightning:

If it makes you feel any better, HPC basically doesn't agree with any one solution.

12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

...UPPER TROUGH FORMING OVER THE ROCKIES/PLAINS THROUGH THE

PERIOD...

PREFERENCE: GEFS MEAN OR ECMWF ENSEMBLE MEAN

THE GFS WEAKENS AND EJECTS THE LOW INTO THE PLAINS FASTER THAN THE

NAM/00Z ECMWF AND IS OUT OF PHASE WITH ITS OWN ENSEMBLE

MEAN...WHILE THE NAM/ECMWF DEPICTS A MORE CONSOLIDATED CENTER

LINGERING LATER IN THE PERIOD AND POSSIBLY DRIFTING AS FAR SOUTH

AS MEXICO. 00Z SPAGHETTI DIAGRAMS SHOW MUCH GREATER SPREAD

HOWEVER...AND GIVEN THE RUN-TO-RUN VARIABILITY REPRESENTED BY

CURRENT GUIDANCE...THE RECOMMENDATION IS LEAN MOST HEAVILY UPON

THE GLOBAL ENSEMBLE MEANS SUCH AS THE GEFS OR ECMWF ENSEMBLES.

...CYCLONE MOVING FROM THE S. PLAINS TO NEW ENGLAND THROUGH THE

PERIOD...

PREFERENCE: BEFORE 00Z WED...2/3 GFS TO 1/3 GEFS MEAN OR SREF MEAN

00Z WED-00Z THU...1/3 EACH GFS/GEFS MEAN/SREF MEAN

AFTER 00Z WED...1/2 EACH GEFS MEAN/SREF MEAN

THE NAM IS A LITTLE SLOWER THAN THE GFS/00Z ECMWF THROUGH MOST OF

THE PERIOD WITH ITS SLOWER SPEED CONSIDERED DOUBTFUL DUE TO WORSE

INITIALIZATION OF THE EVOLVING TROUGH OVER CALIFORNIA.

OTHERWISE...THE ECMWF LIES TO THE NORTHWEST OF THE GFS TRACKING

THE LOW FROM THE S. PLAINS INTO THE OHIO VALLEY...WHICH IS ALSO

DISCOUNTED DUE TO ITS OWN TRENDS OVER THE LAST 24 HRS AND ITS

POSITION WITHIN THE LATEST SPREAD OF 12Z GUIDANCE WHICH IS ALONG

ITS NORTHWESTERN EDGE. THEN ONCE THE LOW REACHES THE NORTHEAST/NEW

ENGLAND...THE GFS ACCELERATES AHEAD OF MOST GUIDANCE...WHICH IS

ASSOCIATED WITH DIMINISHING CONFIDENCE DUE TO POSSIBLE

INTERACTIONS WITH THE NORTHERN STREAM. THUS...DUE TO A PROCESS OF

ELIMINATION ALONG WITH ITS POSITION WITHIN THE GUIDANCE ENVELOPE

AND FACTORING CONTINUED UNCERTAINTIES...THE RECOMMENDATION IS FOR

A SOLUTION WEIGHTED TOWARD THE DETERMINISTIC GFS EARLY THEN

TRANSITIONING TOWARD ENSEMBLES LATE.

...LOW PRESSURE FORMING ALONG THE MID-ATLANTIC/NORTHEAST COAST

THROUGH TUESDAY...

PREFERENCE: EQUAL BLEND GFS/00Z ECMWF

FORECASTS AT THE SURFACE ARE SIMILAR. HOWEVER...THE NAM LIES NEAR

THE STRONG EDGE OF THE GUIDANCE WITH ITS ASCENT FORMING WITHIN THE

STRENGTHENING BAROCLINIC ZONE NORTH OF THE LOW INCLUDING AREAS

BETWEEN ALBANY AND BOSTON...WHILE THE GFS/00Z ECMWF SHOW SIMILAR

LARGER-SCALE STRUCTURE WHICH IS WEAKER THAN THE NAM. THUS...DUE TO

CONSENSUS RECOMMEND DISCOUNTING THE STRONGER NAM AND RELYING UPON

AN INTERMEDIATE SOLUTION BETWEEN THE GFS/00Z ECMWF TO ACCOUNT FOR

SOME LINGERING MODEL UNCERTAINTY.

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So basically we nowcast because no one knows anything for sure?

If it makes you feel any better, HPC basically doesn't agree with any one solution.

12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

...UPPER TROUGH FORMING OVER THE ROCKIES/PLAINS THROUGH THE

PERIOD...

PREFERENCE: GEFS MEAN OR ECMWF ENSEMBLE MEAN

THE GFS WEAKENS AND EJECTS THE LOW INTO THE PLAINS FASTER THAN THE

NAM/00Z ECMWF AND IS OUT OF PHASE WITH ITS OWN ENSEMBLE

MEAN...WHILE THE NAM/ECMWF DEPICTS A MORE CONSOLIDATED CENTER

LINGERING LATER IN THE PERIOD AND POSSIBLY DRIFTING AS FAR SOUTH

AS MEXICO. 00Z SPAGHETTI DIAGRAMS SHOW MUCH GREATER SPREAD

HOWEVER...AND GIVEN THE RUN-TO-RUN VARIABILITY REPRESENTED BY

CURRENT GUIDANCE...THE RECOMMENDATION IS LEAN MOST HEAVILY UPON

THE GLOBAL ENSEMBLE MEANS SUCH AS THE GEFS OR ECMWF ENSEMBLES.  

...CYCLONE MOVING FROM THE S. PLAINS TO NEW ENGLAND THROUGH THE

PERIOD...

PREFERENCE: BEFORE 00Z WED...2/3 GFS TO 1/3 GEFS MEAN OR SREF MEAN

           00Z WED-00Z THU...1/3 EACH GFS/GEFS MEAN/SREF MEAN

             AFTER 00Z WED...1/2 EACH GEFS MEAN/SREF MEAN

THE NAM IS A LITTLE SLOWER THAN THE GFS/00Z ECMWF THROUGH MOST OF

THE PERIOD WITH ITS SLOWER SPEED CONSIDERED DOUBTFUL DUE TO WORSE

INITIALIZATION OF THE EVOLVING TROUGH OVER CALIFORNIA.

OTHERWISE...THE ECMWF LIES TO THE NORTHWEST OF THE GFS TRACKING

THE LOW FROM THE S. PLAINS INTO THE OHIO VALLEY...WHICH IS ALSO

DISCOUNTED DUE TO ITS OWN TRENDS OVER THE LAST 24 HRS AND ITS

POSITION WITHIN THE LATEST SPREAD OF 12Z GUIDANCE WHICH IS ALONG

ITS NORTHWESTERN EDGE. THEN ONCE THE LOW REACHES THE NORTHEAST/NEW

ENGLAND...THE GFS ACCELERATES AHEAD OF MOST GUIDANCE...WHICH IS

ASSOCIATED WITH DIMINISHING CONFIDENCE DUE TO POSSIBLE

INTERACTIONS WITH THE NORTHERN STREAM. THUS...DUE TO A PROCESS OF

ELIMINATION ALONG WITH ITS POSITION WITHIN THE GUIDANCE ENVELOPE

AND FACTORING CONTINUED UNCERTAINTIES...THE RECOMMENDATION IS FOR

A SOLUTION WEIGHTED TOWARD THE DETERMINISTIC GFS EARLY THEN

TRANSITIONING TOWARD ENSEMBLES LATE.

...LOW PRESSURE FORMING ALONG THE MID-ATLANTIC/NORTHEAST COAST

THROUGH TUESDAY...

PREFERENCE: EQUAL BLEND GFS/00Z ECMWF

FORECASTS AT THE SURFACE ARE SIMILAR. HOWEVER...THE NAM LIES NEAR

THE STRONG EDGE OF THE GUIDANCE WITH ITS ASCENT FORMING WITHIN THE

STRENGTHENING BAROCLINIC ZONE NORTH OF THE LOW INCLUDING AREAS

BETWEEN ALBANY AND BOSTON...WHILE THE GFS/00Z ECMWF SHOW SIMILAR

LARGER-SCALE STRUCTURE WHICH IS WEAKER THAN THE NAM. THUS...DUE TO

CONSENSUS RECOMMEND DISCOUNTING THE STRONGER NAM AND RELYING UPON

AN INTERMEDIATE SOLUTION BETWEEN THE GFS/00Z ECMWF TO ACCOUNT FOR

SOME LINGERING MODEL UNCERTAINTY.

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Wxsim program with 12z NAM/GFS incorporated

Flurries by 10pm temp 19.7

Moderate Snow by 830am Tuesday morning temp 23.5

Snow mixes with IP by 10am temp 25.6 (around 3" of snow/IP accumulation by noon)

Lite ZR and IP during the PM - 3pm temp 29.2

Steady ZR starts around 130am on Wed morning temp 29.7

0.65" of ZR falls between 130am and 8am Wed morning before temps warm above freezing by 830a

another 0.30" of rain falls during the day with a high near 40 (highly doubtful)

Wxsim shows more snow arriving Saturday morning with around 4" of snow by early PM

Current obs

Temp 25.5

Wind NNE 2 - 5mph

RH 54%

DP 11.2

Current snow depth 19.0"

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EUro coming in like gfs a bit..

42, 0 line (surface) south of philly, very light precip... then 48, it jumps to about central berks/bucks up to NYC with heavier precip.. LV up to about scranton getting ice . 850's are on the pa/ny line

.25-.5"

54, it jumps to 30miles north of NYC, most of precip is out of area for PA, nj and NYC still some rain..

Seems like the NAM is on it's own with the colder solution,

total qpf.. PA .75-1", NE PA /poconos to NYC to albany . LI 1"-1.25, eastern CT, southern Mass, and RI to the cape 1.25" +

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To me, the models are moving things along way to quick with the warm up. I'll lean toward the NAM for now. To me there is such strong cold source over New England that will no doubt be a battle to get this cold air scoured out.. Should be really interesting on verifying the observations against the models tomorrow..

EUro coming in like gfs a bit.. 42, 0 line (surface) south of philly, very light precip... then 48, it jumps to about central berks/bucks up to NYC with heavier precip.. LV up to about scranton getting ice . 850's are on the pa/ny line .25-.5" 54, it jumps to 30miles north of NYC, most of precip is out of area for PA, nj and NYC still some rain.. Seems like the NAM is on it's own with the colder solution,
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Very quiet here....I hear the crickets...I have to say...the NWS breifings are pretty neat. How long have they been doing those? Still counting on a significant ice mess in Berks county...not sure we will get to the freezing mark until the bulk of the precip is over...good luck everyone...hopefully the damage is minimal.

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Warning from Mt. Holly for N&W burbs:

Winter Storm Warning

URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE MOUNT HOLLY NJ

318 PM EST MON JAN 31 2011

...WINTRY PRECIPITATION IS EXPECTED FROM TONIGHT INTO WEDNESDAY...

LOW PRESSURE WILL MOVE FROM THE LOWER MISSISSIPPI RIVER VALLEY ON

TUESDAY TO THE UPPER OHIO RIVER VALLEY EARLY ON WEDNESDAY. THE

LOW IS THEN EXPECTED TO JUMP TO THE WATERS OFF NEW JERSEY ON

WEDNESDAY AFTERNOON BEFORE RACING TO THE NORTHEAST. THE WEATHER

SYSTEM WILL BRING A PROLONGED PERIOD OF WINTRY PRECIPITATION TO

PARTS OF OUR REGION FROM TONIGHT INTO WEDNESDAY.

NJZ009-010-012-015-PAZ060-067>069-011000-

/O.UPG.KPHI.WS.A.0004.110201T0800Z-110202T2200Z/

/O.NEW.KPHI.WS.W.0005.110201T0400Z-110202T2100Z/

HUNTERDON-SOMERSET-MIDDLESEX-MERCER-BERKS-CHESTER-MONTGOMERY-

BUCKS-

INCLUDING THE CITIES OF...FLEMINGTON...SOMERVILLE...

NEW BRUNSWICK...TRENTON...READING...WEST CHESTER...NORRISTOWN...

DOYLESTOWN

318 PM EST MON JAN 31 2011

...WINTER STORM WARNING IN EFFECT FROM 11 PM THIS EVENING TO 4 PM

EST WEDNESDAY...

THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY HAS ISSUED A WINTER

STORM WARNING FOR A WINTRY MIX OF PRECIPITATION, ESPECIALLY ICE...

WHICH IS IN EFFECT FROM 11 PM THIS EVENING TO 4 PM EST WEDNESDAY.

THE WINTER STORM WATCH IS NO LONGER IN EFFECT.

* PRECIPITATION TYPES: SNOW TONIGHT WILL MIX WITH SOME SLEET AND

OR FREEZING RAIN ON TUESDAY DAY. A WINTRY MIX OF SLEET AND

FREEZING RAIN IS EXPECTED TUESDAY NIGHT AND THEN TRANSITION TO

ALL FREEZING RAIN WEDNESDAY MORNING AND POSSIBLY PLAIN RAIN

DURING THE DAY ON WEDNESDAY BEFORE ENDING.

* ACCUMULATIONS: CONFIDENCE IS LOW AS TO ACCUMULATION AS THEY ARE

PRECIPITATION TYPE DEPENDENT. BEST ESTIMATE IS FOR 2 TO 4 INCHES

OF SNOW AND SLEET. OF GREATER IMPORTANCE ONE THIRD TO TWO THIRDS

OF AN INCH OF ICE IS LIKELY TO ACCUMULATE ON TREES AND WIRES AS

WELL AS UNTREATED ROADWAYS.

* TIMING: THE PRECIPITATION SHOULD OVERSPREAD THE REGION CLOSE TO

MIDNIGHT TONIGHT. THERE WILL BE A LULL IN THE PRECIPITATION

INTENSITY DURING TUESDAY AFTERNOON AND EVENING BEFORE HEAVIER

PRECIPITATION MOVES BACK IN OVERNIGHT TUESDAY AND WEDNESDAY

MORNING. PRECIPITATION SHOULD TAPER OFF WEDNESDAY AFTERNOON.

* IMPACTS: TRAVEL WILL BECOME DIFFICULT IN THE REGION FROM LATE

TONIGHT THROUGH WEDNESDAY AFTERNOON DUE TO SNOW AND THEN ICE.

ICE WILL ACCUMULATE ON TREE LIMBS AND UTILITY WIRES FROM TUESDAY

NIGHT INTO WEDNESDAY. WIDESPREAD POWER OUTAGES ARE POSSIBLE. THE

TUESDAY MORNING COMMUTE WILL BE IMPACTED BY SNOW. THE TUESDAY

EVENING COMMUTE SHOULD BE EASIER BECAUSE OF THE EXPECTED LULL IN

THE PRECIPITATION INTENSITY. THE WEDNESDAY MORNING COMMUTE WILL

BE EXTREMELY DIFFICULT DUE TO THE ICE. THIS EVENT SHOULD BE

OVER BY THE TIME OF THE WEDNESDAY EVENING COMMUTE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW...

SLEET...AND ICE ARE EXPECTED OR OCCURRING. STRONG WINDS ARE ALSO

POSSIBLE. THIS WILL MAKE TRAVEL VERY HAZARDOUS OR IMPOSSIBLE.

&&

$$

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I am surprised how few posts are on this topic. We are 24 hours away from what could be a very significant event. Obviously not everyone is involved, but it seems like if it is not a heavy deep snow no one cares. In my opinion - heavy ice is more impactful than heavy snow. Heavy snow is an inconvience for a day or so. No power for a day or two or three is more than an inconvienince.

If the public is taking the same lack luster approach to this storm - they may be in for a very rude awakening. It could be the media is down playing this too much. I know they are critized and rightfully so for hyping non events, but this one could be a memorable event. If it even has shades of 1994 the public should be making plans NOW.. I was involved in 1994 running almost 15% of our annual fire calls in one night. That was memorable. Maybe this will be mostly just plain rain - but that is not likely.

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I am surprised how few posts are on this topic. We are 24 hours away from what could be a very significant event. Obviously not everyone is involved, but it seems like if it is not a heavy deep snow no one cares. In my opinion - heavy ice is more impactful than heavy snow. Heavy snow is an inconvience for a day or so. No power for a day or two or three is more than an inconvienince.

If the public is taking the same lack luster approach to this storm - they may be in for a very rude awakening. It could be the media is down playing this too much. I know they are critized and rightfully so for hyping non events, but this one could be a memorable event. If it even has shades of 1994 the public should be making plans NOW.. I was involved in 1994 running almost 15% of our annual fire calls in one night. That was memorable. Maybe this will be mostly just plain rain - but that is not likely.

I think for Philly east there will probably be more plain rain then freezing rain, that being said from Mercer Bucks northward it could be a real headache.

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