Jan 20-22 Threat Potential Part 2

[forkyfork]

I'm going with a wide 3-8 range now.....not a very easy call....the Euro/NAM/GFS are relatively flat while the GEM and RGEM are amped....my concern though is given a different setup than we've seen the GEM is exhibiting its bias for the first time this winter and the American models and Euro are dead on....at the same time I do not like the UKMET being as west as it has been either.

it wouldn't take much digging with the northern stream to make this a low end warning event

that portion of the system doesn't get into a good data area until 0z this evening

[LVblizzard]

Update from JB...to watch the "real arctic front" for where the snow ratios will be 20 or 30 to 1 into Friday AM. The ratios will develop north of where that boundary sets up...even though the surface low will move farther south. Overall he believes in that zone 0.25" will translate to 5 or 6" North of that boundary

I think the highest we see is 20:1 in the Poconos, then 15:1 along I-78 and 12:1 along I-76.. It would have to be super cold (10F?) to get 30:1 ratios.

[MJO812]

Steve D is going with 4-8 for the NYC area. Henry M is going with 6+.

[A-L-E-X]

it wouldn't take much digging with the northern stream to make this a low end warning event

that portion of the system doesn't get into a good data area until 0z this evening

We can get WSW with 4-8" I think... not sure about 3-6", although I remember seeing WSW issued before when 4-6" were forecast.

[A-L-E-X]

I think the highest we see is 20:1 in the Poconos, then 15:1 along I-78 and 12:1 along I-76.. It would have to be super cold (10F?) to get 30:1 ratios.

That Jan 2004 analog might really work out if we get the really high ratios-- but that storm occurred with temps in the upper single digits and lower teens, so I doubt it. NYC, EWR and JFK had 40:1 ratios, while LGA had an astonishing 80:1

[Ed Lizard]

I think the highest we see is 20:1 in the Poconos, then 15:1 along I-78 and 12:1 along I-76.. It would have to be super cold (10F?) to get 30:1 ratios.

Wish I remember which one, but one of the red taggers explained how big snow ratios come to be, and while above freezing surface temps will glom some of the snow together, and cold surface temps are often a sign of colder temps aloft, I believe I was told it is more a factor of relative humidities and temperatures between 700 and 850 mb...

[famartin]

Still liking 3-6

[forkyfork]

Wish I remember which one, but one of the red taggers explained how big snow ratios come to be, and while above freezing surface temps will glom some of the snow together, and cold surface temps are often a sign of colder temps aloft, I believe I was told it is more a factor of relative humidities and temperatures between 700 and 850 mb...

yes.

if high ratio snow is produced at 700 mb, it will still be high ratio unless:

there is partial melting on the way down

there is riming

wind breaks up the dendrites

[famartin]

We can get WSW with 4-8" I think... not sure about 3-6", although I remember seeing WSW issued before when 4-6" were forecast.

NYC's snow criteria is 6", so 4-7 is the lowest (3-8 works too but that's really wide for a WSW product in the east). 4-6 and 3-6 are technically below warning in a 6" criteria area, but there's also impacts to consider.

[SnowGoose69]

We can get WSW with 4-8" I think... not sure about 3-6", although I remember seeing WSW issued before when 4-6" were forecast.

I would guess if nothing changed by tomorrow AM or PM they go with advisories for everyone but the 5 boroughs and LI and maybe E CT where they would have warnings...they'd probably want to see more widespread amounts nearer .50 on the NAM/GFS to go with warnings, even with the ratio factor considered. I cannot remember if the January 04 event has warnings or advisories out. I don't think a watch would ever go out for this event, its been so wintry already and the warning odds are not high enough.

[forkyfork]

I would guess if nothing changed by tomorrow AM or PM they go with advisories for everyone but the 5 boroughs and LI and maybe E CT...they'd probably want to see more widespread amounts nearer .50 on the NAM/GFS to go with warnings, even with the ratio factor considered. I cannot remember if the January 04 event has warnings or advisories out.

the nws did a good job with that event... there were warnings for 4-7"

[jasonli18t]

That Jan 2004 analog might really work out if we get the really high ratios-- but that storm occurred with temps in the upper single digits and lower teens, so I doubt it. NYC, EWR and JFK had 40:1 ratios, while LGA had an astonishing 80:1

I have always felt the liquid QPF measurements are a little inaccurate. 80:1 ratio? on the coast of the atlantic? i would be willing to bet a lot of money that never happened quite like that.

[famartin]

Wish I remember which one, but one of the red taggers explained how big snow ratios come to be, and while above freezing surface temps will glom some of the snow together, and cold surface temps are often a sign of colder temps aloft, I believe I was told it is more a factor of relative humidities and temperatures between 700 and 850 mb...

Good lift around the -15C level with high RH will get you excellent ratios, unless a warm layer below screws you over. Those type of ratios are much more likely here in the west than back east, but it happens sometimes.

[Sey-Mour Snow]

I think the highest we see is 20:1 in the Poconos, then 15:1 along I-78 and 12:1 along I-76.. It would have to be super cold (10F?) to get 30:1 ratios.

AS FAR AS SURFACE TEMPS

INLAND BOTTOMING OUT IN THE LOW TEENS RISING TO LOW 20S WHEN PRECIP ENDS

CT SHORE UPPER TEENS TO UPPER 20S

NYC UPPER 20S TO LOWER 30S

850s

-9 to -12 INLAND

-6 TO -9 SHORE

[SnowGoose69]

yes.

if high ratio snow is produced at 700 mb, it will still be high ratio unless:

there is partial melting on the way down

there is riming

wind breaks up the dendrites

I remember DC busted severely on the 2/10 event last winter and I was telling people before that it was going to happen because the temp at 700-850 was something like -1C even though the surface was probably 24-25 or so...sure enough they badly underachieved, BWI should have too but a mesoband made their amounts closer.

[IsentropicLift]

I wonder if the NWS will use the time of day that the event is taking place to determine adv/warn. Since this will be falling during the morning and having a large impact on the commute they might go with a warning even though the consensus might be for 3-5" with spotty 4-8" totals.

[donsutherland1]

Still liking 3-6

I like 3"-6", too.

[Yes_Probably_Maybe_No]

MM5 surface low looks like crap through 49, still brings in some decent precip

[dssbss]

I like 3"-6", too.

I'm thinking 2-4 for Berks County...

[famartin]

I like 3"-6", too.

Don's vote of confidence is always heartwarming

[SnowGoose69]

MM5 surface low looks like crap through 49, still brings in some decent precip

Its funny that the 00Z SSB MM5 looked weaker and more progressive than the 00Z NAM at 500 and the surface yet it seemed to generate more precip through the end of its run or just better precip appearance...the NAM is about as dry as I ever have seen it, even with a 996-1000mb surface low.

[Stormlover74]

I think it was more like 30:1 at least at EWR. 7.4" of snow out of .25" liquid but again that was with some of the coldest temps I've ever witnessed while it was snowing

That Jan 2004 analog might really work out if we get the really high ratios-- but that storm occurred with temps in the upper single digits and lower teens, so I doubt it. NYC, EWR and JFK had 40:1 ratios, while LGA had an astonishing 80:1

[Yes_Probably_Maybe_No]

ARW looks pretty far south and relatively dry through 48

[NittanyWx]

Steve D is going with 4-8 for the NYC area. Henry M is going with 6+.

Is Steve D the same met who came on here during the Norlun event predicting 6-12 for LI? His name is floated around here a lot, but I'm not sure if it's the same guy.

[SnowGoose69]

I think it was more like 30:1 at least at EWR. 7.4" of snow out of .25" liquid but again that was with some of the coldest temps I've ever witnessed while it was snowing

The best parts of that event was the snow started with a RH of like 25%...it was something like 20/-3....also the bust posts were insane that night because while it started rapidly around 6-7pm it hit a wall after for awhile, sort of like the event that hit one week after it as well...03-04 never really had a comfortable storm when you think about it.

[Sundog]

Is Steve D the same met who came on here during the Norlun event predicting 6-12 for LI?

Yes.

[famartin]

I have always felt the liquid QPF measurements are a little inaccurate. 80:1 ratio? on the coast of the atlantic? i would be willing to bet a lot of money that never happened quite like that.

Yeah that looks a bit too high. Brooklyn Avenue V reported a ratio of 31:1... 0.19" precip for 5.9" of snow. That's probably much more realistic.

[A-L-E-X]

I have always felt the liquid QPF measurements are a little inaccurate. 80:1 ratio? on the coast of the atlantic? i would be willing to bet a lot of money that never happened quite like that.

I agree; even with the Xmas day after event, we had some really wide ranging QPF totals across the area. IMO for Jan 2004 40:1 is plausible, but not anything higher than that.

[SnowGoose69]

Is Steve D the same met who came on here during the Norlun event predicting 6-12 for LI? His name is floated around here a lot, but I'm not sure if it's the same guy.

He's been very good overall this winter though...even in that event there were some places in his 6-12 zone over CT which did well and he nailed the event yesterday with a 1 inch or less forecast for the coast and had only 2-3 inch amounts even into areas quite a bit N&W were some people had as much as 3-5 or 4-7.

[A-L-E-X]

I think it was more like 30:1 at least at EWR. 7.4" of snow out of .25" liquid but again that was with some of the coldest temps I've ever witnessed while it was snowing

It was like 6 degrees as the storm was ending.... I cant remember ever seeing it snow in temps that cold around here. I remember the broadcasts said it would be like a "Great Plains snowstorm."