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PHL CWA JAN 26/27 OBS and Discussion Thread


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for PHL specifically, the 18Z GFS looks to be light slop to light rain to bombs away. At 18Z Wednesday (24hrs), the 0C line at 850mb stretches along the Delaware River. That's as far as it gets. Then the heavy stuff moves in Wednesday night. At hour 36, it has the .75-1.00 QPF line covering all of NJ except extreme NW NJ. 1.00-1.25" goes from Belmar, NJ-->New Hope, PA-->Lancaster, PA-->west of BWI-->west of DCA.

There is still more snowfall coming at this point. NCEP is stuck at 36. We broke the site.

You're a bit generous with that 1" line...

post-39-0-79369600-1295992882.gif

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for PHL specifically, the 18Z GFS looks to be light slop to light rain to bombs away. At 18Z Wednesday (24hrs), the 0C line at 850mb stretches along the Delaware River. That's as far as it gets. Then the heavy stuff moves in Wednesday night. At hour 36, it has the .75-1.00 QPF line covering all of NJ except extreme NW NJ. 1.00-1.25" goes from Belmar, NJ-->New Hope, PA-->Lancaster, PA-->west of BWI-->west of DCA.

There is still more snowfall coming at this point. NCEP is stuck at 36. We broke the site.

Only another .1 or so for some of the area (N NJ) at 42. Not sure if the NCEP issues are regional or what, but it's been working fine for me...

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From HPC.

..TN VLY/CNTRL APPALACHIANS TO CNTRL/NRN MID-ATLANTIC AND ERN NEW

ENGLAND...

A VIGOROUS SHRTWV OVER THE LWR MS VLY THIS AFTN IS EXPECTED TO

EVOLVE INTO A STG CLSD LOW FEATURE OVER THE ERN TN VLY BY WED

MORNING. THIS DYNAMIC FEATURE IS THEN ANTICIPATED TO CROSS THE

CENTRAL/SRN APPALACHIANS FOR THE MID-ATL COASTLINE BY WED

EVENING... NEAR THE DELMARVA. ITS AT THIS TIME... WHERE A VAGUE

AREA OF SURFACE LOW PRESSURE IS EXPECTED TO DEEPEN AND GO THROUGH

INTENSE CYCLOGENESIS BEFORE PROGRESSING RAPIDLY DOWNSTREAM... JUST

OFFSHORE OF COASTAL NORTHEAST/NEW ENGLAND. THE LATEST MDL GUIDANCE

SHOWS SOME AGREEMENT ON THIS FCST SCENARIO AND PARTICULARS BUT

ENOUGH SPREAD AND FLUIDITY EXISTS TO MAKE THIS A VERY PESKY AND

DIFFICULT FCST.

A VERY TRICKY SNOWFALL FORECAST WITH THIS SYS AS THE ORIGINAL COLD

AIR MASS IN PLACE ACROSS THE REGION IS BEING MOSTLY SCOURED OUT.

THIS WILL REQUIRE THE IMPRESSIVE DYNAMIC COOLING AND ENHANCED

VERTICAL LIFT ASSOCIATED WITH THE CLOSED LOW FEATURE TO TRANSITION

RAIN/WINTRY MIX OVER TO ALL SNOW. THE INITIAL THREAT OF LOCALLY

HVY SNOW ON WED IS EXPECTED TO BE ACRS THE TN VLY INTO THE CENTRAL

APPALACHIANS UNDERNEATH THE STRENGTHENING MID LVL DEFORMATION ZONE

AND UPPER LOW...WHERE MDL SOUNDINGS SUPPORT THIS STG DYNAMIC

COOLING. THIS AXIS OF ACCUMULATING SNOWFALL POSSIBLY ENHANCED BY

OROGRAPHICS WILL MAINLY IMPACT TN/KY INTO WV BEFORE WED AFTN.

THEN AROUND WED MIDDAY/WED AFTN... THE I95 CORRIDOR AROUND THE

DC/BWI WILL BEGIN TO GET INVOLVED ON THE ACTION. THE UPPER LOW

CENTER WILL SLIDE SOUTH AND EAST OF THE AREA PRODUCING ENOUGH

COOLING ALOFT TO TRANSLATE DOWN TO THE BOUNDARY LAYER FOR RAIN

CHANGING OVER TO ALL SNOW. THE INSTABILITY AND UVVS ASSOCIATED

WITH THE DEVELOPING DEFORMATION ZONE/COMMA-HEAD WILL BE OFF THE

CHARTS... POSSIBLY ALLOWING A CONVECTIVE ASPECT TO BECOME

INVOLVED. THIS SHOULD TRANSLATE IN INTENSE SNOWFALL RATES ACROSS

THE DC/BWI AREA FROM LATE TMRW AFTN TO VERY EARLY THURS MORNING

BEFORE THE ENTIRE PHASING SYSTEM MOVES RAPIDLY UP THE COAST. THUS

FOR THURS... A QUICK SIDE-SWIPE OF MDT TO HVY SNOWFALL IS EXPECTED

UP I95 THROUGH PHL... NYC AND BOS. HPC WENT WITH 4 TO 12 INCH HVY

SNOW PROBS EACH DAY AND A GENERAL PREFERENCE TOWARD A

ECMWF/CANADIAN/UKMET BLEND OVER THE NAM/GFS ON MASS FIELDS... QPF

AND THERMAL PROFILES.

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I wonder how much of the QPF is actually snow between 24 and 30 for Philly. Certainly looks like the crap snow with low ratios and sleet during that time. Verbatim probably like 6-8" of snow.

hr 27 the only level above is 800 to 850 around a degree above. with the precip just to the west. So on the gfs it may start as sleet very briefly.

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Maybe Jan 22 '87 like. 6 to 8 hours of very heavy fairly wet snow which dumps 8 to 12", except instead of changing over to rain at the coast everybody goes over to snow

Thanks for posting that map. This has all the ear marks for an 8-12 inch snowfall event with locally higher.

Going to be another another notch on the snowbelt for this winter.

Have to hope the 0 Z runs are more bullish

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JB's secret at to why heavier snows will be NW of thi cities and why models have been underoing precip on NW side says american models are not conserving the heat process correctly due to be modeled to be too weak, so the precip only makes it north to a certain point and then collpases. Also says the other american model errors it to try and weaken and push the system into the ridge. With a thickness ridge northeast of the system and not east this modeling is wrong, believes GFS and NAM will begin to figure this out tonight and tomorrow. JMA taking 1" back to I-81 is more likely than what the GFS is showing, and also a rain start in the big cities. Says it makes no sense for the storm to come up intensify and then stop this process. weakness in the american model physics

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Does anyone know why the Mt. Holly snow map shows lower totals in western Somerst amd eastern Hunterdon counties than the area immediately around it. Does the higher snowfall area represent higher elevation? Just curious.

Yes, it's ridges in NW Jersey.

yes, that would be my assumption

I think it has more to do with where they think the heaviest banding will set up. There is no elevation in the Eastern part of Somerset county and they are in the higher snowfall area.

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He doesn't know what he is talking about.

I'll take JB's opinion over a lot of others. Even if he's wrong, he's not afraid to lay it out there and stick with it. As it is, until other models show what he's saying it's terribly hard to see what he's saying. But the 18z RGEM isn't actually dry back here anymore like the 18z GFS.

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I'll take JB's opinion over a lot of others. Even if he's wrong, he's not afraid to lay it out there and stick with it. As it is, until other models show what he's saying it's terribly hard to see what he's saying. But the 18z RGEM isn't actually dry back here anymore like the 18z GFS.

I don't disagree that the US models may be a little too far SE but when he throws out the JMA model and talks about model physics (which I doubt he knows much about) then it starts sounding like BS.

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Wxsim forecast program off of the 18z runs of the GFS/NAM

Ligth snow by 130 pm temp 33.3

Mod snow by 3pm temp 32.0 (Snow by rush hour 1-2")

Heavy Snow by 530pm temp at 30.3

Heavy Snow thru around midnight

Total Snowfall 10" to 12"

Total snow on the ground Thursday AM - 15 to 17"

Current forecast has 2" more of snow early Saturday PM

The winter that keeps giving....won't stop!

I will actually miss this one as I am on a flight tomorrow AM to Ft. Lauderdale for business...I will of course be tracking etc. But I have a trained protege for snow measurements (My wife)

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Wxsim forecast program off of the 18z runs of the GFS/NAM

Ligth snow by 130 pm temp 33.3

Mod snow by 3pm temp 32.0 (Snow by rush hour 1-2")

Heavy Snow by 530pm temp at 30.3

Heavy Snow thru around midnight

Total Snowfall 10" to 12"

Total snow on the ground Thursday AM - 15 to 17"

Current forecast has 2" more of snow early Saturday PM

The winter that keeps giving....won't stop!

I will actually miss this one as I am on a flight tomorrow AM to Ft. Lauderdale for business...I will of course be tracking etc. But I have a trained protege for snow measurements (My wife)

Thanks for you updates, I pay close attention to them being just across the county here in Lancaster. Am hoping to see those heavy bands out my way with hopefully very little mixing.Snowman.gifSnowman.gif

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banter over DT's maps....is in the banter thread :arrowhead:...if anyone wants to back up their thoughts on his map with more detailed analysis its more likely to stay in this thread.

will be interested to see how all the 00z guidance intializes ...helluva lotta lightning from the tip of the Yucatan all the way to off the Ga coast, already a dynamic system

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