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December 9/10 Storm

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Just now, wawarriors4 said:

Agreed

The zone forecast has about 2 inches total for EZF.  Maybe they just don’t buy the north trend. 

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12 minutes ago, losetoa6 said:

a couple nice deform bands  depicted on the 3k. 2 inch /hr rates in central towards northern Va

How do you know that?  Just by the dark blue colors or something else?

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December 8, 2018

this Saturday night

930 PM EST

 

***  Preface:  This writing focuses ONLY on RICHMOND, VIRGINIA  ***

 

Gang --  I researched after several iterations of data that poured in today on tomorrow's Dec. 9, Sunday's snowy event scheduled for Richmond, VA.  Bottom line, for Richmond, is I'm expecting 5" to 8" of snowfall, with HIGHER amounts tapered SOUTH of Richmond and WEST of Richmond.  Lower amounts fanning further North & East.   I thinking Petersburg, for comparison may wind up with 6" to 10" there.  

I think the event will start as SNOW, between 6 AM to 8 AM Sunday morning, for the Richmond area.

Then, around 4 PM Sunday, it's appearing there's going to be a mixture of rain & snow from 4 PM onward Sunday.  As this transition occurs after 4 PM, it's also conceivable a mixture of ice pellets, (sleet), and perhaps freezing rain may become apparent, as you'll have to keep an eye on the air temperature.  Remember, freezing rain can only occur when temperatures at the surface get to 32° & below, but the air temperature need not be freezing for snow or ice pellets to occur.

Each successive iteration I've been watching since 00Z last evening to 6Z this morning, to 12Z this Saturday morning keeps on INCREASING the amounts UPWARD for Richmond.  However, there's a TIGHT gradient between amounts & as liquid as little as 2-3 counties EAST of Richmond, so busting on amounts will be higher in East Richmond, rather than West Richmond, where it's appearing a better solid lock on wintery weather there & in Chesterfield county will be more prominent.

In fact, Chesterfield county was looking like a PEAK local snowfall amount projected by this morning's 12Z, Sat., WRF indicating 1 foot, (12"), over thataways.  

I generally ignore the NAM model as I find it's way overplayed on wintery weather events, so I'll only post what I believe to be more representative & capable of happening, down below.

Another trick here is that once 4 PM onward comes around, not all the QPF will fall as solid form.  Once the rain hits, that'll reduce & compress the snowfall depths, beyond 4 PM.  So, I'm thinking the snowfall depth is likely to be greatest, in the late afternoon, just before changing over to the rain snow mix, around 4 PM.  

I.  Amounts for Richmond

It WILL be HUGE variances spread out across the metro Richmond area.  If you're living in Midlothian -- you'll get the HIGHEST amounts.  If you're living in Mechanicsville, to East Richmond, that's where the lowest amounts will be.  It's not going to be the same everywhere so don't expect it.    

Here are the projection numbers of snowfall based near Richmond, VA for Sunday, Dec. 9th:

00Z, Sat ECMWF -->>  5.5" for Richmond

12Z, Sat ECMWF -->>  8" for Richmond 

6Z, Sat GFS -->>  1.7" for Richmond

12Z, Sat GFS -->>  3.4" for Richmond (MOS: Trace to 2")

18Z, Sat GFS -->>  4.0" for Richmond

12Z, Sat, H-rap -->>  5.6" for Richmond to 7 PM  Rain-snow mix 1 PM to 5 PM, East Richmond

18Z, Sat, H-rap -->>  8.6" for Richmond

12Z, Sat, WRF -->>  9" Richmond; but 12" Chesterfield County, betwen 8 AM Sunday - 1 AM Monday;  8 AM to 4 PM snow; then rain-snow mix 4 PM, Sunday to 1 AM, Monday.

12Z, UKM  -->>  Between 7 AM to 7 PM, 0.68" of QPF, liquid-equivalent.

Referring to UKM's QPF above, This means if it ALL fell as snow in those 12 hours, on a 10:1 ratio given the surface temperatures expected then this would translate to 6.8" of snowfall ~~ approx. 7" of snow. 

** There WILL be compaction AND MELTING, too, once rain mixes-in **

II.  Timing.

Timing looks to start about 7 AM Sunday, Dec. 9th, continue all-day long Sunday, in to Sunday night, concluding 1 AM Monday morning.  All snow & wintery mixture ends by sunrise, Monday morning.

III.  Measuring Snow.

If you'll be measuring snow, do so ONLY over exposed, FLAT grassy areas away from trees, away from buildings, and away from other structures, and make several measurements nearby in UN-drifted areas, and average up the number of readings, and divide by the number of measurements taken.  Snowfall depth measurements are NOT taken from the highest heap of snow you see.  It doesn't work like that.  

IV.  The Surface Low Details

At 7 AM Sunday morning, Dec. 9 --

The surface low will be situated in extreme Southeast Georgia, (29.82"), headed Northeastward.

At 1 PM, Sunday afternoon, Dec. 9 --

The surface low is to be located about 50 - 75 miles Southeast of Myrtle Beach, South Carolina, (at 29.69", deepening), headed Northeastward

At 4 PM, Sunday afternoon, Dec. 9 --

Surface low to be located about 30 to 100 miles South of Beaufort, North Carolina.  Nam & ECMWF is closer to the Eastern North Carolina coast.  Gfs is farther out, away from the coast, as deep as 29.56", still deepening.

After 4 PM surface low slows its forward speed Sunday night, and takes a rightward bend to the East Northeast, about 100-200 miles off the coast of the outer banks of North Carolina by 10 PM Sunday night.   By this time the damage has already been done.     

V.  Upper features.

A broad upper-trough, whose trough axis runs meridionally across the state of Alabama will be in this position at 7 AM Sunday morning.  The vorticity lobe axis will stretch from Western North Carolina to New Orleans, LA at that time, 7 AM Sunday.  This trough will de-amplify with time, flattening & lifting out, exiting the Carolinas' coastlines by 4 PM Sunday.

An upstream kicker will be gliding across the Gulf south states of South Louisiana & Mississippi by 7 PM Sunday, which then exits the Carolinas' coasts by 7 AM Monday.

Richmond, VA will be under a stout right-entrance region of an exiting 250 mb 150+ kt jet max aloft, which is one of the enhanced regions for lift from Sunday morning to Sunday afternoon.  A broad region of moderate upper divergence values will be centered over Virginia & North Carolina from Sunday morning thru early Sunday afternoon, before pulling off the coast.

VI.  Thicknesses

GFS forecast thicknesses from 7 AM Sunday to 7 AM Monday start at 539 dm at 7 AM and gently rise to 541 dm by 7 PM. (What's this thickness all about & why care about it?)  Those who watch winter storms are aware of the 1000 mb to 500 mb thickness values, and knowing where the 540 dm thickness line is at.  Thicknesses at 540 dm & lower often correlate with snow & those values above 540 dm result in a mixture of snow-rain-freezing/frozen precipitation.  A better capture of analyzing a site's specific location is inspection of the Skew-T sounding diagrams, to inspect for levels that rise above freezing to determine an often culprit for pesky ice pellets mixing in.  So thicknesses are for generalization, but Skew-T's are more absolute.

The 1000-850 mb thicknesses, the line to watch here is the 1300 meter, and going below that for snow.  This is analyzing only the lower levels.  Here in Richmond, VA for tomorrow on Sunday, it's forecast to be 1283 m at 7 AM rising to 1303 by 7 PM.

So notice these 2 thicknesses and how they RISE by evening.  This helps explain why there looks to be a transition from snow early in the day to a rain-snow mixture by evening hours.

Sure enough, an inspection of the text product output from the Gfs sounding indicates a +1.0° C above-freezing warmer layer rooted between 900 - 925 mb.  This is between 2600 ft and 3350 ft.  My notes on using the Tau technique is in storage.  Bummer.  I'll dig it out next snow event.  No time for it tonight.  Anyways, you can do some tinkering around yourself with the Tau technique. Looks to be ice pellets for such a shallow, narrowly-above freezing layer.  But during the night, that warm layer aloft grows in depth & peaks at 2.8°C at 925 mb by 1 AM Monday.  That's okay, because that's so late, and I don't see such a warm layer intervening during the daytime so snow should continue on as scheduled during daylight hours.  Although, the surface temperatures will be hovering in the lower 30's, flirting above & below the freezing mark. 

As a last exciting feature to close on the Nam's 18Z output generated 14.6" of snowfall and newest 00Z, Sun, 12/9 data rolling in a short while ago shows 14.1".  As I said at the start of this writing, I ignore & disregard this Nam model; but it's there for your entertainment purposes, anyways!  It's quite an extremist.  

 

--  cyclogenesis

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2 minutes ago, yoda said:

How do you know that?  Just by the dark blue colors or something else?

From TT you could see the narrow dark blue rolling bands and I confirmed on Wxbell 2" hr

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10 minutes ago, wawarriors4 said:

Good deal! Think CHO is in a pretty good spot!

We can only hope! I'm in cvill and we got the shaft on the November snow. We all need a solid shellacking up in this subforum to get the season rolling right.

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33 minutes ago, BristowWx said:

12k south a tick from 18z at 19.  We may have seen the furthest north extent of the ticks. Barely touches extreme south PWC south of Quantico. 

Hang in there. We're only.a couple of counties away from moderate snowfall. I hear PWC closed schools already for Monday. 

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Just now, Wonderdog said:

Hang in there. We're only.a couple of counties away from moderate snowfall. I hear PWC closed schools already for Monday. 

Ha.  Tuesday as well.   Can’t wait for tomorrow.  I am stoked for the obs and tears and obs and tears

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8 minutes ago, BristowWx said:

The zone forecast has about 2 inches total for EZF.  Maybe they just don’t buy the north trend. 

True.... I’m still not sure what to expect around EZF to be honest 

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33 minutes ago, mattie g said:

OK...10%?

Let’s be honest...most of the major contributors and year-round folks are from the Baltimore and DC metro areas. Not sure how anyone can argue against that.

But don’t mind me...I’m just being a wiseacre, not a curmudgeon as @WxWatcher007 claims. He’s just bitter he had to move away, so now he’s telling lies and trying to badmouth the rest of us.

I don't know what the percent is, just wondering how you arrived at your figure.  In the meantime, I'll enjoy my wood stove and my snow tomorrow.  I didn't see you casting a tear or being worried about for those of us in the southern tier during the 11/15 storm!

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1 minute ago, wawarriors4 said:

True.... I’m still not sure what to expect around EZF to be honest 

Me either.  Bust potential is huge on both sides. Where it snows it will snow...where it doesn’t it won’t.  For that I am confident. 

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1 minute ago, WesternFringe said:

I don't know what the percent is, just wondering how you arrived at your figure.  In the meantime, I'll enjoy my wood stove and my snow tomorrow.  I didn't see you casting a tear for us in the southern tier during the 11/15 storm!

He was crying on the inside.  You can’t fault him for that.  We all hide our emotions sometimes. 

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18 minutes ago, cyclogenesis said:

December 8, 2018

this Saturday night

930 PM EST

 

***  Preface:  This writing focuses ONLY on RICHMOND, VIRGINIA  ***

 

Gang --  I researched after several iterations of data that poured in today on tomorrow's Dec. 9, Sunday's snowy event scheduled for Richmond, VA.  Bottom line, for Richmond, is I'm expecting 5" to 8" of snowfall, with HIGHER amounts tapered SOUTH of Richmond and WEST of Richmond.  Lower amounts fanning further North & East.   I thinking Petersburg, for comparison may wind up with 6" to 10" there.  

I think the event will start as SNOW, between 6 AM to 8 AM Sunday morning, for the Richmond area.

Then, around 4 PM Sunday, it's appearing there's going to be a mixture of rain & snow from 4 PM onward Sunday.  As this transition occurs after 4 PM, it's also conceivable a mixture of ice pellets, (sleet), and perhaps freezing rain may become apparent, as you'll have to keep an eye on the air temperature.  Remember, freezing rain can only occur when temperatures at the surface get to 32° & below, but the air temperature need not be freezing for snow or ice pellets to occur.

Each successive iteration I've been watching since 00Z last evening to 6Z this morning, to 12Z this Saturday morning keeps on INCREASING the amounts UPWARD for Richmond.  However, there's a TIGHT gradient between amounts & as liquid as little as 2-3 counties EAST of Richmond, so busting on amounts will be higher in East Richmond, rather than West Richmond, where it's appearing a better solid lock on wintery weather there & in Chesterfield county will be more prominent.

In fact, Chesterfield county was looking like a PEAK local snowfall amount projected by this morning's 12Z, Sat., WRF indicating 1 foot, (12"), over thataways.  

I generally ignore the NAM model as I find it's way overplayed on wintery weather events, so I'll only post what I believe to be more representative & capable of happening, down below.

Another trick here is that once 4 PM onward comes around, not all the QPF will fall as solid form.  Once the rain hits, that'll reduce & compress the snowfall depths, beyond 4 PM.  So, I'm thinking the snowfall depth is likely to be greatest, in the late afternoon, just before changing over to the rain snow mix, around 4 PM.  

I.  Amounts for Richmond

It WILL be HUGE variances spread out across the metro Richmond area.  If you're living in Midlothian -- you'll get the HIGHEST amounts.  If you're living in Mechanicsville, to East Richmond, that's where the lowest amounts will be.  It's not going to be the same everywhere so don't expect it.    

Here are the projection numbers of snowfall based near Richmond, VA for Sunday, Dec. 9th:

00Z, Sat ECMWF -->>  5.5" for Richmond

12Z, Sat ECMWF -->>  8" for Richmond 

6Z, Sat GFS -->>  1.7" for Richmond

12Z, Sat GFS -->>  3.4" for Richmond (MOS: Trace to 2")

18Z, Sat GFS -->>  4.0" for Richmond

12Z, Sat, H-rap -->>  5.6" for Richmond to 7 PM  Rain-snow mix 1 PM to 5 PM, East Richmond

18Z, Sat, H-rap -->>  8.6" for Richmond

12Z, Sat, WRF -->>  9" Richmond; but 12" Chesterfield County, betwen 8 AM Sunday - 1 AM Monday;  8 AM to 4 PM snow; then rain-snow mix 4 PM, Sunday to 1 AM, Monday.

12Z, UKM  -->>  Between 7 AM to 7 PM, 0.68" of QPF, liquid-equivalent.

Referring to UKM's QPF above, This means if it ALL fell as snow in those 12 hours, on a 10:1 ratio given the surface temperatures expected then this would translate to 6.8" of snowfall ~~ approx. 7" of snow. 

** There WILL be compaction AND MELTING, too, once rain mixes-in **

II.  Timing.

Timing looks to start about 7 AM Sunday, Dec. 9th, continue all-day long Sunday, in to Sunday night, concluding 1 AM Monday morning.  All snow & wintery mixture ends by sunrise, Monday morning.

III.  Measuring Snow.

If you'll be measuring snow, do so ONLY over exposed, FLAT grassy areas away from trees, away from buildings, and away from other structures, and make several measurements nearby in UN-drifted areas, and average up the number of readings, and divide by the number of measurements taken.  Snowfall depth measurements are NOT taken from the highest heap of snow you see.  It doesn't work like that.  

IV.  The Surface Low Details

At 7 AM Sunday morning, Dec. 9 --

The surface low will be situated in extreme Southeast Georgia, (29.82"), headed Northeastward.

At 1 PM, Sunday afternoon, Dec. 9 --

The surface low is to be located about 50 - 75 miles Southeast of Myrtle Beach, South Carolina, (at 29.69", deepening), headed Northeastward

At 4 PM, Sunday afternoon, Dec. 9 --

Surface low to be located about 30 to 100 miles South of Beaufort, North Carolina.  Nam & ECMWF is closer to the Eastern North Carolina coast.  Gfs is farther out, away from the coast, as deep as 29.56", still deepening.

After 4 PM surface low slows its forward speed Sunday night, and takes a rightward bend to the East Northeast, about 100-200 miles off the coast of the outer banks of North Carolina by 10 PM Sunday night.   By this time the damage has already been done.     

V.  Upper features.

A broad upper-trough, whose trough axis runs meridionally across the state of Alabama will be in this position at 7 AM Sunday morning.  The vorticity lobe axis will stretch from Western North Carolina to New Orleans, LA at that time, 7 AM Sunday.  This trough will de-amplify with time, flattening & lifting out, exiting the Carolinas' coastlines by 4 PM Sunday.

An upstream kicker will be gliding across the Gulf south states of South Louisiana & Mississippi by 7 PM Sunday, which then exits the Carolinas' coasts by 7 AM Monday.

Richmond, VA will be under a stout right-entrance region of an exiting 250 mb 150+ kt jet max aloft, which is one of the enhanced regions for lift from Sunday morning to Sunday afternoon.  A broad region of moderate upper divergence values will be centered over Virginia & North Carolina from Sunday morning thru early Sunday afternoon, before pulling off the coast.

VI.  Thicknesses

GFS forecast thicknesses from 7 AM Sunday to 7 AM Monday start at 539 dm at 7 AM and gently rise to 541 dm by 7 PM. (What's this thickness all about & why care about it?)  Those who watch winter storms are aware of the 1000 mb to 500 mb thickness values, and knowing where the 540 dm thickness line is at.  Thicknesses at 540 dm & lower often correlate with snow & those values above 540 dm result in a mixture of snow-rain-freezing/frozen precipitation.  A better capture of analyzing a site's specific location is inspection of the Skew-T sounding diagrams, to inspect for levels that rise above freezing to determine an often culprit for pesky ice pellets mixing in.  So thicknesses are for generalization, but Skew-T's are more absolute.

The 1000-850 mb thicknesses, the line to watch here is the 1300 meter, and going below that for snow.  This is analyzing only the lower levels.  Here in Richmond, VA for tomorrow on Sunday, it's forecast to be 1283 m at 7 AM rising to 1303 by 7 PM.

So notice these 2 thicknesses and how they RISE by evening.  This helps explain why there looks to be a transition from snow early in the day to a rain-snow mixture by evening hours.

Sure enough, an inspection of the text product output from the Gfs sounding indicates a +1.0° C above-freezing warmer layer rooted between 900 - 925 mb.  This is between 2600 ft and 3350 ft.  My notes on using the Tau technique is in storage.  Bummer.  I'll dig it out next snow event.  No time for it tonight.  Anyways, you can do some tinkering around yourself with the Tau technique. Looks to be ice pellets for such a shallow, narrowly-above freezing layer.  But during the night, that warm layer aloft grows in depth & peaks at 2.8°C at 925 mb by 1 AM Monday.  That's okay, because that's so late, and I don't see such a warm layer intervening during the daytime so snow should continue on as scheduled during daylight hours.  Although, the surface temperatures will be hovering in the lower 30's, flirting above & below the freezing mark. 

As a last exciting feature to close on the Nam's 18Z output generated 14.6" of snowfall and newest 00Z, Sun, 12/9 data rolling in a short while ago shows 14.1".  As I said at the start of this writing, I ignore & disregard this Nam model; but it's there for your entertainment purposes, anyways!  It's quite an extremist.  

 

--  cyclogenesis

Can you repeat that?

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I'm debating if I should leave my place in Currituck to go back to the Woodbridge house early tomorrow.  I have appointments in Northern Virginia and DC on Tuesday that I cannot miss so either I come back early tomorrow or chance driving back on Monday, assuming the roads are clear. Either way I'm most likely to miss seeing any snow. Unless I leave too late and get caught driving through the Richmond area.

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URGENT - WINTER WEATHER MESSAGE
National Weather Service Baltimore MD/Washington DC
1001 PM EST Sat Dec 8 2018

VAZ026-029-038>040-050-051-055-056-502-507-091115-
/O.EXB.KLWX.WW.Y.0027.181209T1600Z-181210T0500Z/
Rockingham-Page-Greene-Madison-Rappahannock-Orange-Culpeper-
Stafford-Spotsylvania-Southern Fauquier-
Northern Virginia Blue Ridge-
1001 PM EST Sat Dec 8 2018

...WINTER WEATHER ADVISORY IN EFFECT FROM 11 AM SUNDAY TO
MIDNIGHT EST SUNDAY NIGHT...

* WHAT...Snow expected with accumulations around 2 to 4 inches.

* WHERE...Portions of northern and central Virginia.

* WHEN...From 11 AM Sunday to midnight EST Sunday night. The
  heaviest snow will be Sunday afternoon and evening.

* ADDITIONAL DETAILS...Plan on snow covered roads and slippery
  conditions. Travel will be difficult. Temperatures will remain
  well below freezing Sunday night, so any untreated surfaces will
  remain snow covered and slippery.

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One nice thing about this setup is we have plenty of cold air. For those of us south of DC any snow that may fall will stick. We need a 50 mile shift to score a nice event. 

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3 minutes ago, Ji said:
4 minutes ago, yoda said:
00z RGEM 0.07" QPF at DCA

South trend continues

See you in a few for the HRDPS

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9 minutes ago, Ji said:
10 minutes ago, yoda said:
00z RGEM 0.07" QPF at DCA

South trend continues

Precip shield is actually further North of 18z, it's just that precip is light

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10 minutes ago, Ji said:
39 minutes ago, leesburg 04 said:
Who will be the dolt to quote that

Just what I wanted to read

At least you know you are mostly out.  I’m less out but so close to being almost in.  Miles make the difference in 5 mile increments. 

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