Second call Snowfall accumulations and storm stats>>&g

[NEwxgirl]

I’m not too thrilled with model solutions thus far; the GFS and ETA 18z runs are diverging even more than the 12z runs. Even that said I would much rather like to put my forecasting faith in the 0z and 12z packages since they are run off newly ingested RAOB data.

GFS 18z 12/12 500mb heights and vorticity initialization>>>



Sub-tropical jet shortwave energy/500mb trough will continue to progress out of the southwest into the southern plains overnight and Saturday reaching the Mississippi valley on Sunday. Polar jet energy will dig southeastward into the upper Midwest and phase with the sub-tropical jet energy letting the tilt of the 500mb trough to become negative.

GFS 500mb heights and vorticity valid 12z – 12/15>>>



The GFS develops a closed 500mb low (at 534 DM) within the negatively tilted trough on the afternoon of the 15th, over New Jersey.

The secondary (coastal) low pressure center begins to take shape in the inverted trough along the North Carolina coast and rapidly intensifies as it moves northeastward. The surface low should be close to the benchmark by 12z on the 15th.

Surface pressure and 6-hour precipitation valid 12z – 12/14>>>



Surface pressure and 6-hour precipitation valid 18z – 12/14>>>



Surface pressure and 6-hour precipitation valid 0z – 12/15>>>



Surface pressure and 6-hour precipitation valid 6z – 12/15>>>



Surface pressure and 6-hour precipitation valid 12z – 12/15>>>



This will most likely be a rapidly developing low pressure center the likes of what we saw on Christmas 2002, a little less than one year ago. (We may be talking about surface pressures as low as 980mb).

The strength of this system is critical because it will give areas across eastern Pennsylvania and New Jersey which change to sleet and freezing rain the chance to turn back to snow and possibly see some more accumulation with the wrap around moisture. Since low pressure areas like to pull air toward them, the stronger the low becomes the faster the cold air is drawn in, much like Christmas. As the low strengthened, precipitation quickly changed back to snow in Eastern Pennsylvania and New Jersey.

As low pressure closes off in the mid-levels I’m thinking the deformation zone sets up from central and northeast Pennsylvania into southeastern New York, therefore this should be the location which sees the heaviest snow for the longest duration. I would not be shocked to see snowfall rates of 1-2 inches per hour with heavier rates (of 2-3 inches per hour) underneath any CSI induced heavy snowfall bands which develop (until they are wiped out by increasing shear as absolute geostrophic vorticity tries to come back to positive). This all of course depends on the track of the surface low and exact positions of critical mid and upper level features.

Most of the northeast appears to be in a coupled jet pattern. Very strong vertical motions (negative omega) associated with divergence in the left front quadrant of an upper level wind maximum moving up the eastern side of the negatively tilted 300mb trough will nose northeastward into the mid-Atlantic as another speed maximum departs new England (placing the northeast in its rear right quadrant). This as eluted to is very favorable for strong rising air motions and enhanced precipitation (snowfall) rates.

GFS 300mb height, wind and isotachs valid 18z on 12/14>>>



The GFS brings in the best negative omega (within a nearly or completely saturated environment) into central and eastern Pennsylvania around 0z 12/15.

GFS 700mb height, wind, RH and omega valid 0z 12/15>>>



It is possible that the very intense vertical motions allow the column to remain below freezing even in the face of strong warm advection northwest of the major cities, supporting a longer duration of heavy snow. Areas closest to the rain (or IP/ZRA)-snow line where dynamically induced cooling can maintain below freezing temperatures throughout the vertical column could very well see the heaviest accumulations.

Another area which will be susceptible to enhanced accumulations is those areas closest to the -8C isotherm (at 850mb or 5,000 ft). 850mb temperatures around that value normally represent a deep layer thermal profile which is supportive of optimal dendrite growth (leading to heavier snowfall).

Our axis of heaviest snow is 50 to 75 miles either side of a line from Cumberland, Maryland to Bangor Maine.

Heavy freezing rain and sleet will occur just to the northwest of the major cities as a mid-level warm layer develops in response to the strengthening warm air advection and weakening cold air damming as the high moves out.

Snowfall totals (and storm details) for specific locations across the mid-Atlantic and northeast.

Roanoke, VA ---- 3-6 Inches. Precipitation begins as a period of heavy snow, and then changes to a mix of sleet and freezing rain with significant ice accumulation possible.
Martinsburg, WV ---- 4-8 Inches. Prolonged period of heavy snow changes to sleet and freezing rain with significant ice accumulations possible as warm layer moves in aloft.
Cumberland, MD ---- 5-10 Inches. Heavy Snow. Some mixing is possible; though ice accumulations should be limited.
Washington, DC ---- 3-5 Inches. A period of heavy snow followed by a change to sleet and freezing rain, then all rain for a time, precipitation may once again change back to snow before ending as colder air moves in on the back side of the low.
Baltimore, MD ---- 3-7 Inches. A somewhat longer period of heavy snow followed by a change to sleet and freezing rain, then all rain for a time, precipitation may once again change back to snow before ending as colder air moves in on the back side of the low.
Dover, DE ---- 2-3 Inches. Brief period of heavy snow, quickly changing to sleet and rain, then all rain. Little icing is anticipated as low level cold air may not be in place.
Wilmington, DE ---- 3-5 Inches. Short period of heavy snow, quickly changing to sleet and freezing rain, then all rain. Some icing is possible before the boundary layer warms above freezing.
Lancaster, PA ---- 6-10 Inches. Prolonged period of heavy snow, precipitation will mix with and change to sleet and freezing rain. Severe ice accumulations are possible.
Harrisburg, PA ---- 8-12 Inches. Heavy snow, some mixing with sleet or freezing rain.
State College, PA ---- 10-15 Inches. Heavy snow, little if any mixing.
Williamsport, PA ---- 10-16 Inches. Heavy snow, little if any mixing.
Allentown, PA ---- 8-12 Inches. Heavy snow, some mixing with sleet and freezing rain is possible.
Philadelphia, PA ---- 3-6 inches. Period of heavy snow, changing to sleet and freezing rain, (plain rain is possible south and east of the city). Significant ice accumulations are possible, especially just outside of the city to the northwest.
Mount Pocono, PA ---- 10-18 Inches. Heavy snow, little if any mixing.
Scranton/Wilkes-Barre, PA ---- 10-18 Inches. Heavy Snow, little if any mixing.
Binghamton, NY ---- 12-20 Inches. Heavy snow, no mixing.

Our expected totals for New England will be posted tomorrow morning, (along with any changes to the current forecast) which will give me more time to look at things in greater detail, and have the advantage of being able to look at the complete 0z model package late this evening.

RNS will be back tomorrow evening.

[Colin]

AWESOME analysis!

[Stormchaser16]

Good forecast, but no totals for NJ or even NYC??????????

[R0bb0871]

Awesome job. Thanks! But, same question as stormchaser. What about NYC/NJ?

[Fishmn]

I think your totals are high to the SE of Philadelphia especially in the Delmarva, but I'll take the 10 or so inches you forcast for my area any day.

[Squall52]

"Another area which will be susceptible to enhanced accumulations is those areas closest to the -8C isotherm (at 850mb or 5,000 ft). 850mb temperatures around that value normally represent a deep layer thermal profile which is supportive of optimal dendrite growth (leading to heavier snowfall). "

Nicely detailed forecast, and discussion. I don't claim to know the mid-atlantic that well at all, but definetly agree with the threat for heavy ice in NW VA etc. Kind of surprised with ice in Wilmington, DE tho.
One question about above...I know that in lake effect situations, and other heavy snow setups, I believe, the best snow growth occurs when high omega values occur in the -12 to -15C layer. I never heard of the -8C 850 value being especially useful, could you elaborate at all? Thanks.

[nystate]

Great discussion! One question- BUF NWS is saying that areas including Watertown, NY could get more than a foot of snow...do you see this happening?

[NEwxgirl]

Great discussion! One question- BUF NWS is saying that areas including Watertown, NY could get more than a foot of snow...do you see this happening?

Probably not, totals up to a foot are possible, though i think the heaviest accumulations (12+) will fall to the east of watertown.

[Colin]

Erica check your PM

[rick-g]

I got some spare beds at my place, I'll be posting picts if we get anything close to the forecast amounts mentioned by RNS and NEwxGirl

[NEwxgirl]

"Another area which will be susceptible to enhanced accumulations is those areas closest to the -8C isotherm (at 850mb or 5,000 ft). 850mb temperatures around that value normally represent a deep layer thermal profile which is supportive of optimal dendrite growth (leading to heavier snowfall). "

Nicely detailed forecast, and discussion. I don't claim to know the mid-atlantic that well at all, but definetly agree with the threat for heavy ice in NW VA etc. Kind of surprised with ice in Wilmington, DE tho.
One question about above...I know that in lake effect situations, and other heavy snow setups, I believe, the best snow growth occurs when high omega values occur in the -12 to -15C layer. I never heard of the -8C 850 value being especially useful, could you elaborate at all? Thanks.

I'm quite aware of favorable snow growth occuring when the strongest negative omega is in the -12 to -15C layer, however, there was some research done awhile back stating that there was a correlation (RNS uses it quite a bit and it seems to work well for him, especially last year), so i decided to give it a try. I'm sure he could probably explain it a bit better since it is more his forecasting tool (and not to mention little known amongst others). Most of his methods he doesn't share with me or anyone for that matter. the most i was told about it was what you saw in my post.

[R0bb0871]

Here's what I think will occur in the state of New Jersey.

GREEN - Areas under the color green will experience a snow/sleet mixture when precipitation starts. This wintry mix will accumulate to a slushy inch to two inches. As the low pressure system heads up the coast, precipitation will change over to rain rapidly and stay as rain for a good portion of Sunday into Monday. Rain could be heavy at times, causing flooding problems, as the ground is already well saturated.

PURPLE - Areas under the color purple will begin with snow, possibly accumulating 2-3 inches. A period of freezing rain may occur during the transition from snow to rain. How long this period of freezing rain will last is still uncertain and will be in need of watching.

DARK PINK - Areas under dark pink will experience the heaviest snow in the state. Snow may possibly accumulate 3-6 inches. I'm very concerned with significant icing across this area. The freezing line will be crucial in determining whether or not there will be a great deal of freezing rain, and the time when precipitation mixes and ultimately changes to rain, if it does.

Conclusion: There are still many uncertainties on the track of this system, and thus, precipitation type across the state. However, I do believe the entire state will experience some sort of mix at one point or another, whether it be snow and sleet or sleet and rain. A slight change in track can alter this entire forecast, but, I do believe this is the best guess as of right now.

[Lowpressure]

Excellent forecast reasoning, well thought out and descriptive. Thanks-Great job.

[donsutherland1]

Erica,

A really great discussion to read.

Also, as Erica mentions CSI, for those who are interested in learning more about CSI (Conditional Symetric Instability), RNS wrote a lengthy <b>piece</b> on the topic here a while ago. Just click on the hyperlink to access it.

[NEwxgirl]

0z Model initializations were not too good this evening.

[Squall52]

"Another area which will be susceptible to enhanced accumulations is those areas closest to the -8C isotherm (at 850mb or 5,000 ft). 850mb temperatures around that value normally represent a deep layer thermal profile which is supportive of optimal dendrite growth (leading to heavier snowfall). "

Nicely detailed forecast, and discussion. I don't claim to know the mid-atlantic that well at all, but definetly agree with the threat for heavy ice in NW VA etc. Kind of surprised with ice in Wilmington, DE tho.
One question about above...I know that in lake effect situations, and other heavy snow setups, I believe, the best snow growth occurs when high omega values occur in the -12 to -15C layer. I never heard of the -8C 850 value being especially useful, could you elaborate at all? Thanks.

I'm quite aware of favorable snow growth occuring when the strongest negative omega is in the -12 to -15C layer, however, there was some research done awhile back stating that there was a correlation (RNS uses it quite a bit and it seems to work well for him, especially last year), so i decided to give it a try. I'm sure he could probably explain it a bit better since it is more his forecasting tool (and not to mention little known amongst others). Most of his methods he doesn't share with me or anyone for that matter. the most i was told about it was what you saw in my post.

Interesting; thanks anyways. I was curious that this might have to do with why some storms have a region of heaviest snow near the northwest edge of the accumulating snow. Besides just deformation, CSI etc.

Another issue...I see that this storm is progged to cut more ENE as it reaches NJ/LI. Is this going to be an issue of timing; ie when the next s/w kicks this system, versus how fast this one develops...how fast the phase occurs, vort rounds the trough base, trough goes negative etc.? Or am I way off?

[Anonymous]

Good Analysis. This storm does remind me a lot of the Christmas Storm. Here in the Ohio Valley, models did horriably with that storm, until about 12 hours before it began. I am still very skeptical about our region though, as no models are indicating heavy snow. Here in Indiana I am forecasting 2-4 inches of snow with a 3-6 band across Missouri and a 3-6 inch band across Eastern Ohio. Any thoughts?

[NEwxgirl]

"Another area which will be susceptible to enhanced accumulations is those areas closest to the -8C isotherm (at 850mb or 5,000 ft). 850mb temperatures around that value normally represent a deep layer thermal profile which is supportive of optimal dendrite growth (leading to heavier snowfall). "

Nicely detailed forecast, and discussion. I don't claim to know the mid-atlantic that well at all, but definetly agree with the threat for heavy ice in NW VA etc. Kind of surprised with ice in Wilmington, DE tho.
One question about above...I know that in lake effect situations, and other heavy snow setups, I believe, the best snow growth occurs when high omega values occur in the -12 to -15C layer. I never heard of the -8C 850 value being especially useful, could you elaborate at all? Thanks.

I'm quite aware of favorable snow growth occuring when the strongest negative omega is in the -12 to -15C layer, however, there was some research done awhile back stating that there was a correlation (RNS uses it quite a bit and it seems to work well for him, especially last year), so i decided to give it a try. I'm sure he could probably explain it a bit better since it is more his forecasting tool (and not to mention little known amongst others). Most of his methods he doesn't share with me or anyone for that matter. the most i was told about it was what you saw in my post.

Interesting; thanks anyways. I was curious that this might have to do with why some storms have a region of heaviest snow near the northwest edge of the accumulating snow. Besides just deformation, CSI etc.

Another issue...I see that this storm is progged to cut more ENE as it reaches NJ/LI. Is this going to be an issue of timing; ie when the next s/w kicks this system, versus how fast this one develops...how fast the phase occurs, vort rounds the trough base, trough goes negative etc.? Or am I way off?

Tonight's model initials are terrible (and even RNS thinks the ETA is way off), i think this is more an issue of all those factors combined. The phase should occur in the mississippi valley, once that happens the trough will then tilt negative. Coastal cyclogenesis takes place just east of cape Hatters and then the low rapidly deepens as the negative tilt to the 500mb trough increases and the low closes off (much like what i talked about in my post). The track of the surface low from there will most likely be very close to the coast (let's say 25-50 miles offshore).

And as far as the 850mb temperature correlation, you could be right, the january 19 snowstorm. Binghamton saw up to 12 inches of snow along the norther edge of the precipitation sheild even though the highest QPFs were observed much further to the south.

[JCT777]

Excellent analysis, NEwxgirl. The snow amounts are a little higher than my current thinking, but I certainly hope it verifies!

[WXBUFFJIM]

I'll handle 3-7 inches of snow anyday. Around here, it's always that rain/snow line issue though. I'm thinking the city of Baltimore on south will see the lower end of those amounts, possibly less than 3 near the bay and down towards BWI and Reagan National as it changes over to rain sooner usually in those areas. Being from Baltimore myself, it seems the trends favor less snow se of the city, and more nw of the city.
3-7 inches sounds perfect to me from Carroll, Howard,and Montgomery Counties, MD on north and west towards Hagerstown. Ice accumulation could be 1/4-1/2 inch in these places potentially as well. I would seriously keep an eye on the Blue Ridge Parkway and the Skyline Drive. Get ready to lose power from northwestern Virginia through eastern West Virginia and into western North Carolina. That maybe the hot zone for major ice accumulation of over 1/2 inch thick. That's enough to knock down trees and powerlines and most likely some places will lose power down there because of this. I'll keep ya posted on that possibility.

Jim