Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 6:35 PM GMT on January 18, 2012
Light snow is likely associated along the cold front with an area of warm air advection. Amounts will remain light and around 1-3in for most areas. A strong storm system will approach the region towards the weekend with widespread wintry weather. I will post a new blog for this next event on Friday. For now this blog will focus primarily on the nuisance snows Thursday night.
Current Surface Plot...
(Courtesy of HPC)
January 19 Clipper/Occluded Front Timeline and Discussion...
12pm-2pm Thursday: A reinforcing shot of cold air behind a cold front will begin to move across western New York and western Pennsylvania. Warm air advection ahead of the cold front will add a bit of additional lift ahead of the front with widespread light snows from the mountains of Maryland up through western New York in this period. Dry air will inhibit moisture aloft preventing snow rates reaching much higher than .5in/hr. Orographic lift across the higher elevations in western areas will assist in light snow totals of 1-3in.
2pm-4pm Thursday: The fast movement of the cold front and weak shortwave over northern New York will keep snows rapidly advancing east. Light snows will move into central New York and central Pennsylvania. Downsloping east of the higher elevations will begin to weaken snows across Pennsylvania south into Maryland. Light snows will only last at one location for no more than 2-4hrs with visibilities primarily ranging from 1-3mi. Given the northern track of the shortwave, it is not a favorable track for most areas for the heaviest snow swath. Warm air advection will continue to along for a minor area of frontogenesis-enhanced light snow before coming to an end from west to east. Snows will already begin to be moving out of extreme western areas.
4pm- 7pm Thursday: The stratiform light snow shield will begin to move into southern New England and into eastern New York and Pennsylvania. The precipitation shield will begin to deteriorate across eastern Pennsylvania courtesy of downsloping and minimal lift given the large displacement from the shortwave. Snow amounts for most areas will be in the 1-3in range through this period and again will only last for 2-4 hours at any one location. Snow will already be out of areas such as Pittsburgh and Buffalo.
7pm- 10pm Thursday: As the shortwave progresses east along the cold front, a southeasterly flow off the Atlantic will add a bit of additional moisture across eastern New England. Light snow will begin to break out ahead of the main WAA snow shield, but accumulations will be minimal and limited to a coating. The main WAA snows will be progressing across central New England down through New York City. The steadiest snows will be limited north of the New York City metro region limiting accumulations in this region.
10pm- 2am Friday: Light snow will continue to move into eastern New England and begin to push off into the Atlantic coast. The shortwave will begin to amplify as it moves east; a weak southeasterly flow will also exist. These factors will aid in a narrow band of snow along the area of highest frontogenic forcing. Snow totals will be enhanced in this region ranging from 2-5in. This advisory criteria snow will be limited to far eastern New England. By 3am or so, most all snow will be pushed off the coast.
Quick Discussion: Temperatures at the surface will remain below freezing for all areas and will not be a major concern. A bit of light rain/snow is possible for Long Island, but all other areas will be pure snow. H85s around -8C and warm air advection aloft will add to snow ratios at nearly 15:1 or 20:1 with a widespread light and fluffy snow. Most amounts will be light and nuisance, but given impacts around evening rush, there may be some travel impacts. Also the lack of snow this year makes this appear to be a bigger event than normal for this winter. Behind the cold front, a northwest flow will allow for a bit of lake effect snow, but increased shear levels aloft will limit organization. Any additional accumulations will be below 4in for the general snow belt regions. Another storm system will approach the region by Saturday morning with precipitation breaking out across the northeast before dawn on Saturday.
(Courtesy of NOAA)
(Courtesy of NOAA)
1. Widespread light snow from the Mason-Dixon line on northward.
2. Light snow accumulations for many areas that have not seen much snow this winter.
3. Higher snow amounts in eastern New England due to some eastern enhancement.
4. Snow ratios nearly 20:1 for many areas.
5. Amounts generally at nuisance levels of 1-3in.
***Areas not included in the 1-4in snow range may see spotty coating to one inch snow amounts especially just southeast of the 1-4in vs. 0in border
Current Great Lakes Water Temperatures...
(Courtesy of NOAA)
Selected City Accumulations for the Northeast...
Hagerstown, MD- Dusting of snow
Baltimore, MD- Dusting of snow
Salisbury, MD- A few flurries; no accumulation
Pittsburgh, PA- Light snow; 1-3in
State College PA- Light snow; 1-3in
Williamsport, PA- Light snow; 1-3in
Altoona, PA- Light snow; 1-3in
Harrisburg, PA- Light snow; C-1in
Lancaster, PA- Light snow; C-1in
Philadelphia, PA- Light snow; dusting
Allentown, PA- Light snow; C-1in
Scranton, PA- Light snow; 1-3in
Washington, DC- Flurries; 0in-dusting
Wilmington, DE- Light snow showers; dusting
Dover, DE- Light snow showers; dusting
Trenton, NJ- Light snow; C-1in
New York City, NY- Light snow; 1-3in
Poughkeepsie, NY- Light snow; 1-3in
Binghamton, NY- LIght snow; 1-3in
Ithaca, NY- Light snow; 1-3in
Albany, NY- Light snow; 1-3in
Hartford, CT- Light snow; 1-4in
Concord, NH- Light snow; 2-4in
Providence, RI- Light snow; 2-5in
Worcester, MA- Light snow; 2-4in
Boston, MA- Light snow; 2-4in
Nantucket, MA- Light snow; 1-4in
Hyannis, MA- Light snow; 2-5in
Burlington, VT- Light snow; 1-3in
Portland, ME- Light snow; 2-5in
Bangor, ME- Light snow; 2-5in
"Subject to Change"
Current Northeast Snow Depth and Northeast Wind chills...
(Courtesy of Wunderground)
General model guidance differences exist in QPF totals across most areas. NAM and ECMWF tend to be a bit drier especially for southern areas along and east of the Appalachians. NAM indicates QPF less than .01in across southern and eastern portions of New Jersey and Pennsylvania. Meanwhile the GFS shows a more widespread area of snow showers with QPF totals about 0.05-0.1in higher. Given the increase in warm air advection ahead of the cold front, it is likely the higher QPF totals from the GFS will verify. Latest high resolution guidance including the 4km NMM indicates a bit of enhancement across eastern areas in New England particularly towards eastern Massachusetts up through Maine. This enhancement is also signaled by global guidance. The enhanced area of QPF is associated with a digging shortwave as the low begins to strengthen as it moves east over the Atlantic. Snow rates will generally stay below 0.5in/hr for most all areas as visibilities will range from 1-3mi. This will keep conditions at IFR or MVFR at aviation fields. Timing differences in the models are very minimal, at general consensus for my forecast is about 60/30/10 for GFS/ECMWF/NAM, etc.
After the Storm
A weak shortwave in the western United States will translate eastward by the weekend spreading a shield of precipitation courtesy of strong WAA into the Middle Atlantic and New England regions. This southwest flow event (SWFE) is very consistent in La Nina-like patterns. A 1024mb high pressure to the north will stay wedged across the region in southern Quebec, but will begin to slowly lift away to the northeast. This anticyclone will allow for a wedge of cold air to remain lodged in across the Northeast south towards the Mason-Dixon line for areas along and east of the Appalachian mountains. Overrunning precipitation along a thermal boundary will allow QPF totals from .25in-.6in. Weak dynamics and some dry air advecting south out of Canada will limit higher QPF totals. Given the close proximity of the thermal gradient and the enhanced area of warm air advection, precipitation type will likely be a major concern for this storm system. It remains too early to begin to note precipitation transition lines, but given past history with SWFE's, it is likely the cold air at the surface will be underestimated by models, while mid level warmth is also underestimated. Therefore many areas that are just about the 0C H85 line will see sleet due to a warm tongue. Also models typically underestimate the extent of the QPF shield, so therefore a bit of snow is likely for many areas before the warmth advects into the region. Freezing rain will be a big concern, but will depend will the thermal gradient sets up. Dry air across northern New England will likely inhibit most precipitation in this region and therefore most of the QPF will stay south of southern Vermont and southern New Hampshire. It should be noted the NAM is farther north than most guidance, but for now it remains an outlier.
As I mentioned the other day, I am not on the heat wave bus anymore for next week. I would expect cool air to hang around for a few days with chances of wintry precipitation. There will be a 1-2 very warm period ahead of a Great Lakes cutter, but that does not likely until the end of the week or so.
Snow Map Storm 2...
***This is a rough estimate of precipitation types for the Saturday event. The precipitation types were determined by the type of precipitation during the height of the event for each individual locations. It is likely many southern areas start as snow and changing to freezing rain and then perhaps plain rain. But I chose to indicate types based on the height of the event. Snow accumulations are possible even in some parts of the freezing rain area.
Please post storm reports in this blog from across the Northeast during the winter storm and please post location of observation in each report...
This blog is in progress. Check back soon...
Winter Forecast 2011-2012... Link
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Lower Susquehanna Valley Doppler...
(Courtesy of WGAL)
"10mi northeast of Harrisburg 2011-2012 winter statistics"
Current Snow Cover- 0.0in
Monthly Total (October)- 5.5in
Monthly Total (November)- 0.0in
Monthly Total (December)- 0.4in
Monthly Total- (January)- 0.2in
Seasonal Total- 6.1in
Winter Weather Advisories- 1
Winter Storm Warnings- 1
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 0
Winter Storm Watches- 1
Lowest High Temperature- 29F
Lowest Low Temperature- 10F
Wind Chill Advisories- 0
Wind Chill Warnings- 0
(Snow Storms Stats)
Historic October Nor'easter - October 29 - 5.5in of wet snow
322 Lake Effect Snow Band - December 17 - 0.3in of wet snow
Weak Clipper - December 29 - 0.1in of snow
322 Lake Effect Snow Band - January 18 - 0.2in of snow
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