Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 1:04 PM GMT on October 25, 2011
Well it is official... the first winter storm blog of the year. A wet snow is possible across the higher elevations of New England on October 27 with rain elsewhere. Another, potentially larger, threat of snow looms towards the weekend. I will post more on that in this blog later today. Stay tuned!
Thoughts on October 27 Rain/Snow Event
As the cold front begins to slow sink south, a 1004mb low will traverse along the front across northern Maryland through southern New Jersey. Precipitation will generally be light to moderate in most locations with the heaviest bands located about 50-100mi north of the 850hPa low center. Current guidance suggests rain will be the dominant precipitation type as it begins to funnel into the region during the first half of Thursday with only a few higher elevations in the Catskills and Berkshires getting a rain/snow mix (primarily above 2000ft).
As the low begins to strengthen in southern New Jersey before it exits the coast, a northwest flow will advect colder air into the region midday Thursday. H85 thermals will drop from +4C to (-1)-(-3)C across northern locations particularily in southern New York/northern Pennsylvania and across central New England. 2m temperatures will begin to fall below 34F as precipitation begins mixing with and then changing to a wet snow. Given the warmer boundary layer temperatures, snow will begin to fall only above 1000ft elevation for most locations. Snow ratios near 6/7:1 will keep accumulations minimal given warm ground temperatures and the higher sun angle. Also lower precipitation rates will prevent major accumulations.
The now 1000mb low will begin to slowly deepen off the coast of New England as cold air continues to advect into the region Thursday evening. A deformation band of snow along a concentrated area of frontogenesis will enhance precipitation rates for southern New York and northern Pennsylvania in through central New England. 6hr QPF totals in high resolution guidance suggest 0.25-0.5in of precipitation in this period. This is likely the time of greatest snow accumulation. Elevations above 1500ft will likely see 1-4in of snow with isolated higher amounts. Valley locations will likely see only a trace to 2in of snow. This snow area will again be concentrated from northern Pennsylvania up through New Hampshire in a narrow band.
Total QPF will range from a low near .3in around the Pittsburgh region gradually increasing to over 1in near Boston. For locations south of I-80 across Pennsylvania little to no snow is likely unless higher precipitation rates can be met, which are not likely at this point. Temperatures will remain in the chilly upper 30s to lower 40s with rain. No I-95 locations are likely to see any snowfall in this round.
This is my current rain/snow line...
Du Bois, PA - Jersey Shore, PA - Towanda, PA - Carbondale, PA - Monticello, NY - Poughkeepsie, NY - Torrington, CT - Amherst, MA - Concord, NH
*Locations along and to the north of this line remain at the greatest risk for accumulation snow for the October 27 period particularily for elevations above 800ft.
1. Heavy leaf foliage and the combination of wet snow may cause increased falling trees and powerlines with widespread effects for snow accumulation areas.
2. Wet snow may fall heavy at times for elevations above 2000ft particularily in the Catskills.
3. Coldest diurnal temperatures of the year for many locations.
4. More rainfall for already water-sogged locations adding to the record annual totals.
5. Second round snowfall is possible Saturday with wider impacts if cyclogenesis is met.
*Elevations above 800ft have the highest threat for snow accumulations.
Selected City Accumulations for the Northeast...
Hagerstown, MD- Light to moderate rain up to .5in
Baltimore, MD- Light to moderate rain up to .5in
Salisbury, MD- Rain showers up to .5in
Washington, DC- Rain showers up to .5in
Wilmington, DE- Rain showers up to .5in
Dover, DE- Rain showers up to .5in
Trenton, NJ- Moderate steady rain up to .6in
New York City, NY- Moderate steady rain up to .7in
Poughkeepsie, NY- Moderate rain changing to rain/snow mix. No snow accumulation. Higher elevations up to 1in
Binghamton, NY- Light rain changing to rain/snow and then snow. Snow accumulations C-2in
Ithaca, NY- Light rain changing to rain/snow then snow. Snow accumulations C-2in
Albany, NY- Light rain then snow. Snow accumulations C-1in
Hartford, CT- Light rain then rain/snow mix. No snow accumulation.
Concord, NH- Rain/snow then all snow. Snow accumulations C-2in
Providence, RI- Moderate rain up to .75in
Worcester, MA- Moderate rain then rain/snow mix. No snow accumulation
Boston, MA- Moderate rain up to 1.0in
Nantucket, MA- Moderate rain up to 1.0in and gusty winds up to 30mph
Hyannis, MA- Moderate rain up to 1.0in and gusty winds up to 30mph
Portland, ME- Moderate rain up to 1.0in
Bangor, ME- Light rain up to .25in
"Subject to Change"
All guidance suggests a class overrunning precipitation event along the cold front. Differences arise in terms of temperature thermals considering the NAM and GFS. ECMWF takes a middle route between the two. GFS remains on the warmer side of guidance favoring H85 heights near 0C for the majority of the precipitation event across New York State into New England. 2m temperatures remain marginal to perhaps a tad too warm with KITH readings even into the upper 30s. Given recent analysis of the GFS global versus the ensemble track, the operational remains warmer for H85 thermals in comparison to the majority of the ensembles. Looking at the air mass advecting southward and climatological means, it would suggest GFS 2m temperatures with NAM H85 temperatures. The NAM takes a colder route for boundary layer temperatures favoring low 30s for many locations in my favored snow accumulation region. This would allow advisory type snow accumulations particularily above 2000ft. QPF is similar for all guidance ranging from 0.5-1in depending on location with higher amounts towards New England and lower amounts towards western and northern areas. It is very important to note precipitation rates given this will pull colder air to the surface and allow the transition from rain to snow. Most locations will see light to moderate rates inhibiting the majority of snow accumulation. Keep an eye on the next 48 hours of models runs particularily to 2m temperatures between the NAM and GFS. The SREF is closer to the NAM with 12hr snow probabilities for 1in+ very close to my snow map above.
October 28-29 Coastal Storm Forecast
Higher cirrus will begin to flood the northern Middle Atlantic later in the day Friday after high temperatures in the mid 40s with partly cloudy skies. Clouds will begin to thicken and lower Friday night with precipitation moving northward as a 1000hPa coastal low pressure moves up the coast. The low pressure will follow an ideal track up and along the coast and if it were winter... this would be a major snowstorm for all of the Northeast including towards the coast. But given climatological means during late October, snow will only fall in certain locations well to the northwest. Precipitation will move northward as rain into Virginia and Maryland Friday night and move up into southern Pennsylvania also as rain. Evaporational cooling will begin as 2m temperatures fall to near dewpoint values late Friday night changing over to snow for southern Pennsylvania particularily for elevations above 800ft with a rain/snow mix in the valleys.
As the low begins to intensify further, a deformation axis will likely form well to the west of the center of circulation. The placement of this axis is key to the snow accumulation region as it will bring cold air down the surface in the form of dynamic cooling. Given the low track this axis is likely to form in eastern Pennsylvania up through central New England. Saturday will feature well below normal highs withs highs not reaching 40 as far south as Washington DC. Precipitation will intensify during the day. Ground temperatures initially in the 40s and marginal boundary layer temperatures will keep the highest accumulations in the higher elevations with several inches possible above 1000ft (perhaps up to 6in as far south as South Mountain, Pennsylvania). Elsewhere valley locations can also expect some light snow accumulation as far south as northern Maryland. For the I-95 corridor, a mix of rain and snow is likely with no accumulation. Snow accumulations up through New England are likely 1-4in for the valleys and 3-7in for the higher elevations. I could even envision higher amounts given the strength of the deformation axis. Total QPF printout from guidance such as the ECMWF and GEFS suggest .4in-1.0in across the entire Northeast.
Most of the snow will fall during the day Saturday. If timing were a bit more favorable such as Saturday night, this would have been a potentially record breaking, rare October snow event.
Given the high leaf foliage in some areas, the combination of wet snow will cause major tree damage in some locations especially in eastern Pennsylvania. Power outages are possible. Snow ratios will be near 6/7:1 with rates up to 0.5in/hr at times. Given the heavier snow rates at times, even areas with boundary layer temperatures at 34-35F may see a quick accumulation.
There are still some concerns about this storm being too far southeast such as the operational GFS suggests, but it is likely given the ensemble and ECMWF support that this coastal low will affect a large area of the Northeast giving a quick taste of winter. Stay tuned!
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...
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