Wednesday Middle Atlantic Light Snow Event...
A weak low pressure along a frontal boundary will spread light snow across the Middle Atlantic with light amounts in the 1-4in for many areas especially in southern Pennsylvania and northern Maryland.
Current Surface Plot...
(Courtesy of HPC)
February 8 Middle Atlantic Light Snow Event Timeline and Discussion...
A weak low pressure will move along a stationary front across northern Virginia during the day Wednesday. An enhanced jet and increasing southerly flow will advect a bit of moisture around 700mb enhancing a light area of precipitation from West Virginia up through southern Pennsylvania. This area will primarily be driven by isentropic lift maintaining light to moderate precipitation rates. Cold air advection originating out of Ontario will continue to funnel south through the Northeast on Tuesday setting the stage for a light snow event on Wednesday as precipitation enters the Middle Atlantic. The current track of the primary vortex of energy will be across northern Virginia. This track is favorable to spread the heaviest QPF 50-100mi north of the vort using the typical rule of thumb. QPF totals will range from .1-.25in for most areas with the highest amounts on either side of the Mason-Dixon line within 25mi. PWATs will increase to near .5in during the day Wednesday as moisture begins to funnel through the entire atmospheric column. Dry air will battle the northern edges of the shield of precipitation particularily towards I-80. Surface temperatures will be in the lower to mid 30s across central and northern Maryland to around 30-32F for southern Pennsylvania. This will limit snowfall especially given antecedent mild temperatures. Snowfall will generally occur in grassy locations especially for Maryland.
Temperatures in the mid 30s towards Washington DC will set up the battleground across this region for rain vs. snow. Temperatures through 950mb will be below freezing, but the warm bounday layer temperatures will allow for the mix. If the vort travels a bit farther south than expected an area of enhanced moisture may occur across the capital district with bursts of moderate snow, but at this time this looks unlikely. Still the city and surrounding suburbs may see up to 1in of snow. The highest QPF and coldest surface temperatures will favor the highest accumulations across extreme southern Pennsylvania into Somerset, Bedford, Fulton, and Franklin counties. I cannot rule out a spotty 5in or 6in amount across the Mt. Laurel/Davis area. Elsewhere in those counties 2-4in amounts are more likely especially above 1000ft.
Spotty 2-4in amounts are also possible across the high ground (above 600ft) in far northern Maryland.
9am-12pm Wednesday- Light snow will begin to across western and central Maryland/Pennsylvania/Virginia. Temeperatures will slowly fall below freezing for areas near the Mason-Dixon line given initial low dew point values. Elsewhere temperatures will also fall, but hover around 34-36F towards Washington DC. Snow accumulations will be limited to 1-2in generally across western Maryland and the Laurel Highlands.
12pm-4pm Wednesday- This time period will feature the primary event with light to occasionaly moderate snow occuring. Visibilities will generally range from 1-3mi during this period with brief TAF IFR conditions possible. Accumulations in this period will be around 1-3in for most areas.
4pm-6pm Wednesday- Precipitation will change to light snow as far south as Washington DC before ending for eastern areas also. Additional accumulations will be 1in or less for all areas.
6pm-8pm Wednesday- Downsloping and waning isentropic lift will weaken the precipitation shield for extreme eastern Pennsylvania, Delaware, and New Jersey. By 8pm all precipitation should be over across the Middle Atlantic.
(Courtesy of Intellicast)
(Courtesy of NOAA)
This is my current rain/snow line...
Warrenton, VA - Washington DC - Annapolis, MD - Dover, DE - Vineland, NJ
***Areas north of this line will feature a mostly snow event with the region 25mi either south/north of this line featuring a rain/snow mix. Even areas along the line may see a very light accumulation of snow. Given the upper level thermal profile, there will likely be no mixed precipitation and either a rain or snow event.
1. Light snow accumulations of 1-4in for most areas.
2. Snow will falling during the daylight areas including the evening commute with travel impacts likely.
3. High snow accumulations will be along the southern Pennsylvania border counties particularily in the Laurel Highlands.
4. Snow will fall across a region that has not been exposed to much winter weather weather this season.
5. Most of the accumulating snow will end by 8pm for all areas.
***There will likely be a few spotty coatings to 1in amounts just north of the 1-4in region, but virga should reduce amounts along and north of I-80 to near nothing. The highest amounts will be across the Laurel Highlands and Garret County, Maryland with a few isolated 5-6in amounts possible in the favored upslope regions.
Current Great Lakes Water Temperatures...
(Courtesy of NOAA)
Selected City Accumulations for the Northeast...
Hagerstown, MD- 1-3in of wet snow
Baltimore, MD- 1-2in of wet snow mixed with rain at times
Salisbury, MD- Light rain
Pittsburgh, PA- Light snow; Up to 1in of snow possible
State College PA- Light snow showers, up to 1in of snow possible
Williamsport, PA- Light snow showers, little to no accumulation
Altoona, PA- 2-4in of snow
Harrisburg, PA- 1-4in of snow
Lancaster, PA- 1-4in of snow
Philadelphia, PA- Light rain and snow mix; Up to 1in of snow is possible
Allentown, PA- Light snow; Up to 1in of snow is possible
Scranton, PA- Few light snow showers; no accumulation
Washington, DC- Light rain/snow mix; Up to 1in of snow is possible
Wilmington, DE- Light rain/snow mix; Up to 1in of snow is possible
Dover, DE- Light rain/snow; coating of snow is possible
Trenton, NJ- A few light snow showers; no accumulation
New York City, NY- A few stray flurries
Poughkeepsie, NY- Cloudy
Binghamton, NY- Cloudy
Ithaca, NY- Cloudy
Albany, NY- Cloudy
Hartford, CT- Mostly cloudy
Concord, NH- Cloudy
Providence, RI- Mostly cloudy
Worcester, MA- Mostly cloudy
Boston, MA- Mostly cloudy
Nantucket, MA- Partly cloudy
Hyannis, MA- Partly cloudy
Burlington, VT- A few flurries
Portland, ME- Mostly cloudy
Bangor, ME- Mostly cloudy
"Subject to Change"
Current Northeast Snow Depth and Northeast Wind chills...
(Courtesy of Wunderground)
Model guidance is in general agreement for this weak surface wave, but a few differences arise especially for boundary layer thermals across the Washington DC area. The ECMWF remains a bit warmer than other guidance, but I tend to find it runs a tad too warm. This was certainly exhibited last Saturday with the light snow event across the Middle Atlantic. General SREF/NAM/ECMWF/GFS QPF is in the .1-.25in range for most areas with a northern cutoff around I-80. The track of the vort will be critical for areas in the rain/snow area, but most models have generally agreed on a similar track. In the longer range, models indicate colder air plunging across the Northeast this weekend although nothing out of the ordinary for early February standards. GFS and ECMWF argue for a few potential snow squalls along the arctic front, but this remains a low probability especially east of the Alleghany Front. After a 4-5 day cooler period, warmer temperatures are likely to move back in across the Northeast with a zonal Pacific flow in control with limited precipitation events.
After the Storm
The next two week period looks to feature well above normal temperatures with well below normal precipitation; therefore the likelihood of snowfall is below climatological averages. The MJO will continue to rotate through phases 6-8 over the next two weeks with strong forcing. Composites indicate a mild pattern from this regime over the Northeast. The arctic oscillation is actually anomalously low (near the record low values of 2010) which is quite coincidental given the record high values back in December. But the other teleconnections are not in favor to send this arctic air across North America especially given the swirling Alaskan Vortex. Much of this cold air has been focused across Europe into parts of Siberia. Model prognostics indicate a dominate 1060hPa anticyclone (models will verify too high for pressure) over Siberia. Arctic air will flood this region of the world over the next two weeks, while North America is sitting under a zonal Pacific regime. Very few perturbations in the jet will characterize a very dry period over the next two weeks. This is supported by recent global model runs indicating less than .4in for most of the Northeast over a 16 day period.
Any potential for snow will remain slim. A few ensemble runs have noted the February 10-12 period as of particular interest, but the placement of the polar and subtropical jet do not appear favorable. While there will be occasional cold fronts with 1-2 day periods of cooler weather, the overall pattern is mild with many days running 5-10F above normal. I cannot rule out an unexpected snow threat, but it is likely this will appear at the last minute on guidance if it should occur. Given the end of the Nina flow, chaos has consumed most model guidance especially post 3 days. Therefore any model output should be taken with a grain of salt. If one can get past operational and ensemble model output, the overall pattern is similar to that of much of this winter.
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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Lower Susquehanna Valley Doppler...
(Courtesy of WGAL)
"10mi northeast of Harrisburg 2011-2012 winter statistics"
Monthly Total (October)- 5.5in
Monthly Total (November)- 0.0in
Monthly Total (December)- 0.4in
Monthly Total- (January)- 5.2in
Monthly Total- (February)- 2.3in
Seasonal Total- 13.4in
Winter Weather Advisories- 2
Winter Storm Warnings- 1
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 1
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
Southwest Flow Event - January 21 - 5.0in of dry snow
Weak Shortwave - February 8 - 2.3in of wet snow