Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 2:54 PM GMT on December 20, 2008
Thoughts on December 19 storm...
So another winter storm in the long line of recent winter storms is headed our way. This seems to be the coldest of the storms with snow likely over a widespread area. An alberta clipper is dropping down through the Great Lakes with an area of snow within its path. An arctic front is also dropping dwon from the Great Lakes and will works its way into our region later in the day Sunday. A secondary low pressure will form across the Tennessee Valley and track across Virginia and up the coast. Meanwhile light to moderate synoptic snow will develop in between the two systems giving many areas a nice 2-4inches. The coastal low will tend to enhance amounts towards the Poconos on northward and may also enhance some precipitation in eastern Pennsylvania. QPF looks generally .25-.35inches across the state, but with snow ratios near 15:1 we will be able to squeeze out some higher amounts mainly across the region north of the turnpike. Surface temperatures should not be a problem for this storm with most areas well below freezing. The 850 line generally stays around the Mason-Dixon line then up through the Philadelphia region. The snow should be generally a fluffy snow with cold temperatures and decent Omega and dendritic ice crystal growth. Overall the event should not pose to many problems and will likely be out of the region by early to mid Sunday afternoon.
This is my current rain/snow line...
This event is a much colder scenario therefore rain/freezing rain lines will be found for areas south of Pennsylvania for the most part. Freezing rain and snow line will jump across several states. Confidence is high in rain/snow lines. These lines are for placement of main precipitation types during height of storm.
My rain/freezing rain line is... Elkins, WV - Moorefield, WV - Winchester, VA - Westminster, MD - Bel Air, MD - Wilmington, DE - Philadelphia, PA - Trenton, NJ - Newark, NJ
My freezing rain/snow line is... Mt. Washinton, PA - Cumberland, MD - Hagerstown, MD - Hanover, PA - Quarryville, PA - Coatesville, PA - Quakertown, PA - Morristown, NJ
These are overall precipitation types. Precipitation types can wander several miles on either side of the lines.
1. Low impact snow event with light to moderate totals.
2. Nuisance freezing rain across southeastern Pennsylvania.
3. Blowing and drifting snow limiting visibility likely.
4. Dangerous windchills below zero statewide.
5. Freezing rain and snow on trees may cause falling limbs.
*Note this does not include lake effect snow.
Selected City Accumulations for the Northeast...
Hagerstown, MD- Snow, sleet, and freezing rain. Snowfall amounts up to one inch.
Baltimore, MD- Sleet and rain at times. Little to no accumulation.
Washington, DC- Rain with sleet at times. Little to no accumulation.
Wilmington, DE- Sleet and freezing rain changing to all rain. A trace of a glaze of ice is possible.
Dover, DE- Rain with sleet mixing in at times. Rainfall up to .25inches.
Cape May, NJ- Rain with amounts up to .4inches.
Trenton, NJ- Sleet and snow changing to freezing rain then rain. Trace to a coating of wintry mix is possible.
New York City, NY- Sleet and snow mixing with a little rain. Snow amounts from C-2inches.
Poughkeepsie, NY- Moderate snow at times. Snow accumulations 3-6inches.
Binghamton, NY- Moderate snow at times. Snow accumulations 3-6inches.
Albany, NY- Heavy blowing and drifing snow with accumulations 6-11inches.
Hartford, CT- Snow and sleet heavy at times. Snow accumulations 3-7inches.
Concord, NH- Heavy snow with blizzard conditions. Snow accumulations from 7-13inches.
Providence, RI- Initial snow changing to a sleet mix. Snow accumulations 2-4inches.
Worcester, MA- Heavy snow likely with accumulations 5-10inches.
Boston, MA- Snow and sleet. Snow accumulations 3-6inches.
Nantucket, MA- Initial snowfall changing to rain. Snowfall up to 1inch.
Portland, ME- Heavy snow mixing with sleet at times. Snowfall 6-12inches.
Bangor, ME- Blizzard conditions with very heavy snow and dangerous windchills. Snowfall from 9-15inches.
"Subject to Change"
Models have been zoning in on this event for quite a while with all snow being the main threat for most areas except far southeastern Pennsylvania. This still seems to be the case with most models including short term high resolution models indicating the 540 line staying right around the Mason-Dixon line. GFS seems to be the colder of the models, but similar to the WRF HIRES NMM. EURO is a tad warmer and NAM remains the warmest of the models. I still feel the main sleet and freezing rain effects will be across the southeastern Piedmont into the coastal region in Philadelphia. Areas west of the Lancaster-Coatesville-Quakertown line should be fine to see an all snow event. Though both the GFS and NAM bring a sliver of above 0C 850s to southwestern Pennsylvania near Pittsburgh. For this event though the best rain/snow line seems to be the 1000-500mb 540line. Looking at each model, the NAM seems to be initiating the QPF way too low for where precipitation already has been and temperatures at the surface too warm. Therefore I am not using it in my model blend. But I do give credit as the NAM picked up on this scenario for the most part along with definitely the most consistency for storm track. QPF though has gone from quite a bit to very dry over the past week. Looking at the GFS it seems to have a pretty good hold on QPF and air temperatures. It may be a tad to cold in far eastern areas, though, warm air advection should be pretty strong into the Philadelphia and Pittsburgh metro areas. SREF model blend seems to have the best hold on QPF totals with .25inches over a wide region with some eastern areas getting .5inches. It keeps 1inch+ amounts over much of the state with some areas possibily over 4inches. EURO has also had a good hold on this system and one of the earlier models to pick up on the secondary coastal low development. NMM high resolution model is my model of choice for this forecast as it seems to have the best idea for placement of precipitation with what seems to be an accurate simulated radar. Here is the radar for the height of the storm...
After the storm...
After the double-barrel low pressure system, the coldest air of the season will move into the region with temperatures aloft dropping to almost -20C in some locations across the mountains. Winds will be quite gusty from the departing and strengthening Nor'easter off in the Gulf of Maine so winds will turn gusty nearly 45mph during the afternoon Sunday with gusts up to 50mph on the ridgetops. This will cause considerable drifting and blowing snow across the region in all areas that have snow on the ground. Wind chills will fall below zero statewide with western and northern locations seeing windchills below -10C. Windchills may approach -20C above 2000ft near Bradford. Temperatures will fall during the day Sunday with highs in the upper 20s for most areas falling into the teens across western Pennsylvania by dusk. Cold air advection and northwesterly winds will aide in a non-radiational cooling temperature scenario with lows dropping into the single digits and low teens statewide combined with snow cover making some areas likely to approach zero. The air mass will be dry but with the strong instability and some 50 j/kg CAPE developing, lake effect snow bands will form with a potentially strong band forming near Erie, Pennsylvania traveling up the lake shore. Dendritic growth and decent Omega combined with 20:1 snow ratios will cause northwestern snowbelts to pick up nearly a foot of snow. Snow bands will also develop in the Laurel Highlands in the form of multibands which will limit accumulations to about 2-5inches for the western facing slopes. Lake effect snows will end by late Sunday night as drier air and high pressure works into the region. Still northwestern areas will see snowflurries and snowshowers Monday with additional accumulations up to one inch. High presssure for Monday will cause very cold temperatures with highs in the mid teens to mid 20s. Lows will also fall greatly Monday night with them possibly below zero in some locations. Tuesday will also remain very cold with highs below freezing statewide. High pressure then moves out of area and out into the Atlantic as another weaker front approaches bringing in a strong southwesterly flow bringing up mild temperatures for a wet Christmas eve day across the entire Northeast. System clears out for Christmas day bringing seasonable temperatures until late weekend as a new pattern works into the region with very mild temperatures and slim chances of snow through the end of the month. There are very strong signals though that an approach of a strong trough moves over the east come end of the first week in January. So all in all it appears from Christmas to New Years, a very mild pattern will be instore with some highs potentially getting to near 60 for Philadelpia. Not what snowlovers want to hear, but it does not appear it will be a long pattern as EURO weeklies show a decent negative orientation NAO setting up for early to mid January and beyond.
Please post storm reports in this blog from across the Northeast during the winter storm...
This blog is in progress. Check back soon...
"Here northeast of Harrisburg 2008-2009 winter statistics"
Current Snow Cover- Trace
Monthly Total- 4.35inches
Seasonal Total- 10.45inches
Winter Weather Advisories- 5
Winter Storm Warnings- 0
Heavy Snow Warnings- 0
Blizzard Warnings- 0
Snow Advisories- 0
Winter Storm Watches- 1
Lowest High Temperature- 23
Lowest Low Temperature- 10
Wind Chill Advisories- 0
Wind Chill Warnings- 0
(Snow Storms Stats)
First Snow - October 29 - Trace
First Snow on Ground - November 18 - Coating
Lake Effect Snow - November 21/22 - 6.00inches
Synoptic Snow - December 16 - 3.5inches
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