Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 9:20 PM GMT on December 17, 2008
Thoughts on December 19 storm...
For once it appears a very decent accuracy rating is possible with this winter storm across the region. I am going a little bit less for snow amounts especially over eastern Pennsylvania compared to what the NWS forecasts, but I see my forecast doing pretty well.
Another winter storm is headed our way on the heels of a past storm that still has caused remnants of snow around here in southern Pennsylvania. The low pressure is developing over the southwestern United States and gave Vegas some snow in the area. Low pressure will move across Midwest then across Ohio Valley becoming very transient in nature and fastly moving. Gulf moisture and moisture from the Baha of California will aid in high QPF totals along a relatively narrow path mainly to the north of the center of low pressure. With a departing weak high pressure moving out of the Northeast it will be difficult for H85s to stay below freezing for much of Pennsylvania. North of I-80 though it will be a different story. Front end snows look quite likely once again with this system, but much lighter for southern areas, and mainly to the north of those areas. But the high pressure will provide a northeast wind, which should keep the warm air south of the Mason-Dixon line. There is a very tight temperature gradient with this storm keeping nearly 50-60degree temperatures down across southern Middle Atlantic while nearly 30degree temperatures are across the northern Middle Atlantic. Low pressure will track across the Mason-Dixon line to just a bit north of there with the 850 0C line traveling right along and just to the south of I-80 during the height of the precipitation. Front end snows will be most significant across east-northeast Pennsylvania especially across northern Lehigh Valley where much of their accumulations will occur during the front end with 2-5inches being likely amounts as QPF is only up to a max of .4inches. Heights rise with low moving across state turning most areas south of the Du Bois-State College-Allentown line over to sleet and freezing rain by Friday morning. That line will lift north to just about north of I-80. Warm air aloft should overcome the cold air at the surface for southern Pennsylvania, but I do expect the cold air to win out longer than expected with Laurel Highlands and the Coal Regions likely seeing quite a bit of freezing rain especially above 1700ft and in the deep valleys. Precipitation should eventually changeover to plain rain as the day progresses. Heavy snow will be across Pennsylvania/New York border counties and farther south in northeastern Pennsylvania. Max dendrite growth and Omega values will be reached for snow ratios up to 15:1 for elevations above 2000ft. Snow totals may occur up to 15inches for parts of northern Wayne County. Sleet will keep accumulations down for south of that region across State College where amounts more on the order of 3-6inches seems likely. PWATs will be on the rise across southeastern Pennsylvania and southwestern Pennsylvania where mostly rain is likely to occur with amounts generally at a max of one inch. Low pressure should pull away to east by late in the evening with a few leftover snow showers and freezing rain showers across Pennsylvania for a damp Friday night. Stay tuned for more updates throughout the day as many areas will be affected by this major winter storm.
This is my current rain/snow line...
These lines are only estimates for main precipitation types during height of the storm. Many areas will see front end snow along with sleet especially just south of the I-80 corridor.
My rain/freezing rain line is... Mercer (Mercer County) - Butler (Butler County) - Indiana (Indiana County) - Latrobe (Westmoreland County) - Somerset (Somerset County) - Raystown Lake (Huntingdon County) - Harrisburg (Dauphin County) - Indiantown Gap (Lebanon County) - Reading (Berks County) - Quakertown (Bucks County)
My freezing rain/snow line is... Meadville (Crawford County) - St. Marys (Elk County) - Jersey Shore (Lycoming County) - Laporte (Sullivan County) - Scranton (Lackawanna County) - Milford (Pike County)
These are overall precipitation types. Precipitation types can wander several miles on either side of the lines.
1. Heavy snow north of I-80 locally up to 12inches.
2. Significant ice storm possible across northern Lehigh Valley westward across Central Mountains.
3. Nuisance to moderate impacts likely even across southern Pennsylvania.
4. Possible front end snows across much of state.
5. Heavy rain across southwestern Pennsylvania.
Selected City Accumulations for the Northeast...
Hagerstown, MD- Slight chance of freezing rain then plain rain.
Baltimore, MD- Rain with amounts up to .75inches.
Washington, DC- Moderate rain likely with amounts up to .5inches.
Wilmington, DE- Heavy rain likely with amounts up to 1inch.
Dover, DE- Moderate rain likely up to .5inches.
Cape May, NJ- Moderate rain likely and mild with amounts up to .75inches.
Trenton, NJ- Front end snow up to 3inches followed by freezin rain up to .2inches changing to all rain.
New York City, NY- Snow and sleet with some freezin rain. Snow accumulations 3-7inches.
Poughkeepsie, NY- Heavy snow likely accumulating up to 12inches.
Binghamton, NY- Heavy snow likely with accumulations from 9-13inches.
Albany, NY- Heavy snow likely accumulating 6-11inches.
Hartford, CT- Heavy snow mixed with sleet at times. Snow accumulations up to 8inches.
Concord, NH- Moderate snow with accumulations 4-7inches.
Providence, RI- Heavy snow with accumulations 5-9inches.
Worcester, MA- Heavy snow with accumulations 8-13inches.
Boston, MA- Heavy snow with accumulations 8-12inches.
Nantucket, MA- Heavy snow mixed with sleet at times. Snow accumulations 8-12inches.
Portland, ME- Light snow accumulating 2-4inches.
Bangor, ME- Cloudy with a few snow showers. No accumulation.
"Subject to Change"
For once we had a wonderful model consensus with very few trends on the models, with the biggest trend on the GFS with it tracking the low pressure originally over Erie, but now the track is over the Mason-Dixon line. The NAM and EURO triumphed other models once again catching onto the more southern track. NAM did another great job showing its higher resolution to the fullest with these overruning type events. The WRF short term HIRES NMM model did a pretty decent job with few significant changes to track or temperatures aloft in the short term. There appears to be a great consensus of all snow north of I-80 as this storm is moving from due west to east with snow/sleet line also running nearly due west to east. There is also a bit of deceiving information on the model runs as areas may be north of the 0C line, but there is a warm mid level thanks to lack of strong high to north so sleet may be a big issue right across the central part of the state running from west to east with State College and Williamsport being likely targets. The SREF short term corrilation model has been fairly consistent with snow accumulations kept north of turnpike and heavy snow accumulations north of I-80. Low level cold air is the only issue I believe the models are progging a bit wrong thanks to the typical lack of cold air damming scenarios even with the higher resolution models... NMM, while a bit extreme, seems to show the cold air damming holding more ground than what the GFS appears to show...
GFS seems to be a tad to warm with these storms likely thanks to some initial errors with 850s. Again my model of choice for this storm is a EURO/NAM blend about 60/40. We do have some major timing issues with this storm with the NAM considerably slow with development and track of storm. Higher resolution model NMM seems though to have a decent grab on precipitation placement by Friday morning...
After the storm...
It still appears we have several more waves of low pressure in this pattern one of which could be Christmas eve. I do not have time to write out a full discussion for the storms in the short to medium term, but it does appear the Sunday storm will be pretty significant with heavy snow likely across inland areas of Pennsylvania. Models take a low pressure to the west of us initially bringing in some front end snows then changing to a mix. But models, especially NAM and EURO have been hinting at secondary low pressure formation just south of Delmarva which could quickly turn the mix back to snow for many areas. This secondary low formation is still under question at this point. Temperatures will be overall colder with this storm so even with above 0C 850 isotherm there will still be significant icing at the surface. For the Wednesday storm it appears another low pressure tracks to our west, but that has yet to be seen. In any case pattern is active and looks interesting through end of month with EURO and GFS both hinting at finally a favorable east coast negative NAO, which we have not seen in quite a few winters. But again that too remains to be seen.
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 to 1.00inches
Monthly Total- 3.25inches
Seasonal Total- 10.35inches
Winter Weather Advisories- 3
Winter Storm Warnings- 0
Heavy Snow Warnings- 0
Blizzard Warnings- 0
Snow Advisories- 0
Winter Storm Watches- 1
Lowest High Temperature- 26
Lowest Low Temperature- 14
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
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
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