Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 2:07 AM GMT on November 29, 2008
Thoughts on November 30 to December 1 storm...
Complex and messy storm system headed our way as severa lows move up either side of the Appalachians putting all of Pennsylvania in the warm sector. Deep trough moving into the central part of the country along with a weak disturbance dropping out of Canada. H85 temperatures along the gulf coast may even drop to 0C possibly bringing some flurries to parts of the northern deep south. Trough becomes situated across the Ohio Valley and becomes negatively tilted allowing a low pressure from the disturbance out of Canada to be the primary low and head up through western Ohio. A secondary low appears to form just inland across the Outerbanks on up through the Delmarva. Surging high PWATs from the Gulf will bring widespread moisture aloft to areas from the Ohio Valley eastward. High pressure moving out of northern New England will move eastward across the north Atlantic shipping lanes. Cold air will begin to shift northward as precipitation moves in. Warm air advection will allow slowly rising temperatures during non-diurnal hours as the low pressure to the west allows temperatures aloft to surge above 0C in the 850 layer. The inland coastal low will also drag along a warm front that will cause very mild air along the coastline. Thunderstorms cannot be ruled out for some locations as there is a bit of instability aloft towards the coastal plains. As upper level low to west begins to move across Lake Erie the heaviest precipitation should occur across Pennsylvania as coastal low will align right along I-95. Looking at bufkit plumes it appears most of the precipitation will be rain across Pennsylvania during this time as cold air damming will be limited. In situations like this cold air damming is usually quite common as Pennsylvania is stuck in between two lows, but really there is no cold air out ahead of this system. The double barrel low will race across the north by Monday allowing the upper level trough to work across the region changing any residual moisture back over to snow showers.
12:00am-2:00am Sunday... Precipitation will be working across the Mason-Dixon line during this time as a wintry mix of snow and sleet. H85 temperatures will be hovering around -1C along with light precipitation, I will add the chance of sleet. Clouds will inhibit any further radiational cooling that has already occured. Mountain locations across southcentral Pennsylvania may see a dusting to heavy coating of snow during this time. Areas across southwestern Pennsylvania will see a quick changeover to rain as temperatures aloft rise above +1C for areas west of the mountains.
2:00am-6:00am... Precipitation will advance northward as the shield of gulf moisture works into the region. Generally precipitation will be snow and sleet as radiational cooling keeps a cold boundary layer and temperatures aloft stay near -1C. Snow accumulations may occur up to 1inch for some central ridge and valley locations. By 6am some of the precipitation across southern Pennsylvania will turn over to a quick period of freezing rain.
6:00am-11:00am... Warm air advection will quickly move into southern areas turning most of the precipitation over to plain rain from the turnpike on southward. Rain amounts in this period will be between a tenth and a quarter of an inch. Areas between the turn pike and I-80 will see a mix of sleet and freezing rain generally turning to plain rain by 11am. Sleet accumulations may occur up to a coating on the grass. Areas north of I-80 will get into the snow action with some of the higher elevations across the northern border counties seeing up to 2inches of snow.
11:00am-4:pm... Rain will be ongoing across areas south of I-80 after the mixed frontend precipitation during the morning. Rainfall amounts will generally be around .25inches with heavier amounts occuring in southeastern Pennsylvania. Temperatures will slowly be on the rise especially towards Philadelphia. Some of the deeper valleys across the ridge and valley region and Laurel Highlands may see some freezing rain with .05inches-.1inches of ice accumulations occuring, but by 4pm that should be all rain. North of I-80 precipitation will turn to a snow and sleet mix with additional snow accumulations near 1inch. Freezing rain will begin to move from south to north causing some ice accretions in the deeper valleys and higher elevations especially in the northern Poconos and northeastern mountains where accumulations up to .15inches could occur causing some issues on the roadways and powerlines.
4pm-12:00am... During this extended period most of the precipitation will turn to plain rain across much of the state with some spotty lingering freezing rain across favored cold air damming locations in northern and northeastern Pennsylvania. Rainfall amounts will be up to .4inches across southern areas especially in the east. Colder air will begin to work into the region later during the night towards early morning Monday across western Pennsylvania. Temperatures though for most areas overnight will slowly rise or hover just above freezing.
12:00am-through rest of day... Cold air aloft and at the surface will move across the state from west to east causing any residual moisture to changeover from rain to snow with even a few leftover flurries working in towards eastern Pennsylvania. Snow accumulations will generally be light. Flow will turn more northwesterly by afternoon causing the start of a lake effect snow outbreak that will last for a few days. See more details in section below labled after the storm.
This is my current rain/snow line...
Rain and snow lines will be hard to predict thanks to the storm situation of wintry mix to rain back to wintry mix type precipitation timing, but these lines are an average of where the differences will occur during the max hour of precipitation.
My rain/mix line is... Washington, PA - Johnstown PA, - Altoona, PA - Lewistown, PA - Lewisburg, PA - Wilkes-Barre, PA - Milford, PA
My mix/snow line is... Mercer, PA - Clarion, PA - Du Bois - Jersey Shore, PA - Mansfield, PA - Elmira, NY
These lines are estimates for most of the overall precipitation types. Precipitation types can wander several miles on either side of the lines.
1. Widespread moderate impact on busiest travel day of year.
2. Potential for freezing rain for elevations above 1800ft.
3. Front-end snows possible for many areas with a 1-3inches.
4. Moderate snow/sleet accumulations across north country.
5. Slippery, wet roads across the eastern parts of PA.
Selected City Accumulations for the Northeast...
Hagerstown, MD- Rain likely mixed with sleet early
Baltimore, MD- Rain likely up to .5inches
Washington, DC- Rain likely up to .75inches
Wilmington, DE- Rain likely up to 1inch possibly more
Dover, DE- Rain likely up to 1inch or more
Cape May, NJ- Rain likely between 1-2inches
Trenton, NJ- Rain likely mixed with sleet at times
New York City, NY- Rain likely with sleet on onset
Poughkeepsie, NY- Snow early mixing with sleet then rain, 1-2inches of snow possible
Binghamton, NY- Snow at onset mixing with sleet 1-2inches of snow/sleet, then freezing rain up to .1inches, then rain likely
Albany, NY- Snow at onset likely turning to rain, 1-4inches of snow possible
Hartford, CT- Snow with rain at onset then all rain up to .5inches of rain
Concord, NH- Snow early then turning to rain, 1-2inches of snow possible
Providence, RI- Rain likely up to 1inch possible
Worcester, MA- Rain likely mixed with snow early, up to 1inch of snow possible
Boston, MA- Rain likely up to .75inches
Nantucket, MA- Rain likely up to 1inch
Portland, ME- Rain likely mixed with a bit of sleet at times
Bangor, ME- Mix of snow/sleet at onset then freezing rain then snow, up to 2inches of snow/sleet possible
"Subject to Change"
Looks as if finally we are getting a model consensus on the double barrel low pressure that is headed across the east. Most models have a general consensus that the primary low will be the on heading up through Ohio and with a slow to form coastal low that will likely head up I-95. With a strong primary to west warm air advection will likely be a plague for snow lovers as latest 12z runs by GFS and NAM show H85s above the 0C threshold for much of Pennsylvania during the height of the precipitation. Latest 0z NMM model simulated radar shows a large plume of heavy precipitation stretched across from the Ohio Valley to the Atlantic coastline...
During this period temperatures are above freezing for most areas. Latest 12z GFS tries to indicate some cold air damming, but with no high pressure to north and no real dense cold air mass, it should not hold for long. Note the lower H85s across central and eastern Pennsylvania...
A problem also with many of the models with this storm was the placement and strength of the incoming trough that will bring very cold air down to as far south as the southeast Gulf Coast. Looking at the 500mb chart on the high resolution NAM this is quite evident with a deep trough that has almost a negative tilt coming into towards the Ohio Valley...
Overall most models are in a pretty decent correspondance for this storm after a rough couple of days. There could be a few surprises as with any storm, but I doubt that any major wintry precipitation will affect Pennsylvania, more nuisance type amounts with generally rain.
After the storm...
This is a very complex scenario for a winter storm, but it seems that a general, and I mean generaly consensus has been reached by the models along with the makings for a forecast. Looking ahead this week it seems to be fairly quiet with temperatures below normal with highs generally in the upper 30s to low 40s across the state with lows in the 20s. The first half of the week there may be some significant lake effect snows under a northwestern trajectory that may cause some heavy accumulations across the nortwest snow belts. Also there will be residual moisture leftover from the double barrel lows that never quite phase so this may cause some upsloping and orographic snow across the Laurel Highlands and central mountains. By Wednesday high pressure will move back into the region causing some more mild conditions with highs getting up into the upper 40s across the far southeast. But a cold front with a much stronger trough will move in for Thursday with some rain/snow showers across mainly northern Pennsylvania. Little to no snow accumulations are expected. Moving towards the weekend things get very interesting in which models have been consistently showing a coastal storm across the region, but the difference from this year's previous storms is the cold air will definitely be around. Teleconnections will favor a coastal storm with a negative NAO that is eastern based and a for once favorable positive PNA. To early to get into details or even remotely excited, but definitely something to watch this week. The CMC, EURO, and GFS have all showed a coastal storm around that time period. My main worry is going to be surpression and that looks entirely possible. Stay tuned for many more details throughout the week.
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- 0.00inches
Monthly Total- 6.10inches
Seasonal Total- 6.10inches
Winter Weather Advisories- 0
Winter Storm Warnings- 0
Heavy Snow Warnings- 0
Blizzard Warnings- 0
Snow Advisories- 0
Winter Storm Watches- 0
Lowest High Temperature- 31
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
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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