Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 8:24 PM GMT on December 09, 2008
Thoughts on December 11-12 storm...
A very fascinating storm system is headed towards the east coast, but first it is delivering rare snowfalls in parts of the Gulf Coast that have not been seen since 1998. Snowfall accumulations have been reported as far south as Houston with winter storm warnings now out for parts of central Mississippi delivering up to 6inches of rare snow. I am sure everyone down there is enjoying this little taste of winter from the north to brighten their holidays, though I imagine there are many issues on the roads thanks to the rarity of the snow. Here is my storm discussion followed by my timeline...
A sharp temperature contrast cold front is stationed across southeastern Pennsylvania this time and will slowly push to the coastline before stalling out. Low level cold air in the bounday layer will slowly push in across the state, but will likely not reach far southeastern Pennsylvania until Friday. The cold air aloft will have a hard time moving in over the region due to lack of arctic high to north. While it may seem that there is a high pressure to the north in the Great Lakes, this will push quickly off to the east as a clipper dives down in the Midwest. We can all thank the clipper for the lack of snow in this sytem. Low pressure in the Gulf of Mexico will form and ride up along the cold front likely taking a track up the east coast and off the southern Delmarva tracking slightly off the coast by about 25-50miles. Lack of easterly track will keep precipitation types across much of Pennsylvania of rain or a mix. A surge of an anomaly of moisture will be moving up the coast with PWATs several deviations above normal. Coastal low moves up the coast bring strong southeasterly winds to southern areas drawing in warmer air for the southeastern Piedmont with once again warm temperatures similar to Wednesday highs. H85s rise to near 10C near Philadelphia, but the sharp contrast leads to the 0C line from Altoona-State College-Scranton where the snow/sleet/freezing rain line will form. With lack of high pressure to north, temperatures aloft for the colder air will be in a bitter battle with the surging warmth. Low level cold air will be filtering in which is sort of different from typical storms in which we have cold air damming with only stagnant cold air. This time we have fresh cold air moving in that should stay locked in for the boundary layer temperatures leading to the development of a signficant ice storm. Temperatures will be marginally around freezing for much of the central and northeastern part of the state. But temperatures near 32degrees seem to be the best for large accretions of ice to form. The problem see is the bust potential as temperatures could be plus or minus 1-3degrees which could completely throw off ice storm potential. Elevations above 1500ft in the Poconos stand the best chance for ice accumulations with nearly .75inches or more possibly accumulating. One aiding factor in lower ice accretions will be the heavy rate of the freezing rain, which tends to make accumulations of ice harder to form thanks to run-off. Many other lower elevations though will see a damaging ice storm particurily from the Laurel Highlands up through the Middle Susquehanna Valley on up through the Northeastern Mountains. As for rainfall it will be quite heavy over extreme southeastern Pennsylvania likely totaling near 2inches by the end period of the storm. A few minor flooding issues are possible, but I do not see any problems developing. There will be a definite lack of snow with this system as the northwestern end of the precipitation sheild will form right at the 0C H85. Snow accumulations will likely be highest over the northeastern mountains. Overall this system looks to be a potentially damaging ice storm for a widespread area and should be taken very serious. As the low pulls to the northeast a deformation of snow may form as cold air aloft comes rushing in. This may cause a band of 1-2inches of snow in central and east-central Pennsylvania before the storm is all said and done and that would likely be around for the Friday morning commute. Please be prepared for widespread power outages in the ice storm prone locations along with the possibility of widespread tree damage thanks to the added addition of a northeast wind gusting up to 30mph particularily in eastern Pennsylvania. Snow accumulations do not look to be overally heavy, but could be widespread on a light level. Remember a change of 1 or 2 degrees could be the difference between rain and a devastating ice storm. That means this system has a large bust potential, which is making forecasts very difficult. My maps are below and are of my latest thoughts. The only issues I see with them is maybe a bit to far south on the extent of the frozen precipitation, but for now with many models slowly trending and east surface analysis showing a bit more southeasterly track, I will keep the maps the way they area.
Spotty precipitation will be scattered across the state of Pennsylvania with slowly falling temperatures especially across central areas on westward. Across western and northern Pennsylvania spotty freezing rain is being reported including around the Pittsburgh metro area. Post frontal mixed precipitation with sleet and snow may also occur across western Pennsylvania with ice accumulations up to .1inches in some areas and a trace of snow. Across eastern areas spotty drizzle with some dense fog will be the main issues for tonight. Temperatures will be falling into the 30s towards 12am.
Precipitation shield will be advancing across southern areas of Pennsylvania crossing over the Mason-Dixon line. Rain is primarily expected in the southern border counties, but out towards the Laurel Highlands, the freezing rain will begin with areas near Mt. Davis and Laurel Summit seeing a trace of ice accumulation in this time period. Temperatures will continue to slowly fall.
Precipitation sheild will be across much of the state with freezing rain now falling in my areas including the lower elevations from about the turnpike on northward. Ice accumulations may form up to .1inches in this time period. Across southeastern Pennsylvania heavy rain will begin to start to fall with mild temperatures. Further west in the northcentral mountains precipitation will begin as a period of snow/sleet with accumulations up to 2inches.
Precipitation will be widespread from about westcentral Pennsylvania on eastward with areas seeing freezing rain and plain rain. Temperatures will begin to stop falling and become more steady. I do not anticipate a rise in temperatures during the day, except for southeastern Pennsylvania near Philadelphia. Ice accumulations will be up to .15inches in parts of the Laurel Highlands and Poconos. Elsewhere ice accumulations will be less than .1inches
Coastal low will be strengthening drawing in some colder air aloft changing the western extent of the precipitation over to snow and sleet with accumulations up to 2inches. Elsewhere freezing rain and rain will persist with damaging ice storm accretions beginning to form across northeastern Pennsylvania.
Precipitation will slowly change from freezing rain to snow from west to east, with southeastern Pennsylvania still seeing plain rain and mild temperatures which will slowly be falling in the later portion of the period. Ice accumulations could be up to an additional .15inches in parts of the Poconos. Snowfall amounts will generally be less than 3inches.
The end of the storm will be nearing with backend of the precipitation slowly advancing northeastward changing some areas back over to snow for a time period with snow accumulations up to 3inches in parts of central and east-central Pennsylvania. Cold air will move in for later in the morning for finally southeastern Pennsylvania.
This is my current rain/snow line...
Tough prediction to put exact estimates on the rain/snow lines due to the fact that the situation is continuing to look colder than earlier surface patterns and guidance suggested. But here are my main precipitation lines. These lines are for precipitation at the height of the storm and are subject to change. Many areas will get in on wintry precipitation, but not until the end of the storm. West of the lines is the colder of the two types of precipitation.
My rain/freezing rain line is... Greencastle (Franklin County) - Gettysburg (Adams County) - Lewisberry (York County - Elizabethtown (Lancaster County) - Mt. Gretna (Lebanon County) - Hamburg (Berks County) - Allentown (Lehigh County) - Easton (Northampton County)
My freezing rain/snow line is... Indiana (Indiana County) - Altoona (Blair County) - Milroy (Mifflin County) - Jersey Shore (Lycoming County) - Laporte (Sullivan County) - Scranton (Wyoming County) - Milford (Pike County)
These are overall precipitation types. Precipitation types can wander several miles on either side of the lines.
1. Significant ice accumulations possible across interior.
2. Significant snow accumulations likely across central areas.
3. Heavy QPF across a widespread region of Pennsylvania.
4. Heavy rain likely across eastern areas with minor flooding possible.
5. Duration of event is relatively short with fast moving system.
*A few higher amount could be expected across parts of Bradford, Susquehanna, and Wayne Counties for elevations above 1900ft.
*Map includes elevation for the higher ice accumulations.
Selected City Accumulations for the Northeast...
Hagerstown, MD- Rain changing to moderate freezing rain accumulating up to near .25inches. Back end snow possible up to 2inches
Baltimore, MD- Mainly rain possibly mixed with sleet at end of storm up to 2.5inches
Washington, DC- Rainfall up to 2.5inches
Wilmington, DE- Rain mixed with a trace of backend snow
Dover, DE- All rain accumulating up to 3inches
Cape May, NJ- All rain up to 3inches. May become breezy gusting up to 45mph
Trenton, NJ- Mainly rain with a trace of backend snow Rainfall up to 2inches or more
New York City, NY- All rain likely up to 2.5inches
Poughkeepsie, NY- Severe ice storm up to .5inches of ice or more. Back end snow may also accumulate up to 1inch
Binghamton, NY- Mainly snow with a bit of sleet. Snowfall accumulations from 5-9inches
Albany, NY- Snow mixed with sleet and freezing rain. Ice accumulations up to .25inches with 3-6inches of snow
Hartford, CT- Moderate ice storm with freezing rain totaling slightly over .25inches
Concord, NH- Snow/sleet/freezing rain with snowfall up to 3inches and near .5inches of freezing rain
Providence, RI- All rain likely totaling up to 2inches or slightly more
Worcester, MA- Severe ice storm accumulations up to .75inches
Boston, MA- All rain mixing with sleet at times. Rainfall up to 2inches
Nantucket, MA- High winds and heavy rain. Winds up to 55mph with heavy rain totaling over 2inches
Portland, ME- Freezing rain with rain at times also. Up to .25inches of freezing rain and likely over 1.5inches of plain rain
Bangor, ME- Freezing rain up to .3inches changing to sleet and snow. Snow accumulations less than one inch
"Subject to Change"
Well we have been tracking this storm for over a week and have seen a variety of solutions on the modelst. I must say just when you think the models cannot get any worse, they do actually get worse. Still no consensus on the model runs and we are still getting trends with shifts nearly 50miles to the east on models such as the 18z NAM. Also with 12z EURO we had a major shift east. Overall though, despite what some may say, I think the GFS did the best job in spotting this second system and for its consistent placement for a coastal storm. The EURO took longer to catch onto the system and seemed to have a western outlier type track for a majority of the time. Before I start in on my quick analysis of the models, I do think they are overestimating some of this warm air especially aloft. Looking at latest mesoanlysis from the Storm Prediction Center, then critical thickness lines such as the 540line are already much farther south than progged at this models at this time. This is not to say though this will be a more snowy solution as I do not think that is too likely. I think the models have a pretty good grab on the track of the system with my model of choice being the NAM/NMM combo. The SREF mean seems to have a good hold on this system too. EURO remains a bit too far west along with CMC. The GFS seems to have the system initiated too wrong. Another fault I see with the models is over predicting QPF totals which I do not see such high end totals. They have consistently all had a wet bias this year.
So here is a quick look at the latest runs of the models for the American Models...
The 18z NAM is sort of my model of choice for this sytem as it has been a bit farther east than other models and it seems to be estimating the cold air pretty well. The QPF sheild is pretty decent throwing precipitation back in west-central Pennsylvania and into southwestern Pennsylvania. It also shows the sharp cut-off, which I think will be evident in this storm. But the interesting part is about the 18z NAM is the deformation band that forms. While it seems a bit extreme and slightly unlikely some areas may see a bit of snow out of this...
The 18z GFS on the other hand seemed to have some initiation problems with the cold air aloft. When the model run came out the initial 0 hour had the 540 line over Lake Erie, when in fact it was actually over northwestern Pennsylvania according to actual upper air data. Overall it just seemed to be a faulty run with a track about 25miles farther west than it showed in the 12z run...
The NMM or otherwise known as the WRF HIRES model has a very high resolution power able to pick up on banding and orographic lift. The model seems to have the best hold on QPF, but still a bit over the top in my opinion...
Another interesting part is the simulated radar, which does also develop a strong deformation band of snow as 850s crach down below 0C. This simulated radar is for late Thursday night into Friday...
Overall the models have yet to reach a consensus and I would not really expect them too. For those stills monitoring the models, tonight's 0z runs are the last ones of significane.
After the storm...
So after the storm snowlovers will go back in hiding as a mild spell is headed our way, which could potentially hinder the accuracy of my December Outlook. This pattern shift is somewhat expected after a brutally cold end of November to beginning of December with record lows being broke all across the region and very unusual events, such as the lake effect snow squalls that dropped nearly 4inches all the way to Philadelphia in a very small streamers. And we cannot forget back on October 28 where our own blogger Stan999 even reported 18inches of snow in northeastern Pennsylvania in Wayne County. That was quite a rarity type event where unusual snows also fell in Bucks County during that event. The next day brought traces of snow for everyone across the state. Note after the big October nor'easter, a very mild period hit in the beginning of November with highs approaching 85degrees near records. This period lasted for nearly two weeks eventually giving way to a full month period of arctic cold with occasional snows. I believe most everyone has finally seen their first accumulating snow. So here we go with another big storm, which will eventually bring a pattern shift for a deep western trough bringing nearly record cold temperatures and even snow across the Pacific Northwest. Generally speaking their seems to be an above normal amount of cold air available across the north. Laws of equilibrium suggested a eventual shift in the pattern for a period of time, and that time has come. There has been a general model consensus for nearly a week on the new gained warmth across the east with cold situated over places such as Montana. Other developments prove now that we do have an official La Nina I believed after some rapidly declining SST in the Pacific. Warm weather will bring highs to near 10degrees above normal for some periods, but I do not really see any great signs of blowtorch type weather headed towards the east. More so temperatures should just be above seasonal levels. MJO pattern shift moves into phase 4 bringing very warm anomalies up the eastcoast and generally cold conditions across the west. NAO and PNA all situated for eastcoast ridging along with positive AO. Signs do point to a general return to cold air later in the month. MJO shows signs of maybe future shift to a move favorable east coast troughing phase near 6 or 7, but that remains to be seen. Also teleconnection indices are showing signs of more favorable snowy pattern. Something to keep in mind for past few winters is the lack of Greenland Blocking and lack of true definition of negative NAO. This prevented any major storm from forming and which will eventually lead to a non-snowy nor'easter in the short term. The hope would be for a shift to a more favorable negative NAO towards the end of the month, and a development of blocking. We really have not been in a good pattern for snowstorms this entire season despite the anomalous cold air. So I guess one snowlover could consider this all wasted cold. My concluding thoughts bring the idea of a 1-2week reloading period with deep trough over west and warm conditions elsewhere across the east. Long term GFS does favor back door cold fronts so some areas in New England may escape the warmest of the pattern. Those looking for a white Christmas this year may be sort of out of luck, despite the current pattern we have been in.
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- 0.75inches
Seasonal Total- 6.85inches
Winter Weather Advisories- 1
Winter Storm Warnings- 0
Heavy Snow Warnings- 0
Blizzard Warnings- 0
Snow Advisories- 0
Winter Storm Watches- 0
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
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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