Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 8:26 PM GMT on December 04, 2009
Thoughts on December 5th Snowstorm...
Well surprise, surprise... It appears for once we have a decent coastal storm to start December. But look at that date, the infamous and magical December 5th did its dirty work again. This will be the third year in a row for accumulating snow on December 5th here in Harrisburg and many surrounding areas along with many other past seasons also. I think this storm is going to take many average "joe" citizens by the surprise. For those of us in the Middle Atlantic it looks like most of us will cash in with at least a coating or more and some areas unexpectantly may be the jackpot areas where originally it looked like meager accumulations. I am quite enthused for this event considering March 1 was the last accumulating snowfall for many areas. This snowstorm may help to push snow totals across the southern Middle Atlantic for average accumulation for the entire month. Keep in mind December monthly totals are rarely above 5in in the Middle Atlantic. I do not have too many immediate concerns for this system, even though the forecast has changed dramatically in the last 12hrs. Initially at the beginning of the week this chance looked very good with an amplflied trough and strong southwest cutoff allowing the trough to turn negatively tilted. The main factor lacking was a high pressure to the north and upstream blocking. But during the week models moved east with the system which made some sense, but did not. First off low pressures near the Panhandle of Florida typically do track near benchmark or east especially without a real arctic airmass with an anomalous negatively tilted trough, but without upstream blocking in this scenario I saw it being trended west and not east. Think of it this way, without blocking many times storms track to our west and not east. Anyways then the GFS and ECMWF showed great interaction between a Pacific Northwest shortwave and a Great Lakes cutoff weak shortwave. This was the initiating feature to push this storm west and this type of interaction is often the kiss of death for coastal runners. But along came the high resolution model, which is actually very good at predicting coastals, but anyways it came along and showed a farther west low. Many meteorologists threw the NAM out being 84hrs out at the end of the NAM range. But then the models began to swing west and this is now continuing. There is quite a bit of gulf moisture; note current Florida radar. A widespread snowstorm is coming with initially rainfall south of the Mason-Dixon line. There are a lot of things on my to do list tonight for making this forecast, but I think this blog will be completely finished by 10pm or so. So who is ready!!!
***The timeline for the second system will be issued tomorrow afternoon.
This is my current rain/snow line...
It appears that cold air will be a problem for those south of the Mason-Dixon Line especially below 700ft. Many areas will start out as rain with nearly .25in QPF being used for pure rain especially towards I-95 on southward including the major metropolitans. But as the storms wraps out off the coast it appears cold air will be pulled from the northeast as the primary winds will be out of the north-northeast instead of the east. Therefore this will cause a limited effect on surface temperatures on the coast from the warm SSTs of the Atlantic. Most areas will turn to snow by the second half of the storm with additional QPF for all areas. Many areas south of the Mason-Dixon line will also have ground temperature problems with areas to the north of the line having initial problems. But from north to south snow will accumulate courtesy of colder air and increase in precipitation rates. This rain/snow line is a rough estimate for the precipitation types during the height of the storm.
My rain/snow line is... Charlottesville, VA - Dale City, VA - Annapolis, MD - Georgetown, DE - Lakewood, NJ
*Note these lines are estimates and actual locations may vary. Snow is north of line, rain is south.
*Note in general the forecast was a success!
1. First accumulating snow for season in Middle Atlantic.
2. Initially snow melts upon contact before precipitation rates increase.
3. Snow accumulations will not exceed 6in for most locales.
4. Rain/snow mix is likely towards southern Maryland and southern Delaware.
5. Widespread impacts up and down the I-95 corridor.
*Note especially in the 3-6in region, it is a bit elevation specific and most areas will be in the lower range of that total but isolated 6inches are possible especially towards the Chester County hills in the northwestern part of the county.
Selected City Accumulations for the Northeast...
Hagerstown, MD- Moderate snow likely; 3-5inch
Baltimore, MD- Rain and snow to all snow; 2-4inch
Washington, DC- Rain and snow to all snow; 1-4inch
Wilmington, DE- Rain and snow to all snow; 1-4inch
Dover, DE- Rain and snow to all snow; 1-3inch
Cape May, NJ- Rain with a few flakes; Trace of snow
Trenton, NJ- Rain and snow to all snow; 1-3inch
New York City, NY- Rain and snow to snow; slushy accumulation of 1-3inch
Poughkeepsie, NY- Moderate snow at times; 2-4inch
Binghamton, NY- Periods of light snow; 1inch
Albany, NY- Light snow showers; Coating of snow
Hartford, CT- Rain and snow to all snow; 1-4inch
Concord, NH- Periods of light snow; 1inch
Providence, RI- Rain and snow to all snow; 1-3inch
Worcester, MA- Moderate periods of snow; 2-5inch
Boston, MA- Rain changing to snow; 1-2inch
Nantucket, MA- Mostly rain with a few flakes; Trace of snow
Hyannis, MA- Rain and snow; Slushy accumulation C-1inch
Portland, ME- Intermittent light snow; 1inch
Bangor, ME- Light snow showers; C-1inch
"Subject to Change"
After the storm...
It appears next week will be quite active with a large amplified storm affecting the Middle Atlantic around the Wednesday time frame. Despite the ECMWF and GFS guidance forecast a Ohio Valley system, I think this has the option to develop a secondary low off of the Delmarva to save us north of the Mason-Dixon line and allow for some accumulating snow. This recent 18z GFS run shows the option beautifully along with the 12z UKMET on board also. I am definitely watching this period as it looked favorable back in November where I highlighted the threat around the 28th. It all depends on if we can get a secondary low pressure to form. At least 1inch of front-end snow is somewhat likely especially across northern Maryland on northward, but southward trends have been noted on several of the models as this system is accompanied by a strong cold front. This cold front will allow for the first cold blast of the season towards the end of next week. Cold air is building across western Canada courtesy of the retrograting Polar Vortex into the region, which will allow for some cold air to begin to advect into the United States. It appears H85s will drop below -10C for many across the northern Middle Atlantic allowing for highs in the 30s for temperatures around 5-10F below normal. This cold blast has been highly advertised on the models for the past 7-10 days. We still are lacking upstream blocking courtesy of the east based negative NAO so storms tracking to our west through the next week or two are definitely possible, but I am keeping a close eye on the system for next 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 2009-2010 winter statistics"
Current Snow Cover- 0.5in
Monthly Total- 4.0in
Seasonal Total- 4.0in
Winter Weather Advisories- 2
Winter Storm Warnings- 0
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 1
Winter Storm Watches- 0
Lowest High Temperature- 30.6F
Lowest Low Temperature- 17.1F
Wind Chill Advisories- 0
Wind Chill Warnings- 0
(Snow Storms Stats)
Dec 5 - 1.5in - First accumulating snow of season
Dec 8-9 - 2.5in - Snow changed to plain rain
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Light Rain Mist