Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 20:21 GMT le 03 février 2010
Most computer guidance is unanimous in a strengthening a double barrel low pressure setup redeveloping on the east coast. Climatology and past analogs support this, featuring a widespread precipitation event for the entire eastern seaboard. Due to animous blocking this will allow the storm system to affect southern areas more so than Northern New England.
Thoughts on February 5-7 Snowstorm...
A anomalous southerly flow is allowing cirrus clouds to stream overhead as 'the calm before the storm' infects the entire Middle Atlantic region. As this flow continues to increase, national water vapor loop is indicating over +4SD moisture anomalies streaming out of the Gulf of Mexico courtesy of a low pressure developing in Louisiana. As the infrared and water vapor loops take on the classic comma head approach, cloud tops continue to cool towards Texas and Louisiana noting the actual intensity of this storm system. As the low deepens below 1004mb, plumes of moisture will stream up the eastern seaboard with PWATs (precipitate waters) rising to near 1.2in across the southern Middle Atlantic. As the low pressure attempts to move northeastward, a low undergoing bombogenesis in the northern Atlantic is slow pulling away. The simple physics element of uniform polars repelling will be the example set forth by the unusual blocking scenario to the north where the low is already progged to be near 944mb. The exact displacement of this low is critical to the northern extent of the SLP (surface low pressure) track. Also to note is the correlating negative NAO (North Atlantic Oscillation) phase below -1 along with a positive PNA (Pacific/North American Pattern) and negative EPO (Eastern Pacific Oscillation) ridge. These all indicative of cyclogenesis along the eastern seaboard. Located in southern Canada is also a polar vortex, which will slowly be retrograding northeastward, but will pose critical again to the northern progression of this storm system.
By Friday morning weak dbz (virga) will likely be across southern Virginia and West Virginia as mid levels around 10000ft are indicative of RH (relative humidity) less than 40% by GFS bufkit prognostics. But shortly thereafter moisture will stream into the region with the stratiform snowshield marching slowly to the north in contrast with a weakening and departing high over northern Pennsylvania. As the SLP tracks into South Carolina Friday mid morning precipitation will be into Washington DC and southern Maryland. A weak easterly flow at the surface will allow for thermals to favor rain for those south of the Virginia/North Carolina border, but increasing inversion heights will allow cold air damming to favor severe freezing rain in the foothills of the Appalachians. By Friday late morning things begin to get interesting as the 850hPa low tracks into southern North Carolina on a east-northeast trajectory. Using the typical rule of thumb of the heavy snow axis about 100+mi north of the 850hPa low track, heavy snow will likely be across northern Virginia into Maryland as a strong convergence zone develops across the region. Increasing isentropic lifts heights will favor precipitation rates over .1/hr for standard QPF (Quantitative Precipitation Forecast). With a favorable low level jet near 60knots around 850-925mb aloft, strong vertical lift will favor frontogenesis heights increasing over Maryland and northern Virginia by early afternoon with snowfall totals already around 2-4in for parts of northern Virginia and into West Virginia. As the 700hPa low tracks through southern Kentucky, the stratiform precipitation shield will finally lift northward above the Pennsylvania I-76 turnpike by early afternoon with precipitation in the form of snow. As for temperatures during most of this event, use a simple rule of thumb... Take your wetbulb/dewpoint temperature at the onset of falling precipitation and add on 3-4F. That then will likely be the temperature for the most part during the entire system especially considering WAA (warm air advection) is confined to southern Virginia on southward.
By Friday evening, the northern extent of the precipitation shield will likely be between I-76 and I-80 with virga to the north. A strong convergence axis in northern Maine with increasing momentum transfer of air particles will favor cold air diving into the northern edge of the storm with favorable snow growth zones highlighted as followed. High resolution models are indicative of increasing dendritic growth along the Pennsylvania turnpike south to northern Maryland with H85s temperatures near (-5)-(-8)C during a majority of the event. With excellent snow growth levels around 10000ft, ratios in this region will be in the realm of 12:1 or 15:1 making for a fluffy snowfall once again. Take for instance KMDT (Middletown/Harrisburg, PA) QPF totals from December 19 at .66in, yet 8.8in of snow was officially measured. Keep in mind ratios are defined by temperatures aloft, and not boundary layer (2m-10m) temperatures. Another mesoscale feature will likely occur from Washington DC northward into northern Maryland and perhaps southern Pennsylvania with the formation of coastal/surface front which will serve as an axis for snowfall rates near 2-3in/hr. Finally the formation of a CIS/CCB band is likely towards central and northern Maryland also as a potential gravity wave forms in central Virginia along the northern right front quadrant north of the warm front as rising air parcels continue to rise and sink favoring anomalous precipitation rates. These mesoscale features will serve in isolated higher amounts of snowfall in the northern Middle Atlantic during the height of the event Friday night.
As pressure falls along the SLP track near the Virginia/North Carolina border increase to -3mb/hr, cyclogenesis will favor in a deformation axis towards Maryland and Virginia in particular adding an additional .5in of QPF that northern areas will not see in the precipitation shield. This axis will also be accompanied by strong vertical lift courtesy of the cold air covergence layer favoring mixing aloft allowing a transfer of winds to the surface with gusts over 35-40mph along the coast with blizzard thesholds being met potentially as far west as Annapolis.
As the low pulls away during the later half of Saturday, precipitation will quickly end from west to east leaving a sigificant snowfall in its wake especially over Maryland and northern Virginia into northern Delaware. The northern edge of this precipitation shield is highly uncertain with guidance recently trending to the south courtesy of anomalous blocking, so at this point those from the Pennsylvania turnpike and on northward should be playing on the conservative route. There will likely be a sharp cutoff between the horizontal lines of Indiana, Pennsylvania-Harrisburg, Pennsylvania-Allentown, Pennsylvania and Butler, Pennsylvania-Williamsport, Pennsylvania-Scranton, Pennsylvania. This exact location is yet to be determined, but guidance suggests this may even sink south especially looking at foreign models. In any case elevation and orographic lift along with higher snow ratios may favor heavy snow along and south of the Pennsylvania turnpike. The bullseye appears to be in northern Maryland from southern to central Hartford County and a country east and west of that. Isolated snow totals may be near 30-32in in this region. See more information below on snow totals. Also for those in southern Pennsylvania, watch for the slim possibility of a mesoscale band forming along the cold conveyor belt of the northern end of the precipitation shield. This sometimes is a common factor in terms of strong blocking with limited northern extent of QPF. This was noted recently from the past light to moderate snowfall that 'overperformed.' At this point the highest "bust" potential so to speak exists from Altoona to Harrisburg to Allentown to New York City. There will be sharp line between 12in and 1-2in. In any case this will be a high impact event, but fortunately the low will not be cutoff from the jet allowing for a general quick motion of the SLP out into the Atlantic with the duration of the storm only around 18hrs or so for most locations as the storm is out of here for many areas especially in Pennsylvania north of the deformation by noon. Stay tune for any updates and/or changes during the day Friday. Have a great day!!!
This is my current rain/snow line...
Farmville, Virginia - Ashland, Virginia - Warsaw, Virginia - Salisbury, Maryland - Ocean View, Delaware
*Note this line is a general estimation for precipitation type (rain vs. snow) during the height of the precipitation. As the deformation axis departs, this line will likely drop southward. Also during any intense convection correlated with a gravity wave development may favor brief periods of sleet especially towards La Plata, Maryland and the southern suburbs of Washington DC. Also south towards the Appalachians in North Carolina a major freezing rain/ice storm is likely to occur with QPF amounts in excess of .5in of pure freezing rain. North of this line by about 20mi will definitely have all snow.
COMING WHEN PRECIPITATION COMMENCES!!!
1. Impressive mesoscale banding in northern quadrant favoring isolated snow totals up to 30in in northern Maryland.
2. High winds near 40-60knots aloft will allow for mixing to filter gusts over 35mph especially within 50mi of the coast.
3. High impact on Friday evening commute with precipitation lasting through Saturday afternoon.
4. Heavy snow (+4in) will fall from western Virginia northward into southern New York state and southern Connecticut.
5. Sharp northern QPF gradient favoring a line horizontally across Pennsylvania between Mansfield, Pennsylvania and Harrisburg, Pennsylvania.
*Note the region at the 5-9in/12in line will more likely be in the range for 8-14in. There is a high bust potential in this event considering the sharp northern cutoff, so any swing of 25mi for the surface low track will change forecasts dramatically.
Selected City Accumulations for the Northeast...
Hagerstown, MD- Heavy snow, 18-26in isolated higher amounts
Baltimore, MD- Blizzard conditions, 14-22in isolate higher amounts
Salisbury, MD- Sleet/freezing rain/snow, 3-7in
Washington, DC- Blizzard conditions, 14-22in isolated higher amounts
Wilmington, DE- Heavy snow, 12-18in
Dover, DE- Heavy snow/sleet/freezing rain, 5-12in
Trenton, NJ- Heavy snow, 6-10in
New York City, NY- Moderate snow at times, 2-5in
Poughkeepsie, NY- Cloudy with flurries, coating of snow
Binghamton, NY- Cloudy with flurries, coating of snow
Albany, NY- Cloudy with flurries
Hartford, CT- Cloudy with light snow, C-1in
Concord, NH- Cloudy
Providence, RI- Cloudy
Worcester, MA- Cloudy
Boston, MA- Cloudy
Nantucket, MA- Cloudy with light snow, C-3in
Hyannis, MA- Cloudy with light snow, C-3in
Portland, ME- Mostly cloudy
Bangor, ME- Partly cloudy
"Subject to Change"
Computer model mayhem can best be describing this entire scenario with striking differences for the northern edge of the QPF shield. The GFS/ECMWF combo seems to have the best consistency, but the NAM/ETA/MM5 seem a good deal further south highlighting strong confluence to the north. For now I took a general 1.0in QPF line from Pittsburgh to Harrisburg to Reading with 2.0in QPF along the Mason-Dixon line. This fits well with local SREFs except for a bit of tweaking. The biggest concern is the NAM and GGEM runs, but for now the NAM seems to have have some initiating issues illustrating 5 vortices of energy at the height of the storm indicative of QPF problems. It also has a east-southeast trajectory at one point which is suspicious to say the least. The GFS seems to have a better hold on the system, but looking back at similarities in the December 19th event, the GFS did have the precipitation shield well too far northwest with the NAM scoring on the chalkboard so this arises some concern. In any case high resolution models for the 0z cycle will be interesting, but probably siding more towards the NAM. I also took my .1in line about as far north as KUNV with little QPF towards IPT. In any case this event is marginal in terms of confidency so stay tuned to the latest.
After the storm...
Interesting potential lies ahead in the medium and long range as the AO (Arctic Oscillation) continues to be well below normal negative values diving once again into off the charts territory. With a similar negative AO oriention I expect a constant feed of cold Canadian air into the northern half of the United States. With above normal geopotential heights over the northern Atlantic blocking will continue to favor favorable conditions for east coast cyclogenesis and below normal temperatures. The first threat appears quickly on the horizon for Monday-Tuesday with ECMWF taking a miller B scenario with 6-10in amounts across the entire northeast on the 12z 2/4/10 run. The GFS takes a less amplified approach with light amounts scraping New England perhaps with some higher totals. In any case wavelengths have also favored this time period for an east coast storm threat. I have not really focused, as expected, on this scenario, but it is the next threat posed towards the east coast. Also towards Sunday-Tuesday upslope from weak shortwave rotating through the Great Lakes will favor 1-4in of light snow over the snow belts of northwestern Pennsylvania and the Laurel Highlands into Garret County, Maryland. Cold air advection will also be widespread across the northern Middle Atlantic with highs Sunday-Tuesday ranging 7-14F below normal into the low to mid 20s with lows in the single digits courtesy of 850mb temperatures around -10C or below and 1000-500mb thicknesses below 530dm. After the Monday-Tuesday threat, wavelengths favor a day 8 threat with foreign guidance such as the JMA posing a Miller A winter storm threat with a low pressure ejecting out of the gulf of Mexico. In any case the next two weeks are likely to feature well below normal temperatures with several threats of snow from coastals to clippers. On a side note Lake Erie surface ice has definitely increased especially towards the shallow portions of the lake near Cleveland so the heavy lake effect snow is likely done for the season.
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"Here northeast of Harrisburg 2009-2010 winter statistics"
Current Snow Cover- 20.75in
Monthly Total- 43.25in
Seasonal Total- 61.35in
October Total- 0.0in
November Total- Trace
December Total- 16.0in
January Total- 2.1in
February Total- 43.25in
Winter Weather Advisories- 5
Winter Storm Warnings- 3
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 2
Winter Storm Watches- 3
Lowest High Temperature- 18.8F
Lowest Low Temperature- 11.7F
Wind Chill Advisories- 0
Wind Chill Warnings- 0
(Winter Storms Stats)
Dec 5 - 1.5in - First accumulating snow of season
Dec 8-9 - 2.5in - Snow changed to plain rain
Dec 13 - .1in - Freezing rain
Dec 19 - 9.0in - Heavy snow, higher amounts to south
Dec 31 - 3.0in - 2.5hr warm air advection event
Dec 31 #2 - .2in - Freezing rain/sleet later in day
Jan 8 - 1.5in - Light snow associated with clipper
Feb 2 - 3.75in - Weak coastal storm
Feb 5-7 - 19.0in - 10th largest snowstorm on record
Feb 9-10 - 20.5in - Blizzard conditions/snow depth up to 36in
Weather wizard (Patriot News)Link.
Sure has been a long cold spell" is a lackluster comment you'd hear at a social gathering when a person can't think of anything else to say.
Not so with Zachary Labe. The 17-year-old junior at Central Dauphin High School is passionate about weather. So passionate that he's one of just 28 high school students who've been accepted for membership in the American Meteorological Society, the association for radio and television forecasters.
If that isn't passionate enough, there are the weather instruments in Labe's bedroom. They make noise. Day and night. One goes off if the temperature makes an abrupt change, another when a storm begins, and there are more.
Even if it's 2 a.m. and snow or rain snow begins, the alarm wakes Labe. In seconds he's out of bed, running through the upstairs hall yelling, "There's a storm!" And out he goes in the middle of it. In a rainstorm, he takes a lightning detector.
Among Labe's large collection of weather equipment is a top-of-the-line weather station that the federal government uses, but he doesn't use it. "It's not very accurate," he said.
After taking a National Weather Service class, Labe could get an account from the National Oceanic and Atmospheric Administration, which gives him information to interpret for a weather forecast. And Labe is usually right on. In fact, his prediction is accurate more often than professional forecasters,' he said.
Take the night of Jan. 22-23. Several meteorologists said we'd have rainstorms, perhaps thunder. Labe's prediction said nothing about precipitation. Not a drop fell.
"It's impossible to be perfect in predicting," Labe said. "But you can be less imperfect than others."
Forecasts can't be perfect because forecasters make interpretations. NOAA's "super computers" take information such as wind velocity and humidity and use mathematical equations to transfer the results onto maps and graphs.
Labe interprets NOAA's information, figures out a forecast, then color codes several of NOAA's blank maps of the U.S. to indicate information including temperatures, the jet stream swish and humidity.
In 2007, at age 14, Labe started forecasting with about 10,000 other amateur meteorologists on the Web site Weather Underground -- www.wunderground.com -- under the name "Blizzard92," which he used because he was young and the Internet can be a dangerous place.
The folks at the California-based site noticed Blizzard92's accuracy and in 2009 sent Labe an e-mail asking if he'd be one of nine featured forecaster bloggers in the country, taking on Pennsylvania, Delaware and Maryland. Of course, he would.
As a featured blogger, Blizzard92 had to upload a photograph of himself. This took the cat that was his age right out of the bag. Not only were the Weather Underground people amazed that he was 17 and had expert knowledge, Labe received thousands of comments on the site.
And the other eight people selected? They all have degrees in meteorology.
Labe's interest in weather ignited long before he was 12. He often heard his grandparents and uncle discussing the weather. They were farmers, and weather was vital to their livelihood.
Labe didn't say a whole lot, but he started accumulating books on meteorology and weather history. He stayed up nights watching the skies during storms, recorded information in a weather journal and asked for a weather station. His parents bought him an inexpensive one to start. It, of course, led to more equipment.
Labe belongs to Skywarn Storm Spotter for the National Oceanic and Atmospheric Administration. When there's a storm and tree branches fall or other damage happens, he reports it to NOAA.
Among his other memberships are the Mount Washington Weather Observation Service in New Hampshire and the Community Collaborative Rain, Hail and Snow Network, to which he sends precipitation amounts every 24 hours.
Lower Susquehanna Valley Doppler...
(Courtesy of WGAL)
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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