Cornell University- Atmospheric Sciences Student; Central PA SKYWARN Storm Spotter; American Meteorological Society Member; PA CoCoRaHS Branch Member
By: Zachary Labe , 4:49 PM GMT on December 13, 2009
"Afternoon Thoughts" (Updated 12/13)
Good afternoon!!! Every year the question comes to mind of spending the holidays in a warmer climate. While many traverse southward into places such as Florida for the Christmas season even venturing into the holiday celebrations at places such as Disney World; I can just not see myself spending Christmas next to a palm tree. Part of the enjoyment of the season is running into local malls/shops to avoid the cold brisk winds of winter. Or perhaps it is the idea of everyone asking me whether we will have a white Christmas or not, despite it being only November 3rd. Then looking at media and the movies it does not help the warmer climate appeal, as they are always advertising snow throughout the entire movie. For instance take the "National Lampoons Christmas Vacation" movie (which is my favorite Christmas movie). The film takes place in Chicago, Illinois, yet through the entire 25 days to Christmas there remains a heavy snow pack on the ground; believable, not quite. Still the idea of a consistent snow cover and actual snow falling on Christmas makes the holiday season perfect according to some. Usually when the flocks of people begin asking me for a Christmas forecast, I give them the same old, "There is a 21% climatological chance of a white Christmas." Then they get mad and walk away. The clichéd Christmas of snow falling around a cabin in the woods on Christmas, even has appealed to me as the ideal holiday season. There is just that interesting retrospect surrounding snow falling December despite the fact Harrisburg only measures 4.5in on average in the month and so far we have already seen 40in. Maybe one of these years I will be able to spend Christmas with family out in Deep Creek, Maryland out of one of the vacation homes. So looking at the forecast for this Christmas, while I could say the climatological odds of a white Christmas; I will say this.... Looking at the overall synoptical pattern I think chances of a white Christmas are nearly 30% higher than the past seven years. That does not mean it will snow on Christmas, but odds are higher for snow to already be on the ground. As I will talk about later in my blog, there look to be two chances of significant storms this month, one around the 20-22 and a second in the 27-29 time frames. Happy Holidays!!!
"Current Surface Plot"
(Courtesy of HPC)
(Courtesy of Wunderground)
(Courtesy of NOAA)
"Forecast Discussion"(Pennsylvania, Maryland, Delaware)(Updated 12/13)
After a low pressure moves across the region Sunday, it appears ridging aloft will and high pressure well off the coast will allow for a strong southwest flow favoring well above normal temperatures. MOS suggests highs in the mid 40s, but I am taking it a tad warmer into the low 50s for extreme southern Pennsylvania, but much of Maryland and Delaware. H85s will rise to near +8C, and partly cloudy skies will dominate over the region ahead of the Arctic cold front. With the heavy rain from Sunday, much of the snow pack of Pennsylvania except for the northern sides of mountains will be diminished. This will allow for the sun to cause temperatures to rise greatly on Monday. Towards Monday night approaching cirrus clouds and southwest light winds will inhibit radiational cooling giving way to a mild night. Tuesday a cold front will approach the region with steep lapse rates under the sharp temperature gradient. Highs ahead of the front will be reached during the first half of the day as H85s approach +10C. NAM temperature profiles seem a bit more accurate than the GFS/GEFS combo. With steep lapse rates a few heavy rain shower bands could develop along the front. The event remains sort of similar to a windex event, but temperatures remain to warm for snow squalls in most areas. Model QPF generally is less than .1inch for most areas using SREF QPF profiles. As the front moves through, 2m temperatures will fall throughout the day along with H85 heights. The flow will shift from the southwest to the west and eventually the northwest by Wednesday morning. The lake effect snow machine will turn on by Wednesday as H85s drop to near -10C and 1000-500mb thicknesses drop to below 525dm. Omega values will be unfavorable towards a significant lake effect snow outbreak considering PWATs near .25in and very dry air aloft. But with decent dendritic growth some areas may pick up some moderate accumulations towards northwestern Pennsylvania. By Thursday the core of the cold air will be over the region as the polar vortex retrogrades directly north of the eastern United States into Canada. By Thursday dewpoints will fall into the signal digits with a 1028mb high pressure and upstream ridging over the Middle Atlantic. This will allow for decoupling winds towards Thursday night for one of the coldest nights of the season. The -2SD trough will remain over the region Friday with H85s below -10C as a S/W approaches from the Midwest as a weak Alberta clipper. Typical with moisture starved clippers, QPF looks light. But cold surface temperatures with a favorable track south into central Maryland will put the jet streak over northern Maryland and southern Pennsylvania generating a potential light synoptic snowfall favoring upslope regions near South Mountain and into the Laurel Highlands including the Potomac Highlands. Accumulations may be near 2-4in over the upslope and orographically benefited regions with 1-3in elsewhere and less east of the Susquehanna River. Behind the clipper, 1000-500mb thicknesses fall to near 515-520dm allowing for even colder air. Questions then begin to arise about storm chances also. Stay tuned! In conclusion after the frontal passage on Tuesday temperatures look to be below normal most of the week and generally dry except for the lake effect snow belts with flurries elsewhere.
(Courtesy of Penn State Meteo.)
"Current Water Vapor Loop"
(Courtesy of Penn State Meteo.)
"7-Day Zonal Forecast Outlooks"(Pennsylvania, Maryland, and Delaware)(Updated 12/13)
Monday- High pressure over the Tennessee Valley will allow for partly to mostly cloudy skies over much of the northern Middle Atlantic as a low pressure pulls off to the northeast. Some residual moisture from Sunday night and partial clearing may allow for some fog formation towards Monday morning. Fog may become dense with visibilities below .25mi across some regions especially across the valley locations below 800ft. But diurnal heating of the day will allow the fog to dissipate by 10am with partly cloudy skies over the region. Weak ridging aloft and a southwest flow will allow for warmer than normal temperatures especially with low snowpack over the entire region. Highs may approach values 10F above normal with highs over Maryland and Delaware approaching the lower 50s, highs in southern Pennsylvania including Philadelphia around 50F, and highs in northern Pennsylvania in the mid to upper 40s. Increasing clouds later in the day will be from a cold front approaching from the west. Dewpoints will also be on the rise up through the 20s and 30s. Monday night will feature mostly cloudy skies over the region ahead of the cold front with generally dry conditions and no precipitation. Lows will range from the low 30s to mid 30s across the entire northern Middle Atlantic including Washington DC.
Tuesday- A cold front will approach the region with weak dynamics and dry air aloft. But a sharp temperature contrast along the front may allow for some rain bands especially over western Maryland and western Pennsylvania. Rainfall amounts will generally be less than .25in for all areas with amounts below .1in east of the mountains. As the front moves eastward, temperatures will begin to tumble especially towards Tuesday evening as arctic air overspreads the region. Winds will become breezy as they shift out of the northwest. High temperatures will be into the mid to upper 50s south of the Mason-Dixon line and around 50F for areas north of the Pennsylvania/Maryland line. By Tuesday evening the front should be progressing off the coast as the flow shifts to the northwest allowing for a few lake effect snow showers to begin forming. Initially winds will be out of the due west for most of the night allowing the streamers to generally be north of the Pennsylvania snowbelts, but they will drop southward overnight. Snow accumulation Tuesday night will generally be a Coating-1in for the snowbelts across Pennsylvania and western Maryland. Lows will range from the low 30s for areas east of the Blue Ridge to lows in the mid 20s across the Appalachians.
Wednesday- A northwest flow regime will dominate the weather across the entire northern Middle Atlantic with strato-cumulus over the mountains and downsloping winds across I-95. A favorable northwest lake effect snow regime will allow several streamers to form particularly across the northwestern portions of Pennsylvania towards the northern Laurel Highlands. With breezy conditions and cold temperatures aloft, a few streamers may make it east of the mountains towards the ridge and valley region, but no accumulation is likely. Across the lake effect snow belts a general 2-4in is possible during the day. Highs will be several degrees below normal over the entire region with 30s for highs south of I-80 and 20s to the north. Towards Wednesday evening the flow turns a bit more northerly allowing even portions of northeastern Pennsylvania to see some lake effect snow streamers with accumulation around 1-4in possible particularly across the higher elevations of Wayne and Susquehanna Counties. Lows will generally be in the 20s for all locations with areas towards Bradford dropping down into the teens.
Thursday- Marginal ridging aloft moves over the northern Middle Atlantic with drier air allowing for much of the accumulating lake effect snow streamers to shut off with only residual snow showers and flurries over the region. Additional accumulations in the snow belts will only be around a coating to one inch or so. Partly cloudy skies east of the mountains and most cloudy skies across the Alleghenies will allow for highs to be several degrees below normal with a deep trough over the region. Highs will range from the mid 30s near Washington DC to the low 30s across southern Pennsylvania to the mid to upper 20s over the higher elevations and much of northern Pennsylvania. Thursday night will feature clearing skies and decoupling winds allowing for radiational cooling. With low dewpoints, temperatures should be able to fall into the single digits for northern Pennsylvania across Potter and McKean Counties with teens elsewhere and low to mid 20s towards Philadelphia and areas south of the Mason-Dixon line.
Friday- After a cold morning and heavy frost, sunshine will prevail until a cirrus deck approaches from the west ahead of a weak Alberta clipper towards Friday night. With the deep trough remaining situated over the east coast, temperatures will remain below normal generally in the upper 20s through the 30s for highs over the entire northern Middle Atlantic. By Friday night light snow will move into western Pennsylvania enhanced by orographic lift over the Laurel Highlands. Light snow will progress eastward throughout the night with generally light snow accumulations likely.
"Current River Ice Reports and Ski Conditions" (Updated 12/13)
December is an exciting time for many of the local ski resorts across the northern Middle Atlantic as they can finally start opening their doors after months and months of summer temperatures. Local ski resorts in the Harrisburg area have opened including Whitetail, Ski Liberty, and Ski Roundtop with machine grained snow packs with depths generally around 10-12in. Some of the snowpack is fresh snow from this past Wednesday and the past Saturday in the beginning of the month. After Sunday, Monday, and Tuesday, upstream blocking and a Canadian Polar Vortex should allow for an extended period of cold temperatures heading into the height of the holiday season. Temperatures will remain cold enough for constant snow making across the entire region and this should allow all ski areas to open up by the end of the month. Out towards western Maryland in the Deep Creek resort area, they are off to a great start this season with 27in of snow already being reported this season in McHenry, MD. Up in the Poconos Camelback and Blue Mountain are already off to a great start the season with partial fresh snow pack and residual cold temperatures. Heavy rain on Sunday will allow for very slow and slushy conditions as temperatures rise above freezing, and by early Tuesday temperatures will rise to near 50F in many areas melting some of the snow pack. But towards Wednesday through the end of the week, below normal temperatures will move back into the region for an extended period of time. As for snow chances, back into the Laurel Highlands and western Maryland a great upslope event looks to be in store from Wednesday through Friday as the flow remains out of the northwest. Several inches to a moderate snowfall is possible in this time frame across the lake effect snow belts. Towards Friday and Saturday a marginal Alberta Clipper moves towards the region and may spread a general 1-3in over the region with 2-4in across the Laurel Highlands. This is the next best chance of widespread synoptic snow over the northern Middle Atlantic. Towards the week of Christmas there remain several opportunities for significant winter storms, but there also is the high possibility these systems are pushes offshore. As for river ice reports, ice has begun to form on local waterways such as creeks and streams especially over the north-central Mountains of Pennsylvania. Also local ponds and small lakes are beginning to see some ice formation. But across Lake Erie and the local main stem rivers, ice is slow to form as it is only December. But with colder temperatures in our future ice formation will definitely begin to form by the end of the month.
-Link to official reports page from NWS...Link.
-Link to local ski resort snow conditions...Link.
"Current Northeast Snow Depth and Northeast Wind chills"
(Courtesy of Wunderground)
"Lake Effect Snow Conditions" (Updated 12/13)
A cold front will pass through the region resembling an Arctic front on Tuesday as temperatures will begin to tumble with increasing northwest winds. Lake effect snow will begin Tuesday afternoon and last through Thursday evening as ridging and high pressure over the Great Lakes and a low pressure near Newfoundland allows for a tight pressure gradient out of the northwest for a majority of the week ahead. Directly after the frontal passage Tuesday winds will shift to the 280degree flow allowing for most of the lake effect streamers to remain north of the region, but as the low pressure pulls to the northeast the flow will shift near 300degrees favoring lake effect snow over much of western and northern Pennsylvania and western Maryland. With relatively dry air aloft in this time frame, it does appear the lake effect will be overly significant across the northern Middle Atlantic especially considering Omega values only around (+4)-(-4) most of the week. Dendritic growth will though be excellent as H85s drop -2SD below normal with temperatures near -10C and below. Towards Wednesday winds shift even more northerly to around 325degrees. With model QPF generally be .1in for each frame, only moderate accumulations are likely in this time frame. The most favorable locations for accumulations would be across the northwest mountains in Pennsylvania where locations towards eastern Erie/Crawford Counties and all of Potter, Warren, and McKean Counties may see total accumulations around 3-6in. Towards the Laurel Highlands and western Maryland the flow initially is favorable for 2-4in before streamers become less organized as the flow turns more northerly. Some of the favorable upslope locations in Somerset County may see a quick 3-6in snowfall. Across much of the northern Middle Atlantic the favorable flow will allow for a few snow showers to make it east of the mountains affecting the Ridge and Valley region and into the Poconos where a quick C-.5in of snow is possible. Over the northeastern mountains towards Susquehanna, Bradford, and Wayne Counties the northerly flow will be favorable for the development of a few streamers into the region potentially allowing for 2-4in of snow over the Wednesday to Thursday time frame. Generally dry air will be the inhibiting factor for heavy lake effect snows across northwestern Pennsylvania especially considering the amount of cold air towards Thursday with H85s near -17C. Weak ridging aloft moves over the region towards Thursday night as a weak Alberta Clipper approaches the region and tracks across central West Virginia and central Maryland out of the Delmarva. After the passage of the light synoptic snow, ongoing lake effect will intensify towards Saturday evening under another northwest flow giving light accumulations to the snow belts. Depending on the lake effect forecast in the coming days, a snow map may be necessary to be issued Tuesday. Stay tuned with those with concerns in the lake effect snow regions!!!
"Current Lake Erie Wind Direction and Speed"
(Courtesy of NOAA)
"Current Lake Erie Water Temperature"
(Courtesy of NOAA)
"Long Term Outlook" (Updated 12/13)
The long term pattern is favoring colder than normal temperatures and potentially stormy conditions. As I mentioned yesterday the east-based negative NAO will be retrograding towards a more favorable west-based negative NAO with above normal geopotential heights over the northern Atlantic including Greenland. With rex blocking forming towards the Hudson Bay in northern Canada, the 500mb jet pattern looks favorable going towards the week of Christmas. During my special Middle Atlantic Winter blog last winter I mentioned quite about the favorable trend for a negative to positive trending NAO causing large storms systems over the east coast. This trend may slightly be available around the 20-22 of the month. Another interesting teleconnection is the current negative AO anomaly which is nosing towards -3. This makes it one of the lowest AO anomalies in many years and I have seen statistics proving a negative AO this low in December would allow for a colder than normal winters as patterns similar to this are very difficult to budge under a winter-time regime. With favorable upstream blocking conditions and deep troughing over the east coast under a trough axis over the east coast, I think it is suffice to say the potential for a KU storm over the region is significantly higher than normal. Originally it appeared this current weak would behold the time frame of a significant storm, but guidance suggests that the pattern finally is favorable towards next week. Interesting to note, but December typically has the least amount of coastal storms during the month with significant storms sometimes difficult to come by. In fact here in Harrisburg, the largest snowstorm this month was only 13.9in back in 1960. But anything is possible especially in this February-like coastal pattern. If we can get a S/W in the southwest to buckle the jet and allow for gulf moisture to stream up the coast, this all becomes possible. The scenario would seem to be an Alberta clipper dropping out of the Midwest allowing for a miller B low to form near southern North Carolina south of Hatteras. The chances of a winter storm in this period while are high, I think the odds of a bombogenesis low are higher for an offshore low considering the anomaly of the upstream blocking. Still though today's 12/13/09 guidance was particularly interesting with the 0z GGEM and 0z ECMWF favoring a significant coastal storm just off the coast causing rain around I-95, but heavy snow just inland from there. The 0z GFS is also close to a phase and considering the 500mb chart, I think the surface features are probably too far east, therefore the actual low would probably be near benchmark. But the parallel 0z GFS shows the opportunity for a significant snowstorm for all areas in this time frame. Also wavelengths favor another significant storm between Christmas and New Years. I am doing some research for statistics for back to back coastal storms in this time frame, but so far I have not found much. Anyways let me word it this way, go about in caution but keep in mind there is great opportunity in those time frames that hopefully is not wasted. Stay tuned in the coming week!!!
"Current NAO and PNA Predictions"
(Courtesy of NOAA)
"Anchorage, Alaska Tower Cam"
*Note I am only posting this towercam until snow starts falling over the northern Middle Atlantic, lol. For now we can all be jealous of the Alaskan snow.
"Monthly Outlook" (December)
November temperature forecast was a disaster. There were conflicting evidence for the temperature trend for November and I chose below normal to stay in line with the pattern of many below normal temperature months in a row, nearly 6 or 7. A generally zonal ridge under a Pacific jet occurred across the lower 48 during much of the month after a few below normal days in the beginning of the month across the Northeast. The MJO was the driving force behind the pattern along with the unfavorable Alaskan Vortex causing well below normal temperatures across Alaska. Alaskan vortices and Gulf of Alaskan Lows are the kiss of death for cold, but especially snow chances over the east coast. Also the Polar Vortex mentioned often in November was affecting the other side of the globe across Asia allowing for record snowfall cover in Siberia and record snows as far south as Beijing, China. Generally a large depreciative anomaly in snowfall occurred across the United States with major snowfall generally subject to mountainous areas. Temperatures were generally above normal for most areas across the northern portions of the United States. Closer to home in the Middle Atlantic anomalies for the month look to be near +3.5-4.0F for most areas, which is pretty impressive. As for precipitation, generally most areas received normal to below normal precipitation which actually went according to my forecast especially with my forecast of the storm track becoming more active towards the end of the month. And looking back through at our statistics most of the rain occurred toward the end of the month with nor'easters. The temperature forecast was a disaster though as my call for below normal temperatures was severely wrong for the reasons above. Anyways let’s leave on a positive note and look what is ahead for another difficult forecast, December... December forecast looks tricky and I am taking a slightly different route than many for my forecast. It appears the MJO forcing will weaken despite entering phases 6+7; this will have less of a driving force as it did in November. On the other side though phases 6/7/8 are very favorable towards east coast troughing. Anyways it also appears the Polar Vortex over the eastern hemisphere will retrograde west but over western Canada allowing for the Pacific jet to buckle perhaps leading to very cold weather over the Pacific Northwest into the Rockies for the first half of the month. Despite this Nina-like pattern, all hope is not lost as typically this would cause a strong southeast ridge to form. It appears the east-based negative NAO may become more favorable overtime turning more west-based, which would aid in a generally weak trough flow over much of the Midwest and east coast for the first half of the month. Also there are a few signs that the Omega block will slide east from Alaska to central Canada again favoring a weakening of a southeast ridge. And with the emission of several S/W out of the southwest, there is the possibility for the STJ to cause for some stormy times in the northern Middle Atlantic. A weak trough is better than a real amplified jet for snow chances. In any case I do not think this will be an overly snowy month as blocking will be limited to the north causing inland storms. But towards the second half of the month there are many more conflicting signals as ensembles point to a retrograding of the PV to a more favorable location over the Hudson Bay which would favor very cold air over the eastern United States, but some guidance suggests a breakdown in the negative EPO. I think I will take a middle ground with my transient pattern approach.
Temperature- I am forecasting near normal temperatures for December with general anomalies over the region around (-0.5)-(+0.5) with the colder anomalies across Pennsylvania as Maryland and Delaware may see a bit more impact from any southeast ridge that forms. It looks like the second week of the month will be pretty chilly along with the third week before the pattern begins to breakdown for a time being causing warmer temperatures before winter lashes in during the beginning of January. Overall December should have a bit of fun with storm chances and will not be a blowtorch as this past November.
Precipitation- Generally I expect above normal precipitation especially with a possible active storm track from the southwest along the peripheral of the base of the weak trough over the east coast. This favors overrunning precipitation events and possible east coast storms if the subtropical jet becomes active. This December could be very similar to last year's December with above normal precipitation and overrunning storms. As for snowfall I expect near normal snowfall, although I would not be surprised if some areas end up above normal especially over northwestern Pennsylvania. As for the first snow chance I like the December 5th-8th window for the first widespread snow. Just check out the parallel 11/30/09 12z GFS.
"Temperature and Precipitation Outlooks from Climate Prediction Center for next 30 days"
(Courtesy of NOAA)
-Winter Outlook 2009-2010...Link
"Here northeast of Harrisburg 2009-2010 winter statistics"
Current Snow Cover- Trace
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
(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
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|Dew Point:||15.2 °F|
|Wind Gust:||9.0 mph|
Updated: 10:37 AM EST on January 18, 2014