Cornell University- Atmospheric Sciences Student; Central PA SKYWARN Storm Spotter; American Meteorological Society Member; PA CoCoRaHS Branch Member
By: Zachary Labe , 12:41 AM GMT on January 31, 2014
Operational Forecasting Techniques for the February 5-6 Winter Storm
To create a weather forecast requires the use of an infinite amount of data and guidance. With the technological advances over the last decade, meteorologists can now predict weather forecasts with a reasonable accuracy in a two week or so lead time. This is a remarkable advance in the atmospheric sciences community. However, there are times when the basics of weather forecasting and analysis get lost to an instant gratification of colorful model maps.
This blog takes a new approach. The new approach is simple; to provide a forecast seven days in advance in total ignorance of model output. I will arbitrarily use Philadelphia International Airport (KPHL). And I will arbitrarily select the dates of February 5th and 6th. Yes, I selected those dates because I know there will be a middle latitude low impacting the Northeast. You could say that defeats the purpose of this blog, but please bear with me.
The following forecast will produce a minimum and maximum temperature for both February 5 and 6. It will also produce an estimated 24 hour QPF measured each period from midnight to midnight. It will not utilize any model guidance. No ensembles, no operational, no mesoscale models. However, it will use real-time data provided by global synoptic upper air and surface maps along with upper air balloon soundings, radar/satellite analysis, and access to previous climatological data for the year.
It is critical to note the current weather pattern over the last few weeks in Philadelphia. Due to data processing, analysis is only available as early as the January 1-15 period.
(Courtesy of NRCC)
The middle of January is the coldest climatological point in the year
Normal(s) for January 29 KPHL:
It is evident through the NRCC maps that an anomalously wet and cold period has occurred during the month of January for much of the northern Middle Atlantic. Given this is the heart of the meteorological winter, snow is a threat in any forecast that is below normal temperature-wise in association with above normal precipitation. This can be verified by the following values...
Snowfall for KPHL
January Total- 25.9"
Seasonal Total- 37.1"
Average January Snowfall- 6.4"
Average Seasonal Snowfall- 19.3"
(Averages based on the 1971-2000, 30 year mean)
1977-1978 is the 10th snowiest season on record for KPHL with 40.2". Therefore, we can assume with a near 90% certainty that this winter season will fall within the top 10 snowiest winters on record. January has been a remarkable month and is also now the third snowiest on record for KPHL.
Temperature-wise the last 15 days of January have also been consistently well below normal temperature wise with the following statistics...
1) Only two days featured lows with a temperature above 32.
2) The average mean temperature was -6.7F below normal.
3) Temperature extremes included a maximum of 51F and a minimum of 4F.
4) 7 days had highs of 32F or below.
5) 10/15 days featured a below normal mean temperature.
We can now conclude with certainty that a remarkably cold and snowy pattern has prevailed in the Philadelphia area during the month of January. We will make the assumption that this is consistent for other nearby reporting climatological stations in the northern Middle Atlantic (we know this is not always true). You will notice many assumptions are made in a forecast not utilizing computer model guidance.
Looking at the past seven days, temperatures have struggled to reach freezing and measurable snow accumulations occur with a striking consistency on about every third day. The last measurable snow fell on January 29, 2014 with 1.0 inches. The current snow depth at KPHL is 3.0 inches.
Now that we have a basic picture of the temperature and precipitation trends over the last few weeks, lets zoom out to some present data (4:30pm 30 January 2014).
(Courtesy of Intellicast)
These maps cover most of the basics ranging from satellite temperatures to current temperature anomaly trends. We can infer several things about this data. A trough is deepening over the northern Plains. We will assume that the trough axis is centered is the heart of the coldest temperature anomalies placing it right around North Dakota. An upper level ridge is currently moving into California and ejecting a shortwave out of the southwest into the eastern Rockies bringing rain and snow to some areas. A cold front is draped across the Great Lakes ahead of the next trough. This is allowing a shortwave that appears to be similar to an alberta clipper moving through northern Michigan. It will bring light snow to those areas and continue advancing east. Looking at the latest water vapor loop, we can see significant dry air across the Northeast. Therefore, it is unlikely any significant measurable QPF fall across the Northeast. We can expect this clipper to begin to shear apart. 24 hour temperature trends support this analysis.
(Courtesy of PSU e-wall)
KPHL does not launch any weather balloons. I have selected KIAD for the next closest station. The current upper air sounding does not show anything too remarkable. The entire temperature vertical profile is well below freezing. The horizontal (x) axis is the temperature in degrees celcius. Follow the blue linear line in a northeast angle (it is a log graph). Those are lines of temperature. The vertical (y) axis is pressure levels with increasing altitude. The current surface temperature at 12z was -13C which is around 9F. Keep in mind observations in meteorology use zulu time. Use the following formula to translate to eastern time during daylight savings: Zulu-5=ESDT. So this was around 7am, January 30. Therefore, follow the red line vertically. That is your temperature profile aloft (environmental lapse rate). The green line is your dew point vertically aloft. You can see the great differential between the dew point and environmental lapse rate. This signals very dry air and no precipitation likely.
(Courtesy of SPC)
We have a pretty good idea of the current synoptic weather pattern over the United States. Low pressure ejecting out of the southwest into the central United States. A trough sinking south through the northern Plain. Meanwhile, a wave over Florida will allow rain showers to continue to stream east as the trough over the east coast begins to depart. Over the next three days, we can expect all of these systems to interact and transfer east. We have a pretty darn good idea what will happen during this period. The primary weather influence will be the s/w surface low moving into the Midwest where another round of snow is likely. Ahead of the next trough, temperatures will begin to warm for the east (including the KPHL area)
Let's zoom out even further. Looking at the globe as a whole is a bit difficult in the meteorological field due to lack of data and observations. Mesonet and satellite images are very limited outside the United States. However, one can look at long wave patterns to determine active storm periods across the contiguous United States. I will exclude those messy details from this blog.
The current teleconnection readings for 29 January 2013:
We cannot look at the model ensemble forecast for global teleconnections. However, we will use the present numbers in determining our forecasts. For many, those numbers above do not really mean much. They are just seemingly random numbers, when in fact they a general derivation of the description of climatic features in different parts of the globe. For instance, the NAO is commonly referenced; it is a fluctuation between sea level pressure differences between the Icelandic low and Azores high. A large pressure differential is often derived to a positive (+) anomaly reading. Based on the above readings alone, we can conclude a significant amount of cold air in the Northern Hemisphere. A ridge is likely across the western United States with a trough in the east. But with the positive NAO is a lack in blocking in the pattern. Simply, this prevents large scale middle latitude cyclones from slowing down enough to buckle the jet and move up the east coast. Other indices can be used to look at long waves including analyzing monsoonal patterns in Asia, analyzing convection near the Hadley cell, and following ENSO trends across the equatorial pacific.
So using all of these above techniques, we need to come up with a specific forecast for the February 5th and 6th periods. We know quite a bit of broad information. We have a fairly good idea above the current weather pattern, and nothing screams any dramatic changes in the short term. It seems that the cold and wet pattern will continue over the east coast based on this data. Often, this type of forecast can be referred to as following persistence. So based on our data, it would seem that another trough is moving into the east coast in the 5-7 day time period. This is support by global teleconnections. We'll forecast below normal temperatures. Given this is 7-days in advance, we will temper the below normal anomaly to only a few degrees below normal. The high percentage of days with highs below 32F is pretty stark. Let's also add in the threat of precipitation. Given the recent wet pattern, and seemingly active weather pattern across the USA, it is probably a safe bet that precipitation will fall at some point during those two days. Which day? Who knows. If there is the threat of precipitation, we probably won't be seeing much radiational cooling from katabatic winds given extensive cloud cover and light winds. We will keep lows from dropping too far.
February 5: High of 33. Low of 24. QPF total of 0.25"
February 6: High of 33. Low of 24. QPF total of 0.25"
Using pure climatological information, real-time observations, and global wavelengths, this is about the best guess we can make. And no, there is no typo. There is no information to determine details for individual days so that is why the forecast is the same for both. We are following the cool, wet persistence that is strengthened our other larger-scale observations.
Okay, we can see it is basically throwing a dart in forecasting the weather more than three days or so in advance without the use of model guidance. The image below is the GFS ensemble mean for February 5. We can note the 500mb jet, 500mb height anomalies, and a spaghetti plot for 1000-500mb thicknesses.
Clearly this does not line up with our forecast. But the ensemble mean is a forecast in itself. I am currently enrolled in this semester, Atmospheric Dynamics and Synoptic I. We are applying mathematical equations to understand the algorithms that go into these models. It is a remarkable feet that we even have any super computers such as these. For some of the climate models, millions of mathematical equations run just to produce one output.
Now for a few quick thoughts of mine... I will be attending the American Meteorological Society conference from January 31-February 6. I will be sure to post updates from the events. If anyone else is also going to be down there, be sure to get in touch with me!
I have looked a bit closer at the setup for multiple waves for the upcoming week. Given the current orientation of the incoming waves, I am expecting many precipitation type issue events. In fact, some areas may not squeeze out any snow out of these waves over the next seven days. I do think the potential is there for one wave to produce significant snow. I place this wave in the February 8-10 time frame. Even so, that is also likely to have precipitation type issues. This pattern though is very good for northern New England where I believe they will see anomalous amounts of snow over the next two weeks. Elsewhere, it will be a gradient boundary flow. Probably north of 40N is the best to be in this type of setup. Although all is not lost, as that one wave will probably be widespread snow. Freezing rain will be a major concern in the interior for many of these events. I expect multiple dangerous ice storms for those areas. This pattern is not anything the one we are coming out of. It will be much more reminiscent of a moderate Nina February composites. Check out a warmer version of February 2007. Best bet is to enjoy the warm weather this weekend and take a break from forecasting. Precipitation types are always a crapshoot until a few days before the event. I think odds for above normal snowfall are very high for the interior and northern New England with anomalies declining as one moves south and east. Nevertheless, it will be an active period.
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Lower Susquehanna Valley Doppler...
(Courtesy of WGAL)
"10mi northeast of Harrisburg 2013-2014 Winter Statistics"
Monthly Total (October)- 0.0"
Monthly Total (November)- Dusting
Monthly Total (December)- 9.6"
Monthly Total (January)- 10.3"
Monthly Total (February)- 9.0"
Seasonal Total- 28.9"
(Snow Storms Stats)
Trace - November 8 - First trace of snow - Lake effect snow shower
Dusting - November 12 - First snow on the ground - Anafront
1.5" - December 8 - First inch of snow - WAA double barrel low
4.3" - December 14 - Miller B - Changed to freezing rain/sleet
1.3" - December 17 - Alberta Clipper
2.0" - December 26 - Surprise squall/clipper
4.8" - January 2-3 - Miller B Coastal
1.5" - January 10 - SWFE all snow
3.1" - January 21 - Redeveloping clipper with heavy snow along I-95
6.0" - February 3 - Wet snow from coastal low
1.5" - February 5 - All sleet accumulation with 0.3" of freezing rain
1.5" - February 9 - Light snow with Alberta Clipper
Winter Weather Advisories- 9
Winter Storm Warnings- 3
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 2
Winter Storm Watches- 4
Lowest High Temperature- 9.6F on 1/7/2014
Lowest Low Temperature- -3.1F on 1/7/2014
Wind Chill Advisories- 3
Wind Chill Warnings- 0
(Cornell University (950ft elev.) Snow Stats)
Monthly Total (October)- 0.0"
Monthly Total (November)- 3.7"
Monthly Total (December)- 16.4"
Monthly Total (January)- 18.5"
Monthly Total (February)- 8.0"
Seasonal Total- 46.6"
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|Dew Point:||15.2 °F|
|Wind Gust:||9.0 mph|
Updated: 10:37 AM EST on January 18, 2014