We will be forecasting for Lake-effect-opolis... oh, I mean Syracuse, NY (KSYR) 26 November through 6 December 2012. Forecasts are due by 00 UTC each evening which is still 7 PM local time. We are still forecasting for the 24-hour period 06-06 UTC which is 1 AM - 1 AM EST if you want to look at NWS Binghamton products (hooray for being in our own timezone!).
Syracuse, NY is known for its snow and has a reputation as being the snowiest city in the US. KSYR receives 121.2 in (308 cm) of snow on average every year mostly due to lake-effect events and nor'easters. For a few more interesting facts, I recommend checking out the Wikipedia page on the city. Syracuse is located in central New York State, straddling I-90, southeast of Lake Ontario (the big, important player), southwest of Lake Oneida (the little guy), and just northeast of most of the Finger Lakes. There is no real topography to worry about; parts of the city are hilly while the rest is mostly flat. The real focus as a forecaster is that warm Great Lake.
Taking a moment to stalk the airport, KSYR is located on the northern edge of the city (even closer to the lake). The ASOS station ID number is 72519.
View Larger Map
Just to review what the climate normals are-- cold and snowy. The average temperature for the entire month of December is 30 F with an average snowfall amount of about 35 inches. More climate data and records can be found here.
Before talking about forecasting tips, I think it is a good idea to have a review of lake-effect precipitation. I'm not sure if everyone has had this as part of their coursework or not. It's a fun concept to review, anyway!
Lake-effect Review
In a nutshell
- Cold, dry air blows over a warm lake and destabilizes due to fluxes of heat and moisture into the air and rises, forms clouds and can precipitate.
Ingredients
- Cold, dry air and a warm, ice-free lake
- Air: the colder, the better for fueling lake-effect storms. If you have a polar air mass with temperatures around -5 C to -25 C (23 F to -13 F) then if you warm the air below it, it will rise until it stabilizes, or cools during ascent until it is equal to the temperature of the environment. So the cooler that is, the more the parcel will rise because the environmental lapse rate is greater than the moist adiabatic lapse rate (7 C/km). For forecasting, the 850 mb temperature is used to represent the air temperature.
- Lake surface: the warmer, the better for fueling lake-effect storms. The Great Lakes remain mostly ice-free throughout the winter which will allow for fluxes of heat and moisture to occur from the lake surface to the adjacent air. Especially since it is only late November, the lakes are open. The current temperature of Lake Ontario is about 48 F.
- Air-Lake Temperature Difference: Previous studies have shown that a difference in lake surface temperature and the 850 mb temperature should be at least 10 C for synoptically-forced events (e.g. there's a shortwave trough passing through) or at least 12 C in general.
- A long lake parallel to the wind
- This is known as the lake having a large "fetch". We are trying to get fetch to happen, regardless of what Regina wants. Anyway, the longer the wind blows over the warm lake, the more the air can warm up and by the relationship of the saturation vapor pressure, more water vapor can evaporate into it so it will be warmer and moister and rise more and be more likely to precipitate. So air residence time over the lake is important which depends on the near-surface wind direction.
- More on fetch and lake-effect bands
- Lakes usually aren't perfectly circular and tend to have a long axis and a short axis, just like Lake Ontario. Lake-effect bands tend to be stronger when the wind is parallel to the longer axis with a larger fetch, but bands can still form and precipitate heavily when oriented with the shorter axis of the lake.
- Bands come in a variety of flavors. There's shore-parallel bands, wind-parallel bands, over-lake bands, vortices, etc.
- Bottom line: bands will form if most of the ingredients are present and not only if the wind is exactly parallel to the long-axis of the lake.
- Low directional wind shear
- Lake-effect is shallow, only reaching 2-3 km. But too much directional shear (change in direction of the wind with height) can weaken or disorganize them as they attempt to propagate from the lake where they originate.
- Forecasters look at the 700 mb wind as the "steering wind" that tells where the bands will propagate. Some studies have shown that if there is a directional shear between the boundary layer (10 m wind) and 700 mb wind of less than 30 degrees then the band will propagate in the direction of that wind.
The lake-effect process in an expanded nutshell
A figure from the lake-effect chapter from Severe and Hazardous Weather: An Introduction to Meteorology by Rauber, Walsh, and Charlevoix.
- Cold, dry air blows from the land to over the lake. It experiences a decrease in friction over the smooth lake surface and accelerates. This creates a divergence at the surface so air sinks from above to fill in the void, hence why the upwind shore of the lake usually has clear skies. The lake exchanges heat and moisture with the air, warming up the air and adding moisture. The air rises due to being positively buoyant and forms clouds, but the most clouds are formed when the air decelerates and converges with the shore. Got it now? Awesome.
- Extra Tools
- BUFKIT on the metlab computers
- You can also retrieve text data here of forecast soundings that are displayed in BUFKIT. It's a little hard to read, but the data for each sounding every hour is there for NAM, GFS, RUC-- just click on Syracuse.
- SPC Mesoanalysis
- They actually have lake effect parameters you can plot under Winter Weather --> Lake Effect Snow 1 and Lake Effect Snow 2 but data is not available for future forecast times.
- Lake Effect Snow 1 plots boundary layer RH (because you want it to be moist over the lake), and the sfc-850 mb temperature difference (can take as a first order analysis if you don't have the lake temperature, but oh wait you do!)
- Lake Effect Snow 2 plots the boundary layer wind in barbs and streamlines (sense of wind direction and speed) as well as convergence (look for a maximum convergence on the shore for more uplift for the band).
- Review of Ingredients
Table 1 from Niziol et al. 1995.
- Due to KSYR being located where it is, northwesterly flow off of Ontario with low directional shear should result in a lake-effect band reaching the ASOS station. The synoptic setting for this is a high pressure system to the west and a low pressure system to the east.
- An amazing study by Niziol et al. 1995 entitled "Winter Weather Forecasting throughout the Eastern United States. Part IV: Lake Effect Snow" provides a climatology of lake-effect snowstorms, a thorough overview of the processes involved in band formation, and forecasting tips. (If you can't access it via that link, search through Web of Science or e-mail me for it.)
- Most synoptic or mesoscale textbooks include a chapter on lake effect. I have a few in my office (Challenger 121) if you would like to borrow one. I swear I don't bite and I even have a stash of holiday candy to share in addition to weather books. A basic textbook I used to first learn about lake effect is Severe and Hazardous Weather: An Introduction to Meteorology by Rauber, Walsh, and Charlevoix.
- If you have time, make a free account (if you haven't done so already) and go through a MetEd module on lake effect.
Large-scale Pattern:
A look at forecast 500-hPa heights according to the GFS shows that a shortwave trough will help form a coastal low and the associated precipitation is not expected to reach KSYR. However, the pattern is conducive to west-northwesterly winds in the early period so before the drier air mass behind the trough moves in, there is a threat of lake-effect snow showers.
Tips/Comments for Forecasting in General:
- Check out the current weather first via satellite, radar, surface observations, METAR, etc. You have to understand the present before you can look to the future. To do this quickly, check out the WxChallenge page for Syracuse.
- Get a feel for general pattern from NAM, GFS, etc. (available from here and here, for example). Identify the general pattern of low and high surface pressure systems and their progression, temperature advection at 850 mb, moisture at 700 mb, vorticity at 500 mb and the general jet structure at 300 mb. Make sure you are focusing your attention on Syracuse. Beware of high pressure to the west and low pressure to the east inducing northwesterly flow over Lake Ontario!
- Look at forecast model soundings for the period for KSYR.
- Compare your idea for values with MOS (model output statistics). Keep in mind these are instantaneous output values and you can always have values above/below that between output times.
- Read the Binghamton, NY WFO forecast discussion for KSYR.
Tips/Comments for Forecasting for High/Low temperature (Fahrenheit):
- Recall such basics as nighttime radiative cooling and daytime solar radiative heating, both of which are affected by cloud cover and fog. Cloud cover is more of an issue for Syracuse and I bet you are sick of fog from forecasting for Astoria.
- Frontal passages can affect your temperature forecast. Pay attention to the forecast timing of such frontal passages.
- NWS outputs wind speed in mph so if you are comparing your forecast value to theirs keep that in mind. Otherwise the models output wind speed (WSP) in knots.
- Look through METAR or surface obs for wind direction and temperature changes. For example, northwesterly flow may induce lake-effect bands that could reach Syracuse.
- Take a look at some higher-resolution models (e.g. WRF)
- What does the HPC show?
- Take a look at some ensemble data (e.g. SREF)
- Most products you will be looking at will output the QPF in inches already so no conversion is necessary.
Okie dokie, that's all I have to say as we begin forecasting for Syracuse. It's nice to be back in our home state but the whole threat of lake-effect has me nervous! If any of you have any questions or comments, please e-mail me or comment on this post. I hope you all enjoy forecasting for this exciting city and then enjoy your winter breaks! Take care and best of luck forecasting! Go SBU!
