There has been a plethora of winter weather papers (e.g., Albrecht 1979, Koontz 1986, Weber 1979) written on a wide variety of topics. It is very difficult for an operational forecaster to keep track of all of these manuscripts. The last major winter weather checklist to be published as a regional technical attachment was nearly 10 years ago (Goetsch 1987). Furthermore, there are several local techniques and "rules of thumb" that exist on winter weather that have not been widely circulated to the field. This checklist attempts to fill that void for forecasters. The purpose of this checklist is to help operational forecasters to become more proficient at predicting winter weather and to have a "winter cheat sheet" right at their fingertips.
The following material is an attempt to compile an updated and comprehensive list for forecasting various types of winter weather. In this form, the material can be utilized as a quick and easy reference guide by operational meteorologists during subjective assessment and forecasting of winter weather systems. An in-depth section is included on freezing precipitation, moderate-to-heavy snow, as well as local snow prediction techniques from across the country. References are included, for further study.
The checklist was initially developed for the staff at NWSO Springfield, MO (SGF). However, with the exception of mountainous regions, it can be utilized almost anywhere across the country. Forecasters across the central and eastern United States can use this checklist as a starting point to handle a variety of winter weather. In applying this information, caution must be exercised. No one method can be applied by itself without consideration of all other parameters. Thus, it is essential to know how and when to apply such techniques. Considerable experience and knowledge of the atmosphere, local climatology, and model information are crucial.
First, the forecaster must determine what type of precipitation is expected. Use Table I as a guide to determine whether you will have liquid or frozen precipitation. In addition, one can also use the Freezing Drizzle vs. Snow Checklist (Table II) developed by Headquarters Air Weather Service, Technology Training Division at Scott AFB, IL (1996). It will help determine whether to forecast freezing or frozen precipitation.
|Critical Thickness||Rain/Snow Line|
|1000-500 mb||5400 m|
|1000-700 mb||2840 m|
|1000-850 mb||1300 m|
|850-700 mb||1540 m|
|850-500 mb||4100 m|
|700-500 mb||2560 m|
Additional information on winter precipitation type can be found in Albrecht (1979), McNulty (1988), and McNulty (1991). When certain about the precipitation type, either use Table III for forecasting freezing precipitation or Table IV for forecasting snow.
|a. For ZR/ZL to occur exposed surfaces must be LTE 32 degrees F||Y||N||Y||N|
|The more yes answers you have, the better chance for freezing precipitation. If (a) through (d) are yes and the thickness value falls within parameters listed above, call and coordinate with surrounding WSFOs immediately for the appropriate watch, advisory or warning.|
|a. Is the surface temp <35 degrees F (1.7 degrees C)?||Y||N||Y||N|
|b. Is the freezing level <1200 ft (366m)?||Y||N||Y||N|
|c. Is the 850 mb temp <0 degrees C?||Y||N||Y||N|
|d. Is the 700 mb temp <-4 degrees C?||Y||N||Y||N|
|e. Is the 1000-500mb thickness <5400m?||Y||N||Y||N|
|f. Is the temp <0 degrees C from 1200ft to 700 mb?||Y||N||Y||N|
|g. Is there a moist layer (T-Td depression 5 degrees C from surface to 700mb?||Y||N||Y||N|
|The more yes answers you have, the better chance you have for snow. If (a) through (g) are yes or forecasted yes, forecast snow!|
If the weather situation has the possibility of moderate or heavy snow, continue with Table V. This table has specific parameters and features to look for at mandatory levels from the surface all the way up to 200 mb. This information was gathered from a multitude of sources, the bulk of which came from McNulty (1991), Terry (1995), and Weber (1979). Other sources came from academicians such as Djuric (1994), Moore (1989), and Ucccellini (1990).
With winter weather lasting 3 or 4 months in most locations, forecasters tend to forget what to look for at various levels. The following information will ease that memory loss, and allow operational forecasters quick and easy reference, to better forecast major snowstorms.
2. 850 mb
3. 700 mb
4. 500 mb
5. 300 mb
6. 200 mb
The next step, after looking at the various levels of the atmosphere, is to forecast snow amounts. Table VI will help you come up with the accumulations. There are four methods listed: Lemo Technique, Magic Chart, Garcia's Method, and Cook Method. Each method keys in on different parameters and levels to come up with accumulations. However, each method has been used quite effectively to better forecast snowfall amounts.
The Lemo Technique was developed by a forecaster several years ago at WSFO CHI. The other three techniques are more widely known and have had numerous papers and studies written about them. The method that seems to have worked best on major snowstorms over the NWSO SGF county warning area is Garcia's Method.
A. Lemo Technique (Used by WSFO CHI)
|MS = (Va - 10) x 30/s||MS - total maximum snowfall in inches|
|Va - absolute vorticity (interpreted from progs)|
|S - estimated speed of vorticity max in knots|
B. Magic Chart (Sangster 1985 and Chaston 1989)
|20 to 40 mb||2 to 4 in|
|40 mb||4 in|
|60 mb||6 in|
|80 mb||8 in|
|100 mb||10 in|
C. Garcia's Method (Garcia 1994)
|1-2 g/kg||2-4 inches|
|2-3 g/kg||4-6 inches|
|3-4 g/kg||6-8 inches|
|4-5 g/kg||8-10 inches|
|5-6 g/kg||10-12 inches|
|6-7 g/kg||12-14 inches|
D. Cook Method (Cook 1980)
There are additional beneficial winter weather products and charts to use at your disposal (Table VII). Skew-T information is critical in forecasting winter weather. The Sharp Workstation enables the forecaster to manipulate the sounding, and better predict what weather will move into your area. AFOS charts K0L, K0S, and K08 can be extremely helpful in winter. They all contain specific critical thicknesses in their plot, and are manually computed twice a day at 12Z and 00Z. Table VII is not complete, but it gives the forecaster additional winter weather information to better forecast the winter precipitation type.
Use the following products and tools to help you better forecast winter weather.
K0L...LOW LEVEL THICKNESS/MEAN WIND CHART. The upper and lower left numbers are the 850 mb temp and dew point respectively. The upper right number is the 1000-850 mb thickness. Wind plot is mean wind from the surface to 5000 ft.
K0S...RAIN/SNOW THICKNESS CHART. The Upper left number is the 850-700mb thickness; the Lower left number is the 1000-850 mb thickness. On the Right side is the 1000-700 mb thickness with the wind plot being the 850 mb level.
K08...COMPOSITE STABILITY/THICKNESS CHART. The upper left number on plot is the K Index; the lower left number is the Total Totals, and the lower right number is SSI. The upper right number is the 850-500 mb thickness. Wind plot is the mean from 5000-10000 ft.
1000/500 mb AVN ETA NGM 0 hr KAK K03 K0K* 12 hr KCK K23 K2K ** 24 hr KEK K43 K4K 36 hr KGK K63 K6K 48 hr KIK K83 K8K
60 hr KJK 72 hr KTK 96 hr KVK 120 hr KXK
- * K1K 06 hr fcst
- **K3K 18 hr fcst
I am very grateful to David Gaede, SOO at NWSO Springfield for all of his help in preparing this lengthy checklist, especially for all of his computer assistance.
Air Weather Service, 1966: A Technique for Forecasting Freezing Drizzle. Technology Training Division, Scott AFB, IL, 32, 14pP.
Albrecht, L.F., 1979: A study of Freezing Precipitation Parameters. WR Technical Attachment 79-2., DOC/NOAA/NWS Western Region, Salt Lake City, UT, 4pp.
Chaston P.R., 1989: The Magic Chart for Forecasting Snow Amounts. Nat Wea Dig., 14, 20-22.
Cook, B.J.,1980: A Snow Index Using 200 mb Warm Advection. Nat. Wea. Dig., 5, 29-40.
Djuric, D., 1994: Weather Analysis. Prentice Hall, 304pp.
Garcia, C., Jr. 1994: Forecasting Snowfall Using Mixing ratios on an Isentropic Surface - An Empirical Study. NOAA Technical Memorandum NWS CR-105. DOC/NOAA/NWS Central Region, Kansas City, MO, 28pp.
Goetsch, E.H., 1987: Checklist of Significant Winter Weather Forecasting Techniques-A Summary of Some Long Established Methods. CR Technical Attachment 87-30. DOC/NOAA/NWS Central Region, Kansas City, MO, 5pp.
Koontz, G., 1986: Heavy Snow Forecasting Aids, CR Technical Attachment 86-26. DOC/NOAA/NWS Central Region, Kansas City, MO, 3pp.
McNulty, R.P., 1988: Winter Precipitation Type, CR Technical Attachment 88-4. DOC/NOAA/NWS Central Region, Kansas City, MO, 9pp.
____________., 1991: Heavy Snow. DOC/NOAA/NWS Training Center, Kansas City, MO, 9pp.
____________, 1991: Precipitation Type. DOC/NOAA/NWS Training Center, Kansas City, MO, 11pp.
Moore, J.T., 1989: Isentropic Analysis and Interpretation. DOC/NOAA/NWS Training Center, Kansas City, MO, 84pp.
Przybylinski, R.W. 1994: New PCGRIDDS Command Files, PCG Note 94-1 (Memorandum to WSFO St Louis Staff), 9pp.
Sangster, W.E., and E. Jagler, 1985: The (7WG,8WT) Magic Chart. CR Technical Attachment 85-1, DOC/NOAA/NWS Central Region, Kansas City, MO, 5pp.
Shea, T.J., and R.W. Przybylinski, 1995: Forecasting the Northern Extent of Significant Snowfall in a Major Winter Storm: An Operational Forecasting Problem, 14th Conference on Weather and Forecasting, AMS (Boston), 6pp.
Terry, B., 1995: Heavy Snow Forecasting at the NMC (Lab sessions A & D), Fourth NWS Winter Weather Workshop, DOC/NOAA/NWS Central Region, Kansas City, MO, 10pp.
Uccellini, L.W., and P.J. Kocin, 1990: The Interaction of Jet Streak Circulation During Heavy Snow Events Along the East Coast of the United States, Wea. Forecast., 2, 298-308.
Weber, E.M., 1979: Major Midwest Snowstorms. USAF 3WW Technical Note 79-2, Offutt AFB, NE, 95pp.