850-hPa temperature is often used to determine precpitation type. For the ensemble run at 12 UTC, seven days prior to the forecast valid time of interest, the uncalibrated 850-hPa ensemble mean temperature (left, contour interval -5°C) and spread (shaded, interval as indicated in color bar, in 0.1°C) are shown below.
Note that the ensemble mean 0°C isotherm is well to the south, from Cape Hatteras NC through the upper South and to the intermountain west. Largest uncertainties are in the upper Mississippi Valley, the Middle-Atlantic and New England coast, and over Newfoundland.
A benchmark value for rain versus snow used by some forecasters is the 850-hPa -2°C isotherm. The spaghetti diagram of -2°C isotherms from the same ensemble members is shown below.
We note that much of the uncertainty in the eastern U.S. relates to one ensemble member that seems much warmer than the others (red contour). The others are near or south of the ensemble mean position we might infer for the -2°C isotherm in the previous graphic. In the Plains states, there is uncertainty as to the amount of cold air and its southward extent, as can be seen in the contours both well to the north and to the south of the ensemble mean position. This reflects the uncertain position of the western/central U.S. short-wave trough and upstream ridge to its west. Note that all members show the -2°C isotherm well to the south in the east-central U.S.