Figure 19: Low-Level Significant Weather (SIGWX) Prognostic Charts

120W 90W 80W 100W 70W 40N VT 18Z Sat Apr 14 2012 12 HR SIG WX PROG LOW LVL SFC-400MB 120 120 040 080 080 120 / 120 / 240 / 180 / 240 / 120W 90W 80W 70W 40N VT 06Z Sun Apr 15 2012 24 HR SIG WX PROG LOW LVL SFC-400MB 120 040 040 040 040 080 080 120 / 120 / 240 / 180 / 080 / 240 / 070 / Flight planning only see TAF for specific terminal forecast Ceiling less than 1,000 feet and/or visibility less than 3 miles Ceiling 1,000-3,000 feet inclusive and/or visibility 3-5 miles incl. Moderate or greater turbulence Freezing level at surface Freezing level above mean sea level Moderate turbulence Severe turbulence Extreme turbulence 100/070 Top (hundreds of feet MSL) Base (hundreds of feet MSL)