
A warm front will approach this afternoon. A brief wintry mix or rain in warmer valleys is likely before a quick transition into moderate to heavy snow takes place during the evening commute. 1-1.5 inch per hour snowfall rates are likely in northeastern New York and much of Vermont. Difficult to very difficult travel is likely this evening. Light snow will continue Friday night into Saturday. Read More >
Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260220_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 02/20 18Z 0.13 1515 81 70 -1 0.00
Fri 02/20 19Z 0.20 1418 83 78 -1 0.01
Fri 02/20 20Z 0.23 1419 87 87 -1 0.04
Fri 02/20 21Z 0.25 1420 90 94 -1 0.07
Sat 02/21 00Z 0.37 1221 95 97 -2 0.08
Sat 02/21 01Z 0.34 1319 96 93 -4 0.10
Sat 02/21 02Z 0.28 1416 96 94 -5 0.12
Sat 02/21 03Z 0.22 1515 95 92 -5 0.11
Sat 02/21 04Z 0.18 1513 95 90 -6 0.11
Sat 02/21 05Z 0.11 1610 95 91 -6 0.08
Sat 02/21 06Z 0.08 1608 96 91 -7 0.04
Sat 02/21 07Z 0.07 1707 96 89 -7 0.03
Sat 02/21 08Z 0.08 1806 96 91 -7 0.03
Sat 02/21 09Z 0.14 2006 97 93 -7 0.02
Sat 02/21 10Z 0.18 2305 97 92 -7 0.02
Sat 02/21 11Z 0.20 2605 98 90 -7 0.02
Sat 02/21 12Z 0.19 2905 98 88 -7 0.02
Sat 02/21 13Z 0.18 3005 98 89 -7 0.02
Sat 02/21 14Z 0.16 3106 99 88 -8 0.02
Sat 02/21 15Z 0.12 3305 98 82 -8 0.01
Sat 02/21 16Z 0.11 3505 97 76 -8 0.01
Sat 02/21 17Z 0.10 0005 93 68 -8 0.00
Sat 02/21 18Z 0.10 0105 88 62 -8 0.00
Sat 02/21 19Z 0.09 0105 83 59 -8 0.00
Sat 02/21 20Z 0.07 0105 80 50 -8 0.00
Sat 02/21 21Z 0.07 0205 77 44 -8 0.00
Sat 02/21 22Z 0.10 0306 74 39 -8 0.00
Sat 02/21 23Z 0.15 0407 72 37 -8 0.00
Sun 02/22 00Z 0.18 0508 67 38 -8 0.00
Sun 02/22 01Z 0.21 0609 61 33 -8 0.00
Sun 02/22 02Z 0.22 0809 60 29 -7 0.00
Sun 02/22 03Z 0.21 0908 62 27 -7 0.00
Sun 02/22 04Z 0.21 1008 60 27 -7 0.00
Sun 02/22 05Z 0.21 1109 55 27 -7 0.00
Sun 02/22 06Z 0.20 1209 54 28 -7 0.00
Sun 02/22 07Z 0.19 1310 54 29 -7 0.00
Sun 02/22 08Z 0.17 1311 53 29 -7 0.00
Sun 02/22 09Z 0.16 1411 50 29 -7 0.00
Sun 02/22 10Z 0.17 1311 50 29 -7 0.00
Sun 02/22 11Z 0.21 1312 52 28 -7 0.00
Sun 02/22 12Z 0.23 1313 55 27 -7 0.00
Sun 02/22 13Z 0.27 1214 58 27 -7 0.00
Sun 02/22 14Z 0.26 1314 61 30 -7 0.00
Sun 02/22 15Z 0.26 1315 62 36 -7 0.00
Sun 02/22 16Z 0.29 1314 62 36 -7 0.00
Sun 02/22 17Z 0.32 1214 62 35 -7 0.00
Sun 02/22 18Z 0.36 1214 65 37 -7 0.00
Sun 02/22 19Z 0.40 1214 70 37 -7 0.00
Sun 02/22 20Z 0.44 1213 75 36 -7 0.00
Sun 02/22 21Z 0.46 1113 76 35 -7 0.00
Sun 02/22 22Z 0.46 1114 76 40 -7 0.00
Sun 02/22 23Z 0.47 1014 71 39 -7 0.00
Mon 02/23 00Z 0.49 1016 68 42 -7 0.00
Mon 02/23 01Z 0.50 0917 64 46 -7 0.00
Mon 02/23 02Z 0.47 1018 53 39 -7 0.00
Mon 02/23 03Z 0.46 1020 47 40 -7 0.00
Mon 02/23 04Z 0.48 0921 43 38 -7 0.00
Mon 02/23 05Z 0.50 0922 40 37 -7 0.00
Run total areal avg QPF for the greens is: 0.96 inches.
Froude Number (Frd#):
Frd# < 0.5 Flow is subcritical and blocked.
Upslope clouds/precip backed farther upwind of and up to mtn crest.
W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
Upslope clouds/precip falls immediately upwind of mtn crest.
W Upslope snow favors western slopes to the Green Mt. spine including:
Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
Gap winds possible.
Frd# 1-2 Flow is critical.
With strong winds, Mountain waves/downslope winds possible.
Precip falls close to mountain ridge crests and on lee side.
W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
Air flows freely over terrain.
Persistent upslope snow not favored. Scattered snow showers and flurries.
Relative Humidity (RH):
925-850 mb RH > 90% needed for upslope precipitation.
with 700mb RH > 70% favors upslope snow.
with 700mb RH > 90% greater amounts of W upslope snow possible.
850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
T > -11 10-15:1
T -11 to -15 25-35:1
T < -15 15-20:1