Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens
Model run: BTV_GRID_D2D_NAM3_20260221_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 02/21 12Z 0.21 2907 99 83 -7 0.00
Sat 02/21 13Z 0.21 2908 99 82 -7 0.00
Sat 02/21 14Z 0.11 3206 99 74 -7 0.01
Sat 02/21 15Z 0.06 3504 98 74 -8 0.00
Sat 02/21 16Z 0.07 0102 98 75 -8 0.00
Sat 02/21 17Z 0.07 3101 98 80 -8 0.00
Sat 02/21 18Z 0.06 3101 98 82 -8 0.00
Sat 02/21 19Z 0.05 3502 97 80 -8 0.00
Sat 02/21 20Z 0.06 0003 96 75 -8 0.00
Sat 02/21 21Z 0.13 0204 96 70 -8 0.00
Sat 02/21 22Z 0.18 0405 97 66 -8 0.00
Sat 02/21 23Z 0.23 0506 97 66 -8 0.00
Sun 02/22 00Z 0.25 0507 95 62 -8 0.00
Sun 02/22 01Z 0.26 0707 93 59 -8 0.00
Sun 02/22 04Z 0.18 1207 90 55 -8 0.00
Sun 02/22 05Z 0.18 1309 88 53 -8 0.00
Sun 02/22 06Z 0.19 1311 87 51 -8 0.00
Sun 02/22 07Z 0.16 1413 80 58 -8 0.00
Sun 02/22 09Z 0.16 1413 72 65 -8 0.00
Sun 02/22 10Z 0.16 1313 71 71 -7 0.00
Sun 02/22 11Z 0.15 1413 63 78 -7 0.00
Sun 02/22 12Z 0.16 1414 53 84 -8 0.00
Sun 02/22 13Z 0.18 1314 51 89 -8 0.00
Sun 02/22 14Z 0.19 1314 54 92 -8 0.00
Sun 02/22 15Z 0.23 1315 56 91 -8 0.00
Sun 02/22 16Z 0.29 1216 58 87 -8 0.00
Sun 02/22 17Z 0.36 1216 60 89 -8 0.00
Sun 02/22 18Z 0.38 1216 66 92 -8 0.00
Sun 02/22 19Z 0.46 1216 72 92 -8 0.00
Sun 02/22 20Z 0.55 1116 75 91 -8 0.00
Sun 02/22 21Z 0.65 1118 76 91 -8 0.00
Sun 02/22 22Z 0.61 1118 80 88 -9 0.00
Sun 02/22 23Z 0.59 1119 82 86 -8 0.00
Mon 02/23 00Z 0.61 1021 81 81 -8 0.00
Mon 02/23 01Z 0.64 0923 80 74 -8 0.00
Mon 02/23 03Z 0.69 0824 76 49 -8 0.00
Mon 02/23 04Z 0.74 0825 75 48 -9 0.00
Mon 02/23 05Z 0.74 0826 66 66 -8 0.00
Mon 02/23 06Z 0.72 0827 65 70 -8 0.00
Mon 02/23 07Z 0.74 0728 62 67 -8 0.00
Mon 02/23 08Z 0.74 0729 59 70 -8 0.00
Mon 02/23 09Z 0.73 0631 52 75 -8 0.00
Mon 02/23 10Z 0.78 0634 45 80 -8 0.00
Mon 02/23 11Z 0.77 0636 38 82 -7 0.00
Mon 02/23 12Z 0.78 0636 37 84 -7 0.00
Mon 02/23 13Z 0.73 0534 37 83 -8 0.00
Mon 02/23 14Z 0.74 0531 41 86 -9 0.00
Mon 02/23 15Z 0.80 0529 54 86 -10 0.00
Mon 02/23 16Z 0.95 0427 81 87 -12 0.00
Mon 02/23 17Z 0.61 0328 90 86 -12 0.00
Mon 02/23 18Z 0.52 0230 90 86 -11 0.00
Mon 02/23 19Z 0.43 0132 90 86 -10 0.00
Mon 02/23 20Z 0.31 0133 91 86 -10 0.03
Mon 02/23 21Z 0.22 0034 91 87 -9 0.07
Mon 02/23 22Z 0.17 0034 92 87 -9 0.07
Mon 02/23 23Z 0.13 3534 92 87 -9 0.05
Run total areal avg QPF for the Central_Greens is: 0.23 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