Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260326_0000
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)
=== ===== === ==== ==== === === === ====
Thu 03/26 00Z 0.06 1818 57 73 -2 0.00
Thu 03/26 01Z 0.18 1824 55 75 -2 0.00
Thu 03/26 02Z 0.35 1928 56 90 -2 0.00
Thu 03/26 03Z 0.90 2031 70 91 -3 0.00
Thu 03/26 04Z 0.56 2034 88 92 -2 0.01
Thu 03/26 05Z 0.64 2134 89 94 -1 0.01
Thu 03/26 06Z 0.65 2234 81 95 -1 0.00
Thu 03/26 07Z 0.67 2235 75 94 0 0.01
Thu 03/26 08Z 0.63 2232 73 95 0 0.01
Thu 03/26 09Z 0.72 2333 76 94 0 0.00
Thu 03/26 10Z 0.69 2431 90 93 0 0.02
Thu 03/26 11Z 0.66 2429 89 94 0 0.02
Thu 03/26 12Z 0.61 2429 87 96 1 0.02
Thu 03/26 13Z 0.68 2432 90 95 1 0.04
Thu 03/26 14Z 0.74 2431 88 88 1 0.03
Thu 03/26 15Z 0.72 2528 84 54 1 0.01
Thu 03/26 16Z 0.81 2527 80 49 2 0.00
Thu 03/26 17Z 0.92 2524 82 65 2 0.00
Thu 03/26 18Z 1.03 2523 82 74 1 0.00
Thu 03/26 19Z 1.24 2523 82 85 2 0.00
Thu 03/26 20Z 1.30 2522 85 93 1 0.02
Thu 03/26 21Z 0.86 2518 87 95 1 0.03
Thu 03/26 22Z 0.51 2613 89 95 1 0.05
Thu 03/26 23Z 0.37 2810 97 95 0 0.12
Fri 03/27 00Z 0.26 3008 96 97 1 0.08
Fri 03/27 01Z 0.30 3114 97 97 0 0.16
Fri 03/27 02Z 0.17 3211 96 98 1 0.08
Fri 03/27 03Z 0.19 3315 96 95 0 0.07
Fri 03/27 04Z 0.27 3217 97 98 -1 0.02
Fri 03/27 05Z 0.29 3220 97 83 -2 0.02
Fri 03/27 06Z 0.35 3223 97 78 -4 0.02
Fri 03/27 07Z 0.39 3226 96 42 -5 0.02
Fri 03/27 08Z 0.35 3326 96 7 -6 0.01
Fri 03/27 09Z 0.38 3328 96 8 -8 0.01
Fri 03/27 10Z 0.37 3329 94 6 -10 0.00
Fri 03/27 11Z 0.36 3329 90 5 -11 0.00
Fri 03/27 12Z 0.31 3329 81 5 -11 0.00
Fri 03/27 13Z 0.28 3327 69 6 -12 0.00
Fri 03/27 14Z 0.25 3326 63 4 -12 0.00
Fri 03/27 15Z 0.23 3323 60 3 -13 0.00
Fri 03/27 16Z 0.23 3321 60 2 -13 0.00
Fri 03/27 17Z 0.34 3318 60 3 -13 0.00
Fri 03/27 18Z 0.60 3315 59 4 -13 0.00
Fri 03/27 19Z 0.84 3314 56 4 -13 0.00
Fri 03/27 20Z 0.87 3212 52 5 -13 0.00
Fri 03/27 21Z 0.35 3212 47 6 -13 0.00
Fri 03/27 22Z 0.21 3311 43 7 -12 0.00
Fri 03/27 23Z 0.20 3210 43 8 -12 0.00
Sat 03/28 00Z 0.20 3210 46 9 -12 0.00
Sat 03/28 01Z 0.19 3210 51 10 -12 0.00
Sat 03/28 02Z 0.21 3110 58 9 -12 0.00
Sat 03/28 03Z 0.22 3111 61 8 -13 0.00
Sat 03/28 04Z 0.18 3211 62 8 -13 0.00
Sat 03/28 05Z 0.14 3310 63 10 -13 0.00
Sat 03/28 06Z 0.12 3309 64 13 -14 0.00
Sat 03/28 07Z 0.13 3309 64 13 -15 0.00
Sat 03/28 08Z 0.14 3309 65 21 -15 0.00
Sat 03/28 09Z 0.11 3308 66 27 -16 0.00
Sat 03/28 10Z 0.11 3308 67 34 -16 0.00
Sat 03/28 11Z 0.13 3308 69 46 -16 0.00
Run total areal avg QPF for the greens is: 0.89 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