Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260527_1200
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)
=== ===== === ==== ==== === === === ====
Wed 05/27 12Z 0.51 2916 77 43 11 0.00
Wed 05/27 13Z 0.47 2914 79 39 11 0.00
Wed 05/27 14Z 0.49 2912 78 37 10 0.00
Wed 05/27 15Z 0.58 2911 76 33 10 0.00
Wed 05/27 16Z 1.25 2911 76 28 10 0.00
Wed 05/27 17Z 2.86 3011 76 27 10 0.00
Wed 05/27 18Z 2.02 3012 81 29 10 0.00
Wed 05/27 19Z 1.34 3112 82 29 10 0.01
Wed 05/27 20Z 1.56 3114 81 28 9 0.00
Wed 05/27 21Z 1.62 3214 79 23 9 0.00
Wed 05/27 22Z 1.15 3315 78 22 9 0.00
Wed 05/27 23Z 0.60 3316 80 22 8 0.00
Thu 05/28 00Z 0.42 3317 84 33 7 0.00
Thu 05/28 01Z 0.28 3418 91 47 7 0.01
Thu 05/28 02Z 0.21 3419 90 51 6 0.01
Thu 05/28 03Z 0.13 3518 92 47 6 0.00
Thu 05/28 04Z 0.10 3518 92 49 6 0.00
Thu 05/28 05Z 0.06 0017 92 57 5 0.00
Thu 05/28 06Z 0.04 3517 91 69 5 0.00
Thu 05/28 07Z 0.12 3517 91 66 5 0.00
Thu 05/28 08Z 0.15 3418 92 64 4 0.00
Thu 05/28 09Z 0.17 3418 92 59 4 0.00
Thu 05/28 10Z 0.20 3419 90 61 4 0.00
Thu 05/28 11Z 0.21 3420 89 66 4 0.00
Thu 05/28 12Z 0.18 3420 91 70 4 0.01
Thu 05/28 13Z 0.17 3419 94 70 3 0.01
Thu 05/28 14Z 0.24 3419 96 72 3 0.01
Thu 05/28 15Z 0.33 3418 96 72 3 0.01
Thu 05/28 16Z 0.43 3419 96 72 3 0.01
Thu 05/28 17Z 0.56 3319 95 70 3 0.01
Thu 05/28 18Z 0.66 3321 92 72 3 0.01
Thu 05/28 19Z 0.99 3321 92 73 3 0.01
Thu 05/28 20Z 1.39 3321 91 69 3 0.01
Thu 05/28 21Z 1.16 3320 93 73 3 0.01
Thu 05/28 22Z 0.55 3323 92 68 3 0.02
Thu 05/28 23Z 0.49 3326 94 56 3 0.02
Fri 05/29 00Z 0.45 3327 92 45 3 0.01
Fri 05/29 01Z 0.34 3425 95 32 3 0.01
Fri 05/29 02Z 0.38 3426 95 28 2 0.01
Fri 05/29 03Z 0.37 3425 95 30 2 0.01
Fri 05/29 04Z 0.33 3424 96 32 2 0.01
Fri 05/29 05Z 0.30 3422 96 32 2 0.01
Fri 05/29 06Z 0.27 3420 98 41 2 0.01
Fri 05/29 07Z 0.33 3319 98 65 2 0.02
Fri 05/29 08Z 0.39 3320 96 79 1 0.01
Fri 05/29 09Z 0.38 3220 95 77 1 0.00
Fri 05/29 10Z 0.37 3220 91 78 2 0.00
Fri 05/29 11Z 0.35 3221 88 80 2 0.00
Fri 05/29 12Z 0.34 3322 86 80 2 0.00
Fri 05/29 13Z 0.37 3219 83 81 2 0.00
Fri 05/29 14Z 0.54 3117 80 78 2 0.00
Fri 05/29 15Z 1.45 3116 74 78 2 0.00
Fri 05/29 16Z 4.42 3013 73 76 3 0.00
Fri 05/29 17Z 5.17 2911 73 81 4 0.00
Fri 05/29 18Z 5.16 2709 70 89 4 0.00
Fri 05/29 19Z 5.72 2612 72 97 5 0.00
Fri 05/29 20Z 3.95 2612 71 83 5 0.01
Fri 05/29 21Z 4.34 2511 71 91 5 0.00
Fri 05/29 22Z 1.64 2214 75 82 5 0.01
Fri 05/29 23Z 0.89 2319 79 87 5 0.01
Run total areal avg QPF for the greens is: 0.30 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