Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260207_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)
=== ===== === ==== ==== === === === ====
Sat 02/07 18Z 0.92 3115  84  76 -21 0.00
Sat 02/07 19Z 1.00 3120  86  78 -21 0.00
Sat 02/07 20Z 0.93 3123  86  77 -22 0.00
Sat 02/07 21Z 0.59 3224  84  76 -22 0.00
Sat 02/07 22Z 0.36 3225  81  75 -22 0.00
Sat 02/07 23Z 0.31 3326  82  76 -22 0.00
Sun 02/08 00Z 0.29 3327  83  76 -22 0.00
Sun 02/08 01Z 0.26 3326  84  77 -22 0.00
Sun 02/08 02Z 0.23 3325  84  79 -21 0.00
Sun 02/08 04Z 0.18 3322  82  80 -21 0.00
Sun 02/08 05Z 0.17 3322  82  80 -20 0.00
Sun 02/08 06Z 0.16 3322  82  78 -20 0.00
Sun 02/08 07Z 0.15 3322  82  78 -20 0.00
Sun 02/08 08Z 0.14 3323  82  77 -19 0.00
Sun 02/08 09Z 0.12 3423  82  79 -19 0.00
Sun 02/08 10Z 0.12 3424  82  77 -18 0.00
Sun 02/08 11Z 0.11 3425  82  74 -18 0.00
Sun 02/08 13Z 0.10 3427  82  64 -17 0.00
Sun 02/08 14Z 0.09 3426  80  58 -17 0.00
Sun 02/08 15Z 0.09 3426  75  55 -16 0.00
Sun 02/08 16Z 0.08 3425  72  53 -16 0.00
Sun 02/08 17Z 0.09 3425  68  47 -15 0.00
Sun 02/08 19Z 0.10 3425  61  54 -13 0.00
Sun 02/08 20Z 0.12 3426  60  54 -13 0.00
Sun 02/08 21Z 0.12 3427  59  47 -12 0.00
Sun 02/08 22Z 0.12 3429  56  41 -12 0.00
Sun 02/08 23Z 0.11 3429  54  31 -12 0.00
Mon 02/09 00Z 0.10 3429  53  30 -11 0.00
Mon 02/09 01Z 0.10 3428  53  33 -11 0.00
Mon 02/09 02Z 0.12 3427  52  41 -11 0.00
Mon 02/09 03Z 0.14 3427  52  43 -12 0.00
Mon 02/09 04Z 0.15 3327  54  40 -12 0.00
Mon 02/09 05Z 0.15 3327  57  38 -12 0.00
Mon 02/09 06Z 0.17 3328  61  33 -12 0.00
Mon 02/09 07Z 0.19 3329  63  32 -12 0.00
Mon 02/09 08Z 0.20 3330  65  30 -13 0.00
Mon 02/09 09Z 0.20 3331  63  28 -13 0.00
Mon 02/09 10Z 0.19 3331  62  26 -13 0.00
Mon 02/09 11Z 0.17 3431  59  21 -13 0.00
Mon 02/09 13Z 0.15 3431  53  12 -12 0.00
Mon 02/09 14Z 0.15 3430  51  11 -12 0.00
Mon 02/09 15Z 0.14 3429  49  16 -12 0.00
Mon 02/09 16Z 0.15 3428  48  31 -12 0.00
Mon 02/09 17Z 0.18 3327  49  48 -12 0.00
Mon 02/09 18Z 0.19 3327  47  57 -12 0.00
Mon 02/09 19Z 0.19 3326  44  56 -11 0.00
Mon 02/09 20Z 0.23 3325  45  50 -11 0.00
Mon 02/09 21Z 0.24 3225  41  51 -10 0.00
Mon 02/09 22Z 0.24 3224  38  52 -10 0.00
Mon 02/09 23Z 0.24 3224  36  56 -10 0.00
Tue 02/10 01Z 0.22 3224  29  45  -9 0.00
Tue 02/10 02Z 0.20 3323  26  44  -9 0.00
Tue 02/10 03Z 0.17 3322  24  43  -9 0.00
Tue 02/10 04Z 0.15 3320  24  39  -8 0.00
Tue 02/10 05Z 0.16 3319  25  35  -8 0.00

Run total areal avg QPF for the greens is: 0.00 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