Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260629_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)
=== ===== === ==== ==== === === === ====
Mon 06/29 00Z 0.17 3411  60  42  14 0.00
Mon 06/29 01Z 0.04 3513  54  42  14 0.00
Mon 06/29 02Z 0.11 0015  52  46  14 0.00
Mon 06/29 03Z 0.21 0115  55  49  13 0.00
Mon 06/29 04Z 0.27 0212  58  55  13 0.00
Mon 06/29 05Z 0.24 0309  61  60  13 0.00
Mon 06/29 06Z 0.20 0207  60  63  13 0.00
Mon 06/29 07Z 0.16 0106  60  57  13 0.00
Mon 06/29 08Z 0.14 3506  60  52  13 0.00
Mon 06/29 09Z 0.14 3506  60  46  13 0.00
Mon 06/29 10Z 0.12 0007  60  41  13 0.00
Mon 06/29 11Z 0.10 3508  60  35  13 0.00
Mon 06/29 12Z 0.11 3408  61  27  13 0.00
Mon 06/29 13Z 0.12 3407  65  20  13 0.00
Mon 06/29 14Z 0.14 3406  67  18  13 0.00
Mon 06/29 15Z 0.23 3304  67  19  13 0.00
Mon 06/29 16Z 0.31 3305  65  24  13 0.00
Mon 06/29 17Z 0.52 3205  63  33  13 0.01
Mon 06/29 18Z 0.99 3106  60  28  13 0.01
Mon 06/29 19Z 1.30 3105  56  22  14 0.00
Mon 06/29 20Z 1.30 3105  53  19  14 0.00
Mon 06/29 21Z 0.81 3105  51  24  14 0.00
Mon 06/29 22Z 0.44 3105  49  24  14 0.00
Mon 06/29 23Z 0.36 3005  48  21  14 0.00
Tue 06/30 00Z 0.41 3006  49  15  14 0.00
Tue 06/30 01Z 0.45 3005  52  12  14 0.00
Tue 06/30 02Z 0.52 2705  55  11  14 0.00
Tue 06/30 03Z 0.47 2505  57   9  14 0.00
Tue 06/30 04Z 0.57 2407  58  10  14 0.00
Tue 06/30 05Z 0.62 2409  60  13  14 0.00
Tue 06/30 06Z 0.71 2311  61  18  14 0.00
Tue 06/30 07Z 0.77 2413  61  22  14 0.00
Tue 06/30 08Z 0.74 2415  60  28  14 0.00
Tue 06/30 09Z 0.80 2416  60  40  14 0.00
Tue 06/30 10Z 0.79 2416  64  46  14 0.00
Tue 06/30 11Z 0.79 2517  69  51  14 0.00
Tue 06/30 12Z 0.79 2518  73  48  14 0.00
Tue 06/30 13Z 0.75 2418  77  40  14 0.00
Tue 06/30 14Z 0.83 2519  83  47  14 0.00
Tue 06/30 15Z 0.69 2517  90  91  13 0.02
Tue 06/30 16Z 0.35 2312  81  95  14 0.07
Tue 06/30 17Z 0.36 2313  83  95  14 0.01
Tue 06/30 18Z 0.39 2315  92  85  14 0.02
Tue 06/30 19Z 0.41 2216  91  75  15 0.00
Tue 06/30 20Z 0.51 2218  91  83  16 0.01
Tue 06/30 21Z 0.60 2221  95  84  16 0.01
Tue 06/30 22Z 0.62 2223  95  83  16 0.01
Tue 06/30 23Z 0.71 2325  94  91  16 0.01
Wed 07/01 00Z 0.68 2325  95  89  17 0.07
Wed 07/01 01Z 0.72 2327  95  79  17 0.14
Wed 07/01 02Z 0.73 2428  97  75  18 0.17
Wed 07/01 03Z 0.82 2529  98  69  18 0.08
Wed 07/01 04Z 0.84 2628  97  52  18 0.09
Wed 07/01 05Z 0.76 2826  97  39  18 0.07
Wed 07/01 06Z 0.69 2823  95  48  18 0.08
Wed 07/01 07Z 0.71 2724  89  67  18 0.20
Wed 07/01 08Z 0.65 2824  86  43  18 0.09
Wed 07/01 09Z 0.61 2823  91  26  18 0.01
Wed 07/01 10Z 0.65 2824  95  21  18 0.06
Wed 07/01 11Z 0.63 2924  96   9  18 0.04

Run total areal avg QPF for the greens is: 1.28 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