Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260630_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)
=== ===== === ==== ==== === === === ====
Tue 06/30 00Z 0.18 3305  58   9  14 0.00
Tue 06/30 01Z 0.17 3405  55   9  14 0.00
Tue 06/30 02Z 0.11 3503  52   9  14 0.00
Tue 06/30 03Z 0.07 3401  50  10  14 0.00
Tue 06/30 04Z 0.07 2200  48  11  14 0.00
Tue 06/30 05Z 0.13 2302  46  13  14 0.00
Tue 06/30 06Z 0.37 2705  45  14  14 0.00
Tue 06/30 07Z 0.63 2706  48  16  14 0.00
Tue 06/30 08Z 0.52 2605  52  16  14 0.00
Tue 06/30 09Z 0.34 2605  55  23  14 0.00
Tue 06/30 10Z 0.30 2605  56  26  14 0.00
Tue 06/30 11Z 0.31 2606  58  32  14 0.00
Tue 06/30 12Z 0.23 2305  60  44  14 0.00
Tue 06/30 13Z 0.26 2206  60  51  14 0.00
Tue 06/30 14Z 0.41 2207  62  52  14 0.00
Tue 06/30 15Z 0.94 2208  65  54  14 0.00
Tue 06/30 16Z 0.83 2209  66  70  15 0.00
Tue 06/30 17Z 0.71 2211  64  75  15 0.00
Tue 06/30 18Z 1.24 2212  62  86  15 0.00
Tue 06/30 19Z 0.59 2110  59  83  15 0.00
Tue 06/30 20Z 0.81 2110  60  91  15 0.00
Tue 06/30 21Z 0.49 2110  59  90  15 0.00
Tue 06/30 22Z 0.42 2113  61  89  16 0.00
Tue 06/30 23Z 0.40 2115  70  89  16 0.00
Wed 07/01 00Z 0.44 2117  74  94  16 0.00
Wed 07/01 01Z 0.50 2118  80  90  17 0.00
Wed 07/01 02Z 0.54 2220  84  88  17 0.01
Wed 07/01 03Z 0.60 2323  95  89  17 0.03
Wed 07/01 04Z 0.62 2421  97  67  17 0.05
Wed 07/01 05Z 0.63 2619  97  55  17 0.02
Wed 07/01 06Z 0.61 2619  97  48  17 0.01
Wed 07/01 07Z 0.59 2618  97  43  17 0.06
Wed 07/01 08Z 0.46 2515  96  35  18 0.05
Wed 07/01 09Z 0.41 2514  95  27  18 0.02
Wed 07/01 10Z 0.40 2514  94  28  18 0.01
Wed 07/01 11Z 0.47 2517  95  31  18 0.01
Wed 07/01 12Z 0.56 2519  96  21  18 0.02
Wed 07/01 13Z 0.60 2620  97  34  18 0.02
Wed 07/01 14Z 0.64 2720  96  44  18 0.02
Wed 07/01 15Z 0.54 2718  91  47  19 0.01
Wed 07/01 16Z 0.50 2816  79  48  20 0.00
Wed 07/01 17Z 0.50 2815  82  43  20 0.00
Wed 07/01 18Z 0.51 2814  86  43  20 0.00
Wed 07/01 19Z 0.45 2813  82  37  21 0.00
Wed 07/01 20Z 0.42 2712  76  28  21 0.00
Wed 07/01 21Z 0.44 2712  73  26  22 0.00
Wed 07/01 22Z 0.39 2612  68  25  22 0.00
Wed 07/01 23Z 0.40 2613  63  26  23 0.00
Thu 07/02 00Z 0.50 2517  59  27  23 0.00
Thu 07/02 01Z 0.77 2623  61  34  22 0.00
Thu 07/02 02Z 0.97 2626  72  41  21 0.00
Thu 07/02 03Z 0.61 2622  72  45  22 0.00
Thu 07/02 04Z 0.71 2526  86  46  21 0.00
Thu 07/02 05Z 0.74 2726  83  49  21 0.03
Thu 07/02 06Z 0.64 2825  72  50  21 0.01
Thu 07/02 07Z 0.57 2923  76  49  20 0.00
Thu 07/02 08Z 0.47 3021  81  53  20 0.00
Thu 07/02 09Z 0.44 2920  83  40  20 0.01
Thu 07/02 10Z 0.43 2920  80  41  20 0.01
Thu 07/02 11Z 0.43 2819  74  31  20 0.01

Run total areal avg QPF for the greens is: 0.41 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