Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260702_0600
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 07/02 06Z 0.61 2722  74  72  20 0.00
Thu 07/02 07Z 0.72 2826  77  66  20 0.00
Thu 07/02 08Z 0.73 2826  77  59  19 0.00
Thu 07/02 09Z 0.67 2926  74  55  19 0.00
Thu 07/02 10Z 0.64 2928  69  51  20 0.00
Thu 07/02 11Z 0.59 2927  63  48  20 0.00
Thu 07/02 12Z 0.56 2925  63  56  20 0.00
Thu 07/02 13Z 0.54 2924  64  60  20 0.00
Thu 07/02 14Z 0.53 3022  63  58  20 0.00
Thu 07/02 15Z 0.56 2919  65  53  19 0.00
Thu 07/02 16Z 0.65 2818  71  54  19 0.00
Thu 07/02 17Z 0.76 2816  78  54  19 0.00
Thu 07/02 18Z 1.28 2715  87  55  19 0.00
Thu 07/02 19Z 2.11 2716  87  55  18 0.00
Thu 07/02 20Z 2.58 2715  84  58  19 0.00
Thu 07/02 21Z 1.56 2714  83  69  19 0.02
Thu 07/02 22Z 0.92 2616  85  64  19 0.07
Thu 07/02 23Z 0.88 2620  83  62  19 0.01
Fri 07/03 00Z 0.88 2620  86  56  19 0.03
Fri 07/03 01Z 1.04 2623  87  57  19 0.01
Fri 07/03 02Z 0.97 2623  85  58  19 0.03
Fri 07/03 03Z 0.88 2725  85  62  18 0.10
Fri 07/03 04Z 0.92 2826  86  67  18 0.04
Fri 07/03 05Z 0.90 2826  88  71  18 0.01
Fri 07/03 06Z 0.89 2826  92  70  17 0.00
Fri 07/03 07Z 0.82 2926  93  57  17 0.00
Fri 07/03 08Z 0.71 2924  92  35  17 0.01
Fri 07/03 09Z 0.63 2923  89  25  17 0.01
Fri 07/03 10Z 0.57 2923  87  19  17 0.01
Fri 07/03 11Z 0.50 3022  83  14  18 0.01
Fri 07/03 12Z 0.41 3020  79  12  18 0.01
Fri 07/03 13Z 0.39 3018  77  15  18 0.01
Fri 07/03 14Z 0.42 3017  78  17  18 0.01
Fri 07/03 15Z 0.43 2916  77  16  18 0.00
Fri 07/03 16Z 0.45 2916  74  25  18 0.00
Fri 07/03 17Z 0.55 2817  73  27  18 0.00
Fri 07/03 18Z 0.63 2816  73  35  18 0.00
Fri 07/03 19Z 0.63 2715  69  32  19 0.00
Fri 07/03 20Z 0.83 2715  70  36  18 0.00
Fri 07/03 21Z 1.36 2616  74  53  18 0.00
Fri 07/03 22Z 1.72 2617  81  59  18 0.00
Fri 07/03 23Z 1.82 2619  80  69  17 0.00
Sat 07/04 00Z 1.54 2719  77  76  17 0.00
Sat 07/04 01Z 1.59 2621  83  87  17 0.00
Sat 07/04 02Z 0.95 2623  93  83  17 0.03
Sat 07/04 03Z 0.87 2723  91  78  17 0.08
Sat 07/04 04Z 0.73 2824  94  72  17 0.06
Sat 07/04 05Z 0.74 2926  94  70  16 0.05
Sat 07/04 06Z 0.59 3023  93  54  16 0.02
Sat 07/04 07Z 0.55 3022  89  44  15 0.01
Sat 07/04 08Z 0.58 3022  89  51  15 0.01
Sat 07/04 09Z 0.57 3022  89  50  14 0.01
Sat 07/04 10Z 0.59 3023  90  51  14 0.01
Sat 07/04 11Z 0.54 3022  89  48  14 0.01
Sat 07/04 12Z 0.50 3123  85  45  13 0.01
Sat 07/04 13Z 0.49 3122  82  39  13 0.00
Sat 07/04 14Z 0.54 3121  79  35  13 0.01
Sat 07/04 15Z 0.56 3020  80  30  12 0.01
Sat 07/04 16Z 0.58 3019  82  22  12 0.01
Sat 07/04 17Z 0.62 3018  83  23  12 0.01

Run total areal avg QPF for the greens is: 0.73 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