Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260701_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)
=== ===== === ==== ==== === === === ====
Wed 07/01 06Z 0.70 2524  83  89  17 0.00
Wed 07/01 07Z 0.68 2623  91  91  17 0.03
Wed 07/01 08Z 0.68 2623  94  89  17 0.04
Wed 07/01 09Z 0.74 2725  96  73  17 0.03
Wed 07/01 10Z 0.67 2925  95  64  17 0.13
Wed 07/01 11Z 0.58 3023  94  64  17 0.05
Wed 07/01 12Z 0.46 3018  93  66  18 0.01
Wed 07/01 13Z 0.44 2916  93  65  18 0.01
Wed 07/01 14Z 0.41 2915  91  67  18 0.01
Wed 07/01 15Z 0.42 2913  89  59  18 0.00
Wed 07/01 17Z 0.53 2710  89  65  18 0.00
Wed 07/01 18Z 0.69 2711  90  69  18 0.00
Wed 07/01 19Z 0.55 2611  93  70  18 0.00
Wed 07/01 20Z 0.70 2615  93  72  19 0.00
Wed 07/01 21Z 0.47 2414  87  63  19 0.01
Wed 07/01 22Z 0.55 2518  83  61  20 0.00
Wed 07/01 23Z 0.64 2619  81  56  20 0.00
Thu 07/02 00Z 0.64 2521  90  50  20 0.00
Thu 07/02 01Z 0.67 2622  89  43  20 0.00
Thu 07/02 02Z 0.65 2722  88  46  20 0.00
Thu 07/02 03Z 0.59 2721  87  46  20 0.00
Thu 07/02 04Z 0.62 2722  87  45  20 0.00
Thu 07/02 05Z 0.60 2823  82  47  20 0.00
Thu 07/02 06Z 0.58 2923  78  51  20 0.00
Thu 07/02 07Z 0.55 2923  82  51  20 0.00
Thu 07/02 08Z 0.52 2922  86  55  19 0.00
Thu 07/02 09Z 0.49 2922  87  54  19 0.00
Thu 07/02 10Z 0.44 2920  83  44  19 0.01
Thu 07/02 11Z 0.43 2920  73  28  20 0.01
Thu 07/02 12Z 0.43 2820  62  34  20 0.01
Thu 07/02 13Z 0.46 2820  65  41  20 0.00
Thu 07/02 14Z 0.51 2820  72  51  19 0.00
Thu 07/02 15Z 0.54 2820  72  56  20 0.00
Thu 07/02 16Z 0.54 2818  72  55  20 0.00
Thu 07/02 17Z 0.55 2818  71  48  20 0.00
Thu 07/02 18Z 0.57 2716  73  35  20 0.00
Thu 07/02 19Z 0.66 2616  78  37  20 0.00
Thu 07/02 20Z 0.84 2517  84  47  20 0.00
Thu 07/02 21Z 1.11 2420  86  51  20 0.00
Thu 07/02 22Z 1.35 2424  87  58  20 0.00
Thu 07/02 23Z 2.10 2528  86  57  20 0.00
Fri 07/03 00Z 1.55 2631  88  62  19 0.03
Fri 07/03 01Z 1.30 2732  79  51  20 0.07
Fri 07/03 02Z 1.10 2732  77  51  19 0.01
Fri 07/03 03Z 1.04 2832  82  52  19 0.00
Fri 07/03 04Z 0.98 2831  86  37  19 0.03
Fri 07/03 05Z 0.97 2831  88  36  18 0.02
Fri 07/03 06Z 0.92 2930  88  46  18 0.00
Fri 07/03 07Z 0.84 2829  87  46  18 0.00
Fri 07/03 08Z 0.74 2928  82  48  18 0.00
Fri 07/03 09Z 0.65 2925  76  41  18 0.01
Fri 07/03 10Z 0.51 2922  63  36  19 0.01
Fri 07/03 11Z 0.47 2921  58  37  19 0.01
Fri 07/03 12Z 0.48 2920  60  25  18 0.01
Fri 07/03 13Z 0.52 2821  63  16  18 0.01
Fri 07/03 14Z 0.58 2822  64  17  18 0.01
Fri 07/03 15Z 0.64 2822  65  19  18 0.01
Fri 07/03 16Z 0.83 2823  70  15  17 0.00
Fri 07/03 17Z 1.66 2822  77  17  16 0.00

Run total areal avg QPF for the greens is: 0.58 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