NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260128_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)
=== ===== === ==== ==== === === === ====
Wed 01/28 00Z 0.82 2514  83  75 -19 0.00
Wed 01/28 01Z 1.10 2719  86  75 -20 0.00
Wed 01/28 02Z 1.09 2720  77  72 -20 0.00
Wed 01/28 03Z 0.95 2721  80  70 -20 0.00
Wed 01/28 04Z 0.86 2722  85  69 -20 0.01
Wed 01/28 05Z 0.83 2821  87  69 -20 0.01
Wed 01/28 06Z 0.71 2920  87  67 -20 0.01
Wed 01/28 07Z 0.62 2919  88  64 -20 0.01
Wed 01/28 08Z 0.60 2919  90  62 -20 0.00
Wed 01/28 09Z 0.62 2920  89  59 -20 0.00
Wed 01/28 10Z 0.58 2920  87  49 -20 0.00
Wed 01/28 11Z 0.59 2920  90  41 -20 0.00
Wed 01/28 12Z 0.56 2919  89  32 -20 0.00
Wed 01/28 13Z 0.48 3017  87  27 -20 0.00
Wed 01/28 14Z 0.40 3015  84  25 -20 0.00
Wed 01/28 15Z 0.40 2914  82  28 -19 0.00
Wed 01/28 16Z 0.44 2813  79  38 -19 0.00
Wed 01/28 17Z 0.49 2812  76  48 -19 0.00
Wed 01/28 18Z 0.59 2810  72  54 -19 0.00
Wed 01/28 19Z 0.86 2809  69  56 -19 0.00
Wed 01/28 20Z 1.04 2809  72  57 -19 0.00
Wed 01/28 21Z 0.64 2809  80  60 -19 0.00
Wed 01/28 22Z 0.53 2809  86  62 -19 0.00
Wed 01/28 23Z 0.57 2810  86  67 -19 0.00
Thu 01/29 00Z 0.64 2811  84  72 -19 0.00
Thu 01/29 01Z 0.65 2811  83  78 -19 0.00
Thu 01/29 02Z 0.55 2911  83  80 -19 0.00
Thu 01/29 03Z 0.44 3011  85  79 -18 0.01
Thu 01/29 04Z 0.41 3012  86  79 -18 0.01
Thu 01/29 05Z 0.45 3013  88  79 -18 0.01
Thu 01/29 06Z 0.47 3113  89  78 -19 0.01
Thu 01/29 07Z 0.48 3114  91  78 -19 0.01
Thu 01/29 08Z 0.52 3115  92  77 -19 0.01
Thu 01/29 09Z 0.51 3115  93  75 -19 0.01
Thu 01/29 10Z 0.46 3115  93  72 -19 0.00
Thu 01/29 11Z 0.43 3115  92  69 -19 0.00
Thu 01/29 12Z 0.41 3114  90  67 -19 0.00
Thu 01/29 13Z 0.40 3014  89  66 -19 0.00
Thu 01/29 14Z 0.40 2914  87  65 -19 0.00
Thu 01/29 15Z 0.45 2914  86  63 -19 0.00
Thu 01/29 16Z 0.58 2915  87  60 -19 0.00
Thu 01/29 17Z 0.83 3016  89  56 -19 0.00
Thu 01/29 18Z 1.47 3017  90  54 -19 0.00
Thu 01/29 19Z 3.11 3017  90  52 -19 0.00
Thu 01/29 20Z 3.36 2918  89  50 -19 0.00
Thu 01/29 21Z 2.69 2920  87  49 -19 0.00
Thu 01/29 22Z 2.64 2923  84  47 -20 0.00
Thu 01/29 23Z 1.56 2925  84  43 -20 0.00
Fri 01/30 00Z 1.34 2926  84  39 -21 0.00
Fri 01/30 01Z 1.15 2927  83  36 -21 0.00
Fri 01/30 02Z 1.03 3027  82  34 -22 0.00
Fri 01/30 03Z 1.04 3027  85  30 -22 0.00
Fri 01/30 04Z 0.95 3026  84  28 -23 0.00
Fri 01/30 05Z 0.82 3027  82  27 -23 0.00
Fri 01/30 06Z 0.75 2927  80  27 -23 0.00
Fri 01/30 07Z 0.69 2927  77  29 -23 0.00
Fri 01/30 08Z 0.64 2927  75  34 -22 0.00
Fri 01/30 09Z 0.59 2927  74  38 -22 0.00
Fri 01/30 10Z 0.53 2927  72  42 -22 0.00
Fri 01/30 11Z 0.46 3026  69  46 -21 0.00

Run total areal avg QPF for the greens is: 0.11 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