NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260102_1800
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)
=== ===== === ==== ==== === === === ====
Fri 01/02 18Z 1.70 2713  85  34 -18 0.00
Fri 01/02 19Z 2.11 2715  89  35 -18 0.00
Fri 01/02 20Z 1.23 2716  92  38 -17 0.00
Fri 01/02 21Z 1.39 2719  91  40 -17 0.00
Fri 01/02 22Z 1.31 2721  86  35 -17 0.00
Fri 01/02 23Z 1.32 2723  83  26 -17 0.00
Sat 01/03 00Z 1.44 2724  84  26 -17 0.00
Sat 01/03 01Z 1.57 2825  87  44 -17 0.00
Sat 01/03 02Z 1.39 2826  87  71 -17 0.00
Sat 01/03 03Z 1.40 2827  86  75 -18 0.01
Sat 01/03 04Z 1.73 2828  89  72 -18 0.00
Sat 01/03 05Z 1.54 2929  84  69 -18 0.00
Sat 01/03 06Z 1.14 2929  83  67 -18 0.00
Sat 01/03 07Z 1.12 2829  87  70 -18 0.00
Sat 01/03 08Z 1.12 2829  89  68 -18 0.00
Sat 01/03 09Z 0.97 2928  91  63 -18 0.00
Sat 01/03 10Z 0.93 2827  93  53 -18 0.00
Sat 01/03 11Z 0.87 2826  94  40 -18 0.00
Sat 01/03 12Z 0.83 2825  94  33 -17 0.00
Sat 01/03 13Z 0.85 2823  95  38 -17 0.00
Sat 01/03 14Z 0.95 2823  95  43 -18 0.01
Sat 01/03 15Z 1.03 2822  94  51 -18 0.00
Sat 01/03 16Z 0.99 2721  94  54 -18 0.00
Sat 01/03 17Z 1.15 2721  93  40 -18 0.00
Sat 01/03 18Z 1.13 2722  92  33 -17 0.00
Sat 01/03 19Z 1.07 2722  91  24 -17 0.00
Sat 01/03 20Z 0.99 2721  91  18 -16 0.00
Sat 01/03 21Z 0.92 2721  93  22 -16 0.00
Sat 01/03 22Z 1.05 2722  94  56 -16 0.00
Sat 01/03 23Z 1.02 2722  93  76 -16 0.00
Sun 01/04 00Z 1.02 2721  94  79 -16 0.00
Sun 01/04 01Z 1.05 2722  95  76 -16 0.00
Sun 01/04 02Z 0.94 2721  95  77 -16 0.00
Sun 01/04 03Z 0.91 2721  94  78 -16 0.00
Sun 01/04 04Z 0.78 2720  92  77 -16 0.00
Sun 01/04 05Z 0.70 2820  91  78 -16 0.00
Sun 01/04 06Z 0.63 2819  91  77 -16 0.00
Sun 01/04 07Z 0.64 2818  92  77 -16 0.00
Sun 01/04 08Z 0.58 2817  91  78 -17 0.00
Sun 01/04 09Z 0.51 2817  88  78 -16 0.00
Sun 01/04 10Z 0.47 2818  84  72 -16 0.00
Sun 01/04 11Z 0.47 2919  83  69 -16 0.00
Sun 01/04 12Z 0.47 2920  83  62 -16 0.00
Sun 01/04 13Z 0.45 2921  83  55 -16 0.00
Sun 01/04 14Z 0.43 2920  84  41 -16 0.00
Sun 01/04 15Z 0.46 2919  88  40 -17 0.00
Sun 01/04 16Z 0.51 2918  89  47 -17 0.00
Sun 01/04 17Z 0.57 2918  88  52 -18 0.00
Sun 01/04 18Z 0.65 2918  87  58 -18 0.00
Sun 01/04 19Z 0.72 2918  89  52 -19 0.00
Sun 01/04 20Z 0.64 2919  91  44 -19 0.00
Sun 01/04 21Z 0.60 3019  91  43 -20 0.00
Sun 01/04 22Z 0.65 3021  91  46 -21 0.00
Sun 01/04 23Z 0.65 3123  89  58 -21 0.00
Mon 01/05 00Z 0.55 3123  87  60 -21 0.00
Mon 01/05 01Z 0.47 3123  84  60 -21 0.00
Mon 01/05 02Z 0.49 3123  82  60 -22 0.00
Mon 01/05 03Z 0.53 3124  82  47 -22 0.00
Mon 01/05 04Z 0.50 3124  81  35 -22 0.00
Mon 01/05 05Z 0.49 3124  82  29 -22 0.00

Run total areal avg QPF for the greens is: 0.02 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