NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260228_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 02/28 12Z 0.57 2131  68  47  -1 0.00
Sat 02/28 13Z 0.66 2135  68  56  -1 0.00
Sat 02/28 14Z 0.67 2136  70  78   0 0.00
Sat 02/28 15Z 0.75 2138  71  90   0 0.00
Sat 02/28 16Z 0.74 2136  77  96   0 0.01
Sat 02/28 17Z 0.87 2236  88  96  -1 0.02
Sat 02/28 18Z 0.83 2235  86  94   0 0.01
Sat 02/28 19Z 0.83 2333  88  88   0 0.01
Sat 02/28 20Z 0.86 2430  90  84  -1 0.01
Sat 02/28 21Z 0.92 2428  91  58  -2 0.00
Sat 02/28 22Z 0.97 2527  91  28  -2 0.00
Sat 02/28 23Z 0.90 2625  86  25  -2 0.01
Sun 03/01 00Z 0.87 2724  79  26  -3 0.01
Sun 03/01 01Z 0.68 2821  68  29  -4 0.00
Sun 03/01 02Z 0.43 2918  67  38  -4 0.00
Sun 03/01 03Z 0.28 3015  63  48  -4 0.00
Sun 03/01 04Z 0.21 3012  63  55  -5 0.00
Sun 03/01 05Z 0.20 3012  69  82  -6 0.00
Sun 03/01 06Z 0.21 3013  72  87  -7 0.00
Sun 03/01 07Z 0.19 3114  71  93  -8 0.00
Sun 03/01 08Z 0.21 3014  73  93  -9 0.00
Sun 03/01 09Z 0.20 3113  80  90 -10 0.00
Sun 03/01 10Z 0.19 3114  86  86 -11 0.00
Sun 03/01 11Z 0.14 3214  86  84 -12 0.00
Sun 03/01 12Z 0.13 3214  84  86 -12 0.00
Sun 03/01 13Z 0.17 3215  82  88 -13 0.00
Sun 03/01 14Z 0.23 3117  79  85 -13 0.00
Sun 03/01 15Z 0.25 3117  67  83 -14 0.00
Sun 03/01 16Z 0.30 3118  57  77 -14 0.00
Sun 03/01 17Z 0.33 3118  53  69 -15 0.00
Sun 03/01 18Z 0.39 3118  59  57 -16 0.00
Sun 03/01 19Z 0.58 3118  68  32 -17 0.00
Sun 03/01 20Z 0.54 3118  69  29 -17 0.00
Sun 03/01 21Z 0.53 3118  69  22 -18 0.00
Sun 03/01 22Z 0.51 3119  69  17 -18 0.00
Sun 03/01 23Z 0.46 3120  69  11 -19 0.00
Mon 03/02 00Z 0.43 3121  64  11 -19 0.00
Mon 03/02 01Z 0.39 3121  59  11 -19 0.00
Mon 03/02 02Z 0.32 3121  55  11 -19 0.00
Mon 03/02 03Z 0.27 3119  53  12 -19 0.00
Mon 03/02 05Z 0.25 3119  47  12 -19 0.00
Mon 03/02 06Z 0.23 3119  44  11 -19 0.00
Mon 03/02 07Z 0.21 3118  41  10 -19 0.00
Mon 03/02 08Z 0.22 3118  40  10 -20 0.00
Mon 03/02 09Z 0.22 3117  40   9 -20 0.00
Mon 03/02 10Z 0.24 3117  39   9 -19 0.00
Mon 03/02 11Z 0.25 3117  38  11 -19 0.00
Mon 03/02 12Z 0.28 3018  38  14 -19 0.00
Mon 03/02 13Z 0.31 3018  39  17 -19 0.00
Mon 03/02 14Z 0.31 3016  41  17 -19 0.00
Mon 03/02 15Z 0.34 2916  45  15 -19 0.00
Mon 03/02 16Z 0.33 2914  43  17 -19 0.00
Mon 03/02 17Z 0.33 3013  41  18 -18 0.00
Mon 03/02 18Z 0.33 2912  42  17 -17 0.00
Mon 03/02 19Z 0.30 2911  43  22 -16 0.00
Mon 03/02 20Z 0.31 2810  47  15 -16 0.00
Mon 03/02 21Z 0.30 2710  49  35 -15 0.00
Mon 03/02 22Z 0.30 2611  50  44 -14 0.00
Mon 03/02 23Z 0.30 2612  46  48 -13 0.00

Run total areal avg QPF for the Central_Greens is: 0.08 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