NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260718_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)
=== ===== === ==== ==== === === === ====
Sat 07/18 06Z 0.30 2308  57  18  12 0.00
Sat 07/18 07Z 0.45 2311  59  46  12 0.00
Sat 07/18 08Z 0.41 2311  61  81  12 0.00
Sat 07/18 09Z 0.40 2213  61  96  12 0.00
Sat 07/18 10Z 0.43 2215  66  93  11 0.01
Sat 07/18 11Z 0.43 2317  68  96  12 0.00
Sat 07/18 12Z 0.42 2220  73  93  12 0.01
Sat 07/18 13Z 0.45 2123  78  76  13 0.02
Sat 07/18 14Z 0.42 2124  75  64  14 0.01
Sat 07/18 15Z 0.46 2128  79  57  15 0.00
Sat 07/18 16Z 0.62 2130  86  86  15 0.00
Sat 07/18 17Z 0.57 2230  93  78  15 0.27
Sat 07/18 18Z 0.61 2232  93  78  15 0.07
Sat 07/18 19Z 0.70 2232  94  75  16 0.01
Sat 07/18 20Z 0.83 2230  94  77  16 0.01
Sat 07/18 21Z 0.87 2328  93  71  16 0.04
Sat 07/18 22Z 0.83 2327  93  74  15 0.01
Sat 07/18 23Z 0.80 2327  94  79  15 0.04
Sun 07/19 00Z 0.83 2429  95  81  15 0.07
Sun 07/19 01Z 0.84 2529  96  67  15 0.04
Sun 07/19 02Z 0.86 2528  96  59  15 0.03
Sun 07/19 03Z 0.91 2529  96  64  14 0.06
Sun 07/19 04Z 0.99 2729  97  67  14 0.11
Sun 07/19 05Z 0.92 2929  98  62  11 0.06
Sun 07/19 06Z 0.71 3129  96  37  10 0.04
Sun 07/19 07Z 0.55 3229  94  29   9 0.02
Sun 07/19 08Z 0.49 3228  91  28   8 0.01
Sun 07/19 09Z 0.48 3229  89  25   8 0.01
Sun 07/19 10Z 0.45 3229  90  20   8 0.01
Sun 07/19 11Z 0.47 3228  91  14   7 0.01
Sun 07/19 12Z 0.45 3227  91  12   7 0.01
Sun 07/19 13Z 0.42 3225  90   9   7 0.01
Sun 07/19 14Z 0.40 3222  87   7   7 0.01
Sun 07/19 15Z 0.42 3221  84   8   7 0.01
Sun 07/19 16Z 0.53 3119  80   9   7 0.00
Sun 07/19 17Z 2.68 3118  77  12   7 0.00
Sun 07/19 18Z 7.64 3018  74  10   7 0.00
Sun 07/19 19Z 10.45 3018  72  10   8 0.00
Sun 07/19 20Z 11.01 3018  69  13   8 0.00
Sun 07/19 21Z 10.94 3019  66  13   8 0.00
Sun 07/19 22Z 9.21 2920  66  10   8 0.00
Sun 07/19 23Z 4.92 3022  66   8   8 0.00
Mon 07/20 00Z 2.81 3024  65   9   8 0.00
Mon 07/20 01Z 2.25 3125  67  10   8 0.00
Mon 07/20 02Z 2.36 3125  71  11   7 0.00
Mon 07/20 03Z 1.74 3125  73  11   7 0.00
Mon 07/20 04Z 1.26 3224  74   9   7 0.00
Mon 07/20 05Z 1.13 3223  75   9   7 0.00
Mon 07/20 06Z 0.86 3221  77  10   7 0.00
Mon 07/20 07Z 0.69 3219  76  11   7 0.00
Mon 07/20 08Z 0.55 3217  77  13   7 0.00
Mon 07/20 09Z 0.46 3216  77  15   7 0.00
Mon 07/20 10Z 0.38 3214  76  18   7 0.00
Mon 07/20 11Z 0.38 3112  76  26   7 0.00
Mon 07/20 12Z 0.40 3011  76  26   7 0.00
Mon 07/20 13Z 0.42 2910  77  32   7 0.00
Mon 07/20 14Z 0.46 2708  76  42   8 0.00
Mon 07/20 15Z 0.91 2607  75  53   8 0.00
Mon 07/20 16Z 1.77 2607  73  55   8 0.00
Mon 07/20 17Z 2.05 2607  70  65   9 0.00

Run total areal avg QPF for the greens is: 1.01 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