NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260524_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)
=== ===== === ==== ==== === === === ====
Sun 05/24 18Z 0.30 1532  97  97   4 0.00
Sun 05/24 19Z 0.30 1535  95  97   5 0.04
Sun 05/24 20Z 0.27 1637  94  96   5 0.05
Sun 05/24 21Z 0.24 1638  93  92   6 0.02
Sun 05/24 22Z 0.22 1638  93  92   6 0.01
Sun 05/24 23Z 0.25 1639  93  86   7 0.02
Mon 05/25 00Z 0.28 1640  94  75   7 0.02
Mon 05/25 01Z 0.26 1641  95  70   7 0.02
Mon 05/25 02Z 0.17 1640  96  66   8 0.02
Mon 05/25 03Z 0.11 1736  96  60   8 0.02
Mon 05/25 04Z 0.04 1730  95  63   9 0.01
Mon 05/25 05Z 0.04 1826  95  71  10 0.01
Mon 05/25 06Z 0.06 1823  96  79  10 0.01
Mon 05/25 07Z 0.10 1921  96  84  11 0.01
Mon 05/25 08Z 0.12 1919  97  89  11 0.04
Mon 05/25 09Z 0.12 1918  99  94  10 0.09
Mon 05/25 10Z 0.10 1917  99  95  10 0.16
Mon 05/25 11Z 0.21 2118  99  96  10 0.22
Mon 05/25 12Z 0.30 2218  99  95   9 0.12
Mon 05/25 13Z 0.31 2415  98  94   9 0.07
Mon 05/25 14Z 0.30 2613  97  82  10 0.01
Mon 05/25 15Z 0.28 2812  96  77  10 0.01
Mon 05/25 16Z 0.28 2913  96  72  10 0.00
Mon 05/25 17Z 0.30 2914  96  72  10 0.00
Mon 05/25 18Z 0.35 2915  95  68  10 0.00
Mon 05/25 19Z 0.41 2916  95  27  10 0.00
Mon 05/25 20Z 0.53 2918  93   5   9 0.00
Mon 05/25 21Z 0.62 2918  94   6   9 0.00
Mon 05/25 22Z 0.62 2918  94   8   9 0.01
Mon 05/25 23Z 0.55 2917  91  15   9 0.01
Tue 05/26 00Z 0.53 2917  89  14   9 0.01
Tue 05/26 01Z 0.56 2918  87  19   9 0.01
Tue 05/26 02Z 0.42 3017  76  12   9 0.01
Tue 05/26 03Z 0.37 3017  68   6  10 0.01
Tue 05/26 04Z 0.38 3017  68   4  10 0.01
Tue 05/26 05Z 0.37 3117  64   5  10 0.01
Tue 05/26 06Z 0.36 3116  62   7   9 0.00
Tue 05/26 07Z 0.45 3116  64  12   9 0.00
Tue 05/26 08Z 0.81 3017  72  16   9 0.00
Tue 05/26 09Z 0.62 3017  73  19   9 0.00
Tue 05/26 10Z 0.58 2917  71  15   9 0.00
Tue 05/26 11Z 0.53 2817  66  11  10 0.00
Tue 05/26 12Z 0.51 2818  64  12  10 0.00
Tue 05/26 13Z 0.53 2818  63  20  10 0.00
Tue 05/26 14Z 0.56 2719  62  56  11 0.00
Tue 05/26 15Z 0.57 2718  57  75  12 0.00
Tue 05/26 16Z 0.61 2718  57  64  12 0.00
Tue 05/26 17Z 0.95 2618  70  66  12 0.00
Tue 05/26 18Z 1.36 2620  81  73  12 0.00
Tue 05/26 19Z 1.28 2522  82  70  12 0.00
Tue 05/26 20Z 1.55 2522  80  65  12 0.00
Tue 05/26 21Z 4.12 2524  76  70  13 0.00
Tue 05/26 22Z 5.60 2528  71  73  13 0.00
Tue 05/26 23Z 2.70 2530  71  74  13 0.00
Wed 05/27 00Z 2.37 2632  76  76  13 0.01
Wed 05/27 01Z 1.98 2635  77  73  13 0.04
Wed 05/27 02Z 1.75 2736  79  67  12 0.02
Wed 05/27 03Z 1.52 2835  83  58  12 0.05
Wed 05/27 04Z 1.33 2831  86  65  12 0.02
Wed 05/27 05Z 1.14 2828  88  55  11 0.01

Run total areal avg QPF for the greens is: 1.21 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