NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260225_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)
=== ===== === ==== ==== === === === ====
Wed 02/25 06Z 0.19 2114  66  39 -13 0.00
Wed 02/25 07Z 0.22 2118  50  59 -12 0.00
Wed 02/25 08Z 0.21 2020  37  55 -11 0.00
Wed 02/25 09Z 0.17 2020  35  62 -10 0.00
Wed 02/25 10Z 0.18 2023  45  85 -10 0.00
Wed 02/25 11Z 0.21 2027  62  93 -10 0.00
Wed 02/25 12Z 0.19 1931  83  87 -10 0.01
Wed 02/25 13Z 0.20 1934  91  85  -9 0.03
Wed 02/25 14Z 0.23 1933  92  86  -9 0.03
Wed 02/25 15Z 0.32 2028  95  78  -9 0.01
Wed 02/25 18Z 0.29 2115  95  89  -7 0.01
Wed 02/25 19Z 0.32 2115  94  90  -7 0.01
Wed 02/25 20Z 0.41 2116  93  58  -7 0.01
Wed 02/25 21Z 0.56 2117  94  75  -7 0.01
Wed 02/25 23Z 0.61 2220  96  80  -7 0.01
Thu 02/26 00Z 0.49 2119  94  80  -6 0.00
Thu 02/26 01Z 0.50 2123  96  88  -6 0.00
Thu 02/26 02Z 0.59 2127  97  90  -5 0.01
Thu 02/26 03Z 0.77 2229  97  91  -5 0.00
Thu 02/26 04Z 1.19 2425  94  83  -6 0.00
Thu 02/26 05Z 1.27 2523  93  78  -7 0.02
Thu 02/26 06Z 1.28 2623  93  66  -8 0.03
Thu 02/26 07Z 1.23 2624  93  30  -9 0.02
Thu 02/26 09Z 1.95 2627  85  36 -12 0.02
Thu 02/26 10Z 1.55 2728  71  40 -13 0.01
Thu 02/26 11Z 1.24 2730  71  34 -13 0.01
Thu 02/26 12Z 1.15 2730  76  18 -14 0.01
Thu 02/26 13Z 1.18 2829  77   7 -14 0.01
Thu 02/26 14Z 1.48 2826  77   3 -15 0.00
Thu 02/26 15Z 4.38 2823  80   4 -15 0.00
Thu 02/26 16Z 5.80 2819  80   6 -16 0.00
Thu 02/26 17Z 6.71 2717  82   7 -15 0.00
Thu 02/26 18Z 5.66 2617  81   9 -15 0.00
Thu 02/26 19Z 5.76 2616  81  10 -14 0.00
Thu 02/26 20Z 6.09 2617  81  13 -14 0.00
Thu 02/26 21Z 4.48 2617  82  17 -14 0.00
Thu 02/26 22Z 2.20 2718  80  25 -14 0.00
Thu 02/26 23Z 1.42 2720  81  29 -14 0.00
Fri 02/27 00Z 1.30 2721  83  35 -14 0.00
Fri 02/27 01Z 1.06 2821  82  43 -14 0.00
Fri 02/27 02Z 0.89 2822  79  42 -15 0.00
Fri 02/27 03Z 0.78 2921  78  41 -15 0.00
Fri 02/27 04Z 0.69 2920  78  42 -14 0.00
Fri 02/27 05Z 0.61 2919  76  40 -14 0.00
Fri 02/27 06Z 0.54 2919  74  44 -13 0.00
Fri 02/27 07Z 0.46 2918  70  45 -12 0.00
Fri 02/27 08Z 0.40 2918  67  49 -12 0.00
Fri 02/27 09Z 0.37 2817  64  53 -11 0.00
Fri 02/27 10Z 0.34 2816  59  67 -10 0.00
Fri 02/27 11Z 0.35 2617  59  73 -10 0.00
Fri 02/27 12Z 0.35 2518  57  76  -9 0.00
Fri 02/27 13Z 0.36 2520  56  78  -8 0.00
Fri 02/27 14Z 0.39 2521  61  84  -7 0.00
Fri 02/27 15Z 0.41 2521  67  89  -6 0.00
Fri 02/27 16Z 0.46 2422  69  85  -6 0.00
Fri 02/27 17Z 0.50 2423  69  77  -6 0.00

Run total areal avg QPF for the greens is: 0.27 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