NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260526_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)
=== ===== === ==== ==== === === === ====
Tue 05/26 06Z 0.45 3015  74   9   9 0.00
Tue 05/26 07Z 0.46 3015  75  14   9 0.00
Tue 05/26 08Z 0.37 3014  77  20  10 0.00
Tue 05/26 09Z 0.35 3115  70  25  10 0.00
Tue 05/26 10Z 0.39 3115  66  26  10 0.00
Tue 05/26 11Z 0.42 3014  65  33  10 0.00
Tue 05/26 12Z 0.46 2915  69  35  10 0.00
Tue 05/26 13Z 0.50 2915  79  34  10 0.00
Tue 05/26 14Z 0.54 2815  83  37  11 0.00
Tue 05/26 15Z 0.56 2814  79  41  11 0.00
Tue 05/26 16Z 0.73 2714  79  53  12 0.00
Tue 05/26 17Z 1.18 2615  75  60  12 0.00
Tue 05/26 18Z 1.98 2515  74  56  12 0.00
Tue 05/26 19Z 3.38 2417  76  60  12 0.00
Tue 05/26 20Z 4.70 2420  75  64  13 0.00
Tue 05/26 21Z 2.37 2422  73  62  13 0.00
Tue 05/26 22Z 2.28 2426  70  49  13 0.00
Tue 05/26 23Z 1.80 2429  65  45  13 0.00
Wed 05/27 00Z 1.72 2431  62  64  13 0.00
Wed 05/27 01Z 1.72 2534  64  71  13 0.00
Wed 05/27 02Z 1.53 2535  62  77  13 0.00
Wed 05/27 03Z 1.65 2636  59  78  13 0.00
Wed 05/27 04Z 1.56 2636  65  76  12 0.00
Wed 05/27 05Z 1.59 2735  70  70  12 0.00
Wed 05/27 06Z 1.28 2832  77  65  11 0.01
Wed 05/27 07Z 1.07 2828  81  61  11 0.00
Wed 05/27 08Z 0.90 2925  83  57  10 0.00
Wed 05/27 09Z 0.78 2923  84  46  10 0.00
Wed 05/27 10Z 0.69 2921  85  42  10 0.00
Wed 05/27 11Z 0.62 2919  83  39   9 0.00
Wed 05/27 12Z 0.54 3017  83  15   9 0.00
Wed 05/27 13Z 0.48 3016  82  15   9 0.00
Wed 05/27 14Z 0.47 3115  79  16   9 0.00
Wed 05/27 15Z 0.89 3114  74  15   9 0.00
Wed 05/27 16Z 1.98 3113  71  15   9 0.00
Wed 05/27 17Z 3.18 3113  74  16   9 0.00
Wed 05/27 18Z 3.21 3012  78  16   9 0.00
Wed 05/27 19Z 3.20 3011  78  19   9 0.00
Wed 05/27 20Z 3.02 3011  79  23   9 0.00
Wed 05/27 21Z 1.93 3112  80  24   9 0.00
Wed 05/27 22Z 1.29 3113  81  25   8 0.00
Wed 05/27 23Z 0.68 3214  83  28   8 0.00
Thu 05/28 00Z 0.49 3216  85  29   8 0.01
Thu 05/28 01Z 0.40 3317  87  32   7 0.00
Thu 05/28 02Z 0.33 3318  89  33   6 0.01
Thu 05/28 03Z 0.30 3419  88  33   6 0.00
Thu 05/28 04Z 0.20 3418  88  34   5 0.00
Thu 05/28 05Z 0.13 3417  89  37   5 0.00
Thu 05/28 06Z 0.08 3516  91  40   4 0.00
Thu 05/28 07Z 0.08 3514  91  40   4 0.00
Thu 05/28 08Z 0.10 3413  92  40   4 0.00
Thu 05/28 09Z 0.10 3414  94  40   3 0.00
Thu 05/28 10Z 0.10 3415  94  42   3 0.00
Thu 05/28 11Z 0.10 3415  95  44   2 0.00
Thu 05/28 12Z 0.10 3516  94  48   2 0.01
Thu 05/28 13Z 0.09 3516  94  50   2 0.01
Thu 05/28 14Z 0.09 3515  93  53   2 0.01
Thu 05/28 15Z 0.12 3515  94  60   2 0.00
Thu 05/28 16Z 0.15 3415  95  69   2 0.00
Thu 05/28 17Z 0.30 3417  94  76   2 0.01

Run total areal avg QPF for the greens is: 0.07 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