NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260819_0000
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 08/19 00Z 0.17 3105  79  29  12 0.00
Wed 08/19 01Z 0.17 3005  73  30  13 0.00
Wed 08/19 02Z 0.21 3106  70  29  12 0.00
Wed 08/19 03Z 0.22 3105  73  34  12 0.00
Wed 08/19 04Z 0.20 3105  76  33  12 0.00
Wed 08/19 05Z 0.24 3106  78  29  12 0.00
Wed 08/19 06Z 0.23 3106  79  15  12 0.00
Wed 08/19 07Z 0.18 3004  79   6  11 0.00
Wed 08/19 08Z 0.20 2804  80   6  11 0.00
Wed 08/19 09Z 0.18 2704  80   8  11 0.00
Wed 08/19 10Z 0.21 2504  80  13  11 0.00
Wed 08/19 11Z 0.24 2505  81  17  11 0.00
Wed 08/19 12Z 0.26 2307  82  25  11 0.00
Wed 08/19 13Z 0.26 2208  81  36  11 0.00
Wed 08/19 14Z 0.34 2209  81  56  11 0.00
Wed 08/19 15Z 0.39 2109  76  54  12 0.00
Wed 08/19 16Z 0.74 2211  72  54  12 0.00
Wed 08/19 17Z 0.63 2312  68  65  12 0.00
Wed 08/19 18Z 0.87 2313  64  81  13 0.00
Wed 08/19 19Z 0.94 2414  68  92  13 0.00
Wed 08/19 20Z 0.79 2315  78  88  13 0.00
Wed 08/19 21Z 0.96 2316  85  83  13 0.00
Wed 08/19 22Z 0.93 2318  85  74  13 0.00
Wed 08/19 23Z 0.90 2421  92  54  13 0.05
Thu 08/20 00Z 1.00 2621  91  50  13 0.03
Thu 08/20 01Z 0.83 2619  92  40  13 0.01
Thu 08/20 02Z 0.68 2618  88  22  13 0.01
Thu 08/20 03Z 0.59 2717  82  24  13 0.01
Thu 08/20 04Z 0.59 2718  81  21  12 0.01
Thu 08/20 05Z 0.56 2817  83  30  12 0.01
Thu 08/20 06Z 0.51 2817  88  13  11 0.01
Thu 08/20 07Z 0.48 2916  87  16  11 0.01
Thu 08/20 08Z 0.45 2916  86  11  10 0.00
Thu 08/20 09Z 0.42 3015  81   8  10 0.00
Thu 08/20 10Z 0.42 3015  80   8  10 0.00
Thu 08/20 11Z 0.39 3013  79   7  10 0.00
Thu 08/20 12Z 0.38 3012  76   8  10 0.00
Thu 08/20 13Z 0.31 3010  73  11  10 0.00
Thu 08/20 14Z 0.32 3009  72  24  10 0.00
Thu 08/20 15Z 0.35 2906  72  17   9 0.00
Thu 08/20 16Z 0.69 2705  69  38  10 0.00
Thu 08/20 17Z 0.73 2705  65  23  10 0.00
Thu 08/20 18Z 0.41 2705  63  31  10 0.00
Thu 08/20 19Z 0.42 2606  63  24  11 0.00
Thu 08/20 20Z 0.39 2606  65  25  11 0.00
Thu 08/20 21Z 0.36 2606  67  36  11 0.00
Thu 08/20 22Z 0.29 2606  68  33  11 0.00
Thu 08/20 23Z 0.29 2606  71  37  10 0.00
Fri 08/21 00Z 0.29 2606  74  27  10 0.00
Fri 08/21 01Z 0.25 2704  76  24  10 0.00
Fri 08/21 02Z 0.21 2804  77  24  10 0.00
Fri 08/21 03Z 0.16 3003  77  25  10 0.00
Fri 08/21 04Z 0.10 3203  78  28   9 0.00
Fri 08/21 05Z 0.10 3302  80  27   9 0.00
Fri 08/21 06Z 0.10 3402  81  27   9 0.00
Fri 08/21 07Z 0.08 0002  83  28   9 0.00
Fri 08/21 08Z 0.06 0002  83  25   9 0.00
Fri 08/21 09Z 0.05 0003  80  20   9 0.00
Fri 08/21 10Z 0.06 0003  78  17   9 0.00
Fri 08/21 11Z 0.08 0204  76  19   9 0.00

Run total areal avg QPF for the greens is: 0.15 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