NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260715_1200
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 07/15 12Z 0.51 3021  88  71  15 0.00
Wed 07/15 13Z 0.58 3023  83  64  15 0.00
Wed 07/15 14Z 0.62 3023  78  55  15 0.00
Wed 07/15 15Z 0.82 3022  75  55  15 0.00
Wed 07/15 16Z 4.45 3022  80  76  14 0.00
Wed 07/15 17Z 12.10 3025  65  79  14 0.00
Wed 07/15 18Z 12.60 3026  60  80  13 0.00
Wed 07/15 19Z 10.79 3027  60  77  13 0.00
Wed 07/15 20Z 11.30 2927  62  70  13 0.00
Wed 07/15 21Z 8.23 2925  62  53  13 0.00
Wed 07/15 22Z 5.16 3026  61  37  13 0.00
Wed 07/15 23Z 2.75 3027  63  36  12 0.00
Thu 07/16 00Z 1.97 3028  64  33  12 0.00
Thu 07/16 01Z 1.76 3029  66  31  12 0.00
Thu 07/16 02Z 1.54 3030  66  36  12 0.00
Thu 07/16 03Z 1.30 3130  64  39  12 0.00
Thu 07/16 04Z 1.21 3128  63  40  12 0.00
Thu 07/16 05Z 1.11 3127  63  39  12 0.00
Thu 07/16 06Z 1.06 3127  62  42  12 0.00
Thu 07/16 07Z 0.85 3126  65  38  12 0.00
Thu 07/16 08Z 0.65 3225  66  38  12 0.00
Thu 07/16 09Z 0.58 3123  67  39  11 0.00
Thu 07/16 10Z 0.55 3121  68  41  11 0.00
Thu 07/16 11Z 0.54 3020  68  36  11 0.00
Thu 07/16 12Z 0.56 2918  69  45  11 0.00
Thu 07/16 13Z 0.66 2819  71  50  11 0.00
Thu 07/16 14Z 0.87 2721  72  56  11 0.00
Thu 07/16 15Z 1.49 2724  71  55  11 0.00
Thu 07/16 16Z 8.26 2724  75  50  12 0.00
Thu 07/16 17Z 7.69 2726  76  48  12 0.01
Thu 07/16 18Z 13.59 2726  67  42  12 0.00
Thu 07/16 19Z 14.28 2828  70  56  12 0.03
Thu 07/16 20Z 7.71 3027  70  52  12 0.02
Thu 07/16 21Z 2.31 3127  76  49  11 0.02
Thu 07/16 22Z 0.72 3125  83  40  10 0.01
Thu 07/16 23Z 0.74 3125  86  21  10 0.01
Fri 07/17 00Z 0.93 3126  86  13   8 0.01
Fri 07/17 01Z 1.28 3127  73   7   8 0.00
Fri 07/17 02Z 1.13 3228  62   6   7 0.00
Fri 07/17 03Z 1.06 3229  64  16   7 0.00
Fri 07/17 04Z 1.10 3230  64  22   6 0.00
Fri 07/17 05Z 1.14 3229  67  26   6 0.00
Fri 07/17 06Z 0.96 3228  67  29   6 0.00
Fri 07/17 07Z 0.70 3227  64  25   6 0.00
Fri 07/17 08Z 0.60 3227  63  22   7 0.00
Fri 07/17 09Z 0.46 3226  57  21   7 0.00
Fri 07/17 10Z 0.40 3225  52  20   8 0.00
Fri 07/17 11Z 0.37 3225  50  19   8 0.00
Fri 07/17 12Z 0.35 3224  51  19   8 0.00
Fri 07/17 13Z 0.32 3222  52  19   8 0.00
Fri 07/17 14Z 0.33 3221  54  20   8 0.00
Fri 07/17 15Z 0.29 3218  55  19   8 0.00
Fri 07/17 16Z 0.29 3316  59  20   8 0.00
Fri 07/17 17Z 0.38 3214  62  20   8 0.00
Fri 07/17 18Z 0.70 3212  61  20   8 0.00
Fri 07/17 19Z 1.45 3011  60  18   8 0.00
Fri 07/17 20Z 1.64 2911  58  15   9 0.00
Fri 07/17 21Z 1.27 2810  58  13   9 0.00
Fri 07/17 22Z 0.82 2710  61  13  10 0.00
Fri 07/17 23Z 0.63 2710  60  13  10 0.00

Run total areal avg QPF for the greens is: 0.11 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