NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260813_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)
=== ===== === ==== ==== === === === ====
Thu 08/13 18Z 0.78 3209  89  77  11 0.00
Thu 08/13 19Z 0.96 3109  86  80  12 0.01
Thu 08/13 20Z 0.81 3009  83  81  12 0.01
Thu 08/13 21Z 0.72 3010  84  77  12 0.00
Thu 08/13 22Z 0.58 3110  82  69  12 0.05
Thu 08/13 23Z 0.55 3011  82  58  12 0.01
Fri 08/14 00Z 0.54 3013  84  55  11 0.06
Fri 08/14 01Z 0.59 2916  88  64  11 0.06
Fri 08/14 02Z 0.55 3118  87  70  11 0.04
Fri 08/14 03Z 0.42 3219  87  66  10 0.01
Fri 08/14 04Z 0.31 3319  82  57  10 0.00
Fri 08/14 05Z 0.32 3218  83  51  10 0.00
Fri 08/14 06Z 0.30 3218  83  48  10 0.01
Fri 08/14 07Z 0.31 3218  81  44   9 0.01
Fri 08/14 08Z 0.32 3218  81  37   9 0.00
Fri 08/14 09Z 0.33 3219  79  35   9 0.00
Fri 08/14 10Z 0.33 3220  78  33   9 0.00
Fri 08/14 11Z 0.33 3220  75  37   9 0.00
Fri 08/14 12Z 0.34 3220  74  36   9 0.00
Fri 08/14 13Z 0.29 3219  73  38   8 0.00
Fri 08/14 14Z 0.30 3218  73  43   8 0.00
Fri 08/14 15Z 0.33 3317  71  48   8 0.00
Fri 08/14 16Z 0.41 3216  71  56   8 0.00
Fri 08/14 17Z 0.96 3215  72  50   8 0.00
Fri 08/14 18Z 2.10 3214  72  47   8 0.00
Fri 08/14 19Z 3.49 3115  73  46   8 0.00
Fri 08/14 20Z 2.11 3016  78  45   8 0.00
Fri 08/14 21Z 1.51 3016  81  40   8 0.00
Fri 08/14 22Z 1.64 3117  78  32   8 0.00
Fri 08/14 23Z 1.26 3118  76  27   8 0.00
Sat 08/15 00Z 0.97 3219  75  19   8 0.00
Sat 08/15 01Z 0.81 3319  76  14   8 0.00
Sat 08/15 02Z 0.50 3319  75  11   8 0.00
Sat 08/15 03Z 0.64 3319  77  11   7 0.00
Sat 08/15 04Z 0.39 3418  74  10   7 0.00
Sat 08/15 05Z 0.21 3416  74  11   7 0.00
Sat 08/15 06Z 0.24 3414  74  12   7 0.00
Sat 08/15 07Z 0.31 3313  73  12   7 0.00
Sat 08/15 08Z 0.37 3214  73  12   7 0.00
Sat 08/15 09Z 0.39 3216  73  12   7 0.00
Sat 08/15 10Z 0.34 3318  76  12   7 0.00
Sat 08/15 11Z 0.28 3319  74  13   7 0.00
Sat 08/15 12Z 0.22 3419  73  14   7 0.00
Sat 08/15 13Z 0.18 3316  71  14   8 0.00
Sat 08/15 14Z 0.19 3312  76  14   7 0.00
Sat 08/15 15Z 0.33 3210  80  18   7 0.00
Sat 08/15 16Z 0.35 3210  77  17   7 0.00
Sat 08/15 17Z 0.64 3212  73  17   7 0.00
Sat 08/15 18Z 0.82 3313  69  15   8 0.00
Sat 08/15 19Z 0.77 3312  66  15   8 0.00
Sat 08/15 20Z 0.44 3411  63  16   8 0.00
Sat 08/15 21Z 0.28 3409  61  16   9 0.00
Sat 08/15 22Z 0.09 3408  57  15   9 0.00
Sat 08/15 23Z 0.04 3506  54  14  10 0.00
Sun 08/16 00Z 0.06 3405  53  14  10 0.00
Sun 08/16 01Z 0.11 3306  50  14  10 0.00
Sun 08/16 02Z 0.09 3306  47  13  10 0.00
Sun 08/16 03Z 0.12 3206  49  12  10 0.00
Sun 08/16 04Z 0.13 3206  53  13  10 0.00
Sun 08/16 05Z 0.12 3105  57  14  10 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