NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260710_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)
=== ===== === ==== ==== === === === ====
Fri 07/10 06Z 0.47 2713  89  86  14 0.00
Fri 07/10 07Z 0.55 2815  94  84  14 0.01
Fri 07/10 08Z 0.57 2917  96  85  14 0.08
Fri 07/10 09Z 0.55 3019  96  87  13 0.12
Fri 07/10 10Z 0.37 3218  95  86  13 0.02
Fri 07/10 11Z 0.30 3219  93  81  13 0.02
Fri 07/10 12Z 0.24 3317  91  68  13 0.01
Fri 07/10 13Z 0.16 3416  88  63  12 0.01
Fri 07/10 14Z 0.11 3415  86  58  12 0.00
Fri 07/10 15Z 0.08 3514  83  50  12 0.00
Fri 07/10 16Z 0.12 3514  81  43  12 0.00
Fri 07/10 17Z 0.49 3413  79  39  12 0.00
Fri 07/10 18Z 0.76 3412  75  33  12 0.00
Fri 07/10 19Z 1.45 3412  72  26  12 0.00
Fri 07/10 20Z 1.86 3412  69  26  12 0.00
Fri 07/10 21Z 1.45 3412  67  24  12 0.00
Fri 07/10 22Z 0.75 3411  67  24  12 0.00
Fri 07/10 23Z 0.42 3411  68  31  12 0.00
Sat 07/11 00Z 0.42 3411  69  38  12 0.00
Sat 07/11 01Z 0.39 3412  69  30  11 0.00
Sat 07/11 02Z 0.29 3413  72  32  11 0.00
Sat 07/11 03Z 0.19 3413  73  33  11 0.00
Sat 07/11 04Z 0.15 3412  74  37  11 0.00
Sat 07/11 05Z 0.09 3512  74  22  10 0.00
Sat 07/11 06Z 0.09 0011  72  16  10 0.00
Sat 07/11 07Z 0.09 0010  71  29  10 0.00
Sat 07/11 08Z 0.08 0009  69  24  10 0.00
Sat 07/11 09Z 0.10 0008  66  21   9 0.00
Sat 07/11 10Z 0.11 0008  64  19   9 0.00
Sat 07/11 11Z 0.10 3508  63  18   9 0.00
Sat 07/11 12Z 0.12 3507  62  20   9 0.00
Sat 07/11 13Z 0.16 3507  62  22   9 0.00
Sat 07/11 14Z 0.34 3406  63  22   9 0.00
Sat 07/11 15Z 0.77 3406  64  20   9 0.00
Sat 07/11 16Z 1.01 3306  65  19   9 0.00
Sat 07/11 17Z 1.32 3307  66  20  10 0.00
Sat 07/11 18Z 1.51 3308  65  20  10 0.00
Sat 07/11 19Z 1.26 3409  66  20  10 0.00
Sat 07/11 20Z 0.99 3410  67  22  10 0.00
Sat 07/11 21Z 0.74 3410  70  24  10 0.00
Sat 07/11 22Z 0.44 3511  73  27  10 0.00
Sat 07/11 23Z 0.19 3511  75  29  10 0.00
Sun 07/12 00Z 0.11 0012  76  30  10 0.00
Sun 07/12 01Z 0.12 0014  76  31   9 0.00
Sun 07/12 02Z 0.15 0015  75  31   9 0.00
Sun 07/12 03Z 0.19 0116  75  30   9 0.00
Sun 07/12 04Z 0.32 0116  74  26   9 0.00
Sun 07/12 05Z 0.35 0216  76  23   9 0.00
Sun 07/12 06Z 0.34 0214  77  22   9 0.00
Sun 07/12 07Z 0.32 0213  76  21   9 0.00
Sun 07/12 08Z 0.25 0211  74  19   9 0.00
Sun 07/12 09Z 0.20 0209  74  17   9 0.00
Sun 07/12 10Z 0.12 0208  74  15   9 0.00
Sun 07/12 11Z 0.10 0107  73  12   9 0.00
Sun 07/12 12Z 0.09 0008  73  11   9 0.00
Sun 07/12 13Z 0.07 0007  76  11   9 0.00
Sun 07/12 14Z 0.13 3506  78   9   9 0.00
Sun 07/12 15Z 0.16 3505  79   8   9 0.00
Sun 07/12 16Z 0.30 3403  81   7   9 0.00
Sun 07/12 17Z 0.42 3203  81   6  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