NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260520_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)
=== ===== === ==== ==== === === === ====
Wed 05/20 06Z 1.18 2532  78  83  16 0.00
Wed 05/20 07Z 1.42 2637  83  74  16 0.00
Wed 05/20 08Z 1.36 2637  89  66  15 0.00
Wed 05/20 09Z 1.20 2634  92  54  14 0.00
Wed 05/20 10Z 1.05 2731  95  75  14 0.01
Wed 05/20 11Z 0.94 2728  95  70  14 0.02
Wed 05/20 12Z 0.91 2726  95  77  14 0.01
Wed 05/20 13Z 1.03 2727  97  86  13 0.01
Wed 05/20 14Z 1.02 2726  97  82  13 0.05
Wed 05/20 15Z 1.11 2725  96  78  12 0.04
Wed 05/20 16Z 1.30 2724  95  79  12 0.04
Wed 05/20 17Z 1.81 2724  91  62  11 0.04
Wed 05/20 18Z 2.22 2823  92  55  11 0.01
Wed 05/20 19Z 3.98 2823  84  48  10 0.01
Wed 05/20 20Z 5.86 2922  82  40   9 0.01
Wed 05/20 21Z 4.81 2922  82  33   9 0.00
Wed 05/20 22Z 2.14 3022  84  25   8 0.00
Wed 05/20 23Z 0.82 3122  85  18   7 0.00
Thu 05/21 00Z 0.66 3124  80  16   6 0.00
Thu 05/21 01Z 0.56 3124  74  13   5 0.00
Thu 05/21 02Z 0.48 3223  72   8   4 0.00
Thu 05/21 03Z 0.43 3223  68   7   4 0.00
Thu 05/21 04Z 0.40 3224  67   6   3 0.00
Thu 05/21 05Z 0.34 3225  64   5   2 0.00
Thu 05/21 06Z 0.32 3226  60   5   2 0.00
Thu 05/21 07Z 0.28 3327  59   4   1 0.00
Thu 05/21 08Z 0.24 3326  58   4   1 0.00
Thu 05/21 09Z 0.19 3325  55   3   0 0.00
Thu 05/21 10Z 0.17 3324  53   3   0 0.00
Thu 05/21 11Z 0.16 3323  52   3   0 0.00
Thu 05/21 12Z 0.14 3321  52   3   0 0.00
Thu 05/21 13Z 0.14 3319  49   4   0 0.00
Thu 05/21 14Z 0.14 3317  47   4   0 0.00
Thu 05/21 15Z 0.16 3317  47   4   0 0.00
Thu 05/21 16Z 0.19 3316  47   4   0 0.00
Thu 05/21 17Z 0.23 3316  46   4   0 0.00
Thu 05/21 18Z 0.34 3316  44   4   0 0.00
Thu 05/21 19Z 0.40 3317  43   3   0 0.00
Thu 05/21 20Z 0.35 3318  43   4   0 0.00
Thu 05/21 21Z 0.33 3317  44   3   0 0.00
Thu 05/21 22Z 0.26 3318  42   3   0 0.00
Thu 05/21 23Z 0.25 3319  40   4   1 0.00
Fri 05/22 00Z 0.21 3420  37   3   1 0.00
Fri 05/22 01Z 0.16 3419  34   3   1 0.00
Fri 05/22 02Z 0.12 3418  32   3   1 0.00
Fri 05/22 03Z 0.10 3516  33   4   1 0.00
Fri 05/22 04Z 0.09 3516  34   5   1 0.00
Fri 05/22 05Z 0.09 3516  35   6   1 0.00
Fri 05/22 06Z 0.08 0016  36   6   1 0.00
Fri 05/22 07Z 0.10 0016  36   5   1 0.00
Fri 05/22 08Z 0.13 0115  37   4   1 0.00
Fri 05/22 09Z 0.17 0214  37   5   1 0.00
Fri 05/22 10Z 0.19 0212  38   6   1 0.00
Fri 05/22 11Z 0.19 0311  40   7   1 0.00
Fri 05/22 12Z 0.20 0309  42   7   1 0.00
Fri 05/22 13Z 0.21 0306  46   8   1 0.00
Fri 05/22 14Z 0.29 0204  49  10   1 0.00
Fri 05/22 15Z 0.46 3503  52   9   1 0.00
Fri 05/22 16Z 0.80 3502  53  10   1 0.00
Fri 05/22 17Z 0.71 3302  53  13   2 0.00

Run total areal avg QPF for the greens is: 0.25 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