NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260422_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 04/22 00Z 0.33 2010  57  69  -4 0.00
Wed 04/22 01Z 0.33 2013  52  79  -3 0.00
Wed 04/22 02Z 0.36 2114  48  75  -3 0.00
Wed 04/22 03Z 0.44 2116  45  71  -3 0.00
Wed 04/22 04Z 0.53 2218  43  85  -2 0.00
Wed 04/22 05Z 0.62 2219  42  93  -2 0.00
Wed 04/22 06Z 0.86 2219  53  94  -3 0.00
Wed 04/22 07Z 0.49 2217  56  94  -2 0.00
Wed 04/22 08Z 0.34 2215  65  96  -2 0.00
Wed 04/22 09Z 0.26 2213  77  97  -1 0.00
Wed 04/22 10Z 0.17 2110  82  98  -1 0.00
Wed 04/22 11Z 0.10 2009  86  98  -1 0.00
Wed 04/22 12Z 0.06 1909  89  96  -1 0.00
Wed 04/22 13Z 0.04 1811  92  95  -1 0.00
Wed 04/22 14Z 0.04 1812  94  89  -1 0.00
Wed 04/22 15Z 0.11 1914  96  89  -1 0.01
Wed 04/22 16Z 0.13 1915  96  69  -1 0.01
Wed 04/22 17Z 0.16 2015  96  58  -1 0.00
Wed 04/22 18Z 0.20 2015  96  50  -1 0.00
Wed 04/22 19Z 0.23 2014  97  42  -1 0.00
Wed 04/22 20Z 0.24 2113  97  38   0 0.01
Wed 04/22 21Z 0.22 2212  98  35   0 0.01
Wed 04/22 22Z 0.21 2210  98  33   0 0.01
Wed 04/22 23Z 0.22 2409  97  24   0 0.01
Thu 04/23 00Z 0.24 2609  96  14   0 0.00
Thu 04/23 01Z 0.25 2810  95  11   0 0.00
Thu 04/23 02Z 0.25 2809  94  27   0 0.00
Thu 04/23 03Z 0.27 2810  94  50   0 0.00
Thu 04/23 04Z 0.26 2910  92  67   0 0.00
Thu 04/23 05Z 0.26 2910  89  75   0 0.00
Thu 04/23 06Z 0.31 2811  86  83   0 0.00
Thu 04/23 07Z 0.45 2715  90  88   0 0.00
Thu 04/23 08Z 0.59 2821  92  88   0 0.04
Thu 04/23 09Z 0.66 2923  94  71   0 0.03
Thu 04/23 10Z 0.64 3024  96  71   0 0.04
Thu 04/23 11Z 0.58 3124  97  43  -1 0.03
Thu 04/23 12Z 0.51 3223  96  20  -1 0.02
Thu 04/23 13Z 0.48 3223  96  13  -2 0.01
Thu 04/23 14Z 0.53 3223  97  17  -3 0.01
Thu 04/23 15Z 0.68 3223  94  19  -4 0.01
Thu 04/23 16Z 0.96 3222  90  15  -4 0.00
Thu 04/23 17Z 1.21 3221  85  15  -3 0.00
Thu 04/23 18Z 2.79 3220  77  17  -3 0.00
Thu 04/23 19Z 3.87 3220  67  11  -2 0.00
Thu 04/23 20Z 4.69 3220  63   9  -2 0.00
Thu 04/23 21Z 4.46 3219  62   8  -2 0.00
Thu 04/23 22Z 2.84 3319  61   6  -2 0.00
Thu 04/23 23Z 1.02 3319  61   7  -2 0.00
Fri 04/24 00Z 0.48 3419  63   6  -2 0.00
Fri 04/24 01Z 0.29 3419  65   3  -2 0.00
Fri 04/24 02Z 0.22 3417  66   2  -3 0.00
Fri 04/24 03Z 0.13 3515  67   2  -3 0.00
Fri 04/24 04Z 0.09 3514  69   1  -3 0.00
Fri 04/24 05Z 0.08 3513  72   1  -4 0.00
Fri 04/24 06Z 0.08 3512  74   2  -4 0.00
Fri 04/24 07Z 0.09 3412  74   3  -4 0.00
Fri 04/24 08Z 0.11 3412  74   4  -5 0.00
Fri 04/24 09Z 0.13 3413  74   6  -5 0.00
Fri 04/24 10Z 0.13 3414  74   7  -5 0.00
Fri 04/24 11Z 0.11 3414  74   7  -5 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