NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260408_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 04/08 06Z 0.54 3119  79  38 -12 0.00
Wed 04/08 07Z 0.62 3120  74  36 -12 0.00
Wed 04/08 08Z 0.51 3119  69  27 -12 0.00
Wed 04/08 09Z 0.46 3118  64  25 -11 0.00
Wed 04/08 10Z 0.39 3117  59  18 -10 0.00
Wed 04/08 11Z 0.33 3115  57  17 -10 0.00
Wed 04/08 12Z 0.29 3113  57  13  -9 0.00
Wed 04/08 13Z 0.26 3011  56  10  -9 0.00
Wed 04/08 14Z 0.26 2909  54   7  -9 0.00
Wed 04/08 15Z 0.25 2808  50   6  -8 0.00
Wed 04/08 16Z 0.22 2806  44   4  -7 0.00
Wed 04/08 17Z 0.24 2704  39   3  -7 0.00
Wed 04/08 18Z 0.40 2504  36   3  -6 0.00
Wed 04/08 19Z 0.39 2404  33   4  -5 0.00
Wed 04/08 20Z 0.42 2305  31   4  -4 0.00
Wed 04/08 21Z 0.32 2406  29   5  -4 0.00
Wed 04/08 22Z 0.27 2408  28   5  -3 0.00
Wed 04/08 23Z 0.25 2308  28   5  -3 0.00
Thu 04/09 00Z 0.24 2210  27   7  -2 0.00
Thu 04/09 01Z 0.25 2212  24   8  -2 0.00
Thu 04/09 02Z 0.29 2215  22  10  -1 0.00
Thu 04/09 03Z 0.33 2217  21  14  -1 0.00
Thu 04/09 04Z 0.35 2218  21  21   0 0.00
Thu 04/09 05Z 0.34 2219  20  31   0 0.00
Thu 04/09 06Z 0.30 2219  19  39   1 0.00
Thu 04/09 07Z 0.27 2120  19  50   2 0.00
Thu 04/09 08Z 0.27 2121  18  57   2 0.00
Thu 04/09 09Z 0.28 2122  17  59   2 0.00
Thu 04/09 10Z 0.29 2122  15  57   2 0.00
Thu 04/09 11Z 0.30 2122  13  52   3 0.00
Thu 04/09 12Z 0.32 2223  10  51   3 0.00
Thu 04/09 13Z 0.32 2124   9  51   3 0.00
Thu 04/09 14Z 0.29 2124   9  67   3 0.00
Thu 04/09 15Z 0.28 2125  10  61   4 0.00
Thu 04/09 16Z 0.28 2025  12  66   4 0.00
Thu 04/09 17Z 0.29 2026  14  68   4 0.00
Thu 04/09 18Z 0.32 2026  17  51   3 0.00
Thu 04/09 19Z 0.33 1927  19  43   4 0.00
Thu 04/09 20Z 0.33 2027  21  43   4 0.00
Thu 04/09 21Z 0.33 2029  22  49   5 0.00
Thu 04/09 22Z 0.32 2030  22  49   5 0.00
Thu 04/09 23Z 0.32 2031  28  44   6 0.00
Fri 04/10 00Z 0.34 2032  36  46   6 0.00
Fri 04/10 01Z 0.45 2134  45  47   6 0.00
Fri 04/10 02Z 0.50 2233  55  49   6 0.00
Fri 04/10 03Z 0.57 2334  61  49   6 0.00
Fri 04/10 04Z 0.65 2335  64  62   5 0.00
Fri 04/10 05Z 0.73 2435  68  72   4 0.00
Fri 04/10 06Z 0.68 2531  71  66   4 0.00
Fri 04/10 07Z 0.65 2529  73  71   4 0.00
Fri 04/10 08Z 0.62 2526  74  42   3 0.00
Fri 04/10 09Z 0.59 2624  78  41   3 0.00
Fri 04/10 10Z 0.56 2622  82  54   3 0.00
Fri 04/10 11Z 0.51 2620  81  20   3 0.00
Fri 04/10 12Z 0.50 2619  81   9   2 0.00
Fri 04/10 13Z 0.50 2618  81   9   2 0.00
Fri 04/10 14Z 0.52 2619  81  14   2 0.00
Fri 04/10 15Z 0.57 2519  82  35   2 0.00
Fri 04/10 16Z 0.62 2618  80  57   1 0.00
Fri 04/10 17Z 0.63 2616  80  94   1 0.00

Run total areal avg QPF for the greens is: 0.00 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