NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260116_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)
=== ===== === ==== ==== === === === ====
Fri 01/16 00Z 0.59 2916  91  16 -13 0.00
Fri 01/16 01Z 1.09 2919  91  28 -14 0.00
Fri 01/16 02Z 1.44 2917  91  41 -15 0.00
Fri 01/16 03Z 2.51 2918  88  51 -16 0.00
Fri 01/16 04Z 2.73 2817  80  59 -16 0.00
Fri 01/16 05Z 2.00 2815  80  60 -17 0.00
Fri 01/16 06Z 1.97 2817  86  56 -18 0.00
Fri 01/16 07Z 2.51 2819  88  50 -19 0.00
Fri 01/16 08Z 5.31 2822  88  42 -20 0.01
Fri 01/16 09Z 4.83 2923  87  37 -21 0.00
Fri 01/16 10Z 2.74 2923  87  34 -21 0.00
Fri 01/16 11Z 0.92 2925  86  40 -20 0.00
Fri 01/16 12Z 0.67 2925  84  48 -20 0.00
Fri 01/16 13Z 0.62 2926  86  43 -19 0.00
Fri 01/16 14Z 0.57 2926  87  66 -18 0.00
Fri 01/16 16Z 0.52 2926  85  21 -15 0.00
Fri 01/16 17Z 0.56 2826  71  10 -14 0.00
Fri 01/16 18Z 0.56 2824  54   9 -13 0.00
Fri 01/16 19Z 0.50 2923  43  16 -12 0.00
Fri 01/16 20Z 0.49 2922  39  17 -12 0.00
Fri 01/16 21Z 0.44 2819  37  16 -12 0.00
Fri 01/16 22Z 0.47 2719  38  16 -12 0.00
Fri 01/16 23Z 0.38 2716  37  32 -11 0.00
Sat 01/17 00Z 0.32 2614  34  56 -10 0.00
Sat 01/17 01Z 0.27 2513  30  73 -10 0.00
Sat 01/17 02Z 0.20 2311  29  74  -9 0.00
Sat 01/17 03Z 0.22 2115  37  80  -9 0.00
Sat 01/17 04Z 0.22 2118  46  90  -9 0.00
Sat 01/17 05Z 0.29 2121  66  89 -10 0.00
Sat 01/17 06Z 0.31 2123  83  89 -10 0.00
Sat 01/17 07Z 0.32 2125  91  86  -9 0.00
Sat 01/17 08Z 0.37 2127  92  88  -9 0.01
Sat 01/17 09Z 0.34 2123  92  90  -9 0.03
Sat 01/17 10Z 0.34 2221  93  78  -9 0.04
Sat 01/17 11Z 0.26 2119  92  63  -9 0.02
Sat 01/17 12Z 0.26 2120  93  65  -8 0.01
Sat 01/17 13Z 0.22 2019  92  81  -7 0.01
Sat 01/17 14Z 0.18 2020  90  86  -7 0.01
Sat 01/17 15Z 0.23 2021  92  90  -6 0.00
Sat 01/17 16Z 0.29 2121  94  89  -7 0.00
Sat 01/17 17Z 0.30 2121  94  88  -7 0.01
Sat 01/17 18Z 0.32 2121  95  88  -7 0.02
Sat 01/17 19Z 0.34 2120  95  87  -7 0.03
Sat 01/17 20Z 0.44 2221  95  90  -7 0.03
Sat 01/17 21Z 0.50 2320  94  89  -7 0.03
Sat 01/17 22Z 0.54 2519  93  81  -7 0.02
Sat 01/17 23Z 0.58 2520  92  61  -7 0.01
Sun 01/18 00Z 0.69 2522  93  58  -8 0.00
Sun 01/18 01Z 0.77 2623  92  65  -8 0.00
Sun 01/18 02Z 0.79 2623  91  62  -8 0.01
Sun 01/18 03Z 0.89 2525  91  61  -8 0.00
Sun 01/18 04Z 0.96 2525  92  59  -9 0.00
Sun 01/18 05Z 0.97 2525  93  55  -9 0.00
Sun 01/18 06Z 0.91 2525  92  48  -9 0.00
Sun 01/18 08Z 0.91 2524  92  40  -9 0.01
Sun 01/18 09Z 0.94 2524  93  39 -10 0.00
Sun 01/18 10Z 0.91 2524  91  35 -10 0.00
Sun 01/18 11Z 0.89 2525  76  30 -11 0.01

Run total areal avg QPF for the greens is: 0.32 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