NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260406_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)
=== ===== === ==== ==== === === === ====
Mon 04/06 00Z 1.15 2624  87  16  -3 0.00
Mon 04/06 01Z 2.21 2630  85  19  -4 0.00
Mon 04/06 02Z 2.69 2733  87  30  -5 0.00
Mon 04/06 03Z 2.14 2732  88  38  -6 0.00
Mon 04/06 04Z 2.25 2732  91  46  -7 0.00
Mon 04/06 05Z 1.89 2732  89  48  -7 0.00
Mon 04/06 06Z 1.59 2832  91  57  -8 0.00
Mon 04/06 07Z 1.37 2832  94  68  -8 0.01
Mon 04/06 08Z 1.29 2832  95  70  -8 0.01
Mon 04/06 09Z 1.42 2931  96  71  -9 0.01
Mon 04/06 10Z 1.76 2931  97  71  -9 0.01
Mon 04/06 11Z 1.89 2931  97  69 -10 0.01
Mon 04/06 12Z 1.82 2929  97  69 -10 0.01
Mon 04/06 13Z 2.23 2927  95  67 -11 0.01
Mon 04/06 14Z 3.92 2925  93  68 -11 0.01
Mon 04/06 15Z 6.45 2824  92  73 -10 0.00
Mon 04/06 16Z 8.81 2823  86  73 -10 0.00
Mon 04/06 17Z 13.14 2822  78  73 -10 0.00
Mon 04/06 18Z 13.99 2821  72  71  -9 0.00
Mon 04/06 19Z 14.16 2820  67  73  -8 0.00
Mon 04/06 20Z 13.97 2820  66  77  -8 0.00
Mon 04/06 21Z 13.77 2821  66  79  -8 0.00
Mon 04/06 22Z 12.33 2821  67  79  -8 0.00
Mon 04/06 23Z 8.59 2822  71  77  -9 0.00
Tue 04/07 00Z 4.16 2922  73  74  -9 0.00
Tue 04/07 01Z 2.62 2922  75  75  -9 0.00
Tue 04/07 02Z 1.88 3020  75  78 -10 0.00
Tue 04/07 03Z 1.16 3018  79  79 -10 0.00
Tue 04/07 04Z 0.90 3016  81  79 -10 0.00
Tue 04/07 05Z 0.61 3014  81  72 -10 0.00
Tue 04/07 06Z 0.47 3012  79  45 -10 0.00
Tue 04/07 07Z 0.46 2911  79  30 -11 0.00
Tue 04/07 08Z 0.42 3011  78  30 -11 0.00
Tue 04/07 09Z 0.41 3011  78  33 -11 0.00
Tue 04/07 10Z 0.35 3010  78  35 -11 0.00
Tue 04/07 11Z 0.33 3010  78  41 -11 0.00
Tue 04/07 12Z 0.36 3010  79  48 -12 0.00
Tue 04/07 13Z 0.54 3008  79  58 -12 0.00
Tue 04/07 14Z 1.03 3007  76  67 -12 0.00
Tue 04/07 15Z 1.31 3006  72  66 -11 0.00
Tue 04/07 16Z 1.74 3007  69  75 -11 0.00
Tue 04/07 17Z 2.06 3008  66  79 -11 0.00
Tue 04/07 18Z 2.17 3109  63  74 -11 0.00
Tue 04/07 19Z 2.66 3009  62  65 -10 0.00
Tue 04/07 20Z 3.19 3010  64  57 -11 0.00
Tue 04/07 21Z 2.78 3011  66  48 -11 0.00
Tue 04/07 22Z 1.79 3112  67  30 -11 0.00
Tue 04/07 23Z 0.82 3113  64  22 -11 0.00
Wed 04/08 00Z 0.62 3015  60  26 -11 0.00
Wed 04/08 01Z 0.63 3016  56  30 -12 0.00
Wed 04/08 02Z 0.71 3017  52  34 -12 0.00
Wed 04/08 03Z 0.74 3018  45  38 -13 0.00
Wed 04/08 04Z 0.72 3019  39  35 -13 0.00
Wed 04/08 05Z 0.64 3019  36  27 -13 0.00
Wed 04/08 06Z 0.63 3019  41  24 -13 0.00
Wed 04/08 07Z 0.61 3019  45  22 -13 0.00
Wed 04/08 08Z 0.55 3018  47  19 -12 0.00
Wed 04/08 09Z 0.47 3016  48  17 -12 0.00
Wed 04/08 10Z 0.40 3014  48  15 -11 0.00
Wed 04/08 11Z 0.34 2913  46  15 -11 0.00

Run total areal avg QPF for the greens is: 0.08 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