NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260505_1800
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)
=== ===== === ==== ==== === === === ====
Tue 05/05 18Z 7.29 2125  59  76  12 0.00
Tue 05/05 19Z 10.20 2128  59  80  12 0.00
Tue 05/05 20Z 7.87 2127  64  93  12 0.00
Tue 05/05 21Z 2.94 2329  79  96  10 0.09
Tue 05/05 22Z 1.80 2428  78  96  10 0.16
Tue 05/05 23Z 0.93 2533  84  84   9 0.24
Wed 05/06 00Z 0.87 2428  87  68   9 0.01
Wed 05/06 01Z 0.79 2424  91  91   8 0.01
Wed 05/06 02Z 0.81 2522  97  95   7 0.07
Wed 05/06 03Z 0.74 2620  97  99   6 0.07
Wed 05/06 04Z 0.73 2718  95  98   5 0.09
Wed 05/06 05Z 0.62 2717  94  95   4 0.09
Wed 05/06 06Z 0.52 2617  89  94   4 0.04
Wed 05/06 07Z 0.43 2615  90  78   4 0.02
Wed 05/06 08Z 0.36 2514  91  84   4 0.02
Wed 05/06 09Z 0.28 2412  85  76   5 0.01
Wed 05/06 10Z 0.19 2210  81  84   5 0.00
Wed 05/06 11Z 0.14 2011  84  87   5 0.00
Wed 05/06 12Z 0.11 2011  91  86   5 0.01
Wed 05/06 13Z 0.06 1813  96  89   6 0.05
Wed 05/06 14Z 0.12 1916  98  95   6 0.07
Wed 05/06 15Z 0.12 1916  99  97   6 0.10
Wed 05/06 16Z 0.11 1817  98  98   7 0.11
Wed 05/06 17Z 0.15 1820  99  98   7 0.10
Wed 05/06 18Z 0.23 1919  99  99   7 0.20
Wed 05/06 19Z 0.28 2117  99  99   7 0.22
Wed 05/06 20Z 0.27 2116  99  99   6 0.11
Wed 05/06 21Z 0.19 2111  99  99   6 0.09
Wed 05/06 22Z 0.15 2506  98  98   5 0.09
Wed 05/06 23Z 0.13 3008  95  99   5 0.08
Thu 05/07 00Z 0.12 3208  93  98   4 0.04
Thu 05/07 01Z 0.12 3209  91  97   3 0.02
Thu 05/07 02Z 0.15 3211  90  96   3 0.01
Thu 05/07 03Z 0.14 3210  87  92   2 0.01
Thu 05/07 04Z 0.19 3112  87  94   2 0.00
Thu 05/07 05Z 0.24 3112  89  76   1 0.01
Thu 05/07 06Z 0.29 3014  87  63   0 0.00
Thu 05/07 07Z 0.35 3015  90  36   0 0.00
Thu 05/07 08Z 0.39 3016  91  23   0 0.00
Thu 05/07 09Z 0.50 2917  92  27  -1 0.00
Thu 05/07 10Z 0.59 2919  89  13  -1 0.00
Thu 05/07 11Z 0.63 2820  82  15  -1 0.00
Thu 05/07 12Z 0.55 2817  71  12  -2 0.00
Thu 05/07 13Z 0.55 2816  63  16  -2 0.00
Thu 05/07 14Z 0.59 2814  65  18  -2 0.00
Thu 05/07 15Z 2.22 2814  74  19  -2 0.00
Thu 05/07 16Z 7.88 2813  76  19  -2 0.00
Thu 05/07 17Z 9.76 2814  73  20  -1 0.00
Thu 05/07 18Z 9.67 2814  70  21  -1 0.00
Thu 05/07 19Z 9.99 2814  68  21   0 0.00
Thu 05/07 20Z 9.57 2814  66  20   0 0.00
Thu 05/07 21Z 8.77 2813  64  21   0 0.00
Thu 05/07 22Z 7.86 2813  64  22   0 0.00
Thu 05/07 23Z 4.59 2913  63  24   0 0.00
Fri 05/08 00Z 1.77 2915  65  22   0 0.00
Fri 05/08 01Z 1.84 2916  72  20  -1 0.00
Fri 05/08 02Z 1.37 2917  77  19  -2 0.00
Fri 05/08 03Z 1.16 2917  78  20  -2 0.00
Fri 05/08 04Z 0.99 2918  80  20  -2 0.00
Fri 05/08 05Z 0.81 2917  81  25  -2 0.00

Run total areal avg QPF for the greens is: 2.24 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