NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260504_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 05/04 00Z 0.76 2914  61  64   0 0.00
Mon 05/04 01Z 0.91 2818  56  47   0 0.00
Mon 05/04 02Z 1.24 2821  54  46   0 0.00
Mon 05/04 03Z 1.11 2722  55  56   0 0.00
Mon 05/04 04Z 1.03 2723  59  71   0 0.00
Mon 05/04 05Z 1.20 2626  67  80   0 0.00
Mon 05/04 06Z 0.98 2626  79  87   0 0.00
Mon 05/04 07Z 0.91 2627  87  90   0 0.01
Mon 05/04 08Z 0.91 2728  92  87   0 0.01
Mon 05/04 09Z 0.95 2631  91  88   1 0.01
Mon 05/04 10Z 0.92 2631  86  83   1 0.01
Mon 05/04 11Z 0.95 2532  79  83   1 0.01
Mon 05/04 12Z 0.97 2532  72  78   2 0.00
Mon 05/04 13Z 1.08 2531  71  84   2 0.00
Mon 05/04 14Z 1.55 2530  75  88   1 0.00
Mon 05/04 15Z 3.18 2527  75  79   1 0.01
Mon 05/04 16Z 11.70 2424  75  78   2 0.01
Mon 05/04 17Z 11.92 2423  72  77   3 0.00
Mon 05/04 18Z 11.27 2423  71  81   3 0.00
Mon 05/04 19Z 11.31 2423  71  66   4 0.00
Mon 05/04 20Z 8.16 2423  74  39   4 0.00
Mon 05/04 21Z 6.75 2421  73  37   5 0.00
Mon 05/04 22Z 3.39 2422  74  50   5 0.00
Mon 05/04 23Z 1.25 2322  75  58   6 0.00
Tue 05/05 00Z 1.08 2425  77  71   6 0.01
Tue 05/05 01Z 0.96 2324  72  32   7 0.00
Tue 05/05 02Z 1.10 2329  71  15   7 0.00
Tue 05/05 03Z 1.06 2232  71  17   7 0.00
Tue 05/05 04Z 1.10 2236  73  14   7 0.00
Tue 05/05 05Z 1.05 2237  74  11   7 0.00
Tue 05/05 06Z 0.96 2236  73   8   7 0.00
Tue 05/05 07Z 0.93 2237  73  10   7 0.00
Tue 05/05 08Z 0.81 2234  75  15   7 0.00
Tue 05/05 09Z 0.75 2232  78  35   7 0.00
Tue 05/05 10Z 0.71 2231  79  52   8 0.00
Tue 05/05 11Z 0.74 2334  86  61   8 0.00
Tue 05/05 12Z 0.74 2332  88  74   8 0.00
Tue 05/05 13Z 0.83 2333  87  63   8 0.00
Tue 05/05 14Z 0.94 2332  82  64   9 0.00
Tue 05/05 15Z 1.14 2330  80  47   9 0.00
Tue 05/05 16Z 3.85 2229  76  46   9 0.00
Tue 05/05 17Z 6.77 2228  74  65  10 0.00
Tue 05/05 18Z 10.57 2129  73  71  11 0.00
Tue 05/05 19Z 11.30 2130  75  73  11 0.00
Tue 05/05 20Z 8.03 2132  73  72  11 0.00
Tue 05/05 21Z 2.63 2230  78  79  11 0.15
Tue 05/05 22Z 1.86 2332  82  75  11 0.14
Tue 05/05 23Z 0.90 2229  82  77  11 0.02
Wed 05/06 00Z 1.10 2426  87  86   9 0.29
Wed 05/06 01Z 0.73 2724  95  95   8 0.23
Wed 05/06 02Z 0.71 2624  97  95   7 0.08
Wed 05/06 03Z 0.80 2525  88  97   6 0.08
Wed 05/06 04Z 0.57 2521  81  91   6 0.05
Wed 05/06 05Z 0.49 2518  78  93   5 0.03
Wed 05/06 06Z 0.38 2316  83  89   5 0.05
Wed 05/06 07Z 0.34 2317  92  78   5 0.05
Wed 05/06 08Z 0.27 2217  93  86   6 0.03
Wed 05/06 09Z 0.25 2119  91  82   7 0.05
Wed 05/06 10Z 0.29 2120  97  86   7 0.01
Wed 05/06 11Z 0.25 2121  98  86   7 0.03

Run total areal avg QPF for the greens is: 1.37 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