NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260530_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)
=== ===== === ==== ==== === === === ====
Sat 05/30 00Z 0.61 2614  83  97   5 0.00
Sat 05/30 01Z 0.49 2711  88  96   5 0.13
Sat 05/30 02Z 0.40 2911  94  97   4 0.14
Sat 05/30 03Z 0.29 3215  91  87   3 0.12
Sat 05/30 04Z 0.32 3215  96  67   2 0.02
Sat 05/30 05Z 0.41 3313  97  74   2 0.03
Sat 05/30 06Z 0.48 0012  96  81   1 0.05
Sat 05/30 07Z 0.48 0318  97  91   0 0.08
Sat 05/30 08Z 0.70 0424  97  94   0 0.10
Sat 05/30 09Z 0.85 0530  98  94  -1 0.12
Sat 05/30 10Z 0.92 0533  98  92  -1 0.12
Sat 05/30 11Z 0.76 0433  97  90  -1 0.10
Sat 05/30 12Z 0.69 0431  96  78  -1 0.07
Sat 05/30 13Z 0.54 0327  94  72  -1 0.05
Sat 05/30 14Z 0.44 0424  92  70  -1 0.05
Sat 05/30 15Z 0.39 0322  86  64   0 0.04
Sat 05/30 16Z 0.52 0320  84  54   0 0.02
Sat 05/30 17Z 1.40 0218  82  50   0 0.00
Sat 05/30 18Z 1.78 0117  78  42   0 0.00
Sat 05/30 19Z 2.27 0117  75  32   0 0.00
Sat 05/30 20Z 2.96 0117  72  35   1 0.00
Sat 05/30 21Z 2.75 0116  70  43   1 0.00
Sat 05/30 22Z 1.61 0116  71  55   1 0.00
Sat 05/30 23Z 0.60 0116  70  58   1 0.00
Sun 05/31 00Z 0.36 0118  68  54   2 0.00
Sun 05/31 01Z 0.46 0220  65  44   2 0.00
Sun 05/31 02Z 0.49 0222  60  35   2 0.00
Sun 05/31 03Z 0.45 0221  57  21   2 0.00
Sun 05/31 04Z 0.38 0219  56  15   2 0.00
Sun 05/31 05Z 0.24 0117  55  14   2 0.00
Sun 05/31 06Z 0.14 0016  59  13   3 0.00
Sun 05/31 07Z 0.14 0015  61  15   3 0.00
Sun 05/31 08Z 0.11 3514  61  17   3 0.00
Sun 05/31 09Z 0.16 3414  63  23   3 0.00
Sun 05/31 10Z 0.25 3314  68  29   3 0.00
Sun 05/31 11Z 0.29 3314  66  38   4 0.00
Sun 05/31 12Z 0.32 3214  64  38   4 0.00
Sun 05/31 13Z 0.42 3113  64  45   4 0.00
Sun 05/31 14Z 0.61 3114  62  53   5 0.00
Sun 05/31 15Z 1.10 3114  60  69   5 0.00
Sun 05/31 16Z 1.59 3114  60  77   5 0.00
Sun 05/31 17Z 2.55 3113  61  79   5 0.00
Sun 05/31 18Z 3.00 3014  65  70   5 0.00
Sun 05/31 19Z 2.27 2913  73  66   5 0.00
Sun 05/31 20Z 1.49 2915  82  89   4 0.02
Sun 05/31 21Z 0.73 3017  75  84   4 0.02
Sun 05/31 22Z 1.03 2918  70  86   4 0.00
Sun 05/31 23Z 0.92 2815  78  92   4 0.01
Mon 06/01 00Z 0.70 2917  74  88   4 0.05
Mon 06/01 01Z 0.66 3016  74  70   5 0.00
Mon 06/01 02Z 0.57 2914  82  63   4 0.00
Mon 06/01 03Z 0.41 3012  84  62   4 0.00
Mon 06/01 04Z 0.28 3109  83  62   4 0.00
Mon 06/01 05Z 0.26 2907  88  58   4 0.02
Mon 06/01 06Z 0.22 2706  90  70   4 0.02
Mon 06/01 07Z 0.16 2804  90  86   4 0.03
Mon 06/01 08Z 0.13 3003  91  89   4 0.03
Mon 06/01 09Z 0.11 3403  93  89   3 0.03
Mon 06/01 10Z 0.13 0105  94  83   3 0.04
Mon 06/01 11Z 0.16 0306  95  78   2 0.05

Run total areal avg QPF for the greens is: 1.56 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