NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260607_1200
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)
=== ===== === ==== ==== === === === ====
Sun 06/07 12Z 0.95 2927  96  81  10 0.00
Sun 06/07 13Z 0.95 2927  97  81  10 0.06
Sun 06/07 14Z 0.91 3024  97  86  10 0.08
Sun 06/07 15Z 0.79 3123  98  91  10 0.09
Sun 06/07 16Z 0.52 3223  98  91  10 0.08
Sun 06/07 17Z 0.30 3424  98  91  10 0.05
Sun 06/07 18Z 0.21 3524  97  91   9 0.02
Sun 06/07 19Z 0.22 3525  94  90   9 0.01
Sun 06/07 20Z 0.32 0024  89  73   9 0.00
Sun 06/07 21Z 0.20 0022  91  42   8 0.00
Sun 06/07 22Z 0.14 0021  86  20   9 0.00
Sun 06/07 23Z 0.18 0122  79   7   9 0.00
Mon 06/08 00Z 0.26 0224  73   2   9 0.00
Mon 06/08 01Z 0.39 0226  70   1   9 0.00
Mon 06/08 02Z 0.55 0329  62   1   9 0.00
Mon 06/08 03Z 0.71 0431  52   1   8 0.00
Mon 06/08 04Z 0.77 0531  47   1   8 0.00
Mon 06/08 05Z 0.80 0629  44   1   8 0.00
Mon 06/08 06Z 0.78 0727  43   2   8 0.00
Mon 06/08 07Z 0.77 0824  43   2   7 0.00
Mon 06/08 08Z 0.76 0822  44   3   7 0.00
Mon 06/08 09Z 0.73 0820  46   4   7 0.00
Mon 06/08 10Z 0.59 0816  48   5   7 0.00
Mon 06/08 11Z 0.48 0712  49   7   7 0.00
Mon 06/08 12Z 0.48 0712  52   9   7 0.00
Mon 06/08 13Z 0.43 0610  55  10   7 0.00
Mon 06/08 14Z 0.54 0608  58  13   7 0.00
Mon 06/08 15Z 0.59 0504  60  14   7 0.00
Mon 06/08 16Z 0.28 0301  63  13   7 0.00
Mon 06/08 17Z 0.70 2602  68  12   8 0.00
Mon 06/08 18Z 0.79 2402  72  11   8 0.00
Mon 06/08 19Z 0.69 2402  72   9   9 0.00
Mon 06/08 20Z 1.21 2604  72   9   9 0.00
Mon 06/08 21Z 0.60 2604  64   8  10 0.00
Mon 06/08 22Z 0.36 2706  53   7  10 0.00
Mon 06/08 23Z 0.26 2607  43   6  11 0.00
Tue 06/09 00Z 0.32 2708  42   5  11 0.00
Tue 06/09 01Z 0.35 2709  45   4  11 0.00
Tue 06/09 02Z 0.36 2709  48   3  11 0.00
Tue 06/09 03Z 0.34 2709  52   3  11 0.00
Tue 06/09 04Z 0.32 2608  53   3  11 0.00
Tue 06/09 05Z 0.34 2609  53   2  11 0.00
Tue 06/09 06Z 0.39 2511  55   2  11 0.00
Tue 06/09 07Z 0.47 2613  60   2  11 0.00
Tue 06/09 08Z 0.49 2714  66   2  11 0.00
Tue 06/09 09Z 0.49 2714  71   1  11 0.00
Tue 06/09 10Z 0.37 2713  65   1  11 0.00
Tue 06/09 11Z 0.32 2712  63   1  11 0.00
Tue 06/09 12Z 0.26 2710  62   1  11 0.00
Tue 06/09 13Z 0.20 2707  63   1  11 0.00
Tue 06/09 14Z 0.20 2607  63   1  11 0.00
Tue 06/09 15Z 0.20 2606  60   1  11 0.00
Tue 06/09 16Z 0.26 2506  57   1  12 0.00
Tue 06/09 17Z 0.37 2507  57   0  12 0.00
Tue 06/09 18Z 0.37 2507  55   1  13 0.00
Tue 06/09 19Z 0.38 2507  55   1  13 0.00
Tue 06/09 20Z 0.41 2507  56   1  13 0.00
Tue 06/09 21Z 0.39 2509  56   1  14 0.00
Tue 06/09 22Z 0.40 2510  58   2  14 0.00
Tue 06/09 23Z 0.39 2511  64   4  14 0.00

Run total areal avg QPF for the greens is: 0.39 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