NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260302_0600
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 03/02 06Z 0.35 3117  68  11 -21 0.00
Mon 03/02 07Z 0.34 3117  66   8 -21 0.00
Mon 03/02 08Z 0.34 3116  65   8 -20 0.00
Mon 03/02 09Z 0.34 3016  65   8 -20 0.00
Mon 03/02 10Z 0.35 3017  62   9 -20 0.00
Mon 03/02 11Z 0.36 3016  59  11 -20 0.00
Mon 03/02 13Z 0.39 3016  61  20 -20 0.00
Mon 03/02 14Z 0.42 2916  65  19 -20 0.00
Mon 03/02 15Z 0.43 2815  67  14 -20 0.00
Mon 03/02 16Z 0.43 2813  67  13 -20 0.00
Mon 03/02 17Z 0.42 2713  62  14 -19 0.00
Mon 03/02 18Z 0.43 2712  57  18 -18 0.00
Mon 03/02 19Z 0.45 2713  55  24 -17 0.00
Mon 03/02 20Z 0.45 2713  56  29 -16 0.00
Mon 03/02 21Z 0.43 2714  55  34 -15 0.00
Mon 03/02 22Z 0.41 2614  53  42 -14 0.00
Mon 03/02 23Z 0.41 2615  50  50 -13 0.00
Tue 03/03 00Z 0.41 2616  46  58 -13 0.00
Tue 03/03 01Z 0.41 2517  42  61 -12 0.00
Tue 03/03 02Z 0.41 2518  37  65 -11 0.00
Tue 03/03 03Z 0.41 2519  31  67 -10 0.00
Tue 03/03 04Z 0.42 2520  26  69  -9 0.00
Tue 03/03 05Z 0.44 2521  23  71  -8 0.00
Tue 03/03 06Z 0.46 2522  24  76  -8 0.00
Tue 03/03 07Z 0.47 2522  22  72  -7 0.00
Tue 03/03 08Z 0.47 2522  22  63  -7 0.00
Tue 03/03 09Z 0.46 2522  23  60  -6 0.00
Tue 03/03 10Z 0.44 2521  23  51  -6 0.00
Tue 03/03 11Z 0.43 2420  24  45  -5 0.00
Tue 03/03 12Z 0.42 2420  25  42  -4 0.00
Tue 03/03 13Z 0.40 2420  28  38  -4 0.00
Tue 03/03 14Z 0.39 2420  34  37  -3 0.00
Tue 03/03 15Z 0.37 2320  39  36  -3 0.00
Tue 03/03 16Z 0.33 2319  46  35  -3 0.00
Tue 03/03 17Z 0.31 2219  53  35  -2 0.00
Tue 03/03 18Z 0.31 2219  61  35  -2 0.00
Tue 03/03 19Z 0.30 2219  71  33  -2 0.00
Tue 03/03 20Z 0.30 2120  83  33  -3 0.00
Tue 03/03 21Z 0.33 2220  91  55  -3 0.00
Tue 03/03 22Z 0.33 2221  94  71  -3 0.01
Tue 03/03 23Z 0.32 2220  95  75  -3 0.02
Wed 03/04 00Z 0.35 2122  97  82  -3 0.02
Wed 03/04 01Z 0.37 2123  98  91  -3 0.03
Wed 03/04 02Z 0.39 2223  98  95  -3 0.03
Wed 03/04 03Z 0.47 2224  98  96  -3 0.05
Wed 03/04 04Z 0.55 2323  98  95  -3 0.05
Wed 03/04 05Z 0.57 2520  98  93  -4 0.05
Wed 03/04 06Z 0.53 2718  98  84  -4 0.04
Wed 03/04 07Z 0.40 2917  97  62  -3 0.02
Wed 03/04 08Z 0.31 3017  93  32  -2 0.01
Wed 03/04 09Z 0.23 3116  77  30   0 0.01
Wed 03/04 10Z 0.21 3116  66  22   0 0.01
Wed 03/04 11Z 0.25 3116  62  22   0 0.00
Wed 03/04 12Z 0.29 3017  60  22   0 0.00
Wed 03/04 14Z 0.35 2916  49   7   0 0.00
Wed 03/04 15Z 0.37 2817  45   2   0 0.00
Wed 03/04 16Z 0.39 2817  44   1   0 0.00
Wed 03/04 17Z 0.44 2718  42   2   0 0.00

Run total areal avg QPF for the greens is: 0.35 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