NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260510_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)
=== ===== === ==== ==== === === === ====
Sun 05/10 18Z 5.50 2411  85  22   3 0.00
Sun 05/10 19Z 5.92 2513  81  26   3 0.00
Sun 05/10 20Z 5.56 2514  77  43   3 0.00
Sun 05/10 21Z 5.05 2515  74  48   3 0.01
Sun 05/10 23Z 4.17 2719  63  40   3 0.00
Mon 05/11 00Z 2.22 2821  64  24   2 0.00
Mon 05/11 01Z 1.64 2823  63  24   1 0.00
Mon 05/11 02Z 1.54 2922  64  28   0 0.00
Mon 05/11 03Z 1.21 2922  71  28  -1 0.00
Mon 05/11 04Z 0.96 3021  75  23  -1 0.00
Mon 05/11 05Z 0.85 3019  77  24  -1 0.00
Mon 05/11 06Z 0.69 3117  80  25  -2 0.00
Mon 05/11 07Z 0.62 3115  79  25  -2 0.00
Mon 05/11 08Z 0.57 3115  80  24  -2 0.00
Mon 05/11 09Z 0.54 3115  80  22  -2 0.00
Mon 05/11 10Z 0.52 3115  79  18  -2 0.00
Mon 05/11 11Z 0.50 3114  76  22  -2 0.00
Mon 05/11 12Z 0.54 3014  77  29  -3 0.00
Mon 05/11 13Z 1.17 3012  77  37  -3 0.00
Mon 05/11 14Z 3.42 3011  75  41  -3 0.00
Mon 05/11 15Z 4.43 2909  71  44  -2 0.00
Mon 05/11 16Z 5.09 2909  70  40  -2 0.00
Mon 05/11 17Z 5.33 2909  69  42  -1 0.00
Mon 05/11 18Z 5.31 2808  67  58  -1 0.00
Mon 05/11 19Z 5.30 2809  67  69   0 0.00
Mon 05/11 20Z 4.91 2909  68  73   0 0.00
Mon 05/11 21Z 3.67 3010  70  78   0 0.00
Mon 05/11 22Z 2.24 3011  69  68  -1 0.00
Mon 05/11 23Z 1.14 3111  69  63  -1 0.00
Tue 05/12 00Z 0.65 3212  72  63  -1 0.00
Tue 05/12 01Z 0.51 3213  76  65  -1 0.00
Tue 05/12 02Z 0.35 3313  75  63  -2 0.00
Tue 05/12 03Z 0.40 3314  77  62  -2 0.00
Tue 05/12 04Z 0.42 3316  75  62  -2 0.00
Tue 05/12 05Z 0.36 3417  72  60  -2 0.00
Tue 05/12 06Z 0.23 3417  70  56  -2 0.00
Tue 05/12 07Z 0.17 3417  67  47  -3 0.00
Tue 05/12 08Z 0.17 3416  66  40  -3 0.00
Tue 05/12 09Z 0.20 3415  66  33  -3 0.00
Tue 05/12 10Z 0.22 3414  66  34  -3 0.00
Tue 05/12 11Z 0.22 3413  68  43  -4 0.00
Tue 05/12 12Z 0.40 3312  70  51  -4 0.00
Tue 05/12 13Z 1.42 3310  72  49  -4 0.00
Tue 05/12 14Z 2.53 3210  72  40  -4 0.00
Tue 05/12 15Z 3.67 3210  71  29  -4 0.00
Tue 05/12 16Z 4.50 3111  68  28  -3 0.00
Tue 05/12 17Z 4.81 3111  67  33  -3 0.00
Tue 05/12 18Z 5.24 3111  67  38  -3 0.00
Tue 05/12 19Z 4.45 3110  66  42  -2 0.00
Tue 05/12 20Z 4.59 3110  67  46  -2 0.00
Tue 05/12 21Z 4.27 3110  68  46  -1 0.00
Tue 05/12 22Z 3.03 3110  68  41  -1 0.00
Tue 05/12 23Z 0.83 3208  68  31  -1 0.00
Wed 05/13 00Z 0.36 3208  67  26  -1 0.00
Wed 05/13 01Z 0.39 3108  67  25  -1 0.00
Wed 05/13 02Z 0.23 3206  66  22  -1 0.00
Wed 05/13 03Z 0.16 3104  66  23  -1 0.00
Wed 05/13 04Z 0.15 2803  66  24  -1 0.00
Wed 05/13 05Z 0.17 2503  66  28  -1 0.00

Run total areal avg QPF for the greens is: 0.01 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