NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260829_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)
=== ===== === ==== ==== === === === ====
Sat 08/29 06Z 0.29 3314  83   8   6 0.00
Sat 08/29 07Z 0.26 3314  79   8   6 0.00
Sat 08/29 08Z 0.26 3313  78   6   6 0.00
Sat 08/29 09Z 0.29 3312  77   6   6 0.00
Sat 08/29 10Z 0.33 3211  75   5   6 0.00
Sat 08/29 11Z 0.41 3112  74   4   6 0.00
Sat 08/29 12Z 0.47 3112  76   5   6 0.00
Sat 08/29 13Z 0.47 3011  79   5   6 0.00
Sat 08/29 14Z 0.48 2909  80   5   6 0.00
Sat 08/29 15Z 0.83 2808  80   6   6 0.00
Sat 08/29 16Z 1.15 2706  79   6   7 0.00
Sat 08/29 17Z 1.43 2606  75   6   7 0.00
Sat 08/29 18Z 1.54 2506  72   5   8 0.00
Sat 08/29 19Z 1.84 2407  70   4   8 0.00
Sat 08/29 20Z 2.14 2409  74   3   8 0.00
Sat 08/29 21Z 1.45 2411  81   5   9 0.00
Sat 08/29 22Z 0.61 2313  77   4   9 0.00
Sat 08/29 23Z 0.58 2415  72  12  10 0.00
Sun 08/30 00Z 0.73 2419  73  37  10 0.00
Sun 08/30 01Z 0.89 2523  71  37  10 0.00
Sun 08/30 02Z 1.01 2525  68  46  10 0.00
Sun 08/30 03Z 1.18 2627  74  52  10 0.00
Sun 08/30 04Z 1.22 2630  77  49  11 0.00
Sun 08/30 05Z 1.24 2632  76  55  11 0.00
Sun 08/30 06Z 1.36 2733  77  52  11 0.00
Sun 08/30 07Z 1.31 2731  80  56  11 0.00
Sun 08/30 08Z 1.14 2829  81  53  11 0.01
Sun 08/30 09Z 1.03 2828  81  54  11 0.02
Sun 08/30 10Z 0.95 2826  83  50  11 0.01
Sun 08/30 11Z 0.92 2825  79  43  11 0.01
Sun 08/30 12Z 0.95 2824  81  38  11 0.00
Sun 08/30 13Z 0.97 2724  80  54  11 0.01
Sun 08/30 14Z 0.91 2622  80  52  11 0.00
Sun 08/30 15Z 0.89 2621  77  70  11 0.00
Sun 08/30 16Z 0.97 2523  76  68  12 0.00
Sun 08/30 17Z 1.09 2523  75  67  12 0.00
Sun 08/30 18Z 1.24 2523  77  62  12 0.02
Sun 08/30 19Z 1.38 2522  80  59  12 0.01
Sun 08/30 20Z 1.96 2521  87  62  12 0.00
Sun 08/30 21Z 1.46 2622  87  77  12 0.05
Sun 08/30 22Z 1.07 2621  87  84  12 0.01
Sun 08/30 23Z 0.87 2622  89  88  12 0.06
Mon 08/31 00Z 0.90 2823  92  93  11 0.05
Mon 08/31 01Z 0.80 2921  93  92  11 0.04
Mon 08/31 02Z 0.63 3018  95  97  10 0.03
Mon 08/31 03Z 0.51 3015  91  97  10 0.06
Mon 08/31 04Z 0.34 3114  88  87  10 0.03
Mon 08/31 05Z 0.28 3214  88  73  10 0.01
Mon 08/31 06Z 0.20 3313  87  60  10 0.01
Mon 08/31 07Z 0.12 3413  82  37  10 0.00
Mon 08/31 08Z 0.09 3411  77  14  10 0.00
Mon 08/31 09Z 0.09 3410  73   5  10 0.00
Mon 08/31 10Z 0.11 3310  70   3  10 0.00
Mon 08/31 11Z 0.12 3310  67   3  10 0.00
Mon 08/31 12Z 0.12 3311  65   4  10 0.00
Mon 08/31 13Z 0.11 3310  63   5  10 0.00
Mon 08/31 14Z 0.12 3309  63   7  10 0.00
Mon 08/31 15Z 0.12 3207  64   8  10 0.00
Mon 08/31 16Z 0.10 3206  64  10  11 0.00
Mon 08/31 17Z 0.11 3205  66  11  10 0.00

Run total areal avg QPF for the greens is: 0.44 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