Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260210_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)
=== ===== === ==== ==== === === === ====
Tue 02/10 00Z 0.26 3121  55  63 -10 0.00
Tue 02/10 01Z 0.25 3222  58  64  -9 0.00
Tue 02/10 02Z 0.21 3221  59  68  -9 0.00
Tue 02/10 03Z 0.17 3319  58  69  -8 0.00
Tue 02/10 04Z 0.14 3317  59  75  -8 0.00
Tue 02/10 05Z 0.14 3317  61  80  -8 0.00
Tue 02/10 08Z 0.17 3114  79  88  -8 0.00
Tue 02/10 09Z 0.17 3113  83  88  -8 0.00
Tue 02/10 10Z 0.16 3112  83  86  -7 0.00
Tue 02/10 11Z 0.15 3110  79  84  -7 0.00
Tue 02/10 12Z 0.16 3009  74  82  -7 0.00
Tue 02/10 13Z 0.13 2907  64  74  -7 0.00
Tue 02/10 14Z 0.13 2706  53  64  -6 0.00
Tue 02/10 15Z 0.13 2506  47  60  -6 0.00
Tue 02/10 16Z 0.12 2306  43  53  -6 0.00
Tue 02/10 17Z 0.10 2107  40  50  -6 0.00
Tue 02/10 18Z 0.12 2109  37  65  -5 0.00
Tue 02/10 19Z 0.12 2010  40  86  -5 0.00
Tue 02/10 20Z 0.13 1914  57  93  -6 0.00
Tue 02/10 21Z 0.05 1816  77  93  -5 0.00
Tue 02/10 22Z 0.03 1819  92  93  -4 0.00
Tue 02/10 23Z 0.06 1823  94  93  -4 0.00
Wed 02/11 00Z 0.09 1925  95  95  -4 0.01
Wed 02/11 01Z 0.20 2025  95  96  -5 0.06
Wed 02/11 02Z 0.29 2124  97  96  -5 0.09
Wed 02/11 03Z 0.33 2222  97  98  -5 0.09
Wed 02/11 04Z 0.34 2319  97  96  -5 0.07
Wed 02/11 05Z 0.34 2417  97  88  -5 0.05
Wed 02/11 06Z 0.34 2415  98  43  -5 0.04
Wed 02/11 07Z 0.37 2515  98  23  -6 0.03
Wed 02/11 08Z 0.43 2616  98  19  -6 0.02
Wed 02/11 09Z 0.49 2717  98  34  -7 0.02
Wed 02/11 10Z 0.57 2818  98  42  -8 0.02
Wed 02/11 11Z 0.60 2919  97  52  -9 0.02
Wed 02/11 12Z 0.56 2920  96  65  -9 0.02
Wed 02/11 13Z 0.55 2921  96  76  -9 0.02
Wed 02/11 14Z 0.57 2920  95  82 -10 0.01
Wed 02/11 15Z 0.62 3020  95  83 -10 0.01
Wed 02/11 16Z 0.74 3019  94  83 -11 0.01
Wed 02/11 17Z 1.32 3019  95  84 -11 0.01
Wed 02/11 18Z 2.28 3018  94  86 -11 0.01
Wed 02/11 19Z 2.20 3018  94  87 -11 0.01
Wed 02/11 20Z 1.57 3119  95  88 -11 0.01
Wed 02/11 21Z 1.01 3120  95  87 -12 0.01
Wed 02/11 22Z 0.80 3223  96  85 -12 0.01
Wed 02/11 23Z 0.66 3324  96  84 -13 0.01
Thu 02/12 00Z 0.61 3324  96  83 -12 0.01
Thu 02/12 01Z 0.51 3325  96  81 -12 0.01
Thu 02/12 02Z 0.43 3324  96  81 -12 0.01
Thu 02/12 03Z 0.33 3323  96  82 -12 0.01
Thu 02/12 04Z 0.27 3422  95  81 -12 0.01
Thu 02/12 05Z 0.24 3422  95  80 -12 0.01
Thu 02/12 06Z 0.23 3423  93  77 -12 0.01
Thu 02/12 07Z 0.21 3424  93  76 -12 0.01
Thu 02/12 08Z 0.21 3424  93  75 -12 0.00
Thu 02/12 09Z 0.23 3425  94  74 -12 0.00
Thu 02/12 10Z 0.26 3426  95  75 -13 0.00
Thu 02/12 11Z 0.30 3326  95  75 -13 0.01

Run total areal avg QPF for the greens is: 0.75 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