Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260210_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)
=== ===== === ==== ==== === === === ====
Tue 02/10 12Z 0.10 3005  60  79  -6 0.00
Tue 02/10 13Z 0.11 2805  62  71  -6 0.00
Tue 02/10 14Z 0.12 2805  63  65  -6 0.00
Tue 02/10 15Z 0.11 2605  62  65  -6 0.00
Tue 02/10 16Z 0.09 2205  59  60  -6 0.00
Tue 02/10 17Z 0.08 2007  55  57  -5 0.00
Tue 02/10 20Z 0.16 2015  43  93  -5 0.00
Tue 02/10 21Z 0.09 1818  64  93  -6 0.00
Tue 02/10 22Z 0.05 1820  91  94  -5 0.00
Tue 02/10 23Z 0.02 1823  95  95  -3 0.00
Wed 02/11 00Z 0.09 1826  95  94  -3 0.01
Wed 02/11 02Z 0.29 2125  95  96  -5 0.06
Wed 02/11 03Z 0.34 2224  96  97  -5 0.07
Wed 02/11 04Z 0.36 2321  97  96  -4 0.08
Wed 02/11 05Z 0.37 2419  97  95  -5 0.09
Wed 02/11 06Z 0.41 2517  98  73  -5 0.07
Wed 02/11 07Z 0.41 2616  98  46  -6 0.05
Wed 02/11 08Z 0.43 2615  97  34  -6 0.04
Wed 02/11 09Z 0.47 2716  97  42  -7 0.03
Wed 02/11 10Z 0.49 2717  97  53  -7 0.02
Wed 02/11 11Z 0.53 2818  97  59  -8 0.02
Wed 02/11 12Z 0.53 2818  97  61  -8 0.02
Wed 02/11 13Z 0.52 2919  96  66  -9 0.01
Wed 02/11 14Z 0.55 2919  96  74  -9 0.01
Wed 02/11 15Z 0.60 2918  96  80  -9 0.01
Wed 02/11 16Z 0.66 2917  95  84 -10 0.01
Wed 02/11 17Z 0.86 2917  95  87 -10 0.01
Wed 02/11 18Z 1.02 2916  95  87  -9 0.01
Wed 02/11 19Z 1.15 2916  96  86  -9 0.01
Wed 02/11 20Z 1.02 2917  96  85 -10 0.01
Wed 02/11 21Z 0.86 3019  95  84 -10 0.01
Wed 02/11 22Z 0.89 3020  96  84 -10 0.02
Wed 02/11 23Z 0.83 3121  96  82 -11 0.02
Thu 02/12 00Z 0.72 3222  96  82 -11 0.02
Thu 02/12 01Z 0.64 3222  97  83 -12 0.02
Thu 02/12 02Z 0.66 3221  97  84 -12 0.02
Thu 02/12 03Z 0.53 3221  97  85 -12 0.01
Thu 02/12 04Z 0.43 3221  96  83 -12 0.01
Thu 02/12 05Z 0.39 3321  95  83 -12 0.01
Thu 02/12 06Z 0.37 3321  95  81 -12 0.01
Thu 02/12 07Z 0.35 3323  95  79 -12 0.01
Thu 02/12 08Z 0.32 3323  95  80 -12 0.01
Thu 02/12 09Z 0.26 3324  95  80 -12 0.01
Thu 02/12 10Z 0.22 3425  94  78 -12 0.01
Thu 02/12 11Z 0.19 3425  94  75 -12 0.01
Thu 02/12 12Z 0.19 3425  94  74 -12 0.01
Thu 02/12 13Z 0.23 3425  94  73 -12 0.01
Thu 02/12 14Z 0.25 3325  94  72 -13 0.01
Thu 02/12 15Z 0.27 3324  94  71 -12 0.01
Thu 02/12 16Z 0.29 3325  94  70 -12 0.01
Thu 02/12 18Z 0.29 3325  94  63 -12 0.01
Thu 02/12 19Z 0.33 3325  92  48 -12 0.01
Thu 02/12 20Z 0.36 3326  85  29 -12 0.00
Thu 02/12 21Z 0.35 3327  73  19 -11 0.00
Thu 02/12 22Z 0.28 3329  69  13 -11 0.00
Thu 02/12 23Z 0.25 3330  72  16 -11 0.00

Run total areal avg QPF for the greens is: 0.91 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