Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260623_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)
=== ===== === ==== ==== === === === ====
Tue 06/23 06Z 0.13 1512  98  98  10 0.00
Tue 06/23 07Z 0.11 1509  98  98  10 0.02
Tue 06/23 08Z 0.06 1706  99  98  10 0.03
Tue 06/23 09Z 0.05 2003  99  95   9 0.02
Tue 06/23 10Z 0.08 2802  99  84   9 0.01
Tue 06/23 11Z 0.06 3204  99  74   9 0.01
Tue 06/23 12Z 0.07 3306  98  61   9 0.00
Tue 06/23 13Z 0.08 3409  96  41   9 0.00
Tue 06/23 14Z 0.07 3411  95  30   9 0.00
Tue 06/23 15Z 0.09 3412  94  24   9 0.00
Tue 06/23 16Z 0.10 3412  91  19   9 0.00
Tue 06/23 17Z 0.11 3412  89  12   9 0.00
Tue 06/23 18Z 0.15 3411  88   7  10 0.00
Tue 06/23 19Z 0.19 3410  87   5  10 0.00
Tue 06/23 20Z 0.27 3410  86   5  10 0.00
Tue 06/23 21Z 0.38 3310  83   6  10 0.00
Tue 06/23 22Z 0.47 3211  83  11  10 0.00
Tue 06/23 23Z 0.45 3214  86  17  10 0.01
Wed 06/24 00Z 0.43 3217  87  19  10 0.01
Wed 06/24 01Z 0.41 3319  87  22   9 0.01
Wed 06/24 02Z 0.40 3320  87  22   9 0.00
Wed 06/24 03Z 0.34 3321  88  23   9 0.00
Wed 06/24 04Z 0.38 3322  87  24   9 0.00
Wed 06/24 05Z 0.38 3322  90  26   8 0.00
Wed 06/24 06Z 0.34 3422  90  25   8 0.00
Wed 06/24 07Z 0.29 3421  90  26   7 0.00
Wed 06/24 08Z 0.26 3319  89  22   7 0.00
Wed 06/24 09Z 0.30 3318  89  20   7 0.00
Wed 06/24 10Z 0.34 3218  89  25   7 0.00
Wed 06/24 11Z 0.40 3118  88  33   7 0.00
Wed 06/24 12Z 0.48 3018  88  40   7 0.00
Wed 06/24 13Z 0.53 3018  90  40   7 0.00
Wed 06/24 14Z 0.61 3020  89  39   6 0.00
Wed 06/24 15Z 0.78 3021  90  35   6 0.00
Wed 06/24 16Z 1.12 2921  91  39   6 0.00
Wed 06/24 17Z 2.43 2920  89  43   7 0.00
Wed 06/24 18Z 6.82 2920  87  38   7 0.00
Wed 06/24 19Z 7.55 2920  85  30   8 0.00
Wed 06/24 20Z 5.89 2919  84  26   9 0.00
Wed 06/24 21Z 4.93 2919  82  26   9 0.00
Wed 06/24 22Z 4.89 2919  80  27   9 0.00
Wed 06/24 23Z 3.30 2920  81  26  10 0.00
Thu 06/25 00Z 2.62 2921  79  23   9 0.00
Thu 06/25 01Z 2.71 3021  77  20   9 0.00
Thu 06/25 02Z 1.94 3020  78  19   9 0.00
Thu 06/25 03Z 1.27 2920  80  20   9 0.00
Thu 06/25 04Z 0.90 3018  81  23   9 0.00
Thu 06/25 05Z 0.71 3017  79  27   9 0.00
Thu 06/25 06Z 0.64 3115  79  26   9 0.00
Thu 06/25 07Z 0.64 3114  78  26   9 0.00
Thu 06/25 08Z 0.69 3113  78  22   9 0.00
Thu 06/25 09Z 0.52 3111  78  13   9 0.00
Thu 06/25 10Z 0.43 3008  77  12   9 0.00
Thu 06/25 11Z 0.37 2906  76  12   9 0.00
Thu 06/25 12Z 0.31 2804  75  13   9 0.00
Thu 06/25 13Z 0.34 2504  75  12   9 0.00
Thu 06/25 14Z 0.78 2304  77  13   9 0.00
Thu 06/25 15Z 1.05 2204  77  12   9 0.00
Thu 06/25 16Z 1.18 2105  77  11   9 0.00
Thu 06/25 17Z 0.82 2005  77  13  10 0.00

Run total areal avg QPF for the greens is: 0.12 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