Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260624_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)
=== ===== === ==== ==== === === === ====
Wed 06/24 06Z 0.33 3315  80  57   9 0.00
Wed 06/24 07Z 0.35 3215  81  45   9 0.00
Wed 06/24 08Z 0.41 3217  85  41   9 0.00
Wed 06/24 09Z 0.43 3219  86  41   9 0.00
Wed 06/24 10Z 0.41 3218  85  38   9 0.00
Wed 06/24 11Z 0.43 3119  86  38   8 0.00
Wed 06/24 12Z 0.45 3119  88  37   8 0.00
Wed 06/24 13Z 0.51 3120  90  41   8 0.00
Wed 06/24 14Z 0.59 3119  90  47   7 0.00
Wed 06/24 15Z 0.78 3018  90  48   7 0.00
Wed 06/24 16Z 1.69 2918  92  47   7 0.00
Wed 06/24 17Z 1.61 2918  91  50   8 0.00
Wed 06/24 18Z 3.04 2916  88  49   8 0.00
Wed 06/24 19Z 6.54 2917  85  48   9 0.00
Wed 06/24 20Z 7.23 2917  82  50   9 0.00
Wed 06/24 21Z 6.87 2920  79  52   9 0.00
Wed 06/24 22Z 4.17 2920  77  49   9 0.00
Wed 06/24 23Z 3.09 2921  75  48   9 0.00
Thu 06/25 00Z 2.57 2921  75  45   9 0.00
Thu 06/25 01Z 1.89 2922  79  44   9 0.00
Thu 06/25 02Z 1.27 2921  81  40   9 0.00
Thu 06/25 03Z 1.09 2921  80  37   9 0.00
Thu 06/25 04Z 0.93 3022  78  35   9 0.00
Thu 06/25 05Z 0.80 3020  75  30   9 0.00
Thu 06/25 06Z 0.69 3019  74  27   9 0.00
Thu 06/25 07Z 0.59 3116  73  17   9 0.00
Thu 06/25 08Z 0.55 3014  72  11   9 0.00
Thu 06/25 09Z 0.50 3012  72  12   9 0.00
Thu 06/25 10Z 0.46 2910  71  19   9 0.00
Thu 06/25 11Z 0.40 2808  71  19   9 0.00
Thu 06/25 12Z 0.36 2707  72  20   9 0.00
Thu 06/25 13Z 0.35 2606  73  27   9 0.00
Thu 06/25 14Z 0.52 2506  75  27   9 0.00
Thu 06/25 15Z 1.25 2406  76  23   9 0.00
Thu 06/25 16Z 1.75 2405  75  27   9 0.00
Thu 06/25 17Z 1.59 2306  74  35  10 0.00
Thu 06/25 18Z 1.84 2208  73  46  10 0.00
Thu 06/25 19Z 1.66 2209  71  52  10 0.00
Thu 06/25 20Z 0.69 2210  68  57  10 0.00
Thu 06/25 21Z 0.50 2210  64  55  10 0.00
Thu 06/25 22Z 0.28 2109  59  63  11 0.00
Thu 06/25 23Z 0.27 2009  57  79  11 0.00
Fri 06/26 00Z 0.22 1910  62  92  10 0.00
Fri 06/26 01Z 0.12 1712  68  95  10 0.00
Fri 06/26 02Z 0.11 1715  75  99  10 0.01
Fri 06/26 03Z 0.13 1618  86  98  10 0.04
Fri 06/26 04Z 0.15 1722  91  96  10 0.14
Fri 06/26 05Z 0.26 1924  95  92  11 0.13
Fri 06/26 06Z 0.30 1926  97  94  11 0.12
Fri 06/26 07Z 0.52 2130  97  89  11 0.18
Fri 06/26 08Z 0.57 2227  93  85  11 0.06
Fri 06/26 09Z 0.64 2326  95  78  11 0.05
Fri 06/26 10Z 0.58 2323  96  51  11 0.02
Fri 06/26 11Z 0.56 2421  93  39  11 0.01
Fri 06/26 12Z 0.55 2420  92  35  11 0.01
Fri 06/26 13Z 0.53 2518  91  36  11 0.01
Fri 06/26 14Z 0.53 2517  91  46  11 0.01
Fri 06/26 15Z 0.52 2415  90  56  11 0.00
Fri 06/26 16Z 0.55 2414  88  64  11 0.00
Fri 06/26 17Z 0.65 2314  89  57  11 0.00

Run total areal avg QPF for the greens is: 0.79 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