Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260614_1800
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)
=== ===== === ==== ==== === === === ====
Sun 06/14 18Z 0.40 2012  81  61  14 0.00
Sun 06/14 19Z 1.30 1914  75  50  14 0.03
Sun 06/14 20Z 1.22 2019  68  53  15 0.00
Sun 06/14 21Z 0.86 2020  65  51  15 0.00
Sun 06/14 22Z 0.30 1919  65  57  16 0.01
Sun 06/14 23Z 0.20 1822  65  59  16 0.00
Mon 06/15 00Z 0.40 2021  80  84  15 0.08
Mon 06/15 01Z 0.50 2022  87  94  14 0.26
Mon 06/15 02Z 0.34 1924  87  86  14 0.15
Mon 06/15 03Z 0.53 2028  90  87  14 0.17
Mon 06/15 04Z 0.51 2129  95  87  13 0.34
Mon 06/15 05Z 0.55 2228  97  87  13 0.18
Mon 06/15 06Z 0.72 2426  97  95  12 0.17
Mon 06/15 07Z 0.64 2720  97  93  11 0.15
Mon 06/15 08Z 0.55 2817  97  97  10 0.05
Mon 06/15 09Z 0.53 3017  96  92   9 0.04
Mon 06/15 10Z 0.65 3021  96  88   9 0.02
Mon 06/15 11Z 0.61 3020  94  55   8 0.02
Mon 06/15 12Z 0.55 3018  89  34   8 0.01
Mon 06/15 13Z 0.56 3017  86  23   8 0.01
Mon 06/15 14Z 0.57 2915  87  19   8 0.01
Mon 06/15 15Z 0.81 2914  89  25   7 0.01
Mon 06/15 16Z 1.44 2914  89  26   7 0.01
Mon 06/15 17Z 1.85 2914  89  26   7 0.01
Mon 06/15 18Z 2.47 2913  90  22   7 0.00
Mon 06/15 19Z 2.55 2914  90  17   7 0.00
Mon 06/15 20Z 2.03 3014  91  15   7 0.00
Mon 06/15 21Z 1.58 3014  91  15   6 0.00
Mon 06/15 22Z 1.41 3015  92  14   6 0.00
Mon 06/15 23Z 1.16 3017  90  15   6 0.00
Tue 06/16 00Z 0.91 3019  89  14   6 0.00
Tue 06/16 01Z 0.82 3020  94  11   5 0.00
Tue 06/16 02Z 0.84 3022  96  12   5 0.01
Tue 06/16 03Z 0.76 3023  95  10   5 0.01
Tue 06/16 04Z 0.76 3123  95   7   4 0.01
Tue 06/16 05Z 0.68 3123  94   4   4 0.00
Tue 06/16 06Z 0.64 3122  95   3   4 0.00
Tue 06/16 07Z 0.59 3221  95   3   3 0.01
Tue 06/16 08Z 0.54 3220  93   6   3 0.00
Tue 06/16 09Z 0.39 3218  88   7   4 0.00
Tue 06/16 10Z 0.25 3317  82  13   4 0.00
Tue 06/16 11Z 0.17 3314  77  16   5 0.00
Tue 06/16 12Z 0.13 3311  72  15   6 0.00
Tue 06/16 13Z 0.15 3209  68  19   6 0.00
Tue 06/16 14Z 0.23 3107  65  28   6 0.00
Tue 06/16 15Z 0.52 2907  63  35   6 0.00
Tue 06/16 16Z 1.27 2807  59  37   6 0.00
Tue 06/16 17Z 2.58 2707  58  40   7 0.00
Tue 06/16 18Z 3.25 2607  59  40   7 0.00
Tue 06/16 19Z 3.27 2507  60  35   8 0.00
Tue 06/16 20Z 2.91 2507  60  34   8 0.00
Tue 06/16 21Z 1.95 2406  60  36   9 0.00
Tue 06/16 22Z 1.24 2307  61  36   9 0.00
Tue 06/16 23Z 0.55 2209  61  29   9 0.00
Wed 06/17 00Z 0.47 2211  59  24   9 0.00
Wed 06/17 01Z 0.49 2212  57  21   9 0.00
Wed 06/17 02Z 0.56 2313  58  21   9 0.00
Wed 06/17 03Z 0.67 2315  60  21   9 0.00
Wed 06/17 04Z 0.72 2315  63  22   9 0.00
Wed 06/17 05Z 0.69 2415  67  25   9 0.00

Run total areal avg QPF for the greens is: 1.77 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