Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260624_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)
=== ===== === ==== ==== === === === ====
Wed 06/24 18Z 4.01 3012  86  66   9 0.00
Wed 06/24 19Z 4.82 2915  84  61   9 0.01
Wed 06/24 20Z 4.62 2915  83  55  10 0.01
Wed 06/24 21Z 4.38 2916  80  49  10 0.01
Wed 06/24 22Z 4.28 2918  77  34  10 0.00
Wed 06/24 23Z 3.44 2920  76  33  10 0.00
Thu 06/25 00Z 2.91 2922  77  30  10 0.00
Thu 06/25 01Z 2.54 2923  78  32   9 0.00
Thu 06/25 02Z 1.60 2923  78  31   9 0.00
Thu 06/25 03Z 1.05 3021  79  30   9 0.00
Thu 06/25 04Z 0.78 3021  80  32   9 0.00
Thu 06/25 05Z 0.71 3020  78  30   9 0.00
Thu 06/25 06Z 0.64 3017  76  26   9 0.00
Thu 06/25 07Z 0.63 3017  75  24   9 0.00
Thu 06/25 08Z 0.56 3014  74  19   9 0.00
Thu 06/25 09Z 0.53 3013  73  21   9 0.00
Thu 06/25 10Z 0.55 2913  73  19   9 0.00
Thu 06/25 11Z 0.54 2913  73  19   9 0.00
Thu 06/25 12Z 0.50 2912  73  21   9 0.00
Thu 06/25 13Z 0.50 2909  73  20   9 0.00
Thu 06/25 14Z 1.04 2807  73  20   9 0.00
Thu 06/25 15Z 2.04 2806  72  19   9 0.00
Thu 06/25 16Z 2.43 2705  71  22  10 0.00
Thu 06/25 17Z 2.38 2604  70  26  10 0.00
Thu 06/25 18Z 2.40 2404  69  33  11 0.00
Thu 06/25 19Z 1.68 2204  69  33  11 0.00
Thu 06/25 20Z 1.70 2105  71  34  11 0.00
Thu 06/25 21Z 0.90 2006  73  34  11 0.00
Thu 06/25 22Z 0.63 2007  74  38  11 0.00
Thu 06/25 23Z 0.23 2007  73  49  11 0.00
Fri 06/26 00Z 0.12 1909  68  69  11 0.00
Fri 06/26 01Z 0.11 1811  67  74  11 0.00
Fri 06/26 02Z 0.07 1813  68  72  11 0.01
Fri 06/26 03Z 0.09 1815  71  79  11 0.00
Fri 06/26 04Z 0.12 1817  73  88  11 0.00
Fri 06/26 05Z 0.14 1819  76  88  11 0.00
Fri 06/26 06Z 0.28 1922  81  93  11 0.00
Fri 06/26 07Z 0.21 1923  87  95  11 0.06
Fri 06/26 08Z 0.20 1924  88  92  11 0.10
Fri 06/26 09Z 0.19 1924  90  82  11 0.07
Fri 06/26 10Z 0.13 1824  90  84  11 0.03
Fri 06/26 11Z 0.19 1920  92  73  11 0.03
Fri 06/26 12Z 0.29 2020  95  68  11 0.01
Fri 06/26 13Z 0.31 2117  93  63  11 0.01
Fri 06/26 14Z 0.31 2116  95  67  11 0.01
Fri 06/26 15Z 0.31 2114  96  66  11 0.01
Fri 06/26 16Z 0.33 2113  96  58  11 0.01
Fri 06/26 17Z 0.34 2112  95  47  11 0.00
Fri 06/26 18Z 0.43 2112  92  49  11 0.00
Fri 06/26 19Z 0.77 2111  88  62  11 0.01
Fri 06/26 20Z 1.03 2212  89  72  11 0.03
Fri 06/26 21Z 0.67 2217  91  67  12 0.12
Fri 06/26 22Z 0.70 2418  94  74  12 0.08
Fri 06/26 23Z 0.74 2619  92  68  11 0.08
Sat 06/27 00Z 0.80 2720  96  48  10 0.04
Sat 06/27 01Z 0.70 2820  96  41  10 0.02
Sat 06/27 02Z 0.57 2919  94  39  10 0.01
Sat 06/27 03Z 0.54 2918  96  40   9 0.01
Sat 06/27 04Z 0.51 2917  96  41   9 0.01
Sat 06/27 05Z 0.52 2817  95  37  10 0.02

Run total areal avg QPF for the greens is: 0.81 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