Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260716_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)
=== ===== === ==== ==== === === === ====
Thu 07/16 12Z 0.62 2920  84  80  12 0.00
Thu 07/16 13Z 0.75 2823  85  87  12 0.01
Thu 07/16 14Z 0.90 2824  82  88  12 0.00
Thu 07/16 15Z 1.16 2824  77  89  12 0.00
Thu 07/16 16Z 6.52 2723  82  91  12 0.00
Thu 07/16 17Z 6.73 2727  76  89  12 0.05
Thu 07/16 18Z 9.02 2827  70  84  12 0.01
Thu 07/16 19Z 5.14 2927  73  75  12 0.05
Thu 07/16 20Z 1.72 3130  75  61  11 0.07
Thu 07/16 21Z 0.75 3232  77  44  10 0.06
Thu 07/16 22Z 1.51 3228  76  15   9 0.01
Thu 07/16 23Z 1.88 3228  74  12   9 0.00
Fri 07/17 00Z 1.98 3129  72  14   8 0.00
Fri 07/17 01Z 1.41 3129  67  24   8 0.00
Fri 07/17 02Z 1.23 3230  64  34   8 0.00
Fri 07/17 03Z 1.42 3230  65  37   7 0.00
Fri 07/17 04Z 1.39 3230  65  39   7 0.00
Fri 07/17 05Z 1.38 3230  65  40   6 0.00
Fri 07/17 06Z 1.13 3229  65  39   6 0.00
Fri 07/17 07Z 0.84 3227  67  37   6 0.00
Fri 07/17 08Z 0.64 3227  67  33   7 0.00
Fri 07/17 09Z 0.54 3126  66  25   7 0.00
Fri 07/17 10Z 0.50 3126  65  23   8 0.00
Fri 07/17 11Z 0.45 3126  62  20   8 0.00
Fri 07/17 12Z 0.43 3126  59  19   8 0.00
Fri 07/17 13Z 0.41 3125  57  17   9 0.00
Fri 07/17 14Z 0.40 3223  56  18   9 0.00
Fri 07/17 15Z 0.40 3220  56  20   9 0.00
Fri 07/17 16Z 0.43 3118  56  21   9 0.00
Fri 07/17 17Z 0.50 3116  55  21   9 0.00
Fri 07/17 18Z 0.68 3015  57  22   9 0.00
Fri 07/17 19Z 1.00 2914  59  22   9 0.00
Fri 07/17 20Z 1.58 2913  59  20   9 0.00
Fri 07/17 21Z 1.98 2913  58  19   9 0.00
Fri 07/17 22Z 1.16 2812  55  17  10 0.00
Fri 07/17 23Z 0.74 2812  50  15  10 0.00
Sat 07/18 00Z 0.73 2813  47  13  10 0.00
Sat 07/18 01Z 0.62 2812  45  11  10 0.00
Sat 07/18 02Z 0.60 2812  45  11  10 0.00
Sat 07/18 03Z 0.55 2811  45  12  10 0.00
Sat 07/18 04Z 0.50 2711  46  13  10 0.00
Sat 07/18 05Z 0.41 2709  46  12  11 0.00
Sat 07/18 06Z 0.32 2607  45  10  11 0.00
Sat 07/18 07Z 0.34 2408  48  12  10 0.00
Sat 07/18 08Z 0.29 2308  49  14  10 0.00
Sat 07/18 09Z 0.25 2209  48  19  10 0.00
Sat 07/18 10Z 0.29 2210  45  30  11 0.00
Sat 07/18 11Z 0.31 2211  44  65  11 0.00
Sat 07/18 12Z 0.33 2311  50  83  11 0.00
Sat 07/18 13Z 0.26 2112  57  78  12 0.00
Sat 07/18 14Z 0.26 2015  61  84  12 0.00
Sat 07/18 15Z 0.38 2019  65  80  12 0.00
Sat 07/18 16Z 0.69 2022  74  82  13 0.00
Sat 07/18 17Z 0.71 2025  74  72  14 0.00
Sat 07/18 18Z 0.92 2029  76  84  14 0.01
Sat 07/18 19Z 0.61 2035  89  81  14 0.02
Sat 07/18 20Z 0.51 2035  93  96  14 0.04
Sat 07/18 21Z 0.47 2037  95  93  14 0.05
Sat 07/18 22Z 0.49 2039  97  79  14 0.05
Sat 07/18 23Z 0.56 2140  97  72  15 0.03

Run total areal avg QPF for the greens is: 0.46 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