Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20251101_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)
=== ===== === ==== ==== === === === ====
Sat 11/01 12Z 1.11 2828  97  33  -3 0.00
Sat 11/01 13Z 1.25 2832  96  20  -3 0.02
Sat 11/01 14Z 1.32 2833  95  19  -3 0.02
Sat 11/01 15Z 1.18 2832  93  16  -3 0.01
Sat 11/01 16Z 1.04 2930  91  12  -3 0.01
Sat 11/01 17Z 1.14 2928  91  10  -3 0.00
Sat 11/01 18Z 2.08 2927  92  10  -3 0.00
Sat 11/01 19Z 1.90 2926  94   9  -4 0.00
Sat 11/01 20Z 1.53 2925  95   7  -4 0.01
Sat 11/01 21Z 1.32 2926  95   5  -5 0.01
Sat 11/01 22Z 1.10 2926  94   4  -5 0.01
Sat 11/01 23Z 0.90 3026  93   3  -5 0.01
Sun 11/02 00Z 0.72 3026  90   3  -5 0.01
Sun 11/02 01Z 0.61 3025  87   3  -4 0.01
Sun 11/02 02Z 0.49 3023  82   3  -3 0.01
Sun 11/02 03Z 0.46 3023  79   3  -3 0.01
Sun 11/02 04Z 0.42 3022  76   4  -2 0.01
Sun 11/02 05Z 0.36 3021  72   5  -2 0.01
Sun 11/02 06Z 0.33 3020  70   5  -2 0.01
Sun 11/02 07Z 0.34 3020  71   6  -2 0.01
Sun 11/02 08Z 0.32 3019  69   7  -2 0.01
Sun 11/02 09Z 0.32 3018  67   8  -2 0.01
Sun 11/02 10Z 0.31 3018  63   9  -2 0.01
Sun 11/02 11Z 0.32 2918  65   9  -2 0.01
Sun 11/02 12Z 0.32 3018  66   9  -2 0.00
Sun 11/02 13Z 0.31 2918  66   9  -2 0.00
Sun 11/02 14Z 0.31 2917  66   9  -2 0.00
Sun 11/02 15Z 0.31 2916  69   9  -3 0.00
Sun 11/02 16Z 0.33 2916  70  10  -3 0.00
Sun 11/02 17Z 0.37 2816  71  11  -3 0.00
Sun 11/02 18Z 0.43 2817  73  11  -3 0.00
Sun 11/02 19Z 0.48 2718  70  11  -3 0.00
Sun 11/02 20Z 0.52 2719  69  10  -2 0.00
Sun 11/02 21Z 0.54 2720  70   9  -2 0.00
Sun 11/02 22Z 0.58 2722  71   8  -2 0.00
Sun 11/02 23Z 0.59 2723  71   8  -1 0.00
Mon 11/03 00Z 0.54 2723  65   7  -1 0.00
Mon 11/03 01Z 0.54 2824  62   9  -1 0.00
Mon 11/03 02Z 0.58 2826  66  11  -1 0.00
Mon 11/03 03Z 0.59 2825  67  13   0 0.00
Mon 11/03 04Z 0.63 2825  69  16   0 0.00
Mon 11/03 05Z 0.66 2725  70  24   0 0.00
Mon 11/03 06Z 0.73 2627  75  27   0 0.00
Mon 11/03 07Z 0.78 2528  74  32   0 0.00
Mon 11/03 08Z 0.84 2531  78  35   1 0.00
Mon 11/03 09Z 0.93 2533  81  43   1 0.00
Mon 11/03 10Z 1.04 2533  82  38   1 0.00
Mon 11/03 11Z 1.03 2534  84  33   1 0.00
Mon 11/03 12Z 1.01 2533  83  40   1 0.00
Mon 11/03 13Z 1.02 2533  82  52   1 0.00
Mon 11/03 14Z 1.01 2533  78  61   1 0.00
Mon 11/03 15Z 1.06 2433  79  60   1 0.00
Mon 11/03 16Z 1.08 2433  79  63   1 0.00
Mon 11/03 17Z 1.10 2333  79  73   2 0.00
Mon 11/03 18Z 1.26 2332  79  75   2 0.00
Mon 11/03 19Z 1.24 2333  80  84   2 0.00
Mon 11/03 20Z 1.32 2233  83  74   2 0.00
Mon 11/03 21Z 1.32 2333  88  71   2 0.01
Mon 11/03 22Z 1.27 2333  92  87   1 0.03
Mon 11/03 23Z 1.58 2335  91  90   1 0.03

Run total areal avg QPF for the greens is: 0.29 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