Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260803_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)
=== ===== === ==== ==== === === === ====
Mon 08/03 12Z 0.10 1820  97  91  15 0.00
Mon 08/03 13Z 0.16 1919  97  91  15 0.01
Mon 08/03 14Z 0.21 1920  98  82  15 0.01
Mon 08/03 15Z 0.29 2019  98  73  15 0.01
Mon 08/03 16Z 0.28 1918  97  66  16 0.01
Mon 08/03 17Z 0.33 1919  96  74  16 0.01
Mon 08/03 18Z 0.36 2019  96  90  16 0.15
Mon 08/03 19Z 0.68 2321  94  80  15 0.23
Mon 08/03 20Z 0.81 2420  93  46  14 0.04
Mon 08/03 21Z 1.04 2621  94  58  13 0.04
Mon 08/03 22Z 0.83 2723  97  77  12 0.06
Mon 08/03 23Z 0.87 3029  99  86  11 0.10
Tue 08/04 00Z 0.86 3133  98  94  10 0.11
Tue 08/04 01Z 0.84 3134  95  73  10 0.06
Tue 08/04 02Z 0.93 3135  87  25   9 0.01
Tue 08/04 03Z 0.84 3232  78  16  10 0.00
Tue 08/04 04Z 0.81 3129  85  18  10 0.00
Tue 08/04 05Z 0.91 3127  86   8  10 0.00
Tue 08/04 06Z 1.03 3026  86   5  10 0.00
Tue 08/04 07Z 0.95 3024  81   5  10 0.00
Tue 08/04 08Z 0.95 3023  77   5  10 0.00
Tue 08/04 09Z 0.92 2923  72   4  11 0.00
Tue 08/04 10Z 0.96 3024  66   3  11 0.00
Tue 08/04 11Z 0.78 3024  60   2  12 0.00
Tue 08/04 12Z 0.67 3023  57   1  12 0.00
Tue 08/04 13Z 0.61 3022  55   2  13 0.00
Tue 08/04 14Z 0.54 3020  53   2  13 0.00
Tue 08/04 15Z 0.48 2917  49   2  14 0.00
Tue 08/04 16Z 0.42 3015  45   1  14 0.00
Tue 08/04 17Z 0.38 2912  45   1  14 0.00
Tue 08/04 18Z 0.38 2810  50   2  14 0.00
Tue 08/04 19Z 0.37 2809  51   4  15 0.00
Tue 08/04 20Z 0.35 2708  50   7  15 0.00
Tue 08/04 21Z 0.32 2707  51  10  15 0.00
Tue 08/04 22Z 0.25 2606  51  14  15 0.00
Tue 08/04 23Z 0.20 2506  50  17  16 0.00
Wed 08/05 00Z 0.17 2406  49  18  16 0.00
Wed 08/05 01Z 0.18 2307  47  19  16 0.00
Wed 08/05 02Z 0.22 2209  45  21  17 0.00
Wed 08/05 03Z 0.21 2209  43  22  17 0.00
Wed 08/05 04Z 0.23 2310  43  22  17 0.00
Wed 08/05 05Z 0.22 2310  43  21  17 0.00
Wed 08/05 06Z 0.22 2409  42  19  17 0.00
Wed 08/05 07Z 0.22 2509  42  17  17 0.00
Wed 08/05 08Z 0.21 2508  45  14  17 0.00
Wed 08/05 09Z 0.20 2508  46  12  16 0.00
Wed 08/05 10Z 0.19 2407  47  10  16 0.00
Wed 08/05 11Z 0.18 2407  47   6  16 0.00
Wed 08/05 12Z 0.18 2407  47   2  16 0.00
Wed 08/05 13Z 0.22 2408  48   1  15 0.00
Wed 08/05 14Z 0.23 2408  49   1  15 0.00
Wed 08/05 15Z 0.22 2308  53   1  15 0.00
Wed 08/05 16Z 0.21 2207  55   2  15 0.00
Wed 08/05 17Z 0.19 2107  52   3  16 0.00
Wed 08/05 18Z 0.23 2109  50   7  16 0.00
Wed 08/05 19Z 0.25 2110  50  10  16 0.00
Wed 08/05 20Z 0.28 2111  52  20  16 0.00
Wed 08/05 21Z 0.29 2111  51  26  16 0.00
Wed 08/05 22Z 0.30 2212  48  32  17 0.00
Wed 08/05 23Z 0.31 2212  48  34  17 0.00

Run total areal avg QPF for the greens is: 0.85 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