Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260802_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)
=== ===== === ==== ==== === === === ====
Sun 08/02 12Z 0.26 2014  80  64  15 0.00
Sun 08/02 13Z 0.28 2015  80  59  15 0.00
Sun 08/02 14Z 0.26 2014  83  53  15 0.00
Sun 08/02 15Z 0.30 1913  89  61  15 0.00
Sun 08/02 16Z 0.20 1813  92  69  15 0.01
Sun 08/02 17Z 0.37 1915  92  78  15 0.10
Sun 08/02 18Z 0.34 1916  93  79  15 0.10
Sun 08/02 19Z 0.26 1817  92  59  15 0.08
Sun 08/02 20Z 0.29 1819  89  41  15 0.01
Sun 08/02 21Z 0.21 1821  87  24  15 0.01
Sun 08/02 22Z 0.12 1823  86  17  16 0.00
Sun 08/02 23Z 0.12 1824  85  17  16 0.00
Mon 08/03 00Z 0.11 1824  85  21  15 0.00
Mon 08/03 01Z 0.11 1825  83  48  15 0.00
Mon 08/03 02Z 0.15 1825  80  77  15 0.01
Mon 08/03 03Z 0.18 1925  79  93  15 0.01
Mon 08/03 04Z 0.15 1924  80  93  15 0.01
Mon 08/03 05Z 0.17 1925  82  93  15 0.01
Mon 08/03 06Z 0.28 1927  88  94  15 0.01
Mon 08/03 07Z 0.21 1926  88  84  15 0.05
Mon 08/03 08Z 0.20 1926  81  84  16 0.01
Mon 08/03 09Z 0.13 1826  83  87  16 0.01
Mon 08/03 10Z 0.11 1828  89  93  16 0.02
Mon 08/03 11Z 0.14 1830  97  95  16 0.10
Mon 08/03 12Z 0.25 1931  96  83  16 0.15
Mon 08/03 13Z 0.43 2031  95  75  16 0.05
Mon 08/03 14Z 0.50 2029  98  74  16 0.02
Mon 08/03 15Z 0.69 2228  99  77  16 0.03
Mon 08/03 16Z 0.67 2223  99  81  16 0.04
Mon 08/03 17Z 0.72 2321  97  81  16 0.08
Mon 08/03 18Z 0.62 2417  96  88  15 0.11
Mon 08/03 19Z 0.62 2417  93  82  15 0.20
Mon 08/03 20Z 0.67 2418  95  69  15 0.04
Mon 08/03 21Z 0.88 2624  98  78  14 0.14
Mon 08/03 22Z 0.88 2828  97  71  12 0.10
Mon 08/03 23Z 0.76 3028  95  52  11 0.05
Tue 08/04 00Z 0.54 3230  94  42  11 0.04
Tue 08/04 01Z 0.46 3228  93  25  11 0.01
Tue 08/04 02Z 0.46 3226  89  20  10 0.00
Tue 08/04 03Z 0.55 3124  87  10  10 0.00
Tue 08/04 04Z 0.65 3125  85   5  11 0.01
Tue 08/04 05Z 0.73 3023  84   4  11 0.00
Tue 08/04 06Z 0.81 3023  83   4  10 0.00
Tue 08/04 07Z 0.83 3023  79   4  11 0.00
Tue 08/04 08Z 0.76 3023  76   3  11 0.00
Tue 08/04 09Z 0.75 3022  71   2  11 0.00
Tue 08/04 10Z 0.60 3021  64   2  12 0.00
Tue 08/04 11Z 0.50 3020  58   2  13 0.00
Tue 08/04 12Z 0.45 3020  55   1  13 0.00
Tue 08/04 13Z 0.42 3018  54   1  13 0.00
Tue 08/04 14Z 0.38 3117  54   1  13 0.00
Tue 08/04 15Z 0.36 3014  54   1  13 0.00
Tue 08/04 16Z 0.31 3011  51   2  13 0.00
Tue 08/04 17Z 0.29 3010  49   3  14 0.00
Tue 08/04 18Z 0.23 2907  46   5  14 0.00
Tue 08/04 19Z 0.21 2906  43  10  15 0.00
Tue 08/04 20Z 0.21 2705  41  15  16 0.00
Tue 08/04 21Z 0.19 2605  38  19  16 0.00
Tue 08/04 22Z 0.16 2605  37  24  16 0.00
Tue 08/04 23Z 0.17 2505  37  26  17 0.00

Run total areal avg QPF for the greens is: 1.62 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