Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261012_0000
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 10/12 00Z 0.10 1919  91  91   7 0.00
Mon 10/12 01Z 0.14 1920  96  95   7 0.05
Mon 10/12 02Z 0.16 2019  98  99   7 0.10
Mon 10/12 03Z 0.17 2114  96  96   8 0.09
Mon 10/12 04Z 0.21 2411  96  95   9 0.05
Mon 10/12 05Z 0.25 2611  95  95   9 0.04
Mon 10/12 06Z 0.25 2811  96  91   9 0.03
Mon 10/12 07Z 0.24 2911  96  84   9 0.02
Mon 10/12 08Z 0.21 3110  97  72   9 0.01
Mon 10/12 09Z 0.19 3212  97  63   9 0.01
Mon 10/12 10Z 0.23 3216  98  55   8 0.01
Mon 10/12 11Z 0.22 3216  97  45   8 0.02
Mon 10/12 12Z 0.16 3214  92  32  10 0.01
Mon 10/12 13Z 0.17 3214  88  29  11 0.01
Mon 10/12 14Z 0.17 3216  83  26  11 0.01
Mon 10/12 15Z 0.18 3216  77  24  12 0.01
Mon 10/12 16Z 0.21 3216  75  34  12 0.00
Mon 10/12 17Z 0.26 3117  74  55  12 0.00
Mon 10/12 18Z 0.31 3017  77  72  12 0.00
Mon 10/12 19Z 0.39 2918  81  70  11 0.01
Mon 10/12 20Z 0.47 2920  88  70  10 0.01
Mon 10/12 21Z 0.50 3021  93  69  10 0.02
Mon 10/12 22Z 0.47 3020  95  73   9 0.03
Mon 10/12 23Z 0.39 3118  96  72   9 0.02
Tue 10/13 00Z 0.32 3117  98  86   8 0.02
Tue 10/13 01Z 0.24 3214  97  89   8 0.02
Tue 10/13 02Z 0.16 3311  97  89   8 0.01
Tue 10/13 03Z 0.11 3309  97  90   7 0.01
Tue 10/13 04Z 0.09 3406  96  95   7 0.00
Tue 10/13 05Z 0.06 3404  96  97   7 0.00
Tue 10/13 06Z 0.03 3500  97  98   7 0.00
Tue 10/13 07Z 0.05 1603  98  97   7 0.01
Tue 10/13 08Z 0.07 1607  99  95   7 0.04
Tue 10/13 09Z 0.06 1611  99  95   7 0.04
Tue 10/13 10Z 0.06 1615  98  92   7 0.06
Tue 10/13 11Z 0.06 1719  97  96   7 0.04
Tue 10/13 12Z 0.06 1722  97  99   7 0.05
Tue 10/13 13Z 0.04 1725  97  95   8 0.05
Tue 10/13 14Z 0.04 1828  97  97   8 0.05
Tue 10/13 15Z 0.06 1830  98  92   8 0.07
Tue 10/13 16Z 0.06 1833  98  91   8 0.05
Tue 10/13 17Z 0.09 1835  98  97   9 0.06
Tue 10/13 18Z 0.15 1934  98  92  10 0.14
Tue 10/13 19Z 0.16 1934  98  93  12 0.17
Tue 10/13 20Z 0.19 2032  97  94  12 0.12
Tue 10/13 21Z 0.22 2030  97  96  12 0.14
Tue 10/13 22Z 0.25 2029  96  91  13 0.14
Tue 10/13 23Z 0.30 2128  96  86  13 0.16
Wed 10/14 00Z 0.36 2228  97  77  13 0.06
Wed 10/14 01Z 0.37 2325  97  81  13 0.04
Wed 10/14 02Z 0.40 2326  99  75  13 0.09
Wed 10/14 03Z 0.45 2326  99  77  13 0.08
Wed 10/14 04Z 0.55 2428  99  73  13 0.08
Wed 10/14 05Z 0.60 2527  99  69  13 0.05
Wed 10/14 06Z 0.65 2626  97  73  13 0.04
Wed 10/14 07Z 0.68 2626  98  74  13 0.04
Wed 10/14 08Z 0.67 2625  98  57  13 0.06
Wed 10/14 09Z 0.70 2625  98  34  12 0.05
Wed 10/14 10Z 0.75 2625  98  24  11 0.05
Wed 10/14 11Z 0.72 2725  97  19  10 0.04

Run total areal avg QPF for the greens is: 2.69 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