Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260625_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)
=== ===== === ==== ==== === === === ====
Thu 06/25 00Z 0.85 2916  79  58  10 0.00
Thu 06/25 01Z 1.14 2919  77  52  10 0.00
Thu 06/25 02Z 1.20 2920  78  46  10 0.00
Thu 06/25 03Z 1.08 2921  80  51  10 0.00
Thu 06/25 04Z 0.80 2920  80  55  10 0.00
Thu 06/25 05Z 0.72 2920  76  60  10 0.00
Thu 06/25 06Z 0.69 2919  73  60  10 0.00
Thu 06/25 07Z 0.66 3018  69  59  10 0.00
Thu 06/25 08Z 0.63 2916  66  44  10 0.00
Thu 06/25 09Z 0.57 2915  65  38  10 0.00
Thu 06/25 10Z 0.55 3014  64  40  10 0.00
Thu 06/25 11Z 0.47 3012  64  48  10 0.00
Thu 06/25 12Z 0.37 3009  64  52  10 0.00
Thu 06/25 13Z 0.32 2907  63  52  10 0.00
Thu 06/25 14Z 0.37 2805  63  53  10 0.00
Thu 06/25 15Z 0.81 2505  65  54  10 0.00
Thu 06/25 16Z 1.58 2505  65  53  10 0.00
Thu 06/25 17Z 2.76 2405  65  47  11 0.00
Thu 06/25 18Z 3.38 2406  65  44  11 0.00
Thu 06/25 19Z 3.52 2306  65  48  11 0.00
Thu 06/25 20Z 2.97 2207  66  53  11 0.00
Thu 06/25 21Z 1.83 2107  67  56  11 0.00
Thu 06/25 22Z 1.23 2107  67  61  11 0.00
Thu 06/25 23Z 0.49 2107  67  64  11 0.00
Fri 06/26 00Z 0.29 2009  65  71  11 0.00
Fri 06/26 01Z 0.29 2010  66  76  11 0.00
Fri 06/26 02Z 0.27 1912  68  81  11 0.00
Fri 06/26 03Z 0.20 1913  69  83  11 0.00
Fri 06/26 04Z 0.19 1914  73  86  11 0.00
Fri 06/26 05Z 0.20 1916  77  87  11 0.00
Fri 06/26 06Z 0.20 1918  82  90  10 0.01
Fri 06/26 07Z 0.20 1919  88  95  10 0.03
Fri 06/26 08Z 0.15 1919  92  94  10 0.08
Fri 06/26 09Z 0.10 1820  93  95  11 0.03
Fri 06/26 10Z 0.15 1920  94  96  10 0.07
Fri 06/26 11Z 0.20 1920  94  95  10 0.14
Fri 06/26 12Z 0.20 1919  94  92  10 0.07
Fri 06/26 13Z 0.25 2016  97  87  10 0.08
Fri 06/26 14Z 0.27 2113  98  78  10 0.03
Fri 06/26 15Z 0.25 2210  97  71  10 0.01
Fri 06/26 16Z 0.23 2307  97  49  10 0.00
Fri 06/26 17Z 0.27 2407  97  49  10 0.00
Fri 06/26 18Z 0.34 2507  96  55  10 0.00
Fri 06/26 19Z 0.34 2505  94  51  11 0.00
Fri 06/26 20Z 0.41 2605  94  51  11 0.00
Fri 06/26 21Z 0.35 2605  93  58  11 0.01
Fri 06/26 22Z 0.27 2505  93  75  11 0.07
Fri 06/26 23Z 0.29 2706  91  59  11 0.06
Sat 06/27 00Z 0.30 2807  93  65  11 0.02
Sat 06/27 01Z 0.27 2807  91  65  11 0.02
Sat 06/27 02Z 0.28 2807  90  66  11 0.01
Sat 06/27 03Z 0.25 2807  92  56  11 0.00
Sat 06/27 04Z 0.28 2808  95  49  11 0.00
Sat 06/27 05Z 0.28 2808  95  45  11 0.01
Sat 06/27 06Z 0.22 2806  94  46  11 0.01
Sat 06/27 07Z 0.20 2806  93  48  10 0.01
Sat 06/27 08Z 0.13 2904  93  47  10 0.01
Sat 06/27 09Z 0.11 2903  94  43  10 0.01
Sat 06/27 10Z 0.06 3002  93  40  10 0.00
Sat 06/27 11Z 0.05 3101  93  42  10 0.00

Run total areal avg QPF for the greens is: 0.79 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