Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260620_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 06/20 12Z 1.00 3025  97  93   7 0.00
Sat 06/20 13Z 0.95 3026  98  92   7 0.04
Sat 06/20 14Z 0.92 3025  98  93   7 0.06
Sat 06/20 15Z 0.87 3024  98  92   8 0.05
Sat 06/20 16Z 0.84 3023  97  91   8 0.04
Sat 06/20 17Z 0.71 3020  96  89   8 0.04
Sat 06/20 18Z 0.78 3020  96  89   8 0.05
Sat 06/20 19Z 0.85 2921  96  86   8 0.08
Sat 06/20 20Z 1.00 3021  96  81   9 0.06
Sat 06/20 21Z 0.98 3020  95  80   9 0.09
Sat 06/20 22Z 0.89 2921  95  79   9 0.05
Sat 06/20 23Z 0.83 2921  94  73   9 0.06
Sun 06/21 00Z 0.84 2921  94  70   9 0.01
Sun 06/21 01Z 0.83 2921  94  68   8 0.01
Sun 06/21 02Z 0.71 2920  94  66   8 0.01
Sun 06/21 03Z 0.57 3019  93  65   9 0.01
Sun 06/21 04Z 0.53 3017  95  67   8 0.01
Sun 06/21 05Z 0.47 3016  95  71   8 0.01
Sun 06/21 06Z 0.41 3014  95  77   8 0.01
Sun 06/21 07Z 0.38 3013  95  77   8 0.01
Sun 06/21 08Z 0.38 2913  96  75   8 0.01
Sun 06/21 09Z 0.37 2913  95  69   8 0.01
Sun 06/21 10Z 0.34 2913  94  62   8 0.01
Sun 06/21 11Z 0.34 2913  93  62   8 0.01
Sun 06/21 12Z 0.32 2912  93  67   8 0.01
Sun 06/21 13Z 0.35 2912  94  75   8 0.01
Sun 06/21 14Z 0.34 2911  93  76   8 0.01
Sun 06/21 15Z 0.35 2910  93  75   8 0.00
Sun 06/21 16Z 0.63 3010  93  76   8 0.00
Sun 06/21 17Z 0.69 3010  93  73   8 0.00
Sun 06/21 18Z 0.62 3010  92  70   8 0.00
Sun 06/21 19Z 0.50 3010  92  68   9 0.00
Sun 06/21 20Z 0.44 3010  92  70   9 0.03
Sun 06/21 21Z 0.33 3110  88  66   9 0.02
Sun 06/21 22Z 0.30 3110  86  59  10 0.01
Sun 06/21 23Z 0.30 3110  86  59  10 0.00
Mon 06/22 00Z 0.34 3011  87  62   9 0.00
Mon 06/22 01Z 0.37 3012  88  62   9 0.00
Mon 06/22 02Z 0.39 3012  88  62   9 0.01
Mon 06/22 03Z 0.35 3012  89  56   9 0.00
Mon 06/22 04Z 0.29 3111  88  48   9 0.00
Mon 06/22 05Z 0.16 3209  81  40  10 0.00
Mon 06/22 06Z 0.12 3207  79  37  10 0.00
Mon 06/22 07Z 0.13 3106  82  39  10 0.00
Mon 06/22 08Z 0.15 2905  84  41   9 0.00
Mon 06/22 09Z 0.14 2604  86  39   9 0.00
Mon 06/22 10Z 0.13 2404  85  29   9 0.00
Mon 06/22 11Z 0.07 2103  82  24   9 0.00
Mon 06/22 12Z 0.04 1803  80  22   9 0.00
Mon 06/22 13Z 0.03 1806  80  22   9 0.00
Mon 06/22 14Z 0.05 1809  81  27   9 0.00
Mon 06/22 15Z 0.05 1712  81  69   9 0.00
Mon 06/22 16Z 0.09 1813  86  85   8 0.02
Mon 06/22 17Z 0.15 1712  88  86   8 0.05
Mon 06/22 18Z 0.21 1515  87  84   7 0.07
Mon 06/22 19Z 0.42 1419  88  97   8 0.06
Mon 06/22 20Z 0.71 1219  92  97   8 0.10
Mon 06/22 21Z 0.75 1224  94  98   8 0.23
Mon 06/22 22Z 0.65 1225  97  99   8 0.21
Mon 06/22 23Z 0.58 1326  96  98   9 0.16

Run total areal avg QPF for the greens is: 1.74 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