Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260618_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)
=== ===== === ==== ==== === === === ====
Thu 06/18 12Z 0.09 1732  90  99  13 0.00
Thu 06/18 13Z 0.14 1835  97  96  13 0.09
Thu 06/18 14Z 0.13 1837  97  97  13 0.19
Thu 06/18 15Z 0.21 1939  94  90  14 0.10
Thu 06/18 16Z 0.20 1936  93  91  14 0.05
Thu 06/18 17Z 0.11 1830  93  89  15 0.05
Thu 06/18 18Z 0.23 1826  96  84  14 0.15
Thu 06/18 19Z 0.92 2224  94  85  14 0.26
Thu 06/18 20Z 0.77 2529  79  65  13 0.36
Thu 06/18 21Z 0.97 2528  84  57  12 0.01
Thu 06/18 22Z 1.15 2528  92  47  12 0.01
Thu 06/18 23Z 1.24 2529  92  58  11 0.01
Fri 06/19 00Z 1.46 2431  93  55  11 0.01
Fri 06/19 01Z 1.45 2431  92  65  10 0.01
Fri 06/19 02Z 1.51 2434  93  75  10 0.02
Fri 06/19 03Z 1.38 2536  95  83   9 0.03
Fri 06/19 04Z 1.27 2636  96  74   9 0.05
Fri 06/19 05Z 1.24 2635  96  71   9 0.04
Fri 06/19 06Z 1.22 2634  97  74   8 0.03
Fri 06/19 07Z 1.19 2634  97  68   8 0.03
Fri 06/19 08Z 1.13 2633  97  65   8 0.03
Fri 06/19 09Z 1.08 2632  96  65   8 0.03
Fri 06/19 10Z 1.06 2632  96  60   8 0.02
Fri 06/19 11Z 1.02 2732  95  60   8 0.02
Fri 06/19 12Z 0.99 2731  96  63   8 0.02
Fri 06/19 13Z 1.00 2730  96  60   8 0.02
Fri 06/19 14Z 1.09 2631  94  61   8 0.02
Fri 06/19 15Z 1.18 2629  95  63   8 0.02
Fri 06/19 16Z 1.58 2628  94  61   8 0.01
Fri 06/19 17Z 3.93 2627  93  56   9 0.01
Fri 06/19 18Z 5.81 2626  91  53   9 0.01
Fri 06/19 19Z 5.90 2625  91  50   9 0.01
Fri 06/19 20Z 4.27 2627  88  54  10 0.01
Fri 06/19 21Z 7.49 2626  79  47  10 0.01
Fri 06/19 22Z 10.99 2627  76  45  10 0.01
Fri 06/19 23Z 5.16 2730  76  53   9 0.06
Sat 06/20 00Z 2.15 2730  78  58   9 0.04
Sat 06/20 01Z 1.81 2729  84  65   8 0.03
Sat 06/20 02Z 1.46 2729  90  76   8 0.04
Sat 06/20 03Z 1.30 2830  93  81   8 0.04
Sat 06/20 04Z 1.08 2829  94  83   7 0.03
Sat 06/20 05Z 0.99 2828  96  88   7 0.05
Sat 06/20 06Z 0.97 2828  96  91   7 0.07
Sat 06/20 07Z 0.95 2928  97  91   7 0.05
Sat 06/20 08Z 0.89 2827  97  92   7 0.04
Sat 06/20 09Z 0.90 2929  98  91   7 0.06
Sat 06/20 10Z 0.95 2930  98  90   7 0.07
Sat 06/20 11Z 0.95 2930  98  92   7 0.09
Sat 06/20 12Z 1.02 3029  98  84   6 0.07
Sat 06/20 13Z 0.95 3127  98  89   5 0.06
Sat 06/20 14Z 1.02 3128  97  89   5 0.05
Sat 06/20 15Z 0.93 3226  96  88   5 0.03
Sat 06/20 16Z 1.07 3224  95  87   5 0.03
Sat 06/20 17Z 0.78 3223  93  90   5 0.02
Sat 06/20 18Z 1.55 3223  94  88   6 0.01
Sat 06/20 19Z 1.24 3221  92  86   6 0.01
Sat 06/20 20Z 1.72 3120  87  81   7 0.00
Sat 06/20 21Z 2.16 3120  83  72   7 0.00
Sat 06/20 22Z 1.45 3019  88  67   8 0.01
Sat 06/20 23Z 0.95 3020  88  57   8 0.01

Run total areal avg QPF for the greens is: 2.72 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