Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260619_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 06/19 00Z 1.11 2523  82  80  12 0.00
Fri 06/19 01Z 1.53 2527  79  77  11 0.00
Fri 06/19 02Z 2.66 2532  76  81  10 0.00
Fri 06/19 03Z 2.84 2535  82  66   9 0.00
Fri 06/19 04Z 2.21 2537  87  74   9 0.01
Fri 06/19 05Z 1.74 2537  92  75   8 0.02
Fri 06/19 06Z 1.35 2636  94  77   8 0.04
Fri 06/19 07Z 1.17 2635  95  75   8 0.04
Fri 06/19 08Z 1.10 2635  95  71   8 0.02
Fri 06/19 09Z 1.05 2734  96  68   8 0.03
Fri 06/19 10Z 1.05 2734  93  60   8 0.02
Fri 06/19 11Z 0.99 2734  90  59   8 0.01
Fri 06/19 12Z 0.99 2734  89  61   8 0.00
Fri 06/19 13Z 1.02 2733  90  61   8 0.00
Fri 06/19 14Z 1.05 2729  92  58   8 0.01
Fri 06/19 15Z 1.19 2727  94  57   8 0.01
Fri 06/19 16Z 1.49 2626  94  70   8 0.01
Fri 06/19 17Z 2.69 2626  94  70   8 0.01
Fri 06/19 18Z 6.93 2625  92  75   9 0.01
Fri 06/19 19Z 9.59 2724  89  75   9 0.00
Fri 06/19 20Z 6.64 2624  89  61  10 0.00
Fri 06/19 21Z 10.05 2625  82  52  10 0.00
Fri 06/19 22Z 14.33 2627  75  49  10 0.00
Fri 06/19 23Z 6.70 2629  79  47   9 0.00
Sat 06/20 00Z 2.55 2630  84  50   9 0.00
Sat 06/20 01Z 1.51 2732  92  66   8 0.02
Sat 06/20 02Z 1.04 2829  93  77   8 0.06
Sat 06/20 03Z 0.98 2828  97  83   8 0.05
Sat 06/20 04Z 0.92 2827  97  79   8 0.09
Sat 06/20 05Z 0.89 2827  97  81   7 0.07
Sat 06/20 06Z 0.87 2727  97  80   7 0.06
Sat 06/20 07Z 0.81 2828  96  89   8 0.05
Sat 06/20 08Z 0.76 2828  97  88   8 0.05
Sat 06/20 09Z 0.62 3028  97  87   7 0.05
Sat 06/20 10Z 0.56 3026  98  86   7 0.05
Sat 06/20 11Z 0.47 3125  97  82   6 0.02
Sat 06/20 12Z 0.40 3224  98  89   6 0.03
Sat 06/20 13Z 0.45 3224  98  90   6 0.03
Sat 06/20 14Z 0.50 3124  97  79   6 0.03
Sat 06/20 15Z 0.58 3122  95  64   6 0.01
Sat 06/20 16Z 1.17 3119  95  66   6 0.00
Sat 06/20 17Z 1.75 3118  93  70   7 0.01
Sat 06/20 18Z 1.92 3117  92  70   7 0.01
Sat 06/20 19Z 1.46 3017  93  68   8 0.01
Sat 06/20 20Z 0.92 3017  91  57   8 0.01
Sat 06/20 21Z 0.65 3017  90  44   8 0.00
Sat 06/20 22Z 0.58 3017  88  41   9 0.00
Sat 06/20 23Z 0.49 3117  75  45  10 0.00
Sun 06/21 00Z 0.52 3018  76  48  10 0.00
Sun 06/21 01Z 0.55 2918  88  49  10 0.00
Sun 06/21 02Z 0.55 2820  90  51  10 0.00
Sun 06/21 03Z 0.51 2920  89  52  10 0.01
Sun 06/21 04Z 0.46 2919  87  55  10 0.00
Sun 06/21 05Z 0.43 2918  86  58  10 0.00
Sun 06/21 06Z 0.40 2918  85  63  10 0.00
Sun 06/21 07Z 0.36 3017  85  62  10 0.00
Sun 06/21 08Z 0.31 3016  85  64  10 0.00
Sun 06/21 09Z 0.31 3016  88  67   9 0.00
Sun 06/21 10Z 0.34 3017  90  71   9 0.00
Sun 06/21 11Z 0.32 3016  88  70   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.96 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