NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261029_1800
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)
=== ===== === ==== ==== === === === ====
Thu 10/29 18Z 0.62 2417  79  54   8 0.00
Thu 10/29 19Z 0.62 2518  77  55   9 0.00
Thu 10/29 20Z 0.67 2421  75  57   9 0.00
Thu 10/29 21Z 0.75 2424  76  49   9 0.00
Thu 10/29 22Z 0.81 2427  76  42   9 0.00
Thu 10/29 23Z 0.86 2430  77  64   9 0.00
Fri 10/30 00Z 0.93 2432  82  86   9 0.00
Fri 10/30 01Z 1.00 2435  86  87   9 0.00
Fri 10/30 02Z 0.98 2435  84  90  10 0.00
Fri 10/30 03Z 1.05 2538  88  89  10 0.00
Fri 10/30 04Z 1.08 2538  96  95   9 0.07
Fri 10/30 05Z 0.94 2633  96  82   9 0.04
Fri 10/30 06Z 0.83 2728  95  69   8 0.03
Fri 10/30 07Z 0.70 2824  90  62   8 0.02
Fri 10/30 08Z 0.74 2724  87  63   7 0.01
Fri 10/30 09Z 0.75 2725  78  62   7 0.00
Fri 10/30 10Z 0.82 2728  72  37   7 0.00
Fri 10/30 11Z 0.86 2829  71  10   6 0.00
Fri 10/30 12Z 0.70 2826  77   9   5 0.01
Fri 10/30 13Z 0.64 2924  83   7   4 0.01
Fri 10/30 14Z 0.64 2923  89   2   2 0.01
Fri 10/30 15Z 0.66 2921  95   3   2 0.01
Fri 10/30 16Z 0.72 2921  97  10   1 0.01
Fri 10/30 17Z 0.87 2922  97  18   0 0.01
Fri 10/30 18Z 1.13 2923  96  18   0 0.01
Fri 10/30 19Z 1.38 2925  96  15   0 0.01
Fri 10/30 20Z 1.49 3028  94  15  -1 0.01
Fri 10/30 21Z 1.16 3029  94  13  -1 0.00
Fri 10/30 22Z 1.07 3030  97  13  -1 0.01
Fri 10/30 23Z 0.94 3030  97  17  -2 0.01
Sat 10/31 00Z 0.79 3129  98  20  -2 0.01
Sat 10/31 01Z 0.90 3131  98  22  -3 0.01
Sat 10/31 02Z 0.90 3131  98  25  -3 0.01
Sat 10/31 03Z 0.79 3231  97  25  -4 0.01
Sat 10/31 04Z 0.60 3230  96  26  -4 0.01
Sat 10/31 05Z 0.42 3230  92  22  -5 0.01
Sat 10/31 06Z 0.31 3330  87  14  -5 0.00
Sat 10/31 07Z 0.26 3330  87   8  -6 0.00
Sat 10/31 08Z 0.25 3328  89   8  -6 0.00
Sat 10/31 09Z 0.23 3325  88  15  -6 0.00
Sat 10/31 10Z 0.18 3324  82  19  -5 0.00
Sat 10/31 11Z 0.17 3322  74  22  -5 0.00
Sat 10/31 12Z 0.18 3222  66  24  -4 0.00
Sat 10/31 13Z 0.17 3221  61  25  -4 0.00
Sat 10/31 14Z 0.17 3220  59  21  -4 0.00
Sat 10/31 15Z 0.18 3218  59  20  -3 0.00
Sat 10/31 16Z 0.18 3217  58  22  -3 0.00
Sat 10/31 17Z 0.24 3116  60  28  -3 0.00
Sat 10/31 18Z 0.27 3116  59  30  -2 0.00
Sat 10/31 19Z 0.23 3115  56  23  -2 0.00
Sat 10/31 20Z 0.27 3115  57   8  -2 0.00
Sat 10/31 21Z 0.33 3016  61  14  -2 0.00
Sat 10/31 22Z 0.40 2917  61  27  -2 0.00
Sat 10/31 23Z 0.44 2919  62  18  -2 0.00
Sun 11/01 00Z 0.42 2919  61  13  -1 0.00
Sun 11/01 01Z 0.38 3019  60   9  -1 0.00
Sun 11/01 02Z 0.36 3019  61   7  -1 0.00
Sun 11/01 03Z 0.34 3017  62   5  -1 0.00
Sun 11/01 04Z 0.29 3016  59   5   0 0.00
Sun 11/01 05Z 0.29 3015  57   4   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.34 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