NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261030_1200
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 10/30 12Z 0.90 2824  84   1   4 0.00
Fri 10/30 13Z 1.06 2826  87   0   4 0.00
Fri 10/30 14Z 0.99 2826  92   4   3 0.01
Fri 10/30 15Z 1.10 2925  94  10   1 0.01
Fri 10/30 16Z 1.44 2925  95  16   0 0.01
Fri 10/30 17Z 1.63 2926  94  20   0 0.01
Fri 10/30 18Z 2.04 2926  94  19  -1 0.00
Fri 10/30 19Z 2.33 2927  92  17  -1 0.00
Fri 10/30 20Z 2.16 3028  91  15  -2 0.00
Fri 10/30 21Z 1.85 3029  92  11  -2 0.00
Fri 10/30 22Z 1.52 3030  93  12  -2 0.00
Fri 10/30 23Z 1.33 3031  95  13  -2 0.00
Sat 10/31 00Z 1.16 3131  96  20  -2 0.00
Sat 10/31 01Z 0.96 3131  96  18  -3 0.01
Sat 10/31 02Z 0.90 3130  96  20  -3 0.01
Sat 10/31 03Z 0.73 3230  96  24  -4 0.01
Sat 10/31 04Z 0.60 3229  94  28  -4 0.01
Sat 10/31 05Z 0.53 3228  95  32  -5 0.00
Sat 10/31 06Z 0.40 3227  90  28  -5 0.00
Sat 10/31 07Z 0.37 3227  90  17  -5 0.00
Sat 10/31 08Z 0.33 3226  88  11  -5 0.00
Sat 10/31 09Z 0.30 3225  87   8  -6 0.00
Sat 10/31 10Z 0.23 3224  85   8  -6 0.00
Sat 10/31 11Z 0.16 3323  81  13  -6 0.00
Sat 10/31 12Z 0.15 3322  77  16  -6 0.00
Sat 10/31 13Z 0.14 3320  74  21  -5 0.00
Sat 10/31 14Z 0.15 3319  69  20  -4 0.00
Sat 10/31 15Z 0.14 3319  64  17  -4 0.00
Sat 10/31 16Z 0.14 3319  60  16  -3 0.00
Sat 10/31 17Z 0.19 3217  60  19  -3 0.00
Sat 10/31 18Z 0.25 3117  60  28  -3 0.00
Sat 10/31 19Z 0.32 3116  62  28  -4 0.00
Sat 10/31 20Z 0.36 3016  67  17  -3 0.00
Sat 10/31 21Z 0.41 3017  70  18  -3 0.00
Sat 10/31 22Z 0.46 3018  69  39  -3 0.00
Sat 10/31 23Z 0.49 3019  67  31  -3 0.00
Sun 11/01 00Z 0.46 3020  65  20  -3 0.00
Sun 11/01 01Z 0.37 3020  61  17  -2 0.00
Sun 11/01 02Z 0.33 3119  60  18  -2 0.00
Sun 11/01 03Z 0.33 3019  60  10  -1 0.00
Sun 11/01 04Z 0.27 3119  56   5  -1 0.00
Sun 11/01 05Z 0.23 3117  54   7   0 0.00
Sun 11/01 06Z 0.23 3117  52  12   0 0.00
Sun 11/01 07Z 0.25 3017  50  14   0 0.00
Sun 11/01 08Z 0.26 3017  48  15   0 0.00
Sun 11/01 09Z 0.27 3017  44  12   0 0.00
Sun 11/01 10Z 0.27 3018  40  13   1 0.00
Sun 11/01 11Z 0.26 3019  36  15   1 0.00
Sun 11/01 12Z 0.27 3019  34  17   1 0.00
Sun 11/01 13Z 0.29 3020  30  19   2 0.00
Sun 11/01 14Z 0.32 3121  27  12   2 0.00
Sun 11/01 15Z 0.34 3123  26   5   2 0.00
Sun 11/01 16Z 0.33 3123  24   7   2 0.00
Sun 11/01 17Z 0.32 3124  29   6   2 0.00
Sun 11/01 18Z 0.32 3225  56   3   2 0.00
Sun 11/01 19Z 0.35 3124  65  32   2 0.00
Sun 11/01 20Z 0.40 3024  56  37   3 0.00
Sun 11/01 21Z 0.50 3025  59  29   3 0.00
Sun 11/01 22Z 0.57 3027  58  26   3 0.00
Sun 11/01 23Z 0.59 3028  57  21   3 0.00

Run total areal avg QPF for the Central_Greens is: 0.08 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