NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260304_0600
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)
=== ===== === ==== ==== === === === ====
Wed 03/04 06Z 0.34 2818  98  74  -2 0.00
Wed 03/04 07Z 0.27 3018  92  39  -1 0.00
Wed 03/04 08Z 0.24 3120  80  46   0 0.01
Wed 03/04 09Z 0.21 3118  61  38   0 0.01
Wed 03/04 10Z 0.21 3117  47  21   0 0.00
Wed 03/04 11Z 0.24 3017  43  12   0 0.00
Wed 03/04 12Z 0.30 2918  45  11   0 0.00
Wed 03/04 13Z 0.34 2920  43  10   0 0.00
Wed 03/04 14Z 0.35 3021  36   9   0 0.00
Wed 03/04 15Z 0.33 3021  35   8   0 0.00
Wed 03/04 16Z 0.27 3018  39   5   0 0.00
Wed 03/04 17Z 0.25 2913  44   5   0 0.00
Wed 03/04 18Z 0.28 2812  46   7   0 0.00
Wed 03/04 19Z 0.31 2712  46   7   0 0.00
Wed 03/04 21Z 0.39 2715  47  10   1 0.00
Wed 03/04 22Z 0.42 2717  46  12   1 0.00
Wed 03/04 23Z 0.41 2717  44  14   2 0.00
Thu 03/05 01Z 0.43 2718  47  19   2 0.00
Thu 03/05 02Z 0.41 2718  48  20   2 0.00
Thu 03/05 03Z 0.37 2816  46  19   2 0.00
Thu 03/05 04Z 0.40 2717  46  21   2 0.00
Thu 03/05 06Z 0.36 2815  48  16   1 0.00
Thu 03/05 07Z 0.32 2914  53  16   1 0.00
Thu 03/05 08Z 0.29 2914  59  15   1 0.00
Thu 03/05 09Z 0.28 2913  63  14   1 0.00
Thu 03/05 10Z 0.26 2913  65  15   1 0.00
Thu 03/05 11Z 0.20 2911  65  15   1 0.00
Thu 03/05 12Z 0.17 2910  62  14   1 0.00
Thu 03/05 13Z 0.12 3008  62  13   1 0.00
Thu 03/05 14Z 0.07 3105  65  15   1 0.00
Thu 03/05 15Z 0.04 3003  68  16   1 0.00
Thu 03/05 16Z 0.02 3001  69  16   1 0.00
Thu 03/05 17Z 0.02 1700  72  16   1 0.00
Thu 03/05 18Z 0.03 1402  76  16   0 0.00
Thu 03/05 19Z 0.05 1203  78  16   0 0.00
Thu 03/05 20Z 0.10 1104  81  16   0 0.00
Thu 03/05 21Z 0.18 1107  87  15  -1 0.00
Thu 03/05 22Z 0.21 1110  91  15  -1 0.00
Thu 03/05 23Z 0.18 1211  88  16   0 0.00
Fri 03/06 00Z 0.16 1212  83  17   0 0.00
Fri 03/06 01Z 0.14 1213  79  20   1 0.00
Fri 03/06 02Z 0.15 1315  77  21   1 0.01
Fri 03/06 03Z 0.15 1316  78  23   0 0.01
Fri 03/06 04Z 0.17 1318  79  26   0 0.01
Fri 03/06 05Z 0.17 1318  78  28   0 0.01
Fri 03/06 06Z 0.17 1320  78  30   0 0.01
Fri 03/06 07Z 0.16 1320  80  33   0 0.01
Fri 03/06 08Z 0.13 1419  86  38   0 0.01
Fri 03/06 09Z 0.13 1418  90  41   0 0.01
Fri 03/06 10Z 0.10 1417  91  43   0 0.01
Fri 03/06 11Z 0.09 1517  93  44   0 0.01
Fri 03/06 12Z 0.09 1416  93  46   0 0.00
Fri 03/06 13Z 0.10 1416  93  41   0 0.00
Fri 03/06 14Z 0.08 1516  94  43   0 0.00
Fri 03/06 15Z 0.09 1517  93  39   0 0.00
Fri 03/06 16Z 0.08 1516  93  36   0 0.00
Fri 03/06 17Z 0.06 1517  94  35   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.12 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