NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260717_1800
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)
=== ===== === ==== ==== === === === ====
Fri 07/17 18Z 3.96 3010  64  15   9 0.00
Fri 07/17 19Z 2.79 2911  62  17  10 0.00
Fri 07/17 20Z 2.27 2911  59  18  10 0.00
Fri 07/17 21Z 1.54 2910  57  19  11 0.00
Fri 07/17 22Z 0.87 2810  54  17  11 0.00
Fri 07/17 23Z 0.53 2809  52  13  11 0.00
Sat 07/18 00Z 0.56 2710  51  11  12 0.00
Sat 07/18 01Z 0.60 2610  53  11  11 0.00
Sat 07/18 02Z 0.55 2610  56  11  11 0.00
Sat 07/18 03Z 0.59 2511  57   9  11 0.00
Sat 07/18 04Z 0.55 2511  57   9  11 0.00
Sat 07/18 05Z 0.55 2511  56   9  11 0.00
Sat 07/18 06Z 0.48 2412  53  19  12 0.00
Sat 07/18 07Z 0.43 2412  50  51  12 0.00
Sat 07/18 08Z 0.44 2413  47  73  12 0.00
Sat 07/18 09Z 0.47 2415  45  87  12 0.00
Sat 07/18 10Z 0.56 2414  49  91  11 0.00
Sat 07/18 11Z 0.38 2215  56  95  12 0.00
Sat 07/18 12Z 0.43 2120  62  88  12 0.00
Sat 07/18 13Z 0.57 2126  70  83  13 0.00
Sat 07/18 14Z 0.67 2128  77  63  14 0.00
Sat 07/18 15Z 0.73 2129  81  63  15 0.00
Sat 07/18 16Z 0.66 2128  82  57  16 0.00
Sat 07/18 17Z 0.73 2129  87  62  15 0.01
Sat 07/18 18Z 0.71 2130  91  81  15 0.02
Sat 07/18 19Z 0.52 2031  95  94  15 0.04
Sat 07/18 20Z 0.57 2131  97  48  16 0.04
Sat 07/18 21Z 0.66 2230  97  52  16 0.02
Sat 07/18 22Z 0.62 2231  94  61  17 0.02
Sat 07/18 23Z 0.68 2232  94  73  17 0.04
Sun 07/19 00Z 0.82 2333  93  64  16 0.06
Sun 07/19 01Z 0.77 2331  95  56  16 0.12
Sun 07/19 02Z 0.77 2427  95  44  15 0.14
Sun 07/19 03Z 0.77 2624  95  60  15 0.06
Sun 07/19 04Z 0.71 2821  98  68  14 0.10
Sun 07/19 05Z 0.58 3023  98  73  12 0.08
Sun 07/19 06Z 0.44 3226  96  60  11 0.03
Sun 07/19 07Z 0.41 3227  96  44   9 0.01
Sun 07/19 08Z 0.39 3328  94  33   9 0.01
Sun 07/19 09Z 0.34 3328  91  29   8 0.01
Sun 07/19 10Z 0.32 3328  90  27   8 0.01
Sun 07/19 11Z 0.34 3326  91  22   8 0.02
Sun 07/19 12Z 0.38 3224  93  21   7 0.02
Sun 07/19 13Z 0.44 3224  95  15   7 0.02
Sun 07/19 14Z 0.48 3223  94   9   7 0.01
Sun 07/19 15Z 0.51 3222  92   8   7 0.01
Sun 07/19 16Z 0.83 3219  89  13   7 0.00
Sun 07/19 17Z 5.02 3118  85  18   7 0.00
Sun 07/19 18Z 8.43 3118  76  22   8 0.00
Sun 07/19 19Z 10.18 3018  72  27   8 0.00
Sun 07/19 20Z 10.52 3019  69  18   8 0.00
Sun 07/19 21Z 10.02 3019  68   8   9 0.00
Sun 07/19 22Z 9.20 3020  67   4   9 0.00
Sun 07/19 23Z 3.51 3020  67   7   9 0.00
Mon 07/20 00Z 2.09 3022  67  10   9 0.00
Mon 07/20 01Z 1.73 3022  66  11   8 0.00
Mon 07/20 02Z 1.45 3122  66  15   8 0.00
Mon 07/20 03Z 1.21 3123  65  14   8 0.00
Mon 07/20 04Z 0.89 3222  64  14   8 0.00
Mon 07/20 05Z 0.75 3221  63  17   8 0.00

Run total areal avg QPF for the greens is: 0.90 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