NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260717_0000
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 00Z 0.51 3221  76   8  10 0.00
Fri 07/17 01Z 0.72 3226  66  15  10 0.00
Fri 07/17 02Z 0.91 3128  60  24  10 0.00
Fri 07/17 03Z 0.90 3130  56  30   9 0.00
Fri 07/17 04Z 0.90 3231  54  34   9 0.00
Fri 07/17 05Z 0.88 3231  54  33   9 0.00
Fri 07/17 06Z 0.87 3229  55  29   9 0.00
Fri 07/17 07Z 0.87 3228  59  28   8 0.00
Fri 07/17 08Z 0.68 3226  64  24   8 0.00
Fri 07/17 09Z 0.55 3225  67  18   8 0.00
Fri 07/17 10Z 0.49 3224  68  17   8 0.00
Fri 07/17 11Z 0.42 3224  67  15   8 0.00
Fri 07/17 12Z 0.39 3223  66  15   8 0.00
Fri 07/17 13Z 0.37 3221  66  16   8 0.00
Fri 07/17 14Z 0.38 3218  64  17   8 0.00
Fri 07/17 15Z 0.42 3216  62  18   8 0.00
Fri 07/17 16Z 0.44 3214  58  19   9 0.00
Fri 07/17 17Z 0.69 3113  55  20   9 0.00
Fri 07/17 18Z 0.97 3113  54  20   9 0.00
Fri 07/17 19Z 1.20 3011  56  20   9 0.00
Fri 07/17 20Z 1.48 2911  58  21  10 0.00
Fri 07/17 21Z 1.47 2810  58  21  10 0.00
Fri 07/17 22Z 0.81 2810  57  19  10 0.00
Fri 07/17 23Z 0.58 2810  53  16  11 0.00
Sat 07/18 00Z 0.56 2810  51  15  11 0.00
Sat 07/18 01Z 0.52 2710  49  14  11 0.00
Sat 07/18 02Z 0.51 2710  48  13  11 0.00
Sat 07/18 03Z 0.47 2609  48  12  11 0.00
Sat 07/18 04Z 0.47 2509  49  12  11 0.00
Sat 07/18 05Z 0.43 2509  49  12  11 0.00
Sat 07/18 06Z 0.44 2409  48  14  11 0.00
Sat 07/18 07Z 0.41 2409  49  17  11 0.00
Sat 07/18 08Z 0.38 2309  50  15  11 0.00
Sat 07/18 09Z 0.35 2211  49  15  11 0.00
Sat 07/18 10Z 0.38 2213  48  24  11 0.00
Sat 07/18 11Z 0.46 2216  50  59  12 0.00
Sat 07/18 12Z 0.47 2218  53  73  12 0.00
Sat 07/18 13Z 0.50 2220  57  64  13 0.00
Sat 07/18 14Z 0.58 2221  67  60  13 0.00
Sat 07/18 15Z 0.64 2122  71  65  14 0.00
Sat 07/18 16Z 1.24 2123  71  75  14 0.00
Sat 07/18 17Z 1.84 2024  69  80  15 0.00
Sat 07/18 18Z 2.80 2025  68  80  16 0.00
Sat 07/18 19Z 2.04 2025  74  76  16 0.00
Sat 07/18 20Z 0.89 2029  86  87  16 0.05
Sat 07/18 21Z 0.55 2032  90  78  15 0.04
Sat 07/18 22Z 0.56 2033  96  78  15 0.01
Sat 07/18 23Z 0.51 2033  98  63  15 0.02
Sun 07/19 00Z 0.57 2133  98  66  16 0.04
Sun 07/19 01Z 0.61 2232  90  71  16 0.19
Sun 07/19 02Z 0.60 2228  81  55  16 0.44
Sun 07/19 03Z 0.73 2330  91  32  15 0.04
Sun 07/19 04Z 0.75 2430  94  27  15 0.02
Sun 07/19 05Z 0.78 2628  94  39  14 0.03
Sun 07/19 07Z 0.93 2728  98  50  12 0.04
Sun 07/19 08Z 0.93 2928  98  27  10 0.07
Sun 07/19 09Z 0.71 3028  96  15   9 0.06
Sun 07/19 10Z 0.64 3129  94  21   8 0.04
Sun 07/19 11Z 0.57 3129  93  26   8 0.03

Run total areal avg QPF for the greens is: 1.12 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