NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260524_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)
=== ===== === ==== ==== === === === ====
Sun 05/24 18Z 0.25 1530  98  98   4 0.00
Sun 05/24 19Z 0.24 1534  95  98   5 0.05
Sun 05/24 20Z 0.20 1536  94  96   5 0.06
Sun 05/24 21Z 0.17 1536  93  92   6 0.02
Sun 05/24 22Z 0.16 1536  94  94   7 0.02
Sun 05/24 23Z 0.19 1537  94  91   7 0.03
Mon 05/25 00Z 0.22 1539  94  83   7 0.02
Mon 05/25 01Z 0.17 1540  95  77   8 0.02
Mon 05/25 02Z 0.08 1637  96  72   8 0.02
Mon 05/25 03Z 0.04 1631  96  67   9 0.02
Mon 05/25 04Z 0.06 1726  96  73   9 0.01
Mon 05/25 05Z 0.06 1723  97  84  10 0.01
Mon 05/25 06Z 0.11 1821  97  91  11 0.01
Mon 05/25 07Z 0.16 1920  97  91  11 0.01
Mon 05/25 08Z 0.17 1919  98  90  11 0.04
Mon 05/25 09Z 0.18 1918  99  93  11 0.09
Mon 05/25 10Z 0.16 1918  99  94  11 0.16
Mon 05/25 11Z 0.28 2118  99  95  10 0.26
Mon 05/25 12Z 0.35 2218  99  95  10 0.13
Mon 05/25 13Z 0.35 2416  99  94   9 0.09
Mon 05/25 14Z 0.32 2614  97  84  10 0.02
Mon 05/25 15Z 0.27 2713  95  75  10 0.01
Mon 05/25 16Z 0.26 2812  95  68  10 0.00
Mon 05/25 17Z 0.27 2913  95  62  10 0.00
Mon 05/25 18Z 0.30 3014  95  64  10 0.00
Mon 05/25 19Z 0.33 3015  93  22  10 0.00
Mon 05/25 20Z 0.46 3017  92   5  10 0.00
Mon 05/25 21Z 0.56 3017  93   7   9 0.00
Mon 05/25 22Z 0.59 2917  95   9   9 0.00
Mon 05/25 23Z 0.49 2916  92  12   9 0.00
Tue 05/26 00Z 0.48 2916  89  12   9 0.00
Tue 05/26 01Z 0.54 2918  88  15   9 0.00
Tue 05/26 02Z 0.34 3017  75  11  10 0.00
Tue 05/26 03Z 0.29 3117  66   8  11 0.00
Tue 05/26 04Z 0.28 3116  65   3  10 0.00
Tue 05/26 05Z 0.26 3116  62   2  10 0.00
Tue 05/26 06Z 0.24 3115  59   4  10 0.00
Tue 05/26 07Z 0.22 3215  56   9  10 0.00
Tue 05/26 08Z 0.27 3216  62  11   9 0.00
Tue 05/26 09Z 0.33 3115  66  16   9 0.00
Tue 05/26 10Z 0.43 3016  67  11   9 0.00
Tue 05/26 11Z 0.43 2916  64  10  10 0.00
Tue 05/26 12Z 0.40 2917  64  12  10 0.00
Tue 05/26 13Z 0.47 2817  62  20  10 0.00
Tue 05/26 14Z 0.51 2717  63  44  11 0.00
Tue 05/26 15Z 0.53 2818  57  69  12 0.00
Tue 05/26 16Z 0.53 2817  57  65  12 0.00
Tue 05/26 17Z 0.70 2716  66  61  12 0.00
Tue 05/26 18Z 1.14 2617  79  65  12 0.00
Tue 05/26 19Z 1.12 2519  83  65  12 0.00
Tue 05/26 20Z 1.40 2520  82  54  12 0.00
Tue 05/26 21Z 3.78 2523  78  62  13 0.00
Tue 05/26 22Z 4.81 2526  73  68  13 0.00
Tue 05/26 23Z 2.39 2529  72  67  13 0.00
Wed 05/27 00Z 2.18 2533  73  67  13 0.00
Wed 05/27 01Z 2.02 2635  73  64  13 0.00
Wed 05/27 02Z 1.86 2636  74  56  13 0.00
Wed 05/27 03Z 1.64 2736  77  52  12 0.00
Wed 05/27 04Z 1.44 2833  82  63  12 0.00
Wed 05/27 05Z 1.22 2830  86  60  12 0.00

Run total areal avg QPF for the Central_Greens is: 1.10 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