NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260525_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)
=== ===== === ==== ==== === === === ====
Mon 05/25 12Z 0.32 2415  99  92   8 0.00
Mon 05/25 13Z 0.39 2517  98  90   8 0.04
Mon 05/25 14Z 0.38 2717  98  86   8 0.02
Mon 05/25 15Z 0.31 2915  96  74   9 0.01
Mon 05/25 16Z 0.35 3018  95  69   9 0.00
Mon 05/25 17Z 0.39 3019  95  62   9 0.00
Mon 05/25 18Z 0.45 3019  92  55   9 0.00
Mon 05/25 19Z 0.47 3016  92  34   9 0.00
Mon 05/25 20Z 0.57 2916  95  17   9 0.00
Mon 05/25 21Z 0.58 2916  96   9   9 0.01
Mon 05/25 22Z 0.60 2817  93   7   9 0.01
Mon 05/25 23Z 0.53 2917  83   6   9 0.01
Tue 05/26 00Z 0.45 2918  70   5  10 0.00
Tue 05/26 01Z 0.45 3018  62   6  10 0.00
Tue 05/26 02Z 0.43 3019  58   8  10 0.00
Tue 05/26 03Z 0.42 3121  55   9  10 0.00
Tue 05/26 04Z 0.44 3120  57  12   9 0.00
Tue 05/26 05Z 0.51 3121  61  15   9 0.00
Tue 05/26 06Z 0.57 3021  64  17   9 0.00
Tue 05/26 07Z 0.56 3021  64  18  10 0.00
Tue 05/26 08Z 0.48 3021  67  17  10 0.00
Tue 05/26 09Z 0.42 3121  69  17  10 0.00
Tue 05/26 10Z 0.40 3122  71  18  10 0.00
Tue 05/26 11Z 0.36 3120  77  17  10 0.00
Tue 05/26 12Z 0.37 3119  78  17  10 0.00
Tue 05/26 13Z 0.35 3117  75  14  10 0.00
Tue 05/26 14Z 0.38 3015  72  25  11 0.00
Tue 05/26 15Z 0.53 3014  72  46  11 0.00
Tue 05/26 16Z 0.63 2912  68  55  11 0.00
Tue 05/26 17Z 0.97 2811  67  59  12 0.00
Tue 05/26 18Z 1.81 2611  68  53  12 0.00
Tue 05/26 19Z 3.11 2513  69  50  12 0.00
Tue 05/26 20Z 4.41 2415  69  37  12 0.00
Tue 05/26 21Z 3.73 2318  73  29  12 0.00
Tue 05/26 22Z 2.08 2320  70  25  13 0.00
Tue 05/26 23Z 1.41 2324  61  26  13 0.00
Wed 05/27 00Z 1.43 2427  61  21  13 0.00
Wed 05/27 01Z 1.45 2429  66  20  12 0.00
Wed 05/27 02Z 1.39 2530  69  24  12 0.00
Wed 05/27 03Z 1.25 2531  60  33  13 0.00
Wed 05/27 04Z 1.17 2531  53  42  13 0.00
Wed 05/27 05Z 1.03 2630  48  51  13 0.00
Wed 05/27 06Z 1.00 2729  53  51  13 0.00
Wed 05/27 07Z 0.98 2728  59  58  12 0.00
Wed 05/27 08Z 0.88 2826  63  61  12 0.00
Wed 05/27 09Z 0.78 2925  77  62  11 0.00
Wed 05/27 10Z 0.73 2823  81  66  11 0.00
Wed 05/27 11Z 0.68 2822  82  58  11 0.00
Wed 05/27 12Z 0.67 2821  83  61  11 0.00
Wed 05/27 13Z 0.60 2818  86  69  11 0.00
Wed 05/27 14Z 0.62 2817  89  57  11 0.00
Wed 05/27 15Z 0.73 2815  87  56  11 0.00
Wed 05/27 16Z 1.07 2814  90  59  11 0.00
Wed 05/27 17Z 2.13 2813  93  49  11 0.01
Wed 05/27 18Z 0.67 2912  95  50  11 0.01
Wed 05/27 19Z 0.41 3012  93  45  11 0.02
Wed 05/27 20Z 0.66 3113  89  44  10 0.01
Wed 05/27 21Z 0.70 3213  85  34  10 0.00
Wed 05/27 22Z 0.50 3214  80  24   9 0.00
Wed 05/27 23Z 0.25 3315  81  18   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.15 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