NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20250602_0600
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 06/02 06Z 0.71 2815  98  87   0 0.00
Mon 06/02 07Z 0.71 2817  97  96   0 0.01
Mon 06/02 08Z 0.70 2719  96  98   0 0.02
Mon 06/02 09Z 0.74 2820  95  97   0 0.02
Mon 06/02 10Z 0.77 2819  93  93   1 0.01
Mon 06/02 11Z 0.86 2821  93  68   1 0.00
Mon 06/02 12Z 0.81 2822  94  35   1 0.01
Mon 06/02 13Z 0.71 2720  91  22   2 0.00
Mon 06/02 14Z 0.76 2718  86  13   2 0.00
Mon 06/02 15Z 1.51 2718  87   5   2 0.01
Mon 06/02 16Z 6.46 2717  86   3   2 0.00
Mon 06/02 17Z 9.34 2717  74   9   2 0.00
Mon 06/02 18Z 10.16 2715  63  11   3 0.00
Mon 06/02 19Z 10.20 2715  57  13   3 0.00
Mon 06/02 20Z 8.75 2713  56  13   4 0.00
Mon 06/02 21Z 5.70 2713  56  14   4 0.00
Mon 06/02 22Z 2.36 2813  55  14   4 0.00
Mon 06/02 23Z 1.24 2814  55  15   5 0.00
Tue 06/03 00Z 1.37 2815  56  15   5 0.00
Tue 06/03 01Z 2.62 2916  59  24   4 0.00
Tue 06/03 02Z 1.08 2915  59  13   5 0.00
Tue 06/03 03Z 0.93 2914  59  12   5 0.00
Tue 06/03 04Z 1.24 2813  65  11   5 0.00
Tue 06/03 05Z 0.86 2810  62  10   5 0.00
Tue 06/03 06Z 0.83 2810  60   9   5 0.00
Tue 06/03 07Z 0.79 2809  56   8   5 0.00
Tue 06/03 08Z 0.69 2808  53   8   5 0.00
Tue 06/03 09Z 0.53 2908  49   9   6 0.00
Tue 06/03 10Z 0.41 2906  47   9   6 0.00
Tue 06/03 11Z 0.30 2905  44   8   6 0.00
Tue 06/03 12Z 0.23 2804  44   4   6 0.00
Tue 06/03 13Z 0.31 2505  45   2   6 0.00
Tue 06/03 14Z 0.32 2305  45   3   7 0.00
Tue 06/03 15Z 0.57 2306  46   5   7 0.00
Tue 06/03 16Z 1.19 2405  44   9   7 0.00
Tue 06/03 17Z 0.67 2405  43  40   8 0.00
Tue 06/03 18Z 0.93 2406  41  93   9 0.00
Tue 06/03 19Z 0.56 2408  44  94   9 0.00
Tue 06/03 20Z 0.40 2409  49  95   9 0.00
Tue 06/03 21Z 0.27 2309  51  85  10 0.00
Tue 06/03 22Z 0.20 2309  52  68  11 0.00
Tue 06/03 23Z 0.19 2308  60  50  12 0.00
Wed 06/04 00Z 0.19 2309  62  39  12 0.00
Wed 06/04 01Z 0.22 2311  55  29  13 0.00
Wed 06/04 02Z 0.24 2313  48  32  14 0.00
Wed 06/04 03Z 0.23 2313  47  31  14 0.00
Wed 06/04 04Z 0.19 2312  46  27  14 0.00
Wed 06/04 05Z 0.15 2211  45  21  14 0.00
Wed 06/04 06Z 0.14 2212  45  19  14 0.00
Wed 06/04 07Z 0.16 2213  46  13  14 0.00
Wed 06/04 08Z 0.19 2214  47  14  14 0.00
Wed 06/04 09Z 0.30 2317  50  17  14 0.00
Wed 06/04 10Z 0.34 2318  52  19  14 0.00
Wed 06/04 11Z 0.44 2318  53  20  13 0.00
Wed 06/04 12Z 0.45 2317  52  21  13 0.00
Wed 06/04 13Z 0.39 2317  53  14  13 0.00
Wed 06/04 14Z 0.29 2215  52  13  14 0.00
Wed 06/04 15Z 0.18 2114  52  12  14 0.00
Wed 06/04 16Z 0.06 2013  55  13  14 0.00
Wed 06/04 17Z 0.37 1912  59  16  14 0.00

Run total areal avg QPF for the Northern_Greens is: 0.08 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