NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260510_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 05/10 18Z 4.22 2411  91  20   3 0.00
Sun 05/10 19Z 4.06 2513  88  29   3 0.00
Sun 05/10 20Z 3.17 2513  86  35   3 0.00
Sun 05/10 21Z 2.63 2515  83  31   3 0.01
Sun 05/10 23Z 4.17 2719  62  21   3 0.01
Mon 05/11 00Z 2.36 2822  59  18   2 0.00
Mon 05/11 01Z 1.71 2822  54  20   1 0.00
Mon 05/11 02Z 1.38 2921  50  24   0 0.00
Mon 05/11 03Z 1.09 2921  64  22   0 0.00
Mon 05/11 04Z 0.78 3020  74  17  -1 0.00
Mon 05/11 05Z 0.70 3119  75  18  -1 0.00
Mon 05/11 06Z 0.55 3116  76  18  -2 0.00
Mon 05/11 07Z 0.47 3115  78  18  -2 0.00
Mon 05/11 08Z 0.42 3114  79  16  -2 0.00
Mon 05/11 09Z 0.38 3114  78  16  -2 0.00
Mon 05/11 10Z 0.37 3115  76  16  -2 0.00
Mon 05/11 11Z 0.39 3114  73  20  -2 0.00
Mon 05/11 12Z 0.47 3114  74  26  -2 0.00
Mon 05/11 13Z 1.27 3013  74  33  -3 0.00
Mon 05/11 14Z 3.99 3011  68  36  -3 0.00
Mon 05/11 15Z 4.47 3010  63  40  -2 0.00
Mon 05/11 16Z 5.11 3010  63  37  -1 0.00
Mon 05/11 17Z 5.36 2909  63  38  -1 0.00
Mon 05/11 18Z 5.07 2808  64  57   0 0.00
Mon 05/11 19Z 5.01 2808  64  65   0 0.00
Mon 05/11 20Z 4.72 2909  63  73   0 0.00
Mon 05/11 21Z 4.21 2909  63  76   0 0.00
Mon 05/11 22Z 2.50 3009  63  70   0 0.00
Mon 05/11 23Z 1.06 3109  65  68   0 0.00
Tue 05/12 00Z 0.38 3210  69  67  -1 0.00
Tue 05/12 01Z 0.19 3311  73  68  -1 0.00
Tue 05/12 02Z 0.09 3412  74  70  -1 0.00
Tue 05/12 03Z 0.11 3414  78  68  -2 0.00
Tue 05/12 04Z 0.12 3416  78  68  -2 0.00
Tue 05/12 05Z 0.12 3418  76  71  -2 0.00
Tue 05/12 06Z 0.09 3419  72  71  -2 0.00
Tue 05/12 07Z 0.04 3419  67  57  -2 0.00
Tue 05/12 08Z 0.05 3419  65  46  -3 0.00
Tue 05/12 09Z 0.06 3418  66  31  -3 0.00
Tue 05/12 10Z 0.06 3417  66  24  -3 0.00
Tue 05/12 11Z 0.09 3415  67  33  -3 0.00
Tue 05/12 12Z 0.26 3313  68  47  -4 0.00
Tue 05/12 13Z 1.10 3311  70  56  -4 0.00
Tue 05/12 14Z 1.73 3211  70  49  -4 0.00
Tue 05/12 15Z 2.41 3211  68  33  -3 0.00
Tue 05/12 16Z 3.07 3211  64  25  -3 0.00
Tue 05/12 17Z 3.76 3112  62  25  -2 0.00
Tue 05/12 18Z 4.28 3111  64  31  -2 0.00
Tue 05/12 19Z 3.57 3110  64  38  -1 0.00
Tue 05/12 20Z 3.59 3110  65  44  -1 0.00
Tue 05/12 21Z 3.32 3110  66  45  -1 0.00
Tue 05/12 22Z 2.34 3109  67  43  -1 0.00
Tue 05/12 23Z 0.34 3207  66  33   0 0.00
Wed 05/13 00Z 0.21 3207  65  30   0 0.00
Wed 05/13 01Z 0.23 3107  65  29   0 0.00
Wed 05/13 02Z 0.10 3205  65  26   0 0.00
Wed 05/13 03Z 0.08 3102  65  27   0 0.00
Wed 05/13 04Z 0.12 2502  66  29   0 0.00
Wed 05/13 05Z 0.16 2303  66  32   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.02 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