NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260518_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 05/18 12Z 0.25 1916  65  74  13 0.00
Mon 05/18 13Z 0.32 1920  66  62  13 0.00
Mon 05/18 14Z 0.40 2022  68  41  14 0.00
Mon 05/18 15Z 0.50 2023  68  27  14 0.00
Mon 05/18 16Z 0.72 2121  72  26  15 0.00
Mon 05/18 17Z 0.87 2219  74  24  15 0.00
Mon 05/18 18Z 2.34 2217  74  21  15 0.00
Mon 05/18 19Z 6.56 2318  76  22  15 0.00
Mon 05/18 20Z 5.34 2418  80  34  15 0.01
Mon 05/18 21Z 2.16 2317  84  25  15 0.01
Mon 05/18 22Z 1.42 2318  86  28  15 0.01
Mon 05/18 23Z 0.88 2319  86  42  16 0.01
Tue 05/19 00Z 0.96 2321  87  27  16 0.02
Tue 05/19 01Z 0.99 2323  85  34  16 0.00
Tue 05/19 02Z 0.91 2325  83  26  16 0.00
Tue 05/19 03Z 1.02 2328  78  27  16 0.00
Tue 05/19 04Z 1.15 2331  75  20  17 0.00
Tue 05/19 05Z 1.47 2436  75  21  17 0.00
Tue 05/19 06Z 1.77 2540  76  17  16 0.00
Tue 05/19 07Z 1.73 2539  78  17  15 0.02
Tue 05/19 08Z 1.74 2538  78  10  15 0.00
Tue 05/19 09Z 1.48 2638  79  14  15 0.03
Tue 05/19 10Z 1.39 2637  85  23  15 0.03
Tue 05/19 11Z 1.14 2537  73  42  16 0.01
Tue 05/19 12Z 1.08 2635  77  59  16 0.00
Tue 05/19 13Z 1.09 2633  86  55  15 0.00
Tue 05/19 14Z 1.15 2629  92  67  14 0.00
Tue 05/19 15Z 1.20 2626  93  72  14 0.00
Tue 05/19 16Z 1.34 2623  92  79  14 0.00
Tue 05/19 17Z 1.49 2621  91  76  14 0.00
Tue 05/19 18Z 1.78 2521  90  81  14 0.00
Tue 05/19 19Z 3.75 2622  88  84  14 0.00
Tue 05/19 20Z 2.15 2624  88  83  14 0.02
Tue 05/19 21Z 3.43 2622  84  76  14 0.00
Tue 05/19 22Z 3.70 2622  84  68  14 0.00
Tue 05/19 23Z 1.73 2623  84  68  15 0.00
Wed 05/20 00Z 0.97 2624  83  72  15 0.00
Wed 05/20 01Z 0.80 2626  79  61  16 0.00
Wed 05/20 02Z 0.95 2630  80  64  16 0.00
Wed 05/20 03Z 1.26 2535  88  70  16 0.00
Wed 05/20 04Z 1.10 2535  84  73  16 0.02
Wed 05/20 05Z 1.20 2535  91  75  16 0.00
Wed 05/20 06Z 1.23 2535  92  84  15 0.14
Wed 05/20 07Z 1.24 2535  91  80  15 0.10
Wed 05/20 08Z 1.22 2535  92  65  15 0.02
Wed 05/20 09Z 1.09 2533  91  54  15 0.00
Wed 05/20 10Z 1.04 2632  93  55  15 0.00
Wed 05/20 11Z 1.04 2631  92  72  15 0.01
Wed 05/20 12Z 1.03 2530  93  72  14 0.01
Wed 05/20 13Z 1.12 2528  95  81  13 0.01
Wed 05/20 14Z 1.13 2627  95  85  13 0.02
Wed 05/20 15Z 1.18 2627  96  92  13 0.04
Wed 05/20 16Z 1.07 2726  96  92  12 0.06
Wed 05/20 17Z 1.14 2727  93  91  11 0.06
Wed 05/20 18Z 4.75 2726  84  68  10 0.02
Wed 05/20 19Z 10.15 2822  78  39   9 0.00
Wed 05/20 20Z 8.69 2922  78  17   8 0.01
Wed 05/20 21Z 7.37 2924  81  15   8 0.00
Wed 05/20 22Z 2.73 3025  86   5   6 0.00
Wed 05/20 23Z 1.21 3026  89   2   5 0.00

Run total areal avg QPF for the Central_Greens is: 0.69 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