NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260518_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 05/18 06Z 0.13 2505  61  42  12 0.00
Mon 05/18 07Z 0.14 2306  61  47  12 0.00
Mon 05/18 08Z 0.11 2107  62  52  13 0.00
Mon 05/18 09Z 0.12 2009  63  64  13 0.00
Mon 05/18 10Z 0.13 2011  64  84  13 0.00
Mon 05/18 11Z 0.15 2014  68  92  12 0.00
Mon 05/18 12Z 0.05 1818  72  87  13 0.01
Mon 05/18 13Z 0.23 2022  88  88  11 0.11
Mon 05/18 14Z 0.27 2025  89  78  12 0.10
Mon 05/18 15Z 0.34 2125  92  57  12 0.00
Mon 05/18 16Z 0.36 2222  92  36  13 0.00
Mon 05/18 17Z 0.37 2219  88  26  13 0.00
Mon 05/18 18Z 0.46 2318  83  19  14 0.00
Mon 05/18 19Z 0.72 2320  85  22  14 0.00
Mon 05/18 20Z 1.27 2321  85  21  14 0.00
Mon 05/18 21Z 1.00 2320  82  21  14 0.00
Mon 05/18 22Z 0.95 2321  85  21  15 0.00
Mon 05/18 23Z 1.05 2323  86  18  15 0.00
Tue 05/19 00Z 1.04 2323  87  18  15 0.00
Tue 05/19 01Z 1.09 2324  88  22  15 0.00
Tue 05/19 02Z 1.14 2327  89  19  15 0.00
Tue 05/19 03Z 1.23 2429  87  17  15 0.00
Tue 05/19 04Z 1.29 2432  82  15  16 0.00
Tue 05/19 05Z 1.39 2433  80  18  16 0.01
Tue 05/19 06Z 1.44 2536  79  37  15 0.00
Tue 05/19 07Z 1.60 2636  81  37  15 0.00
Tue 05/19 08Z 1.35 2634  82  29  15 0.01
Tue 05/19 09Z 1.23 2633  79  43  15 0.01
Tue 05/19 10Z 1.27 2633  78  39  15 0.00
Tue 05/19 11Z 1.24 2632  80  44  15 0.00
Tue 05/19 12Z 1.08 2630  82  48  15 0.00
Tue 05/19 13Z 1.07 2529  83  63  15 0.00
Tue 05/19 14Z 1.09 2529  82  68  15 0.00
Tue 05/19 15Z 1.18 2526  87  77  15 0.00
Tue 05/19 16Z 1.19 2523  91  76  14 0.00
Tue 05/19 17Z 2.11 2523  91  78  14 0.01
Tue 05/19 18Z 1.62 2524  87  76  14 0.01
Tue 05/19 19Z 3.12 2622  84  64  14 0.00
Tue 05/19 20Z 6.33 2622  85  72  15 0.00
Tue 05/19 21Z 6.57 2522  83  65  15 0.00
Tue 05/19 22Z 4.82 2523  82  66  15 0.00
Tue 05/19 23Z 2.27 2426  84  72  15 0.00
Wed 05/20 00Z 1.61 2430  80  63  16 0.00
Wed 05/20 01Z 1.57 2532  81  65  15 0.00
Wed 05/20 02Z 1.39 2433  84  65  16 0.00
Wed 05/20 03Z 1.47 2435  88  60  16 0.00
Wed 05/20 04Z 1.46 2436  91  57  16 0.00
Wed 05/20 05Z 1.31 2536  90  57  16 0.00
Wed 05/20 06Z 1.41 2539  92  63  15 0.00
Wed 05/20 07Z 1.20 2638  87  64  16 0.02
Wed 05/20 08Z 1.09 2536  86  61  16 0.02
Wed 05/20 09Z 1.36 2537  92  58  14 0.00
Wed 05/20 10Z 1.11 2635  88  65  14 0.01
Wed 05/20 11Z 1.09 2633  94  67  14 0.00
Wed 05/20 12Z 1.01 2631  94  59  14 0.01
Wed 05/20 13Z 1.09 2629  96  70  12 0.02
Wed 05/20 14Z 1.20 2628  97  76  12 0.05
Wed 05/20 15Z 1.27 2626  94  75  11 0.04
Wed 05/20 16Z 1.50 2625  92  79  10 0.02
Wed 05/20 17Z 4.84 2723  89  65   9 0.02

Run total areal avg QPF for the greens is: 0.48 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