NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260517_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)
=== ===== === ==== ==== === === === ====
Sun 05/17 06Z 1.06 2830  87  41  10 0.00
Sun 05/17 07Z 1.02 2831  85  36   9 0.00
Sun 05/17 08Z 0.90 2930  84  26   9 0.00
Sun 05/17 09Z 0.77 2929  75  18  10 0.00
Sun 05/17 10Z 0.67 2926  61  36  10 0.00
Sun 05/17 11Z 0.64 2925  52  49  10 0.00
Sun 05/17 12Z 0.64 2823  53  53  10 0.00
Sun 05/17 13Z 0.65 2822  59  50  10 0.00
Sun 05/17 14Z 0.72 2722  66  47  10 0.00
Sun 05/17 15Z 0.83 2719  82  42   9 0.00
Sun 05/17 16Z 1.19 2819  88  46   9 0.02
Sun 05/17 17Z 1.02 2819  86  46   9 0.03
Sun 05/17 18Z 1.20 2918  81  32   9 0.04
Sun 05/17 19Z 1.63 2917  81  33   9 0.02
Sun 05/17 20Z 1.60 3016  82  23   9 0.01
Sun 05/17 21Z 2.59 3017  77  25   9 0.00
Sun 05/17 22Z 1.88 3016  75  24   8 0.00
Sun 05/17 23Z 0.95 3015  72  21   8 0.00
Mon 05/18 00Z 0.68 3116  73  17   8 0.00
Mon 05/18 01Z 0.57 3115  73  15   8 0.00
Mon 05/18 02Z 0.47 3115  68  12   8 0.00
Mon 05/18 03Z 0.41 3115  61  10   8 0.00
Mon 05/18 04Z 0.35 3114  58  11   8 0.00
Mon 05/18 05Z 0.28 3012  55  21   9 0.00
Mon 05/18 06Z 0.25 3011  52  39  10 0.00
Mon 05/18 07Z 0.23 2910  49  60  11 0.00
Mon 05/18 08Z 0.21 2909  48  31  11 0.00
Mon 05/18 09Z 0.17 2807  47  26  11 0.00
Mon 05/18 10Z 0.20 2608  48  28  11 0.00
Mon 05/18 11Z 0.20 2409  49  40  11 0.00
Mon 05/18 12Z 0.19 2210  52  76  12 0.00
Mon 05/18 13Z 0.19 2113  60  80  12 0.00
Mon 05/18 14Z 0.21 2017  70  83  12 0.00
Mon 05/18 15Z 0.25 2020  78  59  12 0.00
Mon 05/18 16Z 0.28 2024  88  32  12 0.00
Mon 05/18 17Z 0.37 2026  89  54  12 0.00
Mon 05/18 18Z 0.52 2125  89  27  13 0.01
Mon 05/18 19Z 0.69 2224  85  25  13 0.00
Mon 05/18 20Z 0.97 2223  85  24  14 0.00
Mon 05/18 21Z 0.98 2224  88  21  14 0.01
Mon 05/18 22Z 0.82 2226  89  19  15 0.00
Mon 05/18 23Z 0.69 2228  89  20  15 0.00
Tue 05/19 00Z 0.68 2230  89  26  16 0.00
Tue 05/19 01Z 0.71 2331  90  30  16 0.01
Tue 05/19 02Z 0.80 2334  88  27  17 0.00
Tue 05/19 03Z 0.94 2437  87  21  17 0.01
Tue 05/19 04Z 1.08 2439  90  30  16 0.01
Tue 05/19 05Z 1.20 2538  92  29  16 0.02
Tue 05/19 06Z 1.37 2537  90  32  14 0.02
Tue 05/19 07Z 1.29 2635  88  41  14 0.01
Tue 05/19 08Z 1.16 2634  86  51  14 0.00
Tue 05/19 09Z 1.10 2633  85  37  14 0.00
Tue 05/19 10Z 0.88 2728  83  36  15 0.01
Tue 05/19 11Z 0.86 2628  85  41  14 0.00
Tue 05/19 12Z 0.77 2626  89  53  15 0.00
Tue 05/19 13Z 0.70 2624  84  76  15 0.01
Tue 05/19 14Z 0.75 2624  86  78  15 0.00
Tue 05/19 15Z 0.79 2621  87  79  14 0.00
Tue 05/19 16Z 0.91 2618  96  88  14 0.03
Tue 05/19 17Z 0.81 2720  92  80  13 0.15

Run total areal avg QPF for the greens is: 0.42 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