NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260413_0000
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 04/13 00Z 0.16 1823  76  98   0 0.00
Mon 04/13 01Z 0.14 1828  70  99   0 0.02
Mon 04/13 02Z 0.20 1930  71  94   1 0.03
Mon 04/13 03Z 0.28 2031  79  98   2 0.04
Mon 04/13 04Z 0.35 2034  83  97   4 0.04
Mon 04/13 05Z 0.42 2235  88  98   7 0.05
Mon 04/13 06Z 0.44 2236  86  96   9 0.06
Mon 04/13 07Z 0.47 2239  78  97  10 0.03
Mon 04/13 08Z 0.54 2341  78  91  11 0.01
Mon 04/13 09Z 0.59 2440  79  82  11 0.01
Mon 04/13 10Z 0.60 2438  78  81  11 0.02
Mon 04/13 11Z 0.63 2439  74  81  12 0.01
Mon 04/13 12Z 0.67 2539  73  80  12 0.00
Mon 04/13 13Z 0.72 2539  73  65  11 0.00
Mon 04/13 14Z 0.68 2535  73  54  11 0.00
Mon 04/13 15Z 0.80 2436  77  65  10 0.00
Mon 04/13 16Z 0.77 2434  74  44  11 0.00
Mon 04/13 17Z 0.97 2337  74  78  10 0.01
Mon 04/13 18Z 1.25 2238  89  98   8 0.05
Mon 04/13 19Z 1.06 2341  97  94   8 0.11
Mon 04/13 20Z 1.24 2542  98  97   8 0.09
Mon 04/13 21Z 1.19 2639  98  86   9 0.08
Mon 04/13 22Z 1.29 2739  98  81   9 0.04
Mon 04/13 23Z 1.27 2738  97  81   9 0.05
Tue 04/14 00Z 1.33 2738  98  76   9 0.04
Tue 04/14 01Z 1.35 2836  97  69   8 0.03
Tue 04/14 02Z 1.26 2834  97  58   8 0.03
Tue 04/14 03Z 1.16 2932  98  43   7 0.03
Tue 04/14 04Z 0.97 2928  98  38   7 0.03
Tue 04/14 05Z 0.75 3025  97  36   7 0.03
Tue 04/14 06Z 0.60 3024  94  41   7 0.02
Tue 04/14 07Z 0.51 3022  91  42   7 0.01
Tue 04/14 08Z 0.45 2922  87  42   7 0.01
Tue 04/14 09Z 0.37 3020  82  37   8 0.01
Tue 04/14 10Z 0.32 3018  78  32   9 0.01
Tue 04/14 11Z 0.30 2916  73  32   9 0.01
Tue 04/14 12Z 0.28 2815  68  33  10 0.00
Tue 04/14 13Z 0.25 2713  62  47  10 0.00
Tue 04/14 14Z 0.23 2612  61  56  11 0.00
Tue 04/14 15Z 0.22 2511  60  49  11 0.00
Tue 04/14 16Z 0.26 2413  62  36  11 0.00
Tue 04/14 17Z 0.34 2416  61  53  11 0.00
Tue 04/14 18Z 0.28 2217  66  45  12 0.00
Tue 04/14 19Z 0.42 2222  76  53  12 0.00
Tue 04/14 20Z 0.38 2026  70  49  13 0.00
Tue 04/14 21Z 0.43 2031  61  54  14 0.00
Tue 04/14 22Z 0.68 2133  69  59  13 0.00
Tue 04/14 23Z 0.98 2137  80  59  13 0.00
Wed 04/15 00Z 1.13 2237  87  66  12 0.12
Wed 04/15 01Z 1.20 2534  94  78  12 0.35
Wed 04/15 02Z 1.23 2633  96  78  11 0.12
Wed 04/15 03Z 1.25 2632  97  76  11 0.05
Wed 04/15 04Z 1.19 2729  98  59  10 0.03
Wed 04/15 05Z 1.15 2728  98  26  10 0.03
Wed 04/15 06Z 1.04 2726  98  14  10 0.03
Wed 04/15 07Z 0.91 2725  96   9  10 0.03
Wed 04/15 08Z 0.76 2724  92  19  10 0.02
Wed 04/15 09Z 0.58 2822  85  40  11 0.02
Wed 04/15 10Z 0.47 2720  78  45  12 0.01
Wed 04/15 11Z 0.46 2619  79  46  12 0.01

Run total areal avg QPF for the greens is: 1.83 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