Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260621_1800
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 06/21 18Z 2.68 2909  91  79   9 0.00
Sun 06/21 19Z 1.02 2910  90  77   9 0.04
Sun 06/21 20Z 0.57 3013  85  73   9 0.12
Sun 06/21 21Z 0.63 2913  86  77   9 0.01
Sun 06/21 22Z 0.53 2913  87  75  10 0.01
Sun 06/21 23Z 0.53 2915  86  75  10 0.02
Mon 06/22 00Z 0.56 2916  88  72  10 0.02
Mon 06/22 01Z 0.55 2917  87  66  10 0.04
Mon 06/22 02Z 0.50 3017  88  58  10 0.06
Mon 06/22 03Z 0.46 3016  89  59   9 0.01
Mon 06/22 04Z 0.40 3014  87  53   9 0.00
Mon 06/22 05Z 0.35 3013  86  47  10 0.00
Mon 06/22 06Z 0.31 3012  84  38  10 0.00
Mon 06/22 07Z 0.31 2911  84  33  10 0.00
Mon 06/22 08Z 0.29 2810  83  29  10 0.00
Mon 06/22 09Z 0.32 2810  85  29   9 0.00
Mon 06/22 10Z 0.35 2710  86  27   9 0.00
Mon 06/22 11Z 0.40 2711  86  28   9 0.00
Mon 06/22 12Z 0.37 2710  83  25   9 0.00
Mon 06/22 13Z 0.28 2707  78  21   9 0.00
Mon 06/22 14Z 0.18 2704  74  23  10 0.00
Mon 06/22 15Z 0.25 2504  80  29   9 0.00
Mon 06/22 16Z 0.33 2405  80  47   9 0.00
Mon 06/22 17Z 0.26 2107  80  68   9 0.00
Mon 06/22 18Z 0.30 2010  85  77   9 0.01
Mon 06/22 19Z 0.24 2011  83  85   9 0.04
Mon 06/22 20Z 0.19 2012  81  90   9 0.05
Mon 06/22 21Z 0.12 1913  80  87   9 0.04
Mon 06/22 22Z 0.11 1814  80  91   9 0.03
Mon 06/22 23Z 0.12 1715  87  92   9 0.08
Tue 06/23 00Z 0.19 1516  90  93   9 0.15
Tue 06/23 01Z 0.24 1515  93  95   9 0.18
Tue 06/23 02Z 0.28 1417  95  97   9 0.16
Tue 06/23 03Z 0.28 1419  96  99   9 0.19
Tue 06/23 04Z 0.25 1518  97  97   9 0.11
Tue 06/23 05Z 0.25 1419  98  99  10 0.06
Tue 06/23 06Z 0.24 1416  98  97  10 0.16
Tue 06/23 07Z 0.18 1513  97  97  10 0.06
Tue 06/23 08Z 0.15 1509  98  95  10 0.02
Tue 06/23 09Z 0.11 1404  98  93  10 0.01
Tue 06/23 10Z 0.06 0202  98  90  10 0.01
Tue 06/23 11Z 0.04 0005  98  89  10 0.00
Tue 06/23 12Z 0.04 3509  98  79   9 0.00
Tue 06/23 13Z 0.06 3512  98  58   9 0.00
Tue 06/23 14Z 0.06 3514  95  48   9 0.00
Tue 06/23 15Z 0.09 3415  94  43   9 0.01
Tue 06/23 16Z 0.12 3416  91  37   9 0.01
Tue 06/23 17Z 0.17 3417  89  28  10 0.00
Tue 06/23 18Z 0.22 3418  86  20  10 0.00
Tue 06/23 19Z 0.31 3419  86  18  10 0.00
Tue 06/23 20Z 0.47 3318  86  18  10 0.00
Tue 06/23 21Z 0.38 3317  85  16  10 0.00
Tue 06/23 22Z 0.39 3316  88  33  10 0.02
Tue 06/23 23Z 0.52 3220  85  43  10 0.04
Wed 06/24 00Z 0.55 3222  87  43   9 0.01
Wed 06/24 01Z 0.61 3223  84  30   9 0.01
Wed 06/24 02Z 0.60 3223  85  25   9 0.00
Wed 06/24 03Z 0.51 3223  87  22   9 0.01
Wed 06/24 04Z 0.43 3222  90  19   9 0.01
Wed 06/24 05Z 0.38 3222  90  23   9 0.01

Run total areal avg QPF for the greens is: 1.82 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