NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260904_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)
=== ===== === ==== ==== === === === ====
Fri 09/04 00Z 0.77 3018  82  51  13 0.00
Fri 09/04 01Z 0.89 3018  86  45  13 0.00
Fri 09/04 02Z 0.92 3019  86  47  12 0.00
Fri 09/04 03Z 0.67 3017  82  46  12 0.01
Fri 09/04 04Z 0.63 3016  80  45  12 0.01
Fri 09/04 05Z 0.58 3016  82  43  12 0.01
Fri 09/04 06Z 0.47 3014  83  45  12 0.00
Fri 09/04 07Z 0.41 3012  85  42  12 0.01
Fri 09/04 08Z 0.41 3013  89  44  12 0.01
Fri 09/04 09Z 0.35 3112  90  39  12 0.01
Fri 09/04 10Z 0.30 3112  88  38  11 0.01
Fri 09/04 11Z 0.25 3211  86  41  11 0.00
Fri 09/04 12Z 0.30 3212  85  43  11 0.00
Fri 09/04 13Z 0.33 3213  82  34  10 0.01
Fri 09/04 14Z 0.37 3112  81  25  10 0.00
Fri 09/04 15Z 0.73 3112  84  26  10 0.00
Fri 09/04 16Z 1.84 3112  85  31  10 0.00
Fri 09/04 17Z 2.21 3112  87  40  10 0.00
Fri 09/04 18Z 1.40 3013  89  49  10 0.01
Fri 09/04 19Z 1.11 3014  89  45  10 0.01
Fri 09/04 20Z 1.05 3014  88  47  10 0.00
Fri 09/04 21Z 0.87 3115  89  44  10 0.00
Fri 09/04 22Z 0.59 3116  90  40  10 0.00
Fri 09/04 23Z 0.48 3216  91  44  10 0.00
Sat 09/05 00Z 0.36 3216  92  47  10 0.01
Sat 09/05 01Z 0.25 3316  93  55  10 0.02
Sat 09/05 02Z 0.22 3316  93  58  10 0.01
Sat 09/05 03Z 0.18 3416  93  56  10 0.01
Sat 09/05 04Z 0.13 3416  93  56  10 0.01
Sat 09/05 05Z 0.10 3416  93  57  10 0.01
Sat 09/05 06Z 0.08 3514  93  55  10 0.01
Sat 09/05 07Z 0.08 0013  93  59  10 0.01
Sat 09/05 08Z 0.10 0014  93  64   9 0.01
Sat 09/05 09Z 0.09 0014  93  65   9 0.01
Sat 09/05 10Z 0.10 0015  94  66   9 0.01
Sat 09/05 11Z 0.12 0116  95  71   9 0.01
Sat 09/05 12Z 0.15 0116  94  72   9 0.00
Sat 09/05 13Z 0.15 0116  93  70   9 0.00
Sat 09/05 14Z 0.15 0115  94  68   9 0.00
Sat 09/05 15Z 0.17 0114  95  67   9 0.00
Sat 09/05 16Z 0.18 0113  96  66   8 0.00
Sat 09/05 17Z 0.16 0112  96  66   8 0.00
Sat 09/05 18Z 0.21 0211  97  65   8 0.01
Sat 09/05 19Z 0.20 0211  97  65   8 0.01
Sat 09/05 20Z 0.22 0211  97  66   8 0.01
Sat 09/05 21Z 0.29 0311  96  68   8 0.01
Sat 09/05 22Z 0.33 0311  96  71   8 0.00
Sat 09/05 23Z 0.33 0412  96  75   8 0.01
Sun 09/06 00Z 0.39 0513  97  79   8 0.02
Sun 09/06 01Z 0.52 0714  95  80   8 0.03
Sun 09/06 02Z 0.59 0716  91  79   7 0.02
Sun 09/06 03Z 0.55 0716  89  77   7 0.00
Sun 09/06 04Z 0.51 0715  88  75   7 0.00
Sun 09/06 05Z 0.51 0715  84  71   7 0.00
Sun 09/06 06Z 0.44 0714  84  67   6 0.00
Sun 09/06 07Z 0.37 0712  84  61   7 0.00
Sun 09/06 08Z 0.29 0511  85  58   6 0.00
Sun 09/06 09Z 0.26 0411  84  54   6 0.00
Sun 09/06 10Z 0.24 0411  84  50   6 0.00
Sun 09/06 11Z 0.23 0312  83  52   6 0.00

Run total areal avg QPF for the greens is: 0.35 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