NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260217_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 02/17 06Z 0.24 2211  85  82  -4 0.00
Tue 02/17 07Z 0.28 2313  86  89  -3 0.00
Tue 02/17 08Z 0.28 2313  86  92  -3 0.00
Tue 02/17 09Z 0.29 2413  83  89  -2 0.00
Tue 02/17 10Z 0.29 2413  82  89  -2 0.00
Tue 02/17 11Z 0.27 2412  83  95  -2 0.00
Tue 02/17 12Z 0.24 2311  86  97  -2 0.00
Tue 02/17 13Z 0.27 2312  90  90  -2 0.00
Tue 02/17 16Z 0.30 2312  97  72  -2 0.00
Tue 02/17 17Z 0.33 2314  97  50  -2 0.00
Tue 02/17 18Z 0.37 2514  98  34  -2 0.01
Tue 02/17 19Z 0.34 2613  98  19  -2 0.01
Tue 02/17 20Z 0.34 2813  98  13  -2 0.01
Tue 02/17 21Z 0.36 2814  98  11  -3 0.01
Tue 02/17 22Z 0.41 2814  97  18  -3 0.01
Tue 02/17 23Z 0.46 2816  96  15  -3 0.00
Wed 02/18 00Z 0.49 2918  94  16  -3 0.00
Wed 02/18 01Z 0.54 2920  90  21  -3 0.01
Wed 02/18 02Z 0.53 2921  85  14  -3 0.01
Wed 02/18 03Z 0.52 2922  78  19  -3 0.01
Wed 02/18 04Z 0.52 2924  66  22  -2 0.01
Wed 02/18 05Z 0.56 2926  62  29  -3 0.01
Wed 02/18 06Z 0.55 2927  62  23  -3 0.00
Wed 02/18 07Z 0.51 2927  60  17  -3 0.00
Wed 02/18 08Z 0.45 3026  61  17  -3 0.00
Wed 02/18 09Z 0.36 3025  58  18  -3 0.00
Wed 02/18 10Z 0.32 3024  52  22  -3 0.00
Wed 02/18 11Z 0.27 3123  47  29  -3 0.00
Wed 02/18 12Z 0.26 3122  42  45  -3 0.00
Wed 02/18 13Z 0.23 3120  41  53  -3 0.00
Wed 02/18 14Z 0.20 3117  39  53  -3 0.00
Wed 02/18 15Z 0.17 3014  36  50  -3 0.00
Wed 02/18 16Z 0.16 3012  36  51  -3 0.00
Wed 02/18 17Z 0.13 3010  35  48  -3 0.00
Wed 02/18 18Z 0.10 3107  36  52  -3 0.00
Wed 02/18 19Z 0.07 3106  35  62  -3 0.00
Wed 02/18 20Z 0.06 3206  37  68  -3 0.00
Wed 02/18 21Z 0.03 3305  40  64  -3 0.00
Wed 02/18 23Z 0.04 0005  51  81  -4 0.00
Thu 02/19 00Z 0.09 0108  51  86  -4 0.00
Thu 02/19 01Z 0.13 0211  51  88  -5 0.00
Thu 02/19 02Z 0.10 0111  54  86  -6 0.00
Thu 02/19 03Z 0.08 0110  47  68  -7 0.00
Thu 02/19 04Z 0.07 0011  38  53  -6 0.00
Thu 02/19 05Z 0.08 0012  37  26  -6 0.00
Thu 02/19 06Z 0.09 0112  36   3  -6 0.01
Thu 02/19 07Z 0.06 0011  36   2  -6 0.00
Thu 02/19 08Z 0.05 0012  34   2  -6 0.00
Thu 02/19 09Z 0.08 0013  31   2  -6 0.00
Thu 02/19 10Z 0.06 0012  30   3  -6 0.00
Thu 02/19 11Z 0.08 0011  28   5  -5 0.00
Thu 02/19 12Z 0.10 0110  29   3  -5 0.00
Thu 02/19 13Z 0.09 0109  30   3  -5 0.00
Thu 02/19 14Z 0.08 0207  31   3  -5 0.00
Thu 02/19 15Z 0.05 0204  31   3  -4 0.00
Thu 02/19 16Z 0.06 0203  32   3  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.11 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