NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260407_1200
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 04/07 12Z 0.08 1808  91  76  -7 0.00
Tue 04/07 13Z 0.12 1810  93  87  -7 0.00
Tue 04/07 14Z 0.16 1812  94  90  -7 0.00
Tue 04/07 15Z 0.34 2113  97  87  -7 0.02
Tue 04/07 16Z 1.35 2418  98  86  -7 0.04
Tue 04/07 17Z 2.77 2520  97  77  -8 0.01
Tue 04/07 18Z 7.04 2623  89  50  -9 0.01
Tue 04/07 20Z 1.07 2820  93  66  -9 0.00
Tue 04/07 21Z 0.71 3027  94  66 -10 0.01
Tue 04/07 22Z 0.51 3129  88  73 -11 0.02
Tue 04/07 23Z 0.58 3128  86  44 -12 0.00
Wed 04/08 00Z 0.72 3127  88  20 -12 0.00
Wed 04/08 01Z 0.74 3127  86  15 -13 0.00
Wed 04/08 02Z 0.70 3127  80  23 -13 0.00
Wed 04/08 04Z 0.55 3126  59  21 -13 0.00
Wed 04/08 05Z 0.46 3226  53  19 -12 0.00
Wed 04/08 06Z 0.37 3225  48  18 -12 0.00
Wed 04/08 07Z 0.33 3224  48  17 -12 0.00
Wed 04/08 08Z 0.29 3222  49  16 -11 0.00
Wed 04/08 09Z 0.25 3221  47  17 -10 0.00
Wed 04/08 10Z 0.22 3219  45  17 -10 0.00
Wed 04/08 11Z 0.19 3117  41  15  -9 0.00
Wed 04/08 12Z 0.17 3114  39  11  -9 0.00
Wed 04/08 13Z 0.18 3112  38   8  -9 0.00
Wed 04/08 14Z 0.18 3010  35   6  -8 0.00
Wed 04/08 15Z 0.17 3009  31   4  -7 0.00
Wed 04/08 16Z 0.18 2908  27   3  -6 0.00
Wed 04/08 17Z 0.20 2807  24   3  -5 0.00
Wed 04/08 19Z 0.28 2504  21   5  -5 0.00
Wed 04/08 20Z 0.29 2404  21   6  -4 0.00
Wed 04/08 21Z 0.23 2305  20   8  -3 0.00
Wed 04/08 22Z 0.20 2206  19   9  -3 0.00
Wed 04/08 23Z 0.21 2109  19   8  -2 0.00
Thu 04/09 00Z 0.26 2013  19   6  -2 0.00
Thu 04/09 01Z 0.29 2115  16   5  -1 0.00
Thu 04/09 02Z 0.35 2118  15   5   0 0.00
Thu 04/09 03Z 0.39 2120  19   5   0 0.00
Thu 04/09 04Z 0.39 2122  23   6   0 0.00
Thu 04/09 05Z 0.38 2123  24   6   1 0.00
Thu 04/09 06Z 0.36 2124  22   5   2 0.00
Thu 04/09 07Z 0.35 2125  19   6   2 0.00
Thu 04/09 08Z 0.36 2125  18   8   2 0.00
Thu 04/09 09Z 0.39 2126  17  14   2 0.00
Thu 04/09 10Z 0.41 2127  13  31   2 0.00
Thu 04/09 11Z 0.43 2129  11  42   2 0.00
Thu 04/09 12Z 0.44 2129   8  53   2 0.00
Thu 04/09 13Z 0.43 2130   7  70   3 0.00
Thu 04/09 14Z 0.40 2129   7  71   4 0.00
Thu 04/09 15Z 0.40 2129   9  60   4 0.00
Thu 04/09 16Z 0.42 2027  12  54   4 0.00
Thu 04/09 17Z 0.43 2026  14  49   3 0.00
Thu 04/09 18Z 0.44 2025  17  43   3 0.00
Thu 04/09 19Z 0.49 2024  19  39   3 0.00
Thu 04/09 20Z 0.51 2024  20  31   3 0.00
Thu 04/09 21Z 0.47 2025  20  28   4 0.00
Thu 04/09 22Z 0.40 2026  19  32   5 0.00
Thu 04/09 23Z 0.35 2027  20  41   6 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