NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260224_0600
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)
=== ===== === ==== ==== === === === ====
Tue 02/24 06Z 0.47 3326  87  37 -13 0.00
Tue 02/24 07Z 0.54 3330  91  32 -14 0.00
Tue 02/24 08Z 0.40 3328  92  32 -14 0.00
Tue 02/24 09Z 0.34 3325  92  35 -14 0.00
Tue 02/24 10Z 0.34 3223  92  39 -15 0.00
Tue 02/24 11Z 0.36 3222  93  46 -15 0.00
Tue 02/24 12Z 0.34 3122  93  48 -15 0.00
Tue 02/24 13Z 0.30 3120  93  48 -15 0.00
Tue 02/24 14Z 0.30 3118  92  48 -16 0.00
Tue 02/24 15Z 0.34 3018  92  47 -16 0.00
Tue 02/24 16Z 0.38 3018  91  48 -16 0.00
Tue 02/24 17Z 0.39 3018  89  50 -16 0.00
Tue 02/24 18Z 0.44 3017  87  53 -16 0.00
Tue 02/24 19Z 0.58 3016  87  48 -16 0.00
Tue 02/24 20Z 0.56 3015  85  39 -15 0.00
Tue 02/24 22Z 0.57 2813  84  12 -15 0.00
Tue 02/24 23Z 0.63 2815  84   5 -15 0.00
Wed 02/25 00Z 0.59 2716  84   1 -15 0.00
Wed 02/25 01Z 0.46 2715  80   3 -15 0.00
Wed 02/25 02Z 0.38 2614  76   5 -14 0.00
Wed 02/25 03Z 0.29 2513  66  15 -13 0.00
Wed 02/25 04Z 0.19 2310  52  41 -12 0.00
Wed 02/25 05Z 0.21 2313  49  54 -11 0.00
Wed 02/25 06Z 0.25 2217  41  81 -11 0.00
Wed 02/25 07Z 0.25 2218  35  74 -10 0.00
Wed 02/25 08Z 0.17 2019  45  37 -10 0.00
Wed 02/25 09Z 0.15 1924  54  57 -10 0.00
Wed 02/25 10Z 0.15 1928  70  86  -9 0.00
Wed 02/25 11Z 0.15 1931  85  89  -9 0.00
Wed 02/25 12Z 0.16 1932  91  87  -9 0.01
Wed 02/25 13Z 0.24 2030  92  87  -9 0.04
Wed 02/25 14Z 0.31 2026  93  87  -9 0.06
Wed 02/25 15Z 0.37 2123  94  89  -9 0.04
Wed 02/25 16Z 0.46 2218  95  85  -9 0.03
Wed 02/25 17Z 0.62 2216  94  74  -8 0.01
Wed 02/25 18Z 1.31 2215  92  64  -8 0.00
Wed 02/25 19Z 2.95 2216  90  47  -8 0.00
Wed 02/25 20Z 2.10 2218  92  55  -8 0.00
Wed 02/25 21Z 0.98 2318  94  81  -8 0.00
Wed 02/25 22Z 0.82 2319  94  80  -7 0.00
Wed 02/25 23Z 0.78 2221  95  85  -7 0.01
Thu 02/26 00Z 0.96 2322  94  83  -7 0.01
Thu 02/26 01Z 1.40 2522  94  79  -8 0.03
Thu 02/26 02Z 1.59 2624  94  51  -9 0.02
Thu 02/26 03Z 1.66 2626  87  40 -10 0.01
Thu 02/26 04Z 1.27 2725  84  35 -11 0.01
Thu 02/26 05Z 1.04 2723  82  48 -11 0.00
Thu 02/26 06Z 1.10 2622  87  63 -11 0.00
Thu 02/26 07Z 1.11 2623  89  62 -12 0.00
Thu 02/26 08Z 1.26 2625  89  60 -12 0.00
Thu 02/26 09Z 1.43 2726  82  50 -13 0.00
Thu 02/26 10Z 1.42 2728  74  36 -14 0.00
Thu 02/26 11Z 1.33 2730  73  27 -15 0.00
Thu 02/26 12Z 1.27 2730  70  18 -15 0.00
Thu 02/26 13Z 1.47 2730  72  10 -16 0.00
Thu 02/26 14Z 1.74 2727  77   7 -16 0.00
Thu 02/26 15Z 6.85 2725  80   6 -17 0.00
Thu 02/26 16Z 11.83 2724  83   7 -17 0.00
Thu 02/26 17Z 13.35 2723  82   8 -16 0.00

Run total areal avg QPF for the greens is: 0.28 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