NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260223_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)
=== ===== === ==== ==== === === === ====
Mon 02/23 06Z 0.50 0715  90  72  -9 0.00
Mon 02/23 07Z 0.53 0717  90  56  -9 0.00
Mon 02/23 08Z 0.51 0619  89  64  -9 0.00
Mon 02/23 09Z 0.49 0521  83  69  -9 0.00
Mon 02/23 10Z 0.52 0525  77  69  -8 0.00
Mon 02/23 11Z 0.51 0527  71  61  -8 0.00
Mon 02/23 12Z 0.51 0528  61  56  -7 0.00
Mon 02/23 13Z 0.52 0529  56  60  -8 0.00
Mon 02/23 14Z 0.52 0529  51  60  -8 0.00
Mon 02/23 16Z 0.43 0325  57  66  -9 0.00
Mon 02/23 17Z 0.38 0223  68  71 -10 0.00
Mon 02/23 18Z 0.23 0123  71  72 -10 0.00
Mon 02/23 19Z 0.13 0023  75  66 -10 0.00
Mon 02/23 20Z 0.09 3524  77  62 -10 0.00
Mon 02/23 21Z 0.10 3526  77  59 -10 0.00
Mon 02/23 22Z 0.14 3529  75  48 -10 0.00
Mon 02/23 23Z 0.15 3533  73  38 -11 0.01
Tue 02/24 00Z 0.11 3536  80  28 -12 0.00
Tue 02/24 01Z 0.12 3534  88  21 -13 0.00
Tue 02/24 02Z 0.28 3432  94  17 -13 0.00
Tue 02/24 03Z 0.38 3430  93  12 -13 0.00
Tue 02/24 04Z 0.36 3328  93  11 -13 0.01
Tue 02/24 05Z 0.41 3327  94  12 -14 0.01
Tue 02/24 06Z 0.36 3328  93  12 -14 0.01
Tue 02/24 07Z 0.45 3328  94  13 -15 0.01
Tue 02/24 08Z 0.64 3325  97  16 -16 0.01
Tue 02/24 09Z 0.50 3224  93  17 -16 0.01
Tue 02/24 10Z 0.37 3224  88  19 -15 0.01
Tue 02/24 11Z 0.34 3223  87  27 -16 0.01
Tue 02/24 12Z 0.32 3223  87  33 -16 0.01
Tue 02/24 13Z 0.30 3122  88  41 -16 0.01
Tue 02/24 14Z 0.28 3121  88  45 -16 0.00
Tue 02/24 15Z 0.31 3120  90  44 -16 0.00
Tue 02/24 16Z 0.32 3119  89  52 -16 0.00
Tue 02/24 17Z 0.35 3017  89  57 -16 0.00
Tue 02/24 18Z 0.42 3017  89  57 -16 0.00
Tue 02/24 19Z 0.44 3016  88  54 -15 0.00
Tue 02/24 20Z 0.48 2915  88  57 -15 0.00
Tue 02/24 21Z 0.59 2914  88  51 -15 0.00
Tue 02/24 22Z 0.60 2815  89  37 -15 0.00
Tue 02/24 23Z 0.58 2816  89  18 -15 0.00
Wed 02/25 00Z 0.45 2815  87   7 -14 0.00
Wed 02/25 01Z 0.39 2715  85   3 -14 0.00
Wed 02/25 02Z 0.30 2613  77   4 -13 0.00
Wed 02/25 03Z 0.24 2512  68  11 -13 0.00
Wed 02/25 04Z 0.21 2411  57  29 -12 0.00
Wed 02/25 05Z 0.20 2312  50  50 -12 0.00
Wed 02/25 06Z 0.21 2214  43  66 -12 0.00
Wed 02/25 07Z 0.23 2216  36  85 -11 0.00
Wed 02/25 08Z 0.21 2117  41  85 -11 0.00
Wed 02/25 09Z 0.17 2019  50  87 -10 0.00
Wed 02/25 10Z 0.21 2023  70  88 -11 0.00
Wed 02/25 11Z 0.15 1925  89  85 -10 0.00
Wed 02/25 13Z 0.23 2025  94  87 -10 0.01
Wed 02/25 14Z 0.27 2022  95  69 -10 0.02
Wed 02/25 15Z 0.28 2119  95  53  -9 0.01
Wed 02/25 16Z 0.29 2118  94  46  -9 0.01
Wed 02/25 17Z 0.31 2116  94  43  -8 0.01

Run total areal avg QPF for the greens is: 0.17 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