NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260223_1800
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)
=== ===== === ==== ==== === === === ====
Mon 02/23 18Z 0.22 0020  80  80 -10 0.00
Mon 02/23 19Z 0.09 3523  79  80  -9 0.00
Mon 02/23 20Z 0.07 3524  78  81  -9 0.00
Mon 02/23 21Z 0.07 3529  75  82  -9 0.00
Mon 02/23 22Z 0.05 3531  77  81  -9 0.00
Mon 02/23 23Z 0.06 3433  77  77 -10 0.00
Tue 02/24 00Z 0.11 3433  78  66 -11 0.00
Tue 02/24 01Z 0.08 3432  81  58 -11 0.00
Tue 02/24 02Z 0.17 3433  90  49 -12 0.00
Tue 02/24 03Z 0.26 3332  94  46 -13 0.00
Tue 02/24 04Z 0.35 3331  93  45 -14 0.00
Tue 02/24 05Z 0.35 3332  92  44 -14 0.00
Tue 02/24 06Z 0.35 3332  93  42 -14 0.00
Tue 02/24 07Z 0.50 3228  96  37 -15 0.01
Tue 02/24 08Z 0.48 3226  95  36 -15 0.01
Tue 02/24 09Z 0.36 3225  93  37 -15 0.00
Tue 02/24 10Z 0.33 3225  92  41 -15 0.00
Tue 02/24 11Z 0.29 3224  91  45 -16 0.00
Tue 02/24 12Z 0.26 3224  90  47 -16 0.00
Tue 02/24 13Z 0.27 3224  91  47 -16 0.00
Tue 02/24 14Z 0.30 3123  91  49 -16 0.00
Tue 02/24 15Z 0.30 3122  90  48 -16 0.00
Tue 02/24 16Z 0.31 3120  88  48 -16 0.00
Tue 02/24 17Z 0.34 3118  85  49 -16 0.00
Tue 02/24 18Z 0.51 3017  85  48 -16 0.00
Tue 02/24 19Z 0.56 3016  85  45 -15 0.00
Tue 02/24 20Z 0.53 2915  85  46 -15 0.00
Tue 02/24 21Z 0.53 2915  84  47 -15 0.00
Tue 02/24 22Z 0.55 2815  85  37 -15 0.00
Tue 02/24 23Z 0.56 2817  86  23 -14 0.00
Wed 02/25 00Z 0.57 2817  87  11 -14 0.00
Wed 02/25 01Z 0.42 2715  85   3 -14 0.00
Wed 02/25 02Z 0.28 2712  78   2 -13 0.00
Wed 02/25 03Z 0.27 2512  72   4 -12 0.00
Wed 02/25 04Z 0.21 2410  62  12 -12 0.00
Wed 02/25 05Z 0.21 2312  51  34 -11 0.00
Wed 02/25 06Z 0.25 2314  43  73 -11 0.00
Wed 02/25 07Z 0.28 2216  32  87 -11 0.00
Wed 02/25 08Z 0.26 2115  42  75 -11 0.00
Wed 02/25 09Z 0.26 2118  53  49 -11 0.00
Wed 02/25 10Z 0.27 2022  67  85 -11 0.00
Wed 02/25 11Z 0.23 1924  89  86 -10 0.01
Wed 02/25 12Z 0.23 1926  91  87 -10 0.03
Wed 02/25 13Z 0.34 2024  95  91 -11 0.02
Wed 02/25 14Z 0.39 2120  96  85 -11 0.01
Wed 02/25 15Z 0.41 2216  96  87 -10 0.01
Wed 02/25 16Z 0.45 2213  96  84 -10 0.01
Wed 02/25 17Z 0.60 2212  95  73 -10 0.01
Wed 02/25 18Z 0.91 2212  93  64  -9 0.00
Wed 02/25 19Z 1.70 2312  89  52  -9 0.00
Wed 02/25 20Z 2.73 2313  87  67  -8 0.00
Wed 02/25 21Z 1.33 2315  87  88  -8 0.00
Wed 02/25 22Z 0.67 2216  92  89  -8 0.00
Wed 02/25 23Z 0.64 2217  93  85  -7 0.00
Thu 02/26 00Z 0.64 2219  94  84  -7 0.00
Thu 02/26 01Z 0.71 2222  96  79  -7 0.00
Thu 02/26 02Z 0.82 2224  97  64  -7 0.01
Thu 02/26 04Z 1.68 2625  96  75  -8 0.02
Thu 02/26 05Z 1.48 2725  94  50 -10 0.04

Run total areal avg QPF for the Central_Greens is: 0.19 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