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_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)
=== ===== === ==== ==== === === === ====
Mon 02/23 12Z 0.51 0321  85  78 -10 0.00
Mon 02/23 13Z 0.50 0322  75  77  -9 0.00
Mon 02/23 14Z 0.51 0325  62  83  -9 0.00
Mon 02/23 15Z 0.52 0326  51  70  -9 0.00
Mon 02/23 16Z 0.51 0225  51  71  -9 0.00
Mon 02/23 17Z 0.48 0223  58  66 -10 0.00
Mon 02/23 18Z 0.50 0122  68  74 -11 0.00
Mon 02/23 19Z 0.30 0023  68  77 -10 0.00
Mon 02/23 20Z 0.16 3524  73  75 -10 0.00
Mon 02/23 21Z 0.08 3525  74  76 -10 0.00
Mon 02/23 22Z 0.05 3527  77  66 -10 0.00
Mon 02/23 23Z 0.05 3430  76  59 -10 0.01
Tue 02/24 00Z 0.09 3433  79  45 -11 0.00
Tue 02/24 01Z 0.06 3435  88  44 -12 0.00
Tue 02/24 02Z 0.12 3435  90  40 -12 0.00
Tue 02/24 03Z 0.23 3333  91  38 -13 0.00
Tue 02/24 04Z 0.34 3333  94  39 -13 0.00
Tue 02/24 05Z 0.42 3333  94  37 -14 0.00
Tue 02/24 06Z 0.42 3331  94  37 -14 0.00
Tue 02/24 07Z 0.39 3329  94  37 -15 0.01
Tue 02/24 08Z 0.43 3226  94  42 -15 0.01
Tue 02/24 09Z 0.37 3225  91  46 -15 0.01
Tue 02/24 10Z 0.33 3224  90  51 -15 0.00
Tue 02/24 11Z 0.30 3223  90  62 -15 0.00
Tue 02/24 12Z 0.29 3123  90  66 -16 0.00
Tue 02/24 13Z 0.29 3123  90  68 -16 0.00
Tue 02/24 14Z 0.27 3122  90  69 -16 0.00
Tue 02/24 15Z 0.26 3120  88  70 -16 0.00
Tue 02/24 16Z 0.27 3119  87  66 -15 0.00
Tue 02/24 17Z 0.30 3118  86  61 -15 0.00
Tue 02/24 18Z 0.40 3016  87  59 -16 0.00
Tue 02/24 19Z 0.53 2915  87  59 -16 0.00
Tue 02/24 20Z 0.50 2915  87  55 -15 0.00
Tue 02/24 21Z 0.43 2914  84  43 -15 0.00
Tue 02/24 22Z 0.52 2815  86  28 -15 0.00
Tue 02/24 23Z 0.46 2816  86  12 -14 0.00
Wed 02/25 00Z 0.43 2815  83   3 -14 0.00
Wed 02/25 01Z 0.33 2713  79   1 -13 0.00
Wed 02/25 02Z 0.33 2614  78   3 -13 0.00
Wed 02/25 03Z 0.26 2412  67   9 -12 0.00
Wed 02/25 04Z 0.20 2311  53  23 -11 0.00
Wed 02/25 05Z 0.21 2213  46  57 -11 0.00
Wed 02/25 06Z 0.28 2217  38  80 -11 0.00
Wed 02/25 07Z 0.31 2218  32  87 -10 0.00
Wed 02/25 08Z 0.26 2117  52  65 -10 0.00
Wed 02/25 09Z 0.24 2021  52  66 -10 0.00
Wed 02/25 10Z 0.29 2025  70  89 -10 0.00
Wed 02/25 11Z 0.27 1928  91  85 -10 0.02
Wed 02/25 12Z 0.30 1928  91  86 -10 0.04
Wed 02/25 13Z 0.36 2024  93  90 -10 0.03
Wed 02/25 14Z 0.38 2120  95  89 -10 0.01
Wed 02/25 15Z 0.42 2217  96  86  -9 0.01
Wed 02/25 16Z 0.47 2214  96  66  -9 0.01
Wed 02/25 17Z 0.58 2212  95  64  -9 0.01
Wed 02/25 18Z 0.95 2312  93  59  -9 0.00
Wed 02/25 19Z 2.14 2313  90  61  -8 0.00
Wed 02/25 20Z 3.46 2314  88  70  -8 0.00
Wed 02/25 21Z 2.14 2316  89  73  -8 0.00
Wed 02/25 22Z 1.00 2318  94  68  -8 0.00
Wed 02/25 23Z 0.83 2319  94  82  -8 0.00

Run total areal avg QPF for the Central_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