NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260324_0600
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 03/24 06Z 0.29 3321  93  32 -10 0.00
Tue 03/24 07Z 0.24 3320  88  24 -10 0.00
Tue 03/24 08Z 0.21 3318  86  18 -10 0.00
Tue 03/24 09Z 0.20 3317  86  13 -10 0.00
Tue 03/24 10Z 0.19 3317  84   9 -10 0.00
Tue 03/24 11Z 0.16 3317  81   7 -11 0.00
Tue 03/24 12Z 0.17 3318  81   8 -11 0.00
Tue 03/24 13Z 0.20 3318  77  12 -11 0.00
Tue 03/24 14Z 0.32 3215  74  13 -12 0.00
Tue 03/24 15Z 1.26 3111  72  10 -12 0.00
Tue 03/24 16Z 1.50 2808  65   6 -11 0.00
Tue 03/24 17Z 1.40 2508  56   5 -10 0.00
Tue 03/24 18Z 2.20 2410  54   5  -9 0.00
Tue 03/24 19Z 2.66 2412  51   6  -8 0.00
Tue 03/24 20Z 1.91 2413  47   6  -8 0.00
Tue 03/24 21Z 1.37 2416  50  10  -7 0.00
Tue 03/24 22Z 1.04 2419  49  15  -7 0.00
Tue 03/24 23Z 1.02 2423  47  46  -6 0.00
Wed 03/25 00Z 1.57 2528  43  66  -7 0.00
Wed 03/25 01Z 2.89 2630  48  49  -7 0.00
Wed 03/25 02Z 3.06 2630  53  80  -8 0.00
Wed 03/25 03Z 1.33 2728  69  80  -8 0.00
Wed 03/25 04Z 0.87 2825  84  42  -8 0.00
Wed 03/25 05Z 0.78 2824  87  11  -8 0.00
Wed 03/25 06Z 0.73 2823  87   6  -8 0.00
Wed 03/25 07Z 0.62 2822  78  12  -8 0.00
Wed 03/25 08Z 0.47 2819  64  14  -7 0.00
Wed 03/25 09Z 0.45 2718  62   9  -7 0.00
Wed 03/25 10Z 0.46 2719  61  10  -6 0.00
Wed 03/25 11Z 0.46 2818  61   8  -7 0.00
Wed 03/25 12Z 0.44 2717  63   9  -7 0.00
Wed 03/25 13Z 0.41 2717  62   9  -7 0.00
Wed 03/25 14Z 0.38 2715  60   9  -6 0.00
Wed 03/25 15Z 0.39 2714  60   8  -6 0.00
Wed 03/25 16Z 0.44 2613  61  21  -6 0.00
Wed 03/25 17Z 0.50 2613  68  29  -6 0.00
Wed 03/25 18Z 0.53 2512  70  45  -5 0.00
Wed 03/25 19Z 0.62 2511  73  79  -5 0.00
Wed 03/25 20Z 0.60 2410  75  93  -4 0.00
Wed 03/25 21Z 0.71 2311  71  95  -4 0.00
Wed 03/25 22Z 1.39 2213  69  96  -4 0.00
Wed 03/25 23Z 0.75 2215  66  92  -4 0.00
Thu 03/26 00Z 0.66 2118  53  93  -3 0.00
Thu 03/26 01Z 0.67 2021  65  90  -3 0.00
Thu 03/26 02Z 0.68 2023  73  81  -2 0.00
Thu 03/26 03Z 0.75 2126  81  88  -2 0.00
Thu 03/26 04Z 1.06 2327  93  88  -3 0.02
Thu 03/26 05Z 0.83 2425  82  89  -2 0.00
Thu 03/26 06Z 0.76 2324  86  89  -1 0.00
Thu 03/26 07Z 0.60 2126  82  85  -1 0.00
Thu 03/26 08Z 0.56 2227  77  89   0 0.00
Thu 03/26 09Z 0.58 2228  84  89   0 0.00
Thu 03/26 10Z 0.62 2328  86  95   0 0.00
Thu 03/26 11Z 0.60 2327  88  95   0 0.01
Thu 03/26 12Z 0.58 2426  93  94   0 0.04
Thu 03/26 13Z 0.60 2329  96  93   1 0.05
Thu 03/26 14Z 0.64 2430  95  91   2 0.03
Thu 03/26 15Z 0.64 2430  95  85   3 0.02
Thu 03/26 16Z 0.72 2432  95  82   3 0.03
Thu 03/26 17Z 0.78 2431  91  45   4 0.01

Run total areal avg QPF for the Central_Greens is: 0.21 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