Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260630_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)
=== ===== === ==== ==== === === === ====
Tue 06/30 12Z 0.37 2311  56  52  15 0.00
Tue 06/30 13Z 0.42 2311  54  48  15 0.00
Tue 06/30 14Z 0.42 2211  54  47  15 0.00
Tue 06/30 15Z 0.47 2210  55  41  16 0.00
Tue 06/30 16Z 1.08 2208  55  42  16 0.00
Tue 06/30 17Z 1.91 2209  56  53  16 0.00
Tue 06/30 18Z 1.74 2109  58  59  16 0.00
Tue 06/30 19Z 1.87 2110  62  64  17 0.00
Tue 06/30 20Z 2.27 2214  79  81  16 0.00
Tue 06/30 21Z 0.42 2313  86  82  16 0.01
Tue 06/30 22Z 0.46 2515  78  85  17 0.00
Tue 06/30 23Z 0.60 2618  83  83  16 0.00
Wed 07/01 00Z 0.61 2718  84  80  16 0.00
Wed 07/01 01Z 0.70 2620  83  78  17 0.00
Wed 07/01 02Z 0.66 2620  86  67  17 0.00
Wed 07/01 03Z 0.65 2519  90  62  17 0.00
Wed 07/01 04Z 0.56 2418  95  63  17 0.01
Wed 07/01 05Z 0.58 2418  96  52  17 0.01
Wed 07/01 08Z 0.64 2620  96  40  17 0.02
Wed 07/01 10Z 0.67 2622  97  29  18 0.02
Wed 07/01 11Z 0.69 2623  95  32  18 0.02
Wed 07/01 12Z 0.66 2623  94  42  19 0.02
Wed 07/01 13Z 0.58 2620  95  51  18 0.04
Wed 07/01 14Z 0.48 2716  94  65  19 0.05
Wed 07/01 15Z 0.36 2712  93  71  19 0.06
Wed 07/01 16Z 0.42 2613  95  68  19 0.06
Wed 07/01 17Z 0.37 2612  87  70  19 0.09
Wed 07/01 18Z 0.40 2612  88  71  20 0.14
Wed 07/01 19Z 0.41 2512  87  72  19 0.05
Wed 07/01 20Z 0.33 2710  79  66  20 0.13
Wed 07/01 21Z 0.51 2615  74  68  20 0.08
Wed 07/01 22Z 0.53 2618  75  52  21 0.24
Wed 07/01 23Z 0.59 2620  74  44  21 0.40
Thu 07/02 00Z 0.61 2823  73  46  21 0.02
Thu 07/02 01Z 0.66 2626  84  51  20 0.08
Thu 07/02 02Z 0.68 2625  70  57  21 0.01
Thu 07/02 03Z 0.60 2724  77  58  21 0.00
Thu 07/02 04Z 0.57 2824  81  42  20 0.01
Thu 07/02 05Z 0.56 2822  85  28  19 0.00
Thu 07/02 06Z 0.49 2821  86  28  19 0.00
Thu 07/02 07Z 0.45 2920  88  36  19 0.00
Thu 07/02 08Z 0.38 3019  85  27  19 0.00
Thu 07/02 09Z 0.35 3019  81   6  20 0.00
Thu 07/02 10Z 0.31 3019  73   3  20 0.00
Thu 07/02 11Z 0.30 3018  63   8  20 0.00
Thu 07/02 12Z 0.33 2918  46   7  21 0.00
Thu 07/02 13Z 0.29 3016  37  18  21 0.01
Thu 07/02 14Z 0.31 2915  36  27  22 0.01
Thu 07/02 15Z 0.31 2813  37  33  22 0.00
Thu 07/02 16Z 0.34 2813  52  28  22 0.00
Thu 07/02 17Z 0.38 2713  67  25  21 0.00
Thu 07/02 18Z 0.47 2713  67  27  21 0.00
Thu 07/02 19Z 0.77 2416  85  33  20 0.00
Thu 07/02 20Z 0.89 2518  88  44  20 0.00
Thu 07/02 21Z 1.04 2521  86  50  20 0.00
Thu 07/02 22Z 1.08 2523  81  48  20 0.00
Thu 07/02 23Z 1.27 2524  80  60  20 0.09

Run total areal avg QPF for the Central_Greens is: 1.68 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