Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260630_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)
=== ===== === ==== ==== === === === ====
Tue 06/30 18Z 2.42 2208  78  83  15 0.00
Tue 06/30 19Z 1.06 2210  77  89  16 0.00
Tue 06/30 20Z 0.52 2210  78  87  16 0.00
Tue 06/30 21Z 0.69 2211  83  89  16 0.00
Tue 06/30 22Z 0.51 2414  85  87  16 0.02
Tue 06/30 23Z 0.42 2415  76  74  16 0.01
Wed 07/01 00Z 0.41 2516  78  79  17 0.01
Wed 07/01 01Z 0.41 2415  77  81  17 0.00
Wed 07/01 02Z 0.43 2220  75  75  18 0.00
Wed 07/01 03Z 0.45 2318  84  69  18 0.00
Wed 07/01 04Z 0.51 2518  90  71  17 0.01
Wed 07/01 05Z 0.52 2518  94  69  17 0.02
Wed 07/01 06Z 0.54 2518  95  67  18 0.01
Wed 07/01 07Z 0.55 2620  95  74  18 0.01
Wed 07/01 08Z 0.53 2620  92  62  18 0.09
Wed 07/01 09Z 0.59 2622  95  56  18 0.03
Wed 07/01 10Z 0.57 2621  95  46  18 0.01
Wed 07/01 11Z 0.48 2518  95  48  19 0.01
Wed 07/01 12Z 0.51 2619  95  44  19 0.01
Wed 07/01 13Z 0.51 2618  96  40  18 0.01
Wed 07/01 14Z 0.50 2616  96  43  18 0.01
Wed 07/01 15Z 0.49 2615  97  50  18 0.01
Wed 07/01 16Z 0.47 2614  96  50  19 0.01
Wed 07/01 17Z 0.49 2614  97  53  19 0.00
Wed 07/01 18Z 0.54 2615  94  57  19 0.00
Wed 07/01 19Z 0.55 2615  88  45  20 0.03
Wed 07/01 20Z 0.64 2416  92  41  20 0.00
Wed 07/01 21Z 0.68 2418  90  45  20 0.02
Wed 07/01 22Z 0.73 2522  94  37  20 0.02
Wed 07/01 23Z 0.69 2522  87  36  20 0.02
Thu 07/02 00Z 0.76 2724  89  40  20 0.01
Thu 07/02 01Z 0.65 2723  84  53  21 0.00
Thu 07/02 02Z 0.70 2726  85  55  21 0.00
Thu 07/02 03Z 0.66 2826  80  57  21 0.00
Thu 07/02 04Z 0.62 2826  79  61  21 0.00
Thu 07/02 05Z 0.60 2825  81  65  20 0.00
Thu 07/02 06Z 0.59 2925  86  55  20 0.00
Thu 07/02 07Z 0.54 2924  84  45  20 0.01
Thu 07/02 08Z 0.43 3022  79  30  20 0.01
Thu 07/02 09Z 0.32 3020  74  26  20 0.01
Thu 07/02 10Z 0.27 3018  67  22  21 0.01
Thu 07/02 11Z 0.27 3016  65  24  21 0.01
Thu 07/02 12Z 0.29 2916  62  27  21 0.00
Thu 07/02 13Z 0.32 2815  58  27  21 0.00
Thu 07/02 14Z 0.35 2816  54  27  21 0.00
Thu 07/02 15Z 0.39 2816  50  37  21 0.00
Thu 07/02 16Z 0.45 2817  51  43  21 0.00
Thu 07/02 17Z 0.44 2816  52  46  22 0.00
Thu 07/02 18Z 0.49 2815  57  52  21 0.00
Thu 07/02 19Z 0.72 2715  69  59  20 0.00
Thu 07/02 20Z 1.40 2615  71  46  20 0.00
Thu 07/02 21Z 1.94 2517  73  35  20 0.00
Thu 07/02 22Z 1.53 2518  79  46  20 0.00
Thu 07/02 23Z 1.92 2620  85  44  20 0.00
Fri 07/03 00Z 1.43 2622  84  59  20 0.00
Fri 07/03 01Z 1.27 2624  88  66  20 0.00
Fri 07/03 02Z 1.11 2727  89  64  19 0.01
Fri 07/03 03Z 1.05 2728  92  49  19 0.00
Fri 07/03 04Z 1.05 2731  93  51  19 0.01
Fri 07/03 05Z 0.90 2830  87  52  19 0.01

Run total areal avg QPF for the Central_Greens is: 0.46 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