Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260701_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 07/01 00Z 0.37 2214  82  94  16 0.00
Wed 07/01 01Z 0.47 2416  87  97  16 0.08
Wed 07/01 02Z 0.56 2419  90  90  16 0.09
Wed 07/01 03Z 0.63 2421  88  84  17 0.06
Wed 07/01 04Z 0.73 2425  87  72  17 0.02
Wed 07/01 05Z 0.75 2525  90  62  17 0.00
Wed 07/01 06Z 0.77 2525  92  55  17 0.01
Wed 07/01 07Z 0.82 2626  93  54  18 0.01
Wed 07/01 08Z 0.81 2626  93  53  18 0.00
Wed 07/01 09Z 0.85 2727  96  50  18 0.01
Wed 07/01 10Z 0.79 2725  96  50  18 0.02
Wed 07/01 11Z 0.71 2723  96  48  18 0.03
Wed 07/01 12Z 0.64 2821  94  45  18 0.02
Wed 07/01 13Z 0.49 2816  95  42  18 0.01
Wed 07/01 14Z 0.38 2812  95  38  18 0.01
Wed 07/01 15Z 0.34 2709  94  40  18 0.01
Wed 07/01 16Z 0.37 2609  91  40  18 0.00
Wed 07/01 17Z 0.40 2509  90  38  18 0.00
Wed 07/01 18Z 0.48 2511  89  40  19 0.00
Wed 07/01 19Z 0.56 2412  90  49  19 0.00
Wed 07/01 20Z 0.63 2515  91  46  19 0.00
Wed 07/01 21Z 0.63 2516  92  48  20 0.00
Wed 07/01 22Z 0.59 2417  92  46  20 0.00
Wed 07/01 23Z 0.69 2419  94  43  20 0.00
Thu 07/02 00Z 0.82 2521  92  42  20 0.00
Thu 07/02 01Z 0.85 2622  92  41  20 0.01
Thu 07/02 02Z 0.75 2623  90  38  20 0.00
Thu 07/02 03Z 0.80 2624  93  39  20 0.01
Thu 07/02 04Z 0.71 2723  91  38  20 0.00
Thu 07/02 05Z 0.71 2824  93  41  20 0.00
Thu 07/02 06Z 0.67 2823  91  39  20 0.01
Thu 07/02 07Z 0.68 2924  92  39  19 0.01
Thu 07/02 08Z 0.71 2925  93  46  19 0.01
Thu 07/02 09Z 0.68 2924  91  53  19 0.01
Thu 07/02 10Z 0.63 2923  92  40  19 0.01
Thu 07/02 11Z 0.63 2923  88  35  19 0.01
Thu 07/02 12Z 0.49 2920  74  45  20 0.01
Thu 07/02 13Z 0.53 2820  76  37  20 0.01
Thu 07/02 14Z 0.53 2820  76  52  20 0.01
Thu 07/02 15Z 0.54 2820  76  38  20 0.00
Thu 07/02 16Z 0.55 2718  77  30  20 0.00
Thu 07/02 17Z 0.53 2716  81  26  20 0.00
Thu 07/02 18Z 0.57 2617  80  27  21 0.00
Thu 07/02 19Z 0.68 2517  86  30  20 0.00
Thu 07/02 20Z 0.89 2518  89  32  20 0.00
Thu 07/02 21Z 1.48 2521  86  35  20 0.00
Thu 07/02 22Z 1.85 2622  85  33  20 0.00
Thu 07/02 23Z 1.20 2624  86  42  20 0.00
Fri 07/03 00Z 1.11 2626  88  49  20 0.00
Fri 07/03 01Z 1.04 2628  89  48  20 0.00
Fri 07/03 02Z 1.01 2630  88  58  20 0.00
Fri 07/03 03Z 0.97 2730  89  58  19 0.00
Fri 07/03 04Z 0.97 2730  88  58  19 0.00
Fri 07/03 05Z 0.97 2829  86  59  18 0.00
Fri 07/03 06Z 1.00 2829  89  51  18 0.00
Fri 07/03 07Z 0.86 2928  87  34  17 0.00
Fri 07/03 08Z 0.68 3027  84  25  18 0.01
Fri 07/03 09Z 0.58 3025  76  25  18 0.01
Fri 07/03 10Z 0.51 3024  67  19  18 0.01
Fri 07/03 11Z 0.50 3024  72  16  17 0.01

Run total areal avg QPF for the greens is: 0.53 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