Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260701_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)
=== ===== === ==== ==== === === === ====
Wed 07/01 18Z 0.91 2706  82  44  19 0.00
Wed 07/01 19Z 0.62 2507  81  34  20 0.00
Wed 07/01 20Z 0.52 2407  80  26  20 0.00
Wed 07/01 21Z 0.53 2408  81  20  20 0.00
Wed 07/01 22Z 0.72 2413  87  24  20 0.00
Wed 07/01 23Z 0.69 2418  87  36  20 0.01
Thu 07/02 00Z 0.76 2522  82  51  20 0.01
Thu 07/02 01Z 0.85 2623  86  50  20 0.00
Thu 07/02 02Z 0.85 2625  90  56  20 0.01
Thu 07/02 03Z 0.75 2625  83  48  21 0.00
Thu 07/02 04Z 0.53 2720  68  48  22 0.00
Thu 07/02 05Z 0.60 2623  64  54  21 0.00
Thu 07/02 06Z 0.65 2726  68  53  21 0.00
Thu 07/02 07Z 0.63 2827  67  48  21 0.00
Thu 07/02 08Z 0.53 2925  63  48  21 0.00
Thu 07/02 09Z 0.48 2924  58  47  21 0.00
Thu 07/02 10Z 0.45 2924  55  28  21 0.00
Thu 07/02 11Z 0.46 3025  55  37  20 0.00
Thu 07/02 12Z 0.48 2925  62  53  19 0.00
Thu 07/02 13Z 0.51 2924  75  55  19 0.00
Thu 07/02 14Z 0.53 2924  82  51  19 0.00
Thu 07/02 15Z 0.48 3021  82  52  19 0.00
Thu 07/02 16Z 0.48 2918  80  54  19 0.00
Thu 07/02 17Z 0.51 2816  80  60  20 0.00
Thu 07/02 18Z 0.61 2715  82  69  20 0.00
Thu 07/02 19Z 0.70 2616  83  65  20 0.00
Thu 07/02 20Z 0.84 2517  87  44  20 0.00
Thu 07/02 21Z 1.08 2519  89  32  20 0.00
Thu 07/02 22Z 1.25 2620  86  40  20 0.01
Thu 07/02 23Z 1.70 2625  82  51  20 0.02
Fri 07/03 00Z 1.29 2626  89  62  19 0.01
Fri 07/03 01Z 1.08 2627  82  49  20 0.01
Fri 07/03 02Z 1.08 2729  87  64  20 0.01
Fri 07/03 03Z 0.93 2729  84  62  20 0.00
Fri 07/03 04Z 0.85 2828  86  64  19 0.00
Fri 07/03 05Z 0.71 2927  77  60  19 0.00
Fri 07/03 06Z 0.64 2927  73  52  19 0.00
Fri 07/03 07Z 0.59 2926  74  51  19 0.00
Fri 07/03 08Z 0.53 3026  76  44  18 0.00
Fri 07/03 09Z 0.48 3025  74  43  18 0.00
Fri 07/03 10Z 0.45 3024  77  33  18 0.00
Fri 07/03 11Z 0.40 3021  74  27  18 0.00
Fri 07/03 12Z 0.36 3018  72  23  18 0.00
Fri 07/03 13Z 0.35 2917  69  16  18 0.00
Fri 07/03 14Z 0.41 2918  68  17  18 0.00
Fri 07/03 15Z 0.47 2919  69  15  18 0.00
Fri 07/03 16Z 0.57 2919  68  15  18 0.00
Fri 07/03 17Z 0.74 2819  71  13  18 0.00
Fri 07/03 18Z 2.53 2820  76  17  17 0.00
Fri 07/03 19Z 9.35 2820  74  22  17 0.00
Fri 07/03 20Z 10.80 2821  64  18  18 0.00
Fri 07/03 21Z 8.33 2822  59  21  18 0.00
Fri 07/03 22Z 3.46 2821  59  24  18 0.00
Fri 07/03 23Z 1.95 2822  60  24  18 0.00
Sat 07/04 00Z 1.72 2823  58  27  18 0.00
Sat 07/04 01Z 2.07 2825  66  24  17 0.00
Sat 07/04 02Z 1.23 2925  79  23  16 0.00
Sat 07/04 03Z 0.92 2925  82  25  16 0.00
Sat 07/04 04Z 0.82 3025  81  24  16 0.00
Sat 07/04 05Z 0.68 3024  79  23  16 0.00

Run total areal avg QPF for the Central_Greens is: 0.09 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