Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260611_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)
=== ===== === ==== ==== === === === ====
Thu 06/11 12Z 0.31 2709  93  61  15 0.00
Thu 06/11 13Z 0.44 2713  92  42  15 0.00
Thu 06/11 14Z 0.61 2817  93  42  15 0.00
Thu 06/11 15Z 0.48 2915  95  47  15 0.01
Thu 06/11 16Z 0.34 3012  93  63  16 0.00
Thu 06/11 17Z 0.30 3008  92  68  16 0.00
Thu 06/11 18Z 0.48 2809  94  69  16 0.00
Thu 06/11 19Z 0.50 2710  95  71  17 0.01
Thu 06/11 20Z 0.58 2813  95  72  17 0.01
Thu 06/11 21Z 0.51 2813  91  72  18 0.00
Thu 06/11 22Z 0.49 2814  87  78  18 0.00
Thu 06/11 23Z 0.45 2812  87  76  18 0.00
Fri 06/12 00Z 0.44 2811  88  68  18 0.00
Fri 06/12 01Z 0.42 2812  84  60  18 0.00
Fri 06/12 02Z 0.44 2711  84  57  18 0.00
Fri 06/12 03Z 0.47 2613  80  66  18 0.00
Fri 06/12 04Z 0.55 2615  76  71  18 0.00
Fri 06/12 05Z 0.57 2614  73  62  18 0.00
Fri 06/12 06Z 0.59 2514  70  59  18 0.00
Fri 06/12 07Z 0.53 2512  75  52  18 0.00
Fri 06/12 08Z 0.41 2411  79  60  18 0.00
Fri 06/12 09Z 0.31 2310  86  71  18 0.00
Fri 06/12 10Z 0.21 2208  90  81  18 0.00
Fri 06/12 11Z 0.19 2307  93  88  18 0.01
Fri 06/12 12Z 0.12 2304  94  89  17 0.00
Fri 06/12 13Z 0.15 2504  95  90  17 0.00
Fri 06/12 14Z 0.18 2505  93  89  17 0.01
Fri 06/12 15Z 0.20 2405  88  89  17 0.00
Fri 06/12 16Z 0.22 2305  83  46  18 0.00
Fri 06/12 17Z 1.34 2507  84  19  17 0.00
Fri 06/12 18Z 2.47 2709  82  17  18 0.00
Fri 06/12 19Z 1.50 2707  80  15  18 0.00
Fri 06/12 20Z 1.13 2407  81  32  19 0.00
Fri 06/12 21Z 0.92 2310  87  77  18 0.02
Fri 06/12 22Z 0.65 2415  88  68  18 0.13
Fri 06/12 23Z 0.83 2619  93  57  18 0.02
Sat 06/13 00Z 0.74 2721  94  60  16 0.07
Sat 06/13 01Z 0.66 2822  74  53  16 0.01
Sat 06/13 02Z 0.57 2922  59  21  16 0.00
Sat 06/13 03Z 0.49 2922  65  10  15 0.00
Sat 06/13 04Z 0.44 3023  71   5  14 0.00
Sat 06/13 05Z 0.39 3023  72   5  14 0.00
Sat 06/13 06Z 0.38 3123  72   9  13 0.00
Sat 06/13 07Z 0.34 3124  65  10  13 0.00
Sat 06/13 08Z 0.34 3125  60  10  13 0.00
Sat 06/13 09Z 0.32 3125  56  14  13 0.00
Sat 06/13 10Z 0.30 3226  51  13  12 0.00
Sat 06/13 11Z 0.26 3225  49  13  12 0.00
Sat 06/13 12Z 0.21 3222  51  13  13 0.00
Sat 06/13 13Z 0.22 3221  57  11  12 0.00
Sat 06/13 14Z 0.25 3217  62  12  12 0.00
Sat 06/13 15Z 0.32 3113  62   9  12 0.00
Sat 06/13 16Z 0.89 3011  63   8  12 0.00
Sat 06/13 17Z 1.66 3010  67   6  12 0.00
Sat 06/13 18Z 2.38 2809  71   5  12 0.00
Sat 06/13 19Z 2.36 2708  73   6  13 0.00
Sat 06/13 20Z 2.23 2709  76  11  13 0.00
Sat 06/13 21Z 1.97 2709  77  14  13 0.00
Sat 06/13 22Z 1.32 2608  76  14  13 0.00
Sat 06/13 23Z 0.77 2509  75  18  13 0.00

Run total areal avg QPF for the Central_Greens is: 0.30 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