Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260612_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)
=== ===== === ==== ==== === === === ====
Fri 06/12 18Z 2.67 2504  86  38  17 0.00
Fri 06/12 19Z 1.94 2507  80  29  18 0.00
Fri 06/12 20Z 0.99 2510  82  58  18 0.00
Fri 06/12 21Z 0.69 2512  83  70  18 0.01
Fri 06/12 22Z 0.58 2515  85  60  18 0.01
Fri 06/12 23Z 0.64 2616  86  49  18 0.02
Sat 06/13 00Z 0.73 2619  85  20  18 0.00
Sat 06/13 01Z 0.76 2721  90  17  17 0.01
Sat 06/13 02Z 0.76 2824  78  18  16 0.01
Sat 06/13 03Z 0.65 2825  69  17  16 0.00
Sat 06/13 04Z 0.61 2926  67  22  15 0.00
Sat 06/13 05Z 0.59 2926  72  26  14 0.00
Sat 06/13 06Z 0.53 3026  76  10  14 0.00
Sat 06/13 07Z 0.45 3025  79   8  13 0.00
Sat 06/13 08Z 0.37 3124  83   6  13 0.00
Sat 06/13 09Z 0.34 3122  86   8  12 0.00
Sat 06/13 10Z 0.34 3121  87   9  12 0.00
Sat 06/13 11Z 0.37 3120  85  10  11 0.00
Sat 06/13 12Z 0.34 3120  81  12  11 0.00
Sat 06/13 13Z 0.31 3117  77  13  11 0.00
Sat 06/13 14Z 0.32 3114  72  14  12 0.00
Sat 06/13 15Z 0.37 3012  66  17  12 0.00
Sat 06/13 16Z 0.51 2911  63  17  12 0.00
Sat 06/13 17Z 1.08 2810  63  15  12 0.00
Sat 06/13 18Z 3.82 2711  71  18  12 0.00
Sat 06/13 19Z 7.41 2612  79  16  12 0.00
Sat 06/13 20Z 6.18 2614  82  15  12 0.00
Sat 06/13 21Z 4.90 2615  79  15  12 0.00
Sat 06/13 22Z 3.64 2717  78  18  12 0.00
Sat 06/13 23Z 1.82 2718  76  35  12 0.00
Sun 06/14 00Z 1.01 2719  70  55  13 0.00
Sun 06/14 01Z 0.84 2621  62  42  14 0.00
Sun 06/14 02Z 0.89 2623  60  42  14 0.00
Sun 06/14 03Z 0.96 2725  64  48  13 0.00
Sun 06/14 04Z 0.94 2725  70  60  13 0.00
Sun 06/14 05Z 0.93 2626  74  74  13 0.00
Sun 06/14 06Z 0.94 2628  64  66  14 0.00
Sun 06/14 07Z 1.00 2527  64  71  14 0.00
Sun 06/14 08Z 1.09 2529  64  82  13 0.00
Sun 06/14 09Z 1.13 2529  65  61  14 0.00
Sun 06/14 10Z 1.12 2529  67  39  13 0.00
Sun 06/14 11Z 1.08 2529  74  32  13 0.00
Sun 06/14 12Z 0.99 2526  81  28  13 0.00
Sun 06/14 13Z 1.00 2524  82  29  13 0.00
Sun 06/14 14Z 0.92 2421  78  28  14 0.00
Sun 06/14 15Z 0.74 2320  70  28  15 0.00
Sun 06/14 16Z 0.80 2221  64  29  15 0.00
Sun 06/14 17Z 1.23 2121  61  28  15 0.00
Sun 06/14 18Z 2.09 2021  59  25  16 0.00
Sun 06/14 19Z 3.18 2021  58  25  16 0.00
Sun 06/14 20Z 5.20 2020  57  24  17 0.00
Sun 06/14 21Z 4.99 2022  60  38  16 0.00
Sun 06/14 22Z 1.60 2025  63  29  16 0.00
Sun 06/14 23Z 1.67 2127  71  83  16 0.00
Mon 06/15 00Z 0.88 2029  76  54  16 0.06
Mon 06/15 01Z 0.90 2033  78  42  15 0.00
Mon 06/15 02Z 0.89 2033  78  65  15 0.00
Mon 06/15 03Z 1.02 2134  79  62  15 0.00
Mon 06/15 04Z 0.81 2132  76  80  16 0.00
Mon 06/15 05Z 0.80 2134  82  75  15 0.02

Run total areal avg QPF for the Central_Greens is: 0.14 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