Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260627_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)
=== ===== === ==== ==== === === === ====
Sat 06/27 18Z 0.85 3004  87  59  11 0.00
Sat 06/27 19Z 0.49 3105  85  58  12 0.03
Sat 06/27 20Z 0.30 3205  85  57  12 0.02
Sat 06/27 21Z 0.21 3305  86  52  12 0.01
Sat 06/27 22Z 0.11 3404  87  52  12 0.00
Sat 06/27 23Z 0.06 3404  87  58  12 0.00
Sun 06/28 00Z 0.05 3404  84  64  12 0.00
Sun 06/28 01Z 0.06 0004  81  67  12 0.00
Sun 06/28 02Z 0.14 0304  82  72  12 0.00
Sun 06/28 03Z 0.13 0303  84  69  12 0.00
Sun 06/28 04Z 0.10 0203  85  66  12 0.00
Sun 06/28 05Z 0.04 0003  84  59  11 0.00
Sun 06/28 06Z 0.05 0005  82  56  12 0.00
Sun 06/28 07Z 0.06 0005  78  48  12 0.00
Sun 06/28 08Z 0.11 0106  76  37  12 0.00
Sun 06/28 09Z 0.14 0206  76  35  11 0.00
Sun 06/28 10Z 0.16 0207  76  34  11 0.00
Sun 06/28 11Z 0.18 0207  76  35  11 0.00
Sun 06/28 12Z 0.21 0308  76  34  11 0.00
Sun 06/28 13Z 0.22 0308  78  28  11 0.00
Sun 06/28 14Z 0.22 0307  80  24  11 0.00
Sun 06/28 15Z 0.37 0205  83  23  11 0.00
Sun 06/28 16Z 0.67 0203  85  25  11 0.00
Sun 06/28 17Z 0.67 0202  83  31  11 0.02
Sun 06/28 18Z 0.31 0001  82  33  12 0.03
Sun 06/28 19Z 0.14 3402  81  26  12 0.01
Sun 06/28 20Z 0.12 3303  81  24  12 0.01
Sun 06/28 21Z 0.13 3303  81  27  13 0.01
Sun 06/28 22Z 0.13 3305  79  34  13 0.01
Sun 06/28 23Z 0.04 3404  76  33  13 0.01
Mon 06/29 00Z 0.04 3406  72  32  13 0.01
Mon 06/29 01Z 0.04 3507  69  20  13 0.00
Mon 06/29 02Z 0.14 0107  71  18  12 0.00
Mon 06/29 03Z 0.19 0207  76  20  12 0.00
Mon 06/29 04Z 0.13 0107  77  24  12 0.00
Mon 06/29 05Z 0.13 0107  76  24  12 0.00
Mon 06/29 06Z 0.16 0108  75  23  12 0.00
Mon 06/29 07Z 0.11 0008  74  18  12 0.00
Mon 06/29 08Z 0.09 0008  73  14  12 0.00
Mon 06/29 09Z 0.09 0009  74  11  11 0.00
Mon 06/29 10Z 0.13 0009  75   9  11 0.00
Mon 06/29 11Z 0.14 0010  76   7  11 0.00
Mon 06/29 12Z 0.18 0110  76   5  11 0.00
Mon 06/29 13Z 0.23 0109  77   4  11 0.00
Mon 06/29 14Z 0.44 0106  80   4  11 0.00
Mon 06/29 15Z 0.33 3504  82   5  11 0.00
Mon 06/29 16Z 0.24 3303  82  13  12 0.01
Mon 06/29 17Z 0.49 3104  80  25  12 0.02
Mon 06/29 18Z 0.65 3104  77  24  12 0.01
Mon 06/29 19Z 1.08 3005  71  14  13 0.00
Mon 06/29 20Z 1.15 3005  66  12  13 0.00
Mon 06/29 21Z 0.81 3006  65   9  13 0.00
Mon 06/29 22Z 0.45 3006  68   7  13 0.00
Mon 06/29 23Z 0.31 3006  71   5  13 0.00
Tue 06/30 00Z 0.34 3006  75   5  13 0.00
Tue 06/30 01Z 0.31 3006  78   5  12 0.00
Tue 06/30 02Z 0.32 2905  79   6  12 0.00
Tue 06/30 03Z 0.31 2805  80   8  12 0.00
Tue 06/30 04Z 0.36 2806  80  15  12 0.00
Tue 06/30 05Z 0.44 2707  82  19  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.21 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