NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260703_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 07/03 18Z 5.97 2712  86  58  17 0.00
Fri 07/03 19Z 4.11 2714  83  62  18 0.00
Fri 07/03 20Z 3.62 2715  83  74  18 0.01
Fri 07/03 21Z 1.57 2915  77  79  18 0.01
Fri 07/03 22Z 1.24 2814  77  74  18 0.00
Fri 07/03 23Z 0.94 2816  79  80  18 0.01
Sat 07/04 00Z 0.88 2819  82  75  18 0.01
Sat 07/04 01Z 0.67 2918  72  77  18 0.01
Sat 07/04 02Z 0.51 3017  68  73  18 0.01
Sat 07/04 03Z 0.48 2916  66  68  18 0.00
Sat 07/04 04Z 0.48 2916  63  71  18 0.00
Sat 07/04 05Z 0.49 2917  67  70  18 0.00
Sat 07/04 06Z 0.42 3018  69  66  18 0.00
Sat 07/04 07Z 0.51 3020  75  63  17 0.00
Sat 07/04 08Z 0.48 3020  81  57  17 0.00
Sat 07/04 09Z 0.45 3020  85  51  16 0.00
Sat 07/04 10Z 0.43 3020  90  51  16 0.00
Sat 07/04 11Z 0.41 2918  91  53  16 0.00
Sat 07/04 12Z 0.34 3017  89  49  16 0.00
Sat 07/04 13Z 0.29 3117  87  41  16 0.00
Sat 07/04 14Z 0.27 3216  86  48  15 0.00
Sat 07/04 15Z 0.38 3115  86  52  14 0.00
Sat 07/04 16Z 0.80 3114  85  51  14 0.00
Sat 07/04 17Z 1.46 3113  83  48  14 0.00
Sat 07/04 18Z 2.64 3114  80  46  14 0.02
Sat 07/04 19Z 2.24 3114  80  30  14 0.01
Sat 07/04 20Z 2.08 3114  79  26  14 0.00
Sat 07/04 21Z 1.00 3115  77  23  14 0.00
Sat 07/04 22Z 0.65 3114  76  20  14 0.00
Sat 07/04 23Z 0.38 3213  75  18  14 0.00
Sun 07/05 00Z 0.20 3314  73  17  14 0.00
Sun 07/05 01Z 0.10 3415  73  13  13 0.00
Sun 07/05 02Z 0.08 3415  72  13  13 0.00
Sun 07/05 03Z 0.04 3415  72  15  13 0.00
Sun 07/05 04Z 0.06 3514  70  12  13 0.00
Sun 07/05 05Z 0.12 0012  69  12  13 0.00
Sun 07/05 06Z 0.14 0109  67  13  13 0.00
Sun 07/05 07Z 0.15 0206  64  21  13 0.00
Sun 07/05 08Z 0.15 0304  61  25  13 0.00
Sun 07/05 09Z 0.13 0603  61  30  13 0.00
Sun 07/05 10Z 0.16 0903  62  29  12 0.00
Sun 07/05 11Z 0.18 1004  63  35  12 0.00
Sun 07/05 12Z 0.18 1005  64  39  12 0.00
Sun 07/05 13Z 0.18 1105  68  38  12 0.00
Sun 07/05 14Z 0.28 1305  73  36  12 0.00
Sun 07/05 15Z 0.62 1305  78  30  11 0.00
Sun 07/05 16Z 0.64 1305  81  26  11 0.00
Sun 07/05 17Z 1.02 1205  82  28  12 0.01
Sun 07/05 18Z 1.04 1204  81  32  12 0.01
Sun 07/05 19Z 0.69 1203  81  29  12 0.00
Sun 07/05 20Z 0.30 1202  82  26  12 0.00
Sun 07/05 21Z 0.32 0902  83  24  13 0.00
Sun 07/05 22Z 0.42 0904  82  24  13 0.00
Sun 07/05 23Z 0.39 0905  84  23  12 0.00
Mon 07/06 00Z 0.37 1007  86  21  12 0.00
Mon 07/06 01Z 0.33 1108  88  20  12 0.01
Mon 07/06 02Z 0.31 1210  87  18  12 0.00
Mon 07/06 03Z 0.31 1211  83  18  12 0.00
Mon 07/06 04Z 0.32 1314  78  17  12 0.00
Mon 07/06 05Z 0.29 1315  75  20  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.12 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