Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260714_0600
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)
=== ===== === ==== ==== === === === ====
Tue 07/14 06Z 0.85 2823  64  76  16 0.00
Tue 07/14 07Z 0.99 2929  68  60  16 0.00
Tue 07/14 08Z 0.88 2929  71  37  16 0.00
Tue 07/14 09Z 0.75 2927  71  31  17 0.00
Tue 07/14 10Z 0.69 2826  69  38  17 0.00
Tue 07/14 11Z 0.66 2826  69  38  18 0.00
Tue 07/14 12Z 0.66 2826  70  32  18 0.00
Tue 07/14 13Z 0.65 2826  68  31  19 0.00
Tue 07/14 14Z 0.66 2826  68  41  19 0.00
Tue 07/14 15Z 0.69 2726  71  41  19 0.00
Tue 07/14 16Z 0.72 2725  75  30  20 0.00
Tue 07/14 17Z 0.76 2725  81  23  20 0.00
Tue 07/14 18Z 0.74 2624  78  21  21 0.00
Tue 07/14 19Z 1.31 2525  80  19  21 0.00
Tue 07/14 20Z 2.96 2526  79  21  21 0.00
Tue 07/14 21Z 4.22 2626  78  18  21 0.00
Tue 07/14 22Z 4.45 2628  80  15  21 0.00
Tue 07/14 23Z 1.76 2628  82  18  20 0.00
Wed 07/15 00Z 1.70 2731  82  32  20 0.00
Wed 07/15 01Z 1.49 2733  84  40  20 0.00
Wed 07/15 02Z 1.26 2834  85  56  19 0.00
Wed 07/15 03Z 1.10 2833  86  58  19 0.00
Wed 07/15 04Z 0.98 2932  89  57  19 0.01
Wed 07/15 05Z 0.90 2932  91  72  18 0.02
Wed 07/15 06Z 0.68 3030  91  76  18 0.02
Wed 07/15 07Z 0.53 3126  96  75  17 0.04
Wed 07/15 08Z 0.45 3224  93  53  16 0.05
Wed 07/15 09Z 0.36 3223  89  49  16 0.02
Wed 07/15 10Z 0.29 3221  89  61  15 0.01
Wed 07/15 11Z 0.34 3218  89  54  15 0.01
Wed 07/15 12Z 0.31 3216  87  49  14 0.01
Wed 07/15 13Z 0.36 3217  83  52  14 0.02
Wed 07/15 14Z 0.52 3117  73  20  14 0.02
Wed 07/15 15Z 1.23 3118  67  17  14 0.00
Wed 07/15 16Z 6.44 3017  76  23  13 0.00
Wed 07/15 17Z 8.18 3021  73  44  13 0.03
Wed 07/15 18Z 7.29 3023  63  44  13 0.04
Wed 07/15 19Z 10.72 3023  58  49  14 0.00
Wed 07/15 20Z 10.45 3024  59  42  14 0.00
Wed 07/15 21Z 11.04 3025  57  43  14 0.00
Wed 07/15 22Z 5.81 3024  56  34  14 0.00
Wed 07/15 23Z 1.96 3024  56  36  14 0.00
Thu 07/16 00Z 1.61 3025  58  42  14 0.00
Thu 07/16 01Z 1.53 3026  60  37  13 0.00
Thu 07/16 02Z 1.17 3027  62  38  13 0.00
Thu 07/16 03Z 0.87 3126  65  50  13 0.00
Thu 07/16 04Z 0.65 3124  68  48  13 0.00
Thu 07/16 05Z 0.55 3123  70  45  13 0.00
Thu 07/16 06Z 0.57 3123  70  46  12 0.00
Thu 07/16 07Z 0.53 3224  72  40  12 0.00
Thu 07/16 08Z 0.38 3223  71  33  11 0.00
Thu 07/16 09Z 0.39 3223  69  33  11 0.00
Thu 07/16 10Z 0.44 3124  65  32  11 0.00
Thu 07/16 11Z 0.44 3123  64  32  11 0.00
Thu 07/16 12Z 0.44 3121  62  33  11 0.00
Thu 07/16 13Z 0.49 3019  61  32  11 0.00
Thu 07/16 14Z 0.63 2918  62  32  11 0.00
Thu 07/16 15Z 0.87 2916  64  30  11 0.00
Thu 07/16 16Z 2.48 2714  68  29  12 0.00
Thu 07/16 17Z 7.58 2615  75  23  12 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