Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260623_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)
=== ===== === ==== ==== === === === ====
Tue 06/23 18Z 0.05 3509  94  29  10 0.00
Tue 06/23 19Z 0.05 3409  91  26  11 0.00
Tue 06/23 20Z 0.08 3508  90  33  11 0.01
Tue 06/23 21Z 0.06 3508  88  40  11 0.02
Tue 06/23 22Z 0.04 3408  87  39  11 0.00
Tue 06/23 23Z 0.08 3410  88  28  11 0.00
Wed 06/24 00Z 0.10 3412  90  32  11 0.00
Wed 06/24 01Z 0.16 3313  89  40  10 0.01
Wed 06/24 02Z 0.22 3316  90  42  10 0.01
Wed 06/24 03Z 0.22 3318  92  41  10 0.01
Wed 06/24 04Z 0.21 3319  90  36   9 0.00
Wed 06/24 05Z 0.17 3317  87  31   9 0.00
Wed 06/24 06Z 0.15 3317  86  33   9 0.00
Wed 06/24 07Z 0.11 3315  84  36   9 0.00
Wed 06/24 08Z 0.11 3314  84  28   9 0.00
Wed 06/24 09Z 0.13 3314  84  25   9 0.00
Wed 06/24 10Z 0.16 3314  85  19   9 0.00
Wed 06/24 11Z 0.22 3215  87  21   8 0.00
Wed 06/24 12Z 0.27 3215  88  26   8 0.00
Wed 06/24 13Z 0.37 3115  90  30   7 0.00
Wed 06/24 14Z 0.61 3115  90  35   7 0.00
Wed 06/24 15Z 1.51 3114  88  37   7 0.00
Wed 06/24 16Z 2.52 3014  90  29   7 0.00
Wed 06/24 17Z 1.91 3014  89  32   8 0.00
Wed 06/24 18Z 4.08 3013  86  33   8 0.01
Wed 06/24 19Z 6.37 2914  85  38   9 0.00
Wed 06/24 20Z 6.04 2913  83  38   9 0.00
Wed 06/24 21Z 5.27 2915  80  36   9 0.00
Wed 06/24 22Z 2.30 2914  75  24  10 0.00
Wed 06/24 23Z 2.28 2917  76  23  10 0.00
Thu 06/25 00Z 1.71 2919  77  23  10 0.00
Thu 06/25 01Z 1.11 2920  83  20   9 0.00
Thu 06/25 02Z 0.83 3021  82  21   9 0.00
Thu 06/25 03Z 0.65 3019  81  16   9 0.00
Thu 06/25 04Z 0.55 3018  77  15   9 0.00
Thu 06/25 05Z 0.53 3016  77  11   9 0.00
Thu 06/25 06Z 0.47 3015  76   8   9 0.00
Thu 06/25 07Z 0.45 3013  75   8   9 0.00
Thu 06/25 08Z 0.47 2912  76   9   9 0.00
Thu 06/25 09Z 0.43 2910  75  14   9 0.00
Thu 06/25 10Z 0.43 2909  75  17   9 0.00
Thu 06/25 11Z 0.43 2808  76  18   9 0.00
Thu 06/25 12Z 0.41 2708  76  25   9 0.00
Thu 06/25 13Z 0.43 2706  76  39   9 0.00
Thu 06/25 14Z 0.66 2505  76  43   9 0.00
Thu 06/25 15Z 1.13 2406  76  60   9 0.00
Thu 06/25 16Z 1.62 2406  75  66  10 0.00
Thu 06/25 17Z 1.40 2406  71  71  10 0.00
Thu 06/25 18Z 1.21 2305  66  57  11 0.00
Thu 06/25 19Z 0.81 2003  64  24  11 0.00
Thu 06/25 20Z 0.57 1904  64  17  11 0.00
Thu 06/25 21Z 0.27 2003  66  25  11 0.00
Thu 06/25 22Z 0.10 1605  69  51  12 0.00
Thu 06/25 23Z 0.13 1608  71  75  11 0.00
Fri 06/26 00Z 0.20 1610  73  93  11 0.00
Fri 06/26 01Z 0.22 1712  80  90  11 0.00
Fri 06/26 02Z 0.23 1814  83  86  11 0.01
Fri 06/26 03Z 0.31 1918  84  85  11 0.01
Fri 06/26 04Z 0.43 1920  88  90  11 0.04
Fri 06/26 05Z 0.36 1921  90  94  11 0.05

Run total areal avg QPF for the Central_Greens is: 0.18 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