Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260614_1200
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)
=== ===== === ==== ==== === === === ====
Sun 06/14 12Z 0.55 2418  73  34  14 0.00
Sun 06/14 13Z 0.63 2318  73  42  14 0.00
Sun 06/14 14Z 0.83 2319  75  43  14 0.00
Sun 06/14 15Z 2.12 2219  78  35  14 0.00
Sun 06/14 16Z 6.30 2119  80  50  14 0.00
Sun 06/14 17Z 7.72 2121  78  60  15 0.00
Sun 06/14 18Z 4.05 2122  72  52  15 0.01
Sun 06/14 19Z 3.80 2122  71  43  16 0.01
Sun 06/14 20Z 4.61 2317  83  74  15 0.05
Sun 06/14 21Z 0.64 2317  89  86  14 0.05
Sun 06/14 22Z 0.51 2415  94  92  13 0.30
Sun 06/14 23Z 0.31 2116  90  80  14 0.08
Mon 06/15 00Z 0.42 2022  86  87  14 0.01
Mon 06/15 01Z 0.43 2027  84  87  15 0.01
Mon 06/15 02Z 0.33 1927  92  96  15 0.10
Mon 06/15 03Z 0.48 2123  95  85  14 0.44
Mon 06/15 04Z 0.53 2222  94  81  14 0.23
Mon 06/15 05Z 0.60 2419  97  89  13 0.03
Mon 06/15 06Z 0.55 2718  97  92  11 0.07
Mon 06/15 07Z 0.30 2812  91  89  12 0.05
Mon 06/15 08Z 0.37 2814  93  88  11 0.01
Mon 06/15 09Z 0.35 2914  93  82  10 0.00
Mon 06/15 10Z 0.39 2915  94  92   9 0.00
Mon 06/15 11Z 0.38 2915  92  84   9 0.01
Mon 06/15 12Z 0.34 3015  87  60   9 0.00
Mon 06/15 13Z 0.37 3015  83  18   8 0.00
Mon 06/15 14Z 0.43 3015  81   7   8 0.00
Mon 06/15 15Z 0.63 3014  83  15   7 0.00
Mon 06/15 16Z 1.87 3013  87  28   7 0.00
Mon 06/15 17Z 2.42 3014  89  22   7 0.01
Mon 06/15 18Z 2.42 3014  88  13   7 0.00
Mon 06/15 19Z 2.95 3113  85  11   7 0.00
Mon 06/15 20Z 3.35 3113  86  16   7 0.00
Mon 06/15 21Z 2.93 3114  85  19   7 0.00
Mon 06/15 22Z 2.50 3014  85  17   6 0.00
Mon 06/15 23Z 1.13 3015  88  15   6 0.00
Tue 06/16 00Z 0.86 3018  89  15   6 0.00
Tue 06/16 01Z 0.80 3020  90  12   5 0.00
Tue 06/16 02Z 0.66 3020  95   6   5 0.00
Tue 06/16 03Z 0.57 3020  95   3   5 0.01
Tue 06/16 04Z 0.49 3121  96   2   5 0.01
Tue 06/16 05Z 0.41 3120  96   1   4 0.00
Tue 06/16 06Z 0.38 3120  97   4   4 0.01
Tue 06/16 07Z 0.39 3120  97   3   4 0.01
Tue 06/16 08Z 0.36 3219  96   4   4 0.01
Tue 06/16 09Z 0.28 3218  93   6   4 0.01
Tue 06/16 10Z 0.22 3216  91  16   5 0.00
Tue 06/16 11Z 0.21 3114  89  33   5 0.00
Tue 06/16 12Z 0.19 3112  86  43   5 0.00
Tue 06/16 13Z 0.18 3110  82  30   6 0.00
Tue 06/16 14Z 0.18 3009  77  30   6 0.00
Tue 06/16 15Z 0.22 2908  69  30   6 0.00
Tue 06/16 16Z 0.23 3007  60  29   7 0.00
Tue 06/16 17Z 0.60 2906  56  28   7 0.00
Tue 06/16 18Z 1.17 2805  55  32   8 0.00
Tue 06/16 19Z 1.48 2605  54  31   8 0.00
Tue 06/16 20Z 1.59 2506  58  25   9 0.00
Tue 06/16 21Z 1.35 2406  63  13   9 0.00
Tue 06/16 22Z 0.90 2306  66  14   9 0.00
Tue 06/16 23Z 0.42 2207  67  17   9 0.00

Run total areal avg QPF for the Central_Greens is: 1.53 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