Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260624_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)
=== ===== === ==== ==== === === === ====
Wed 06/24 06Z 0.18 3317  79  71   9 0.00
Wed 06/24 07Z 0.21 3316  79  52   9 0.00
Wed 06/24 08Z 0.27 3218  82  40   9 0.00
Wed 06/24 09Z 0.31 3220  83  39   9 0.00
Wed 06/24 10Z 0.30 3220  82  35   9 0.00
Wed 06/24 11Z 0.32 3220  83  34   9 0.00
Wed 06/24 12Z 0.34 3120  86  34   8 0.00
Wed 06/24 13Z 0.39 3120  86  39   8 0.00
Wed 06/24 14Z 0.46 3119  86  43   8 0.00
Wed 06/24 15Z 0.68 3117  87  46   8 0.00
Wed 06/24 16Z 1.97 3017  92  49   8 0.00
Wed 06/24 17Z 1.84 2917  90  44   8 0.00
Wed 06/24 18Z 3.64 2915  86  44   8 0.00
Wed 06/24 19Z 6.86 2916  83  44   9 0.00
Wed 06/24 20Z 7.73 2915  81  41   9 0.00
Wed 06/24 21Z 7.61 2918  76  46   9 0.00
Wed 06/24 22Z 4.64 2918  73  45  10 0.00
Wed 06/24 23Z 2.79 2920  73  46  10 0.00
Thu 06/25 00Z 2.01 2920  73  45   9 0.00
Thu 06/25 01Z 1.42 2921  80  44   9 0.00
Thu 06/25 02Z 0.85 2921  81  38   9 0.00
Thu 06/25 03Z 0.76 3020  78  30   9 0.00
Thu 06/25 04Z 0.69 3021  77  28   9 0.00
Thu 06/25 05Z 0.57 3019  74  22   9 0.00
Thu 06/25 06Z 0.51 3018  73  22   9 0.00
Thu 06/25 07Z 0.43 3116  70  13  10 0.00
Thu 06/25 08Z 0.42 3114  70   9  10 0.00
Thu 06/25 09Z 0.41 3011  70  12   9 0.00
Thu 06/25 10Z 0.40 2909  69  16   9 0.00
Thu 06/25 11Z 0.37 2707  69  14   9 0.00
Thu 06/25 12Z 0.32 2606  70  13   9 0.00
Thu 06/25 13Z 0.35 2506  73  21   9 0.00
Thu 06/25 14Z 0.59 2406  76  21   9 0.00
Thu 06/25 15Z 1.35 2406  77  19   9 0.00
Thu 06/25 16Z 2.07 2406  76  28   9 0.00
Thu 06/25 17Z 1.73 2307  75  40  10 0.00
Thu 06/25 18Z 2.31 2209  73  56  10 0.00
Thu 06/25 19Z 2.22 2211  69  64  10 0.00
Thu 06/25 20Z 0.62 2211  63  65  10 0.00
Thu 06/25 21Z 0.38 2309  54  61  10 0.00
Thu 06/25 22Z 0.25 2108  49  62  11 0.00
Thu 06/25 23Z 0.26 2008  52  81  11 0.00
Fri 06/26 00Z 0.17 1808  63  96  10 0.00
Fri 06/26 01Z 0.05 1612  72  97  10 0.00
Fri 06/26 02Z 0.05 1617  81  99  10 0.01
Fri 06/26 03Z 0.11 1720  91  98  10 0.05
Fri 06/26 04Z 0.19 1825  95  94  11 0.19
Fri 06/26 05Z 0.46 2026  95  91  11 0.11
Fri 06/26 06Z 0.50 2028  97  95  11 0.13
Fri 06/26 07Z 0.78 2232  96  87  11 0.21
Fri 06/26 08Z 0.74 2228  90  86  11 0.02
Fri 06/26 09Z 0.77 2328  94  82  11 0.04
Fri 06/26 10Z 0.65 2424  95  50  11 0.02
Fri 06/26 11Z 0.61 2422  93  37  11 0.02
Fri 06/26 12Z 0.56 2420  90  31  11 0.01
Fri 06/26 13Z 0.52 2518  88  32  12 0.01
Fri 06/26 14Z 0.51 2517  88  50  12 0.00
Fri 06/26 15Z 0.50 2415  86  59  12 0.00
Fri 06/26 16Z 0.55 2415  84  68  12 0.00
Fri 06/26 17Z 0.73 2315  85  56  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.82 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