NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260410_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 04/10 18Z 2.44 2218  59  70   8 0.00
Fri 04/10 19Z 2.08 2219  58  58   9 0.00
Fri 04/10 20Z 1.14 2221  56  59  10 0.00
Fri 04/10 21Z 0.88 2121  58  49  10 0.00
Fri 04/10 22Z 0.87 2124  64  41  10 0.00
Fri 04/10 23Z 0.80 2621  80  95   8 0.05
Sat 04/11 00Z 0.63 2720  91  88   6 0.04
Sat 04/11 01Z 0.60 2721  96  97   6 0.04
Sat 04/11 02Z 0.67 2622  98  95   5 0.04
Sat 04/11 03Z 0.54 2718  99  97   3 0.08
Sat 04/11 04Z 0.35 2915  98  97   3 0.08
Sat 04/11 05Z 0.35 3018  98  85   1 0.03
Sat 04/11 06Z 0.38 3121  98  73   0 0.01
Sat 04/11 07Z 0.39 3122  95  67  -1 0.01
Sat 04/11 08Z 0.44 3125  92  39  -2 0.01
Sat 04/11 09Z 0.46 3127  89  18  -3 0.01
Sat 04/11 10Z 0.49 3128  88   7  -4 0.00
Sat 04/11 11Z 0.47 3129  84   4  -4 0.00
Sat 04/11 12Z 0.47 3230  82   4  -5 0.00
Sat 04/11 13Z 0.49 3228  85   4  -5 0.00
Sat 04/11 14Z 0.58 3127  84   6  -6 0.00
Sat 04/11 15Z 0.85 3126  89   9  -6 0.00
Sat 04/11 16Z 3.93 3124  91  10  -6 0.00
Sat 04/11 17Z 7.30 3122  88  10  -6 0.00
Sat 04/11 18Z 6.92 3020  85  10  -5 0.00
Sat 04/11 19Z 6.03 3018  84  11  -5 0.00
Sat 04/11 20Z 5.60 3117  83  10  -5 0.00
Sat 04/11 21Z 4.43 3118  83  10  -5 0.00
Sat 04/11 22Z 3.03 3119  82  10  -5 0.00
Sat 04/11 23Z 1.43 3121  82  10  -5 0.00
Sun 04/12 00Z 1.52 3122  82   9  -5 0.00
Sun 04/12 01Z 1.24 3124  80  10  -5 0.00
Sun 04/12 02Z 0.72 3125  76  11  -5 0.00
Sun 04/12 03Z 0.57 3226  75  11  -5 0.00
Sun 04/12 04Z 0.50 3226  74  13  -6 0.00
Sun 04/12 05Z 0.35 3225  71  13  -6 0.00
Sun 04/12 06Z 0.26 3323  69  12  -5 0.00
Sun 04/12 07Z 0.20 3321  62  14  -5 0.00
Sun 04/12 08Z 0.18 3320  59  16  -5 0.00
Sun 04/12 09Z 0.16 3319  58  20  -5 0.00
Sun 04/12 10Z 0.13 3317  55  22  -4 0.00
Sun 04/12 11Z 0.09 3316  49  21  -3 0.00
Sun 04/12 12Z 0.05 3413  47  22  -3 0.00
Sun 04/12 13Z 0.05 3308  47  28  -3 0.00
Sun 04/12 14Z 0.07 3205  46  32  -2 0.00
Sun 04/12 15Z 0.14 2804  47  34  -2 0.00
Sun 04/12 16Z 0.20 2504  46  38  -2 0.00
Sun 04/12 17Z 0.40 2305  45  39  -1 0.00
Sun 04/12 18Z 0.47 2206  43  40  -1 0.00
Sun 04/12 19Z 0.65 2108  43  37  -1 0.00
Sun 04/12 20Z 0.46 2211  39  41   0 0.00
Sun 04/12 21Z 0.39 2114  32  61   0 0.00
Sun 04/12 22Z 0.46 2118  35  92   0 0.00
Sun 04/12 23Z 0.54 2119  66  96   0 0.00
Mon 04/13 00Z 0.45 2320  94  97   0 0.01
Mon 04/13 01Z 0.50 2224  91  98   0 0.02
Mon 04/13 02Z 0.52 2129  79  98   0 0.02
Mon 04/13 03Z 0.51 2129  81  97   1 0.01
Mon 04/13 04Z 0.51 2132  84  97   3 0.01
Mon 04/13 05Z 0.53 2235  88  94   5 0.03

Run total areal avg QPF for the Central_Greens is: 0.50 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