NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260716_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)
=== ===== === ==== ==== === === === ====
Thu 07/16 12Z 0.59 2920  80  71  13 0.00
Thu 07/16 13Z 0.74 2824  82  81  13 0.00
Thu 07/16 14Z 0.91 2825  80  87  13 0.00
Thu 07/16 15Z 1.21 2824  77  87  13 0.00
Thu 07/16 16Z 9.02 2722  80  88  13 0.00
Thu 07/16 17Z 9.42 2726  81  87  13 0.04
Thu 07/16 18Z 9.32 2725  71  82  13 0.01
Thu 07/16 19Z 6.26 2827  72  78  13 0.03
Thu 07/16 20Z 2.01 3032  73  77  12 0.07
Thu 07/16 21Z 0.51 3236  68  58  10 0.09
Thu 07/16 22Z 0.63 3230  73  20  10 0.01
Thu 07/16 23Z 0.75 3229  78   9   9 0.00
Fri 07/17 00Z 1.04 3129  78   5   9 0.00
Fri 07/17 01Z 0.89 3130  69  12   8 0.00
Fri 07/17 02Z 0.67 3230  65  24   8 0.00
Fri 07/17 03Z 0.79 3230  65  32   7 0.00
Fri 07/17 04Z 0.68 3230  62  32   7 0.00
Fri 07/17 05Z 0.67 3229  61  30   7 0.00
Fri 07/17 06Z 0.59 3228  61  26   7 0.00
Fri 07/17 07Z 0.55 3227  62  25   7 0.00
Fri 07/17 08Z 0.46 3227  62  23   7 0.00
Fri 07/17 09Z 0.41 3226  61  21   8 0.00
Fri 07/17 10Z 0.39 3126  59  20   8 0.00
Fri 07/17 11Z 0.35 3127  54  17   9 0.00
Fri 07/17 12Z 0.33 3126  50  16   9 0.00
Fri 07/17 13Z 0.33 3126  47  16   9 0.00
Fri 07/17 14Z 0.31 3223  47  17   9 0.00
Fri 07/17 15Z 0.31 3221  48  19   9 0.00
Fri 07/17 16Z 0.35 3119  49  20   9 0.00
Fri 07/17 17Z 0.42 3117  48  20   9 0.00
Fri 07/17 18Z 0.63 3015  52  20   9 0.00
Fri 07/17 19Z 1.08 2914  56  19   9 0.00
Fri 07/17 20Z 1.86 2913  58  18   9 0.00
Fri 07/17 21Z 2.50 2812  59  16  10 0.00
Fri 07/17 22Z 1.33 2811  56  14  10 0.00
Fri 07/17 23Z 0.73 2811  51  10  10 0.00
Sat 07/18 00Z 0.68 2811  48   9  10 0.00
Sat 07/18 01Z 0.54 2810  46   8  11 0.00
Sat 07/18 02Z 0.50 2810  44   9  11 0.00
Sat 07/18 03Z 0.47 2710  45  11  11 0.00
Sat 07/18 04Z 0.44 2710  46  13  11 0.00
Sat 07/18 05Z 0.38 2608  47  11  11 0.00
Sat 07/18 06Z 0.29 2506  47   9  11 0.00
Sat 07/18 07Z 0.35 2408  50  13  10 0.00
Sat 07/18 08Z 0.32 2209  52  13  10 0.00
Sat 07/18 09Z 0.32 2210  51  21  11 0.00
Sat 07/18 10Z 0.34 2211  45  37  11 0.00
Sat 07/18 11Z 0.35 2311  42  79  12 0.00
Sat 07/18 12Z 0.36 2311  52  81  12 0.00
Sat 07/18 13Z 0.37 2212  63  74  12 0.00
Sat 07/18 14Z 0.46 2016  71  78  12 0.00
Sat 07/18 15Z 0.68 2019  72  74  12 0.00
Sat 07/18 16Z 1.27 2020  75  79  13 0.00
Sat 07/18 17Z 1.21 2023  73  72  14 0.00
Sat 07/18 18Z 1.70 2028  76  83  14 0.01
Sat 07/18 19Z 0.95 2035  93  77  13 0.02
Sat 07/18 20Z 0.70 2035  95  96  13 0.07
Sat 07/18 21Z 0.62 2038  97  94  14 0.07
Sat 07/18 22Z 0.70 2041  98  80  14 0.07
Sat 07/18 23Z 0.72 2140  97  70  15 0.04

Run total areal avg QPF for the Central_Greens is: 0.53 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