NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260307_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)
=== ===== === ==== ==== === === === ====
Sat 03/07 18Z 0.42 2226  86  90  10 0.00
Sat 03/07 19Z 0.49 2230  83  81  11 0.00
Sat 03/07 20Z 0.53 2232  86  69  11 0.00
Sat 03/07 21Z 0.56 2236  89  70  12 0.00
Sat 03/07 22Z 0.62 2339  87  38  13 0.00
Sat 03/07 23Z 0.62 2339  77  37  13 0.00
Sun 03/08 01Z 0.70 2345  82  56  13 0.00
Sun 03/08 02Z 0.77 2349  87  75  13 0.00
Sun 03/08 03Z 0.79 2446  91  83  11 0.00
Sun 03/08 04Z 0.80 2446  97  90  10 0.05
Sun 03/08 05Z 0.81 2444  97  87   9 0.08
Sun 03/08 06Z 0.74 2539  95  89   9 0.10
Sun 03/08 07Z 0.70 2537  94  48   9 0.06
Sun 03/08 08Z 0.73 2537  93  67   9 0.01
Sun 03/08 09Z 0.74 2536  97  64   8 0.01
Sun 03/08 10Z 0.77 2535  94  35   8 0.02
Sun 03/08 11Z 0.93 2638  94  34   6 0.04
Sun 03/08 12Z 1.08 2636  92  10   4 0.01
Sun 03/08 13Z 1.07 2635  91   7   3 0.01
Sun 03/08 15Z 0.98 2731  88   8   1 0.02
Sun 03/08 16Z 0.99 2729  89   6   0 0.02
Sun 03/08 17Z 1.04 2726  91   4   0 0.01
Sun 03/08 18Z 1.01 2624  90   7  -1 0.01
Sun 03/08 19Z 0.89 2624  90   7  -1 0.01
Sun 03/08 20Z 0.76 2624  85  14  -1 0.00
Sun 03/08 21Z 0.82 2628  82  14  -1 0.00
Sun 03/08 22Z 0.78 2630  79  22  -1 0.00
Sun 03/08 23Z 0.73 2631  72  54   0 0.00
Mon 03/09 00Z 0.76 2535  69  69   0 0.00
Mon 03/09 01Z 0.86 2538  72  24   0 0.00
Mon 03/09 02Z 1.18 2540  85  11  -1 0.01
Mon 03/09 03Z 1.27 2640  86  16  -1 0.01
Mon 03/09 04Z 1.07 2637  84  18  -1 0.01
Mon 03/09 05Z 0.96 2736  80  18   0 0.01
Mon 03/09 06Z 0.90 2737  75  31   0 0.00
Mon 03/09 07Z 0.83 2736  66  33   1 0.00
Mon 03/09 08Z 0.80 2736  62  27   1 0.00
Mon 03/09 09Z 0.73 2734  59  16   2 0.00
Mon 03/09 10Z 0.69 2632  60  19   2 0.00
Mon 03/09 11Z 0.69 2633  59  36   3 0.00
Mon 03/09 12Z 0.72 2534  58  57   3 0.00
Mon 03/09 13Z 0.70 2534  54  55   5 0.00
Mon 03/09 14Z 0.72 2535  57  75   5 0.00
Mon 03/09 15Z 0.74 2437  56  67   7 0.00
Mon 03/09 16Z 0.76 2437  41  54   8 0.00
Mon 03/09 17Z 0.84 2438  42  51   7 0.00
Mon 03/09 18Z 0.90 2437  42  47   7 0.00
Mon 03/09 19Z 0.98 2436  45  43   7 0.00
Mon 03/09 20Z 1.07 2436  47  36   7 0.00
Mon 03/09 21Z 1.14 2435  47  33   7 0.00
Mon 03/09 22Z 1.16 2436  47  38   7 0.00
Mon 03/09 23Z 1.12 2437  46  44   7 0.00
Tue 03/10 00Z 1.11 2438  45  47   7 0.00
Tue 03/10 01Z 1.09 2438  41  49   7 0.00
Tue 03/10 02Z 1.03 2437  37  48   7 0.00
Tue 03/10 03Z 0.97 2436  34  48   7 0.00
Tue 03/10 04Z 0.89 2535  35  48   7 0.00
Tue 03/10 05Z 0.84 2533  37  46   7 0.00

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