NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260307_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 03/07 18Z 0.40 2229  81  89  10 0.00
Sat 03/07 19Z 0.46 2233  83  85  11 0.00
Sat 03/07 20Z 0.51 2235  85  73  12 0.00
Sat 03/07 21Z 0.52 2238  88  66  12 0.00
Sat 03/07 22Z 0.59 2342  87  36  13 0.00
Sat 03/07 23Z 0.60 2342  76  51  13 0.00
Sun 03/08 01Z 0.68 2346  84  66  13 0.00
Sun 03/08 02Z 0.73 2347  89  77  12 0.01
Sun 03/08 03Z 0.77 2445  92  88  11 0.02
Sun 03/08 04Z 0.79 2444  95  88  10 0.07
Sun 03/08 05Z 0.80 2542  96  81   9 0.08
Sun 03/08 06Z 0.76 2538  95  82   9 0.08
Sun 03/08 07Z 0.72 2536  94  46   9 0.04
Sun 03/08 08Z 0.75 2536  93  67   8 0.02
Sun 03/08 09Z 0.80 2536  94  60   8 0.02
Sun 03/08 10Z 0.85 2535  92  36   7 0.02
Sun 03/08 11Z 1.01 2636  95  27   5 0.03
Sun 03/08 12Z 1.12 2635  94   9   4 0.01
Sun 03/08 13Z 1.18 2634  93   6   2 0.02
Sun 03/08 15Z 1.05 2730  91   8   0 0.02
Sun 03/08 16Z 1.04 2728  92   5   0 0.02
Sun 03/08 17Z 1.02 2726  93   4  -1 0.01
Sun 03/08 18Z 1.00 2624  93  10  -1 0.01
Sun 03/08 19Z 0.89 2624  92   9  -2 0.01
Sun 03/08 20Z 0.77 2624  88  13  -1 0.01
Sun 03/08 21Z 0.81 2628  85  15  -1 0.01
Sun 03/08 22Z 0.79 2629  80  28  -1 0.01
Sun 03/08 23Z 0.72 2531  72  64   0 0.00
Mon 03/09 00Z 0.73 2534  67  78   0 0.00
Mon 03/09 01Z 0.91 2538  72  40   0 0.00
Mon 03/09 02Z 1.20 2540  86  25  -2 0.00
Mon 03/09 03Z 1.25 2640  89  22  -2 0.00
Mon 03/09 04Z 1.12 2738  86  18  -1 0.00
Mon 03/09 05Z 1.03 2738  82  20   0 0.01
Mon 03/09 06Z 0.98 2738  79  28   0 0.00
Mon 03/09 07Z 0.90 2737  71  34   0 0.00
Mon 03/09 08Z 0.87 2736  66  34   1 0.00
Mon 03/09 09Z 0.78 2733  62  26   1 0.00
Mon 03/09 10Z 0.72 2631  60  22   2 0.00
Mon 03/09 11Z 0.70 2631  59  32   2 0.00
Mon 03/09 12Z 0.71 2532  58  57   3 0.00
Mon 03/09 13Z 0.69 2533  53  64   4 0.00
Mon 03/09 14Z 0.71 2535  55  82   5 0.00
Mon 03/09 15Z 0.71 2437  55  73   7 0.00
Mon 03/09 16Z 0.74 2439  41  56   8 0.00
Mon 03/09 17Z 0.81 2439  42  54   7 0.00
Mon 03/09 18Z 0.85 2439  43  49   7 0.00
Mon 03/09 19Z 0.89 2437  47  49   7 0.00
Mon 03/09 20Z 0.98 2437  51  46   7 0.00
Mon 03/09 21Z 1.03 2437  50  45   7 0.00
Mon 03/09 22Z 1.07 2438  49  50   7 0.00
Mon 03/09 23Z 1.08 2439  46  56   7 0.00
Tue 03/10 00Z 1.12 2440  44  59   7 0.00
Tue 03/10 01Z 1.14 2440  41  56   7 0.00
Tue 03/10 02Z 1.11 2439  38  52   7 0.00
Tue 03/10 03Z 1.06 2537  36  54   7 0.00
Tue 03/10 04Z 1.01 2535  37  55   7 0.00
Tue 03/10 05Z 0.98 2533  39  53   6 0.00

Run total areal avg QPF for the 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