NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260328_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 03/28 18Z 6.53 2610  69  70 -14 0.00
Sat 03/28 19Z 6.94 2613  75  78 -13 0.00
Sat 03/28 20Z 4.86 2616  80  77 -13 0.00
Sat 03/28 21Z 5.56 2718  76  70 -13 0.01
Sat 03/28 22Z 4.14 2717  78  65 -13 0.00
Sat 03/28 23Z 2.91 2718  83  64 -13 0.01
Sun 03/29 00Z 2.38 2722  83  60 -13 0.01
Sun 03/29 01Z 3.06 2724  83  41 -14 0.01
Sun 03/29 02Z 3.37 2827  82  27 -14 0.00
Sun 03/29 03Z 3.50 2827  78  23 -14 0.00
Sun 03/29 04Z 2.69 2828  75  35 -14 0.00
Sun 03/29 05Z 2.30 2927  79  46 -14 0.00
Sun 03/29 06Z 1.47 2924  83  60 -14 0.00
Sun 03/29 08Z 0.97 2820  88  69 -13 0.00
Sun 03/29 11Z 0.88 2622  93  82 -11 0.00
Sun 03/29 12Z 0.85 2623  92  78 -11 0.00
Sun 03/29 13Z 0.83 2523  90  78 -10 0.00
Sun 03/29 14Z 0.90 2523  87  82  -9 0.00
Sun 03/29 15Z 1.00 2521  83  88  -9 0.00
Sun 03/29 16Z 2.16 2421  83  87  -9 0.00
Sun 03/29 17Z 3.04 2321  79  88  -8 0.00
Sun 03/29 18Z 5.95 2322  73  81  -7 0.00
Sun 03/29 19Z 6.85 2322  68  68  -7 0.00
Sun 03/29 20Z 4.41 2323  68  66  -6 0.00
Sun 03/29 21Z 1.95 2424  72  77  -5 0.00
Sun 03/29 22Z 1.54 2426  74  74  -5 0.00
Sun 03/29 23Z 1.98 2527  72  60  -4 0.00
Mon 03/30 00Z 1.77 2528  69  49  -4 0.00
Mon 03/30 01Z 1.62 2528  67  24  -4 0.00
Mon 03/30 02Z 1.45 2528  66  12  -3 0.00
Mon 03/30 03Z 1.42 2528  64   7  -3 0.00
Mon 03/30 04Z 1.30 2528  63   6  -3 0.00
Mon 03/30 05Z 1.12 2526  61  12  -2 0.00
Mon 03/30 06Z 0.97 2524  64  28  -2 0.00
Mon 03/30 07Z 0.89 2524  68  45  -2 0.00
Mon 03/30 08Z 0.79 2423  69  59  -1 0.00
Mon 03/30 09Z 0.80 2422  71  67  -1 0.00
Mon 03/30 10Z 0.69 2323  77  58  -1 0.00
Mon 03/30 11Z 0.66 2425  76  48  -1 0.00
Mon 03/30 12Z 0.77 2428  79  65  -1 0.00
Mon 03/30 13Z 0.88 2529  82  66   0 0.00
Mon 03/30 14Z 0.94 2430  84  61   0 0.00
Mon 03/30 15Z 0.96 2530  80  55   0 0.00
Mon 03/30 16Z 0.98 2529  82  62   0 0.00
Mon 03/30 17Z 0.99 2528  80  58   0 0.00
Mon 03/30 18Z 1.13 2528  82  52   1 0.00
Mon 03/30 19Z 1.26 2526  82  57   1 0.00
Mon 03/30 20Z 1.39 2526  83  66   1 0.00
Mon 03/30 21Z 1.36 2525  85  72   1 0.00
Mon 03/30 22Z 1.66 2626  85  74   1 0.00
Mon 03/30 23Z 1.68 2627  87  77   1 0.00
Tue 03/31 00Z 1.32 2727  90  71   2 0.00
Tue 03/31 01Z 1.07 2726  94  69   2 0.01
Tue 03/31 02Z 0.91 2724  97  75   2 0.02
Tue 03/31 03Z 0.80 2722  95  76   2 0.02
Tue 03/31 04Z 0.74 2721  96  68   2 0.02
Tue 03/31 05Z 0.67 2719  96  68   1 0.02

Run total areal avg QPF for the greens is: 0.13 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