NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260503_0600
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)
=== ===== === ==== ==== === === === ====
Sun 05/03 06Z 0.33 3211  92  49  -4 0.00
Sun 05/03 07Z 0.38 3213  92  51  -5 0.00
Sun 05/03 08Z 0.45 3316  92  51  -5 0.01
Sun 05/03 09Z 0.41 3317  90  51  -5 0.00
Sun 05/03 10Z 0.39 3319  87  49  -5 0.00
Sun 05/03 11Z 0.38 3320  84  49  -5 0.00
Sun 05/03 12Z 0.52 3319  83  52  -5 0.00
Sun 05/03 13Z 1.75 3318  81  56  -5 0.00
Sun 05/03 14Z 3.43 3317  78  53  -5 0.00
Sun 05/03 15Z 5.17 3217  77  48  -4 0.00
Sun 05/03 16Z 6.41 3218  73  43  -4 0.00
Sun 05/03 17Z 8.02 3118  72  40  -4 0.00
Sun 05/03 18Z 9.07 3118  68  39  -3 0.00
Sun 05/03 19Z 9.65 3118  65  37  -3 0.00
Sun 05/03 20Z 9.98 3018  63  37  -3 0.00
Sun 05/03 21Z 10.79 3019  63  40  -2 0.00
Sun 05/03 22Z 11.20 3020  64  37  -2 0.00
Sun 05/03 23Z 7.63 2920  65  33  -2 0.00
Mon 05/04 00Z 2.24 2921  65  26  -2 0.00
Mon 05/04 01Z 2.65 2922  65  12  -2 0.00
Mon 05/04 02Z 1.68 2821  61   3  -2 0.00
Mon 05/04 03Z 1.06 2821  58  11  -1 0.00
Mon 05/04 04Z 0.99 2722  66  57  -1 0.00
Mon 05/04 05Z 0.81 2722  79  87   0 0.01
Mon 05/04 06Z 0.69 2623  85  92   0 0.02
Mon 05/04 07Z 0.74 2627  88  94   0 0.04
Mon 05/04 08Z 0.84 2529  87  90   0 0.04
Mon 05/04 09Z 0.88 2529  90  87   0 0.02
Mon 05/04 10Z 0.92 2531  91  79   0 0.02
Mon 05/04 11Z 0.97 2533  93  91   0 0.03
Mon 05/04 12Z 0.95 2533  94  90   1 0.03
Mon 05/04 13Z 0.92 2630  94  90   1 0.03
Mon 05/04 14Z 0.89 2628  95  80   1 0.03
Mon 05/04 15Z 0.93 2527  95  53   1 0.02
Mon 05/04 16Z 1.10 2524  95  22   1 0.01
Mon 05/04 17Z 1.57 2524  95  17   1 0.01
Mon 05/04 18Z 3.26 2523  92  13   1 0.01
Mon 05/04 19Z 5.45 2522  89  21   2 0.00
Mon 05/04 20Z 3.82 2521  86  35   2 0.00
Mon 05/04 21Z 2.86 2520  85  31   3 0.00
Mon 05/04 22Z 1.68 2420  84  18   3 0.00
Mon 05/04 23Z 0.97 2421  82  14   4 0.00
Tue 05/05 00Z 0.82 2422  80  15   5 0.00
Tue 05/05 01Z 0.76 2323  78  12   5 0.00
Tue 05/05 02Z 0.78 2326  77  11   6 0.00
Tue 05/05 03Z 0.84 2328  80  11   6 0.00
Tue 05/05 04Z 0.89 2330  82  10   6 0.00
Tue 05/05 05Z 0.89 2232  84   9   7 0.00
Tue 05/05 06Z 0.99 2333  86  10   7 0.00
Tue 05/05 07Z 0.95 2332  86   7   6 0.01
Tue 05/05 08Z 0.70 2329  79   6   8 0.00
Tue 05/05 09Z 0.65 2230  84   9   8 0.01
Tue 05/05 10Z 0.68 2231  88  29   8 0.01
Tue 05/05 11Z 0.64 2231  89  78   8 0.01
Tue 05/05 12Z 0.73 2332  91  81   8 0.00
Tue 05/05 13Z 0.82 2331  92  77   8 0.00
Tue 05/05 14Z 0.94 2330  93  86   8 0.01
Tue 05/05 15Z 0.96 2327  91  70   8 0.00
Tue 05/05 16Z 1.63 2325  92  72   8 0.00
Tue 05/05 17Z 0.93 2221  92  45   8 0.01

Run total areal avg QPF for the greens is: 0.39 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