Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260404_0000
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 04/04 00Z 0.99 2437  84  21  10 0.00
Sat 04/04 01Z 1.33 2539  88  16   9 0.00
Sat 04/04 02Z 1.29 2639  96  15   9 0.01
Sat 04/04 03Z 1.36 2738  98  20   7 0.05
Sat 04/04 04Z 1.31 2837  97  21   5 0.04
Sat 04/04 05Z 1.22 2836  96  20   3 0.02
Sat 04/04 06Z 0.92 2933  92  20   2 0.01
Sat 04/04 07Z 0.59 3029  90  18   1 0.01
Sat 04/04 08Z 0.38 3125  89  16   1 0.01
Sat 04/04 09Z 0.23 3223  86  14   1 0.01
Sat 04/04 10Z 0.13 3419  81  12   2 0.00
Sat 04/04 11Z 0.09 3517  77  10   2 0.00
Sat 04/04 12Z 0.10 0115  73   9   3 0.00
Sat 04/04 13Z 0.13 0314  63   8   4 0.00
Sat 04/04 14Z 0.17 0513  56   7   4 0.00
Sat 04/04 15Z 0.19 0712  53   9   4 0.00
Sat 04/04 16Z 0.19 0911  52  15   4 0.00
Sat 04/04 17Z 0.19 1212  56  27   4 0.00
Sat 04/04 18Z 0.20 1314  59  41   4 0.00
Sat 04/04 19Z 0.24 1416  64  63   3 0.00
Sat 04/04 20Z 0.43 1420  67  70   2 0.00
Sat 04/04 21Z 0.58 1422  69  68   2 0.00
Sat 04/04 22Z 0.37 1526  68  73   3 0.00
Sat 04/04 23Z 0.22 1529  65  97   5 0.00
Sun 04/05 00Z 0.15 1632  67  97   5 0.00
Sun 04/05 01Z 0.12 1634  75  93   5 0.00
Sun 04/05 02Z 0.11 1635  79  90   5 0.00
Sun 04/05 03Z 0.08 1736  84  88   6 0.00
Sun 04/05 04Z 0.06 1737  91  88   7 0.01
Sun 04/05 05Z 0.05 1740  95  87   7 0.02
Sun 04/05 06Z 0.04 1843  96  79   8 0.02
Sun 04/05 07Z 0.05 1845  96  90   8 0.02
Sun 04/05 08Z 0.06 1846  96  81   9 0.04
Sun 04/05 09Z 0.09 1845  96  80   9 0.02
Sun 04/05 10Z 0.14 1944  97  89   9 0.04
Sun 04/05 11Z 0.20 1942  97  89   9 0.06
Sun 04/05 12Z 0.32 2039  98  93   7 0.10
Sun 04/05 13Z 0.41 2234  98  98   5 0.11
Sun 04/05 14Z 0.51 2331  98  97   4 0.12
Sun 04/05 15Z 0.63 2430  90  80   3 0.06
Sun 04/05 16Z 0.76 2529  87  39   2 0.01
Sun 04/05 17Z 0.87 2527  91  39   0 0.00
Sun 04/05 18Z 1.07 2526  91  28   0 0.01
Sun 04/05 19Z 2.00 2526  95  21  -1 0.01
Sun 04/05 20Z 3.64 2526  92  24  -2 0.00
Sun 04/05 21Z 7.72 2627  87  16  -2 0.01
Sun 04/05 22Z 9.18 2629  86  20  -4 0.00
Sun 04/05 23Z 3.28 2630  86  24  -5 0.00
Mon 04/06 00Z 2.19 2630  86  28  -5 0.00
Mon 04/06 01Z 2.16 2631  88  35  -6 0.00
Mon 04/06 02Z 1.88 2732  90  43  -7 0.00
Mon 04/06 03Z 1.78 2732  95  59  -8 0.01
Mon 04/06 04Z 1.60 2732  96  67  -8 0.01
Mon 04/06 05Z 1.38 2832  96  69  -8 0.01
Mon 04/06 06Z 1.30 2832  97  67  -8 0.01
Mon 04/06 07Z 1.36 2931  97  65  -8 0.01
Mon 04/06 08Z 1.58 2930  98  50  -9 0.01
Mon 04/06 09Z 1.52 3028  98  43 -10 0.01
Mon 04/06 10Z 1.37 3026  97  34 -10 0.01
Mon 04/06 11Z 1.07 3025  95  21 -10 0.00

Run total areal avg QPF for the greens is: 0.90 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