Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260315_0000
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)
=== ===== === ==== ==== === === === ====
Sun 03/15 00Z 1.79 2923  89  64 -10 0.00
Sun 03/15 01Z 1.35 2823  91  51 -10 0.00
Sun 03/15 02Z 1.28 2826  95  41 -10 0.02
Sun 03/15 03Z 1.14 2926  95  14 -11 0.02
Sun 03/15 04Z 0.77 3024  94  10 -11 0.01
Sun 03/15 05Z 0.72 3024  91   9 -11 0.01
Sun 03/15 06Z 0.59 3123  86   9 -11 0.00
Sun 03/15 07Z 0.42 3122  75  10 -11 0.00
Sun 03/15 08Z 0.29 3120  62   9 -10 0.00
Sun 03/15 09Z 0.23 3118  50   8  -9 0.00
Sun 03/15 10Z 0.16 3218  38  10  -8 0.00
Sun 03/15 11Z 0.11 3315  31  11  -7 0.00
Sun 03/15 12Z 0.05 3311  26  12  -7 0.00
Sun 03/15 13Z 0.02 3406  25  37  -7 0.00
Sun 03/15 14Z 0.02 3301  26  86  -7 0.00
Sun 03/15 15Z 0.02 1402  26  97  -7 0.00
Sun 03/15 18Z 0.05 1613  39  98  -6 0.00
Sun 03/15 19Z 0.03 1615  75  98  -7 0.00
Sun 03/15 20Z 0.02 1722  77  96  -5 0.00
Sun 03/15 21Z 0.05 1628  59  91  -5 0.00
Sun 03/15 22Z 0.05 1632  52  89  -4 0.01
Sun 03/15 23Z 0.05 1734  47  88  -2 0.01
Mon 03/16 00Z 0.10 1736  42  89  -1 0.00
Mon 03/16 01Z 0.13 1739  37  77   0 0.00
Mon 03/16 02Z 0.16 1840  36  79   0 0.00
Mon 03/16 03Z 0.18 1842  39  95   1 0.00
Mon 03/16 04Z 0.15 1845  42  91   2 0.00
Mon 03/16 05Z 0.13 1747  44  74   3 0.00
Mon 03/16 06Z 0.10 1749  51  50   3 0.00
Mon 03/16 07Z 0.06 1750  68  33   3 0.00
Mon 03/16 08Z 0.06 1650  79  48   4 0.01
Mon 03/16 09Z 0.07 1650  88  62   5 0.01
Mon 03/16 10Z 0.09 1647  93  95   6 0.01
Mon 03/16 11Z 0.16 1552  94  98   7 0.01
Mon 03/16 12Z 0.15 1552  94  98   8 0.05
Mon 03/16 13Z 0.05 1651  96  57   8 0.09
Mon 03/16 14Z 0.07 1745  96  55   8 0.06
Mon 03/16 15Z 0.19 1842  97  42   8 0.07
Mon 03/16 16Z 0.29 1942  96  21   9 0.02
Mon 03/16 17Z 0.38 1943  95  12   9 0.01
Mon 03/16 18Z 0.42 1943  92   9  10 0.01
Mon 03/16 19Z 0.40 1942  95  31  10 0.01
Mon 03/16 20Z 0.37 1844  96  53  10 0.00
Mon 03/16 21Z 0.29 1845  96  71  10 0.00
Mon 03/16 22Z 0.24 1846  96  79  10 0.00
Mon 03/16 23Z 0.24 1848  96  77  10 0.01
Tue 03/17 00Z 0.24 1846  96  73  10 0.01
Tue 03/17 01Z 0.20 1747  95  72  10 0.01
Tue 03/17 02Z 0.15 1747  95  70  10 0.01
Tue 03/17 03Z 0.18 1745  96  92   9 0.01
Tue 03/17 04Z 0.14 1744  96  91   9 0.01
Tue 03/17 05Z 0.56 1931  99  98   7 0.05
Tue 03/17 06Z 0.81 2430  95  95  -1 0.07
Tue 03/17 07Z 0.90 2430  95  95  -3 0.14
Tue 03/17 08Z 1.22 2426  96  83  -6 0.09
Tue 03/17 09Z 3.70 2626  95   2  -9 0.02
Tue 03/17 10Z 5.41 2527  91   3 -11 0.02
Tue 03/17 11Z 3.57 2430  89  11 -12 0.02

Run total areal avg QPF for the Central_Greens is: 0.91 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