Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260315_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)
=== ===== === ==== ==== === === === ====
Sun 03/15 00Z 1.94 2925  91  66 -10 0.00
Sun 03/15 01Z 1.64 2926  91  57 -10 0.00
Sun 03/15 02Z 1.55 2928  94  42 -10 0.01
Sun 03/15 03Z 1.40 2928  94  15 -11 0.02
Sun 03/15 04Z 1.12 3026  92  10 -11 0.01
Sun 03/15 05Z 1.01 3026  88  10 -12 0.00
Sun 03/15 06Z 0.78 3124  83  11 -12 0.00
Sun 03/15 07Z 0.57 3123  75  11 -11 0.00
Sun 03/15 08Z 0.40 3120  64  10 -11 0.00
Sun 03/15 09Z 0.33 3118  55  10 -10 0.00
Sun 03/15 10Z 0.26 3217  43  11  -9 0.00
Sun 03/15 11Z 0.19 3215  33  11  -8 0.00
Sun 03/15 12Z 0.12 3312  26  12  -8 0.00
Sun 03/15 13Z 0.05 3306  26  28  -8 0.00
Sun 03/15 14Z 0.03 3201  28  64  -7 0.00
Sun 03/15 15Z 0.03 1501  29  87  -7 0.00
Sun 03/15 18Z 0.14 1612  34  97  -7 0.00
Sun 03/15 19Z 0.16 1615  58  97  -7 0.00
Sun 03/15 20Z 0.19 1620  66  97  -6 0.00
Sun 03/15 21Z 0.28 1625  64  94  -6 0.00
Sun 03/15 22Z 0.16 1631  64  91  -5 0.01
Sun 03/15 23Z 0.12 1734  54  90  -3 0.01
Mon 03/16 00Z 0.08 1737  45  89  -2 0.01
Mon 03/16 01Z 0.04 1740  42  82  -1 0.01
Mon 03/16 02Z 0.05 1842  41  84   0 0.00
Mon 03/16 03Z 0.07 1845  41  93   1 0.00
Mon 03/16 04Z 0.07 1848  43  91   2 0.00
Mon 03/16 05Z 0.06 1850  45  72   3 0.00
Mon 03/16 06Z 0.07 1751  49  53   3 0.00
Mon 03/16 07Z 0.09 1753  61  44   4 0.00
Mon 03/16 08Z 0.11 1753  73  56   4 0.00
Mon 03/16 09Z 0.13 1753  85  63   5 0.01
Mon 03/16 10Z 0.17 1651  89  87   6 0.01
Mon 03/16 11Z 0.23 1653  93  94   7 0.01
Mon 03/16 12Z 0.26 1654  94  98   7 0.04
Mon 03/16 13Z 0.20 1654  95  68   8 0.07
Mon 03/16 14Z 0.09 1749  96  54   8 0.07
Mon 03/16 15Z 0.06 1845  96  40   8 0.07
Mon 03/16 16Z 0.13 1843  96  27   9 0.02
Mon 03/16 17Z 0.20 1944  95  14   9 0.01
Mon 03/16 18Z 0.23 1943  93  10  10 0.01
Mon 03/16 19Z 0.21 1943  93  24  10 0.01
Mon 03/16 20Z 0.17 1845  95  45  10 0.01
Mon 03/16 21Z 0.09 1846  95  63  10 0.00
Mon 03/16 22Z 0.05 1848  95  75  10 0.00
Mon 03/16 23Z 0.05 1849  96  76  10 0.01
Tue 03/17 00Z 0.04 1848  96  69  10 0.01
Tue 03/17 01Z 0.05 1749  95  69  10 0.01
Tue 03/17 02Z 0.07 1748  95  62  10 0.01
Tue 03/17 03Z 0.07 1746  96  93   9 0.01
Tue 03/17 04Z 0.09 1744  97  92   9 0.01
Tue 03/17 05Z 0.28 1930  99  98   7 0.05
Tue 03/17 06Z 0.74 2527  96  96  -1 0.07
Tue 03/17 07Z 0.78 2428  96  97  -3 0.13
Tue 03/17 08Z 1.05 2426  97  88  -6 0.12
Tue 03/17 09Z 2.91 2526  96   2  -9 0.03
Tue 03/17 10Z 5.55 2527  87   3 -11 0.02
Tue 03/17 11Z 4.99 2429  86  11 -12 0.02

Run total areal avg QPF for the greens is: 0.92 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