Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260616_1200
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)
=== ===== === ==== ==== === === === ====
Tue 06/16 12Z 0.38 3112  86   8   5 0.00
Tue 06/16 13Z 0.42 3110  81  10   5 0.00
Tue 06/16 14Z 0.88 3009  76  15   6 0.00
Tue 06/16 15Z 2.00 2908  73  20   6 0.00
Tue 06/16 16Z 2.97 2806  71  25   7 0.00
Tue 06/16 17Z 3.70 2706  68  35   7 0.00
Tue 06/16 18Z 3.92 2606  64  49   8 0.00
Tue 06/16 19Z 4.09 2506  64  50   8 0.00
Tue 06/16 20Z 3.98 2507  69  47   8 0.00
Tue 06/16 21Z 2.97 2407  71  44   9 0.00
Tue 06/16 22Z 2.16 2408  72  41   9 0.00
Tue 06/16 23Z 0.94 2309  74  37   9 0.00
Wed 06/17 00Z 0.53 2310  74  37   9 0.00
Wed 06/17 01Z 0.50 2312  73  32   9 0.00
Wed 06/17 02Z 0.57 2413  74  35   9 0.00
Wed 06/17 03Z 0.55 2413  73  39   9 0.00
Wed 06/17 04Z 0.57 2413  73  42   9 0.00
Wed 06/17 05Z 0.55 2412  73  47   9 0.00
Wed 06/17 06Z 0.54 2412  74  56   9 0.00
Wed 06/17 07Z 0.50 2311  75  56   9 0.00
Wed 06/17 08Z 0.47 2311  77  56   8 0.00
Wed 06/17 09Z 0.44 2211  78  58   8 0.00
Wed 06/17 10Z 0.39 2211  79  60   8 0.00
Wed 06/17 11Z 0.37 2111  80  60   8 0.00
Wed 06/17 12Z 0.34 2110  81  57   8 0.00
Wed 06/17 13Z 0.67 2009  81  55   8 0.00
Wed 06/17 14Z 0.66 1808  82  47   8 0.00
Wed 06/17 15Z 0.53 1708  82  45   9 0.00
Wed 06/17 16Z 0.51 1709  84  37   9 0.02
Wed 06/17 17Z 0.30 1710  85  27   9 0.03
Wed 06/17 18Z 0.23 1711  84  24  10 0.03
Wed 06/17 19Z 0.21 1812  82  22  10 0.03
Wed 06/17 20Z 0.24 1813  80  22  10 0.01
Wed 06/17 21Z 0.23 1713  77  33  10 0.01
Wed 06/17 22Z 0.19 1714  77  50  11 0.00
Wed 06/17 23Z 0.11 1715  78  61  11 0.00
Thu 06/18 00Z 0.14 1817  77  72  11 0.00
Thu 06/18 01Z 0.14 1818  77  69  11 0.00
Thu 06/18 02Z 0.20 1920  78  68  11 0.00
Thu 06/18 03Z 0.43 2022  81  60  10 0.00
Thu 06/18 04Z 0.43 2022  84  61  10 0.00
Thu 06/18 05Z 0.37 2023  85  69  10 0.00
Thu 06/18 06Z 0.30 2023  88  60  10 0.00
Thu 06/18 07Z 0.23 1922  89  57  11 0.00
Thu 06/18 08Z 0.22 2022  90  46  11 0.00
Thu 06/18 09Z 0.20 1923  90  39  11 0.00
Thu 06/18 10Z 0.16 1923  89  70  11 0.00
Thu 06/18 11Z 0.08 1823  84  88  12 0.00
Thu 06/18 12Z 0.04 1728  83  97  11 0.01
Thu 06/18 13Z 0.13 1735  91  97  11 0.02
Thu 06/18 14Z 0.06 1738  90  94  12 0.02
Thu 06/18 15Z 0.08 1742  92  97  13 0.03
Thu 06/18 16Z 0.08 1742  96  92  13 0.08
Thu 06/18 17Z 0.15 1837  97  95  13 0.16
Thu 06/18 18Z 0.26 1931  98  76  13 0.13
Thu 06/18 19Z 0.39 2027  98  55  14 0.07
Thu 06/18 20Z 0.48 2023  97  82  14 0.06
Thu 06/18 21Z 0.94 2425  84  58  14 0.29
Thu 06/18 22Z 0.92 2522  88  77  13 0.01
Thu 06/18 23Z 0.95 2422  94  52  12 0.01

Run total areal avg QPF for the greens is: 1.02 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