Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260427_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)
=== ===== === ==== ==== === === === ====
Mon 04/27 12Z 0.18 0803  69  41   4 0.00
Mon 04/27 13Z 0.20 0903  70  37   4 0.00
Mon 04/27 14Z 0.35 0903  71  32   4 0.00
Mon 04/27 15Z 0.71 0903  71  30   4 0.00
Mon 04/27 16Z 0.99 1002  71  30   4 0.00
Mon 04/27 17Z 1.12 1102  70  30   5 0.00
Mon 04/27 18Z 0.80 1401  69  30   5 0.00
Mon 04/27 19Z 0.72 1700  70  32   5 0.00
Mon 04/27 20Z 0.48 2600  71  37   6 0.00
Mon 04/27 21Z 0.38 0700  72  37   6 0.01
Mon 04/27 22Z 0.60 1003  69  26   6 0.00
Mon 04/27 23Z 0.46 1304  66  23   6 0.00
Tue 04/28 00Z 0.37 1406  65  20   6 0.00
Tue 04/28 01Z 0.32 1508  66  16   6 0.00
Tue 04/28 02Z 0.23 1610  64  14   5 0.00
Tue 04/28 03Z 0.06 1711  63  14   5 0.00
Tue 04/28 04Z 0.07 1710  60  11   6 0.00
Tue 04/28 05Z 0.07 1710  58  11   6 0.00
Tue 04/28 06Z 0.10 1712  58  10   5 0.00
Tue 04/28 07Z 0.23 1613  55  10   5 0.00
Tue 04/28 08Z 0.07 1713  54  10   5 0.00
Tue 04/28 09Z 0.09 1813  54   9   5 0.00
Tue 04/28 10Z 0.18 1614  54   8   5 0.00
Tue 04/28 11Z 0.19 1617  55   8   5 0.00
Tue 04/28 12Z 0.30 1519  57   8   4 0.00
Tue 04/28 13Z 0.28 1521  61   7   4 0.00
Tue 04/28 14Z 0.34 1521  64   7   4 0.00
Tue 04/28 15Z 0.38 1620  67   6   4 0.00
Tue 04/28 16Z 0.99 1619  67   6   3 0.00
Tue 04/28 17Z 1.47 1618  66   6   4 0.00
Tue 04/28 18Z 2.23 1617  63   6   4 0.00
Tue 04/28 19Z 2.29 1618  62   7   4 0.00
Tue 04/28 20Z 1.32 1617  64   8   4 0.00
Tue 04/28 21Z 0.83 1617  66  11   4 0.00
Tue 04/28 22Z 0.54 1619  69  47   4 0.00
Tue 04/28 23Z 0.37 1622  71  74   4 0.00
Wed 04/29 00Z 0.19 1623  70  89   4 0.00
Wed 04/29 01Z 0.07 1723  69  94   4 0.00
Wed 04/29 02Z 0.05 1823  70  94   4 0.00
Wed 04/29 03Z 0.11 1923  72  94   4 0.00
Wed 04/29 04Z 0.12 1922  75  92   4 0.00
Wed 04/29 05Z 0.15 1921  73  89   4 0.00
Wed 04/29 06Z 0.22 2022  71  85   4 0.00
Wed 04/29 07Z 0.32 2123  77  87   4 0.00
Wed 04/29 08Z 0.28 2120  88  80   5 0.00
Wed 04/29 09Z 0.17 2114  90  62   7 0.00
Wed 04/29 10Z 0.15 2112  91  50   7 0.00
Wed 04/29 11Z 0.15 2211  92  44   7 0.00
Wed 04/29 12Z 0.10 2108  91  35   7 0.00
Wed 04/29 13Z 0.04 1907  89  32   7 0.00
Wed 04/29 14Z 0.03 1808  89  29   7 0.00
Wed 04/29 15Z 0.02 1709  89  27   6 0.00
Wed 04/29 16Z 0.03 1710  87  30   6 0.00
Wed 04/29 17Z 0.04 1711  85  34   6 0.00
Wed 04/29 18Z 0.15 1712  83  34   6 0.00
Wed 04/29 19Z 0.45 1613  82  35   6 0.00
Wed 04/29 20Z 0.53 1615  83  37   6 0.00
Wed 04/29 21Z 0.30 1617  84  36   6 0.00
Wed 04/29 22Z 0.26 1621  86  33   6 0.00
Wed 04/29 23Z 0.28 1624  86  35   6 0.00

Run total areal avg QPF for the greens is: 0.01 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