Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260428_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 04/28 12Z 0.07 1713  55   9   6 0.00
Tue 04/28 13Z 0.11 1615  56   9   6 0.00
Tue 04/28 14Z 0.12 1616  55   8   6 0.00
Tue 04/28 15Z 0.28 1617  56   7   6 0.00
Tue 04/28 16Z 0.72 1617  57   7   6 0.00
Tue 04/28 17Z 1.65 1616  58   7   6 0.00
Tue 04/28 18Z 3.34 1617  59   7   6 0.00
Tue 04/28 19Z 3.65 1617  61   7   6 0.00
Tue 04/28 20Z 3.08 1617  62   9   6 0.00
Tue 04/28 21Z 1.84 1617  64   8   6 0.00
Tue 04/28 22Z 0.87 1618  67   7   5 0.00
Tue 04/28 23Z 0.35 1620  70   7   5 0.00
Wed 04/29 00Z 0.18 1621  70   9   5 0.00
Wed 04/29 01Z 0.09 1721  70  15   5 0.00
Wed 04/29 02Z 0.06 1720  69  23   5 0.00
Wed 04/29 03Z 0.07 1820  70  33   5 0.00
Wed 04/29 04Z 0.11 1919  73  45   4 0.00
Wed 04/29 05Z 0.19 1919  76  61   4 0.00
Wed 04/29 06Z 0.25 2019  75  67   3 0.00
Wed 04/29 07Z 0.28 2020  71  75   4 0.00
Wed 04/29 08Z 0.29 2119  72  74   4 0.00
Wed 04/29 09Z 0.27 2117  74  66   4 0.00
Wed 04/29 10Z 0.19 2113  75  51   5 0.00
Wed 04/29 11Z 0.15 2110  79  37   6 0.00
Wed 04/29 12Z 0.11 2107  82  30   6 0.00
Wed 04/29 13Z 0.11 2108  83  30   6 0.00
Wed 04/29 14Z 0.09 2006  83  31   6 0.00
Wed 04/29 15Z 0.02 1806  81  31   6 0.00
Wed 04/29 16Z 0.08 1707  78  27   6 0.00
Wed 04/29 17Z 0.19 1807  76  34   6 0.00
Wed 04/29 18Z 0.47 1607  74  36   6 0.00
Wed 04/29 19Z 0.82 1608  73  42   6 0.00
Wed 04/29 20Z 0.73 1709  74  53   7 0.00
Wed 04/29 21Z 0.56 1709  77  69   6 0.00
Wed 04/29 22Z 0.30 1710  80  68   6 0.00
Wed 04/29 23Z 0.22 1611  81  61   6 0.00
Thu 04/30 00Z 0.30 1513  81  54   6 0.00
Thu 04/30 01Z 0.26 1516  82  53   6 0.00
Thu 04/30 02Z 0.25 1518  84  49   6 0.00
Thu 04/30 03Z 0.22 1520  85  45   6 0.00
Thu 04/30 04Z 0.15 1621  88  53   6 0.00
Thu 04/30 05Z 0.15 1623  90  53   6 0.00
Thu 04/30 06Z 0.16 1624  90  55   5 0.00
Thu 04/30 07Z 0.14 1625  90  55   5 0.00
Thu 04/30 08Z 0.13 1623  90  51   5 0.00
Thu 04/30 09Z 0.11 1622  90  55   5 0.00
Thu 04/30 10Z 0.12 1622  89  71   5 0.00
Thu 04/30 11Z 0.13 1622  88  77   5 0.00
Thu 04/30 12Z 0.15 1621  88  80   5 0.01
Thu 04/30 13Z 0.20 1519  87  92   4 0.01
Thu 04/30 14Z 0.26 1419  89  97   4 0.03
Thu 04/30 15Z 0.30 1418  92  98   2 0.05
Thu 04/30 16Z 0.30 1416  94  99   1 0.04
Thu 04/30 17Z 0.24 1412  98  99   1 0.05
Thu 04/30 18Z 0.12 1609  99  99   0 0.04
Thu 04/30 19Z 0.07 1808 100  99   0 0.06
Thu 04/30 20Z 0.18 2107  99  98   0 0.05
Thu 04/30 21Z 0.32 2408  99  96   0 0.03
Thu 04/30 22Z 0.45 2610  98  92   0 0.02
Thu 04/30 23Z 0.59 2814  98  87   0 0.02

Run total areal avg QPF for the greens is: 0.41 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