Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260428_0600
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)
=== ===== === ==== ==== === === === ====
Tue 04/28 06Z 0.15 1910  50   9   7 0.00
Tue 04/28 07Z 0.13 1811  49   6   7 0.00
Tue 04/28 08Z 0.11 1812  50   4   7 0.00
Tue 04/28 09Z 0.19 1915  51   7   7 0.00
Tue 04/28 10Z 0.18 1916  49   7   6 0.00
Tue 04/28 11Z 0.17 1917  49   5   6 0.00
Tue 04/28 12Z 0.07 1716  48   4   6 0.00
Tue 04/28 13Z 0.04 1617  49   3   6 0.00
Tue 04/28 14Z 0.10 1617  52   3   6 0.00
Tue 04/28 15Z 0.19 1618  56   4   5 0.00
Tue 04/28 16Z 0.83 1619  60   5   5 0.00
Tue 04/28 17Z 2.00 1517  63   5   4 0.00
Tue 04/28 18Z 1.96 1616  65   5   5 0.00
Tue 04/28 19Z 2.10 1516  65   5   5 0.00
Tue 04/28 20Z 3.46 1518  65   4   5 0.00
Tue 04/28 21Z 3.40 1519  65   6   5 0.00
Tue 04/28 22Z 1.68 1519  64  10   4 0.00
Tue 04/28 23Z 0.24 1620  65  10   4 0.00
Wed 04/29 00Z 0.16 1621  69  30   4 0.00
Wed 04/29 01Z 0.07 1621  68  49   4 0.00
Wed 04/29 02Z 0.07 1720  65  68   4 0.00
Wed 04/29 03Z 0.15 1820  66  76   3 0.00
Wed 04/29 04Z 0.24 1920  69  88   2 0.00
Wed 04/29 05Z 0.28 1920  71  82   2 0.00
Wed 04/29 06Z 0.30 2019  73  80   2 0.00
Wed 04/29 07Z 0.34 2020  81  79   2 0.00
Wed 04/29 08Z 0.32 2118  87  76   3 0.00
Wed 04/29 09Z 0.21 2113  89  61   5 0.00
Wed 04/29 10Z 0.13 2109  89  43   6 0.00
Wed 04/29 11Z 0.07 1907  90  27   6 0.00
Wed 04/29 12Z 0.15 2110  94  34   6 0.00
Wed 04/29 13Z 0.13 2009  95  30   5 0.00
Wed 04/29 14Z 0.08 1907  94  24   6 0.00
Wed 04/29 15Z 0.05 1806  91  19   6 0.00
Wed 04/29 16Z 0.03 1706  86  16   6 0.00
Wed 04/29 17Z 0.06 1706  83  17   6 0.00
Wed 04/29 18Z 0.13 1707  81  22   6 0.00
Wed 04/29 19Z 0.22 1707  80  27   6 0.00
Wed 04/29 20Z 0.26 1607  81  31   6 0.00
Wed 04/29 21Z 0.13 1708  83  42   5 0.00
Wed 04/29 22Z 0.11 1610  85  53   6 0.00
Wed 04/29 23Z 0.15 1512  86  69   6 0.00
Thu 04/30 00Z 0.21 1415  86  66   6 0.00
Thu 04/30 01Z 0.15 1518  88  59   5 0.00
Thu 04/30 02Z 0.13 1518  91  52   5 0.00
Thu 04/30 03Z 0.13 1519  91  47   6 0.00
Thu 04/30 04Z 0.15 1521  92  43   6 0.00
Thu 04/30 05Z 0.15 1523  93  47   5 0.01
Thu 04/30 06Z 0.14 1525  93  53   5 0.01
Thu 04/30 07Z 0.11 1524  94  60   5 0.01
Thu 04/30 08Z 0.11 1523  93  71   5 0.01
Thu 04/30 09Z 0.13 1523  92  95   5 0.02
Thu 04/30 10Z 0.15 1421  93  99   5 0.04
Thu 04/30 11Z 0.07 1617  99  99   3 0.04
Thu 04/30 12Z 0.03 1614  99  99   1 0.04
Thu 04/30 13Z 0.04 1711  99  99   1 0.04
Thu 04/30 14Z 0.08 1808  99  94   1 0.02
Thu 04/30 15Z 0.15 2007  99  96   0 0.02
Thu 04/30 16Z 0.22 2207  99  98   0 0.02
Thu 04/30 17Z 0.32 2408  99  92   0 0.01

Run total areal avg QPF for the Central_Greens is: 0.29 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