Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260427_1800
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)
=== ===== === ==== ==== === === === ====
Mon 04/27 18Z 0.87 0800  52  46   7 0.00
Mon 04/27 19Z 0.78 0001  54  62   7 0.00
Mon 04/27 20Z 0.69 0301  57  69   7 0.00
Mon 04/27 21Z 0.45 0701  57  70   7 0.00
Mon 04/27 22Z 0.59 1002  58  65   7 0.00
Mon 04/27 23Z 0.11 1501  57  53   7 0.00
Tue 04/28 00Z 0.20 1303  57  28   7 0.00
Tue 04/28 01Z 0.26 1406  57  18   7 0.00
Tue 04/28 02Z 0.17 1509  57  16   6 0.00
Tue 04/28 03Z 0.05 1710  57  15   6 0.00
Tue 04/28 04Z 0.03 1610  57  13   6 0.00
Tue 04/28 05Z 0.04 1711  56  11   6 0.00
Tue 04/28 06Z 0.06 1711  56   9   6 0.00
Tue 04/28 07Z 0.13 1812  56   8   6 0.00
Tue 04/28 08Z 0.15 1813  57   6   6 0.00
Tue 04/28 09Z 0.09 1812  58   5   5 0.00
Tue 04/28 10Z 0.08 1713  58   5   5 0.00
Tue 04/28 11Z 0.05 1715  56   4   5 0.00
Tue 04/28 12Z 0.04 1617  55   4   5 0.00
Tue 04/28 13Z 0.05 1619  55   3   5 0.00
Tue 04/28 14Z 0.14 1619  58   3   4 0.00
Tue 04/28 15Z 0.36 1520  62   3   4 0.00
Tue 04/28 16Z 1.29 1519  65   4   4 0.00
Tue 04/28 17Z 1.96 1517  66   4   4 0.00
Tue 04/28 18Z 1.19 1617  65   6   4 0.00
Tue 04/28 19Z 1.88 1617  63   7   5 0.00
Tue 04/28 20Z 2.32 1517  63   6   5 0.00
Tue 04/28 21Z 1.10 1616  62  11   5 0.00
Tue 04/28 22Z 0.44 1618  63  62   4 0.00
Tue 04/28 23Z 0.15 1620  66  75   4 0.00
Wed 04/29 00Z 0.06 1720  68  86   4 0.00
Wed 04/29 01Z 0.09 1721  68  83   4 0.00
Wed 04/29 02Z 0.17 1821  71  80   3 0.00
Wed 04/29 03Z 0.20 1920  78  74   3 0.00
Wed 04/29 04Z 0.19 1919  77  68   3 0.00
Wed 04/29 05Z 0.24 1920  73  67   3 0.00
Wed 04/29 06Z 0.41 2022  75  62   3 0.00
Wed 04/29 07Z 0.34 2121  82  48   5 0.00
Wed 04/29 08Z 0.28 2118  85  41   6 0.00
Wed 04/29 09Z 0.28 2117  88  41   6 0.00
Wed 04/29 10Z 0.21 2113  89  34   6 0.00
Wed 04/29 11Z 0.19 2112  89  32   6 0.00
Wed 04/29 12Z 0.14 2110  89  25   7 0.00
Wed 04/29 13Z 0.12 2009  90  22   6 0.00
Wed 04/29 14Z 0.07 1810  89  18   6 0.00
Wed 04/29 15Z 0.05 1710  86  18   6 0.00
Wed 04/29 16Z 0.05 1610  82  25   6 0.00
Wed 04/29 17Z 0.10 1710  79  47   5 0.00
Wed 04/29 18Z 0.25 1609  76  67   5 0.00
Wed 04/29 19Z 1.35 1510  74  58   5 0.00
Wed 04/29 20Z 1.46 1511  75  54   5 0.00
Wed 04/29 21Z 1.99 1511  78  59   5 0.00
Wed 04/29 22Z 1.26 1413  81  52   5 0.00
Wed 04/29 23Z 0.35 1415  86  43   5 0.00
Thu 04/30 00Z 0.17 1416  88  42   6 0.00
Thu 04/30 01Z 0.15 1419  87  46   6 0.00
Thu 04/30 02Z 0.18 1422  82  43   6 0.00
Thu 04/30 03Z 0.20 1424  77  41   6 0.00
Thu 04/30 04Z 0.25 1429  89  42   6 0.01
Thu 04/30 05Z 0.30 1434  95  43   6 0.02

Run total areal avg QPF for the Central_Greens is: 0.03 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