Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260219_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)
=== ===== === ==== ==== === === === ====
Thu 02/19 18Z 0.10 1203  56  29  -4 0.00
Thu 02/19 19Z 0.11 1304  57  32  -4 0.00
Thu 02/19 20Z 0.04 1605  57  36  -4 0.00
Thu 02/19 21Z 0.03 1704  56  40  -4 0.00
Thu 02/19 22Z 0.05 1903  57  47  -4 0.00
Thu 02/19 23Z 0.07 1904  57  52  -4 0.00
Fri 02/20 00Z 0.03 1903  53  41  -3 0.00
Fri 02/20 01Z 0.02 1603  52  21  -3 0.00
Fri 02/20 02Z 0.02 1604  55  13  -3 0.00
Fri 02/20 03Z 0.03 1805  57  11  -3 0.00
Fri 02/20 06Z 0.02 1707  63   9  -3 0.00
Fri 02/20 07Z 0.05 1809  66   9  -3 0.00
Fri 02/20 08Z 0.02 1709  68   9  -2 0.00
Fri 02/20 09Z 0.02 1609  69  10  -2 0.00
Fri 02/20 10Z 0.03 1610  67  10  -2 0.00
Fri 02/20 11Z 0.02 1712  65  11  -1 0.00
Fri 02/20 12Z 0.02 1615  64  11  -1 0.00
Fri 02/20 13Z 0.02 1716  63  10  -2 0.00
Fri 02/20 14Z 0.02 1617  61  13  -2 0.00
Fri 02/20 15Z 0.02 1617  62  22  -3 0.00
Fri 02/20 16Z 0.02 1618  62  30  -3 0.00
Fri 02/20 17Z 0.03 1618  66  61  -3 0.00
Fri 02/20 18Z 0.09 1516  79  91  -2 0.00
Fri 02/20 19Z 0.10 1518  92  94   0 0.00
Fri 02/20 20Z 0.14 1419  96  94   0 0.01
Fri 02/20 21Z 0.22 1322  95  97   0 0.04
Fri 02/20 22Z 0.30 1325  94  99  -1 0.08
Fri 02/20 23Z 0.37 1227  94  99  -1 0.08
Sat 02/21 00Z 0.37 1225  96  98  -2 0.07
Sat 02/21 01Z 0.36 1321  96  96  -4 0.05
Sat 02/21 02Z 0.38 1319  96  97  -5 0.09
Sat 02/21 03Z 0.42 1317  95  99  -7 0.16
Sat 02/21 04Z 0.37 1316  95  96  -7 0.11
Sat 02/21 05Z 0.27 1414  95  95  -8 0.07
Sat 02/21 06Z 0.13 1511  95  97  -8 0.03
Sat 02/21 07Z 0.06 1608  94  93  -8 0.02
Sat 02/21 08Z 0.04 1606  94  91  -8 0.02
Sat 02/21 09Z 0.05 1804  95  89  -8 0.02
Sat 02/21 10Z 0.11 2203  96  88  -8 0.01
Sat 02/21 11Z 0.11 2602  96  87  -8 0.01
Sat 02/21 12Z 0.09 2802  98  87  -8 0.01
Sat 02/21 13Z 0.07 2801  99  88  -8 0.01
Sat 02/21 14Z 0.06 3201  99  89  -8 0.01
Sat 02/21 15Z 0.06 0101  99  88  -8 0.01
Sat 02/21 16Z 0.08 0303  98  86  -8 0.00
Sat 02/21 17Z 0.14 0304  97  81  -8 0.00
Sat 02/21 18Z 0.12 0204  96  84  -8 0.00
Sat 02/21 19Z 0.15 0205  90  81  -8 0.00
Sat 02/21 20Z 0.20 0305  83  81  -8 0.00
Sat 02/21 21Z 0.28 0407  75  69  -8 0.00
Sat 02/21 22Z 0.37 0608  73  53  -8 0.00
Sat 02/21 23Z 0.37 0710  75  42  -8 0.00
Sun 02/22 00Z 0.30 0810  63  29  -8 0.00
Sun 02/22 02Z 0.28 1011  53  16  -8 0.00
Sun 02/22 03Z 0.25 1010  56  13  -8 0.00
Sun 02/22 04Z 0.22 1109  56  13  -8 0.00
Sun 02/22 05Z 0.19 1108  56  14  -8 0.00

Run total areal avg QPF for the Central_Greens is: 0.91 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