NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260919_0000
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)
=== ===== === ==== ==== === === === ====
Sat 09/19 00Z 0.33 3420  70   5   5 0.00
Sat 09/19 01Z 0.25 3422  68   6   5 0.00
Sat 09/19 02Z 0.15 3522  70   6   5 0.00
Sat 09/19 03Z 0.05 3522  69   5   4 0.00
Sat 09/19 04Z 0.04 0021  67   5   4 0.00
Sat 09/19 05Z 0.03 0019  63   5   4 0.00
Sat 09/19 06Z 0.03 0017  59   5   5 0.00
Sat 09/19 07Z 0.02 0016  53   5   5 0.00
Sat 09/19 08Z 0.02 0014  49   5   6 0.00
Sat 09/19 09Z 0.02 0014  44   5   6 0.00
Sat 09/19 10Z 0.02 0013  40   5   6 0.00
Sat 09/19 11Z 0.03 0013  38   5   6 0.00
Sat 09/19 12Z 0.05 0112  36   5   6 0.00
Sat 09/19 13Z 0.05 0110  36   6   6 0.00
Sat 09/19 14Z 0.05 0108  37   5   6 0.00
Sat 09/19 15Z 0.05 0206  41   5   5 0.00
Sat 09/19 16Z 0.05 0204  46   6   5 0.00
Sat 09/19 17Z 0.05 0202  51   6   4 0.00
Sat 09/19 18Z 0.06 0200  55   6   4 0.00
Sat 09/19 19Z 0.06 1800  58   5   5 0.00
Sat 09/19 20Z 0.05 2300  60   6   5 0.00
Sat 09/19 21Z 0.04 1400  61   6   5 0.00
Sat 09/19 22Z 0.04 1602  59   6   5 0.00
Sat 09/19 23Z 0.03 1604  54   6   6 0.00
Sun 09/20 00Z 0.02 1705  49   6   7 0.00
Sun 09/20 01Z 0.03 1706  46   6   7 0.00
Sun 09/20 02Z 0.02 1807  46   6   7 0.00
Sun 09/20 03Z 0.03 1810  45   6   7 0.00
Sun 09/20 04Z 0.09 1912  48   6   7 0.00
Sun 09/20 05Z 0.15 2014  53   6   6 0.00
Sun 09/20 06Z 0.18 2016  59   6   6 0.00
Sun 09/20 07Z 0.24 2018  68   7   5 0.00
Sun 09/20 08Z 0.23 2018  75   9   6 0.00
Sun 09/20 09Z 0.24 2019  81  12   6 0.00
Sun 09/20 10Z 0.26 2018  88  16   5 0.00
Sun 09/20 11Z 0.25 2018  91  23   5 0.00
Sun 09/20 12Z 0.20 2017  90  33   6 0.00
Sun 09/20 13Z 0.18 2016  88  44   6 0.00
Sun 09/20 14Z 0.16 2016  88  62   6 0.00
Sun 09/20 15Z 0.13 1915  88  76   6 0.00
Sun 09/20 16Z 0.11 1915  89  87   6 0.00
Sun 09/20 17Z 0.08 1914  90  95   6 0.01
Sun 09/20 18Z 0.07 1914  94  98   7 0.02
Sun 09/20 19Z 0.06 1813  95  99   7 0.03
Sun 09/20 20Z 0.06 1812  96  99   7 0.04
Sun 09/20 21Z 0.07 1912  97  98   7 0.06
Sun 09/20 22Z 0.09 1911  98  99   7 0.05
Sun 09/20 23Z 0.13 2110  98  96   7 0.05
Mon 09/21 00Z 0.15 2210  98  91   7 0.04
Mon 09/21 01Z 0.17 2209  99  82   7 0.04
Mon 09/21 02Z 0.16 2407  99  64   7 0.03
Mon 09/21 03Z 0.13 2605  99  59   6 0.02
Mon 09/21 04Z 0.09 3004  98  54   6 0.01
Mon 09/21 05Z 0.07 3205  96  40   6 0.00
Mon 09/21 06Z 0.04 3407  93  22   6 0.00
Mon 09/21 07Z 0.02 3509  89  17   6 0.00
Mon 09/21 08Z 0.02 0011  83  11   5 0.00
Mon 09/21 09Z 0.03 0013  80   7   5 0.00
Mon 09/21 10Z 0.05 0013  79   5   5 0.00
Mon 09/21 11Z 0.07 0114  77   3   5 0.00

Run total areal avg QPF for the greens is: 0.40 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