NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260823_0600
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)
=== ===== === ==== ==== === === === ====
Sun 08/23 06Z 0.17 1515  95  42  11 0.00
Sun 08/23 07Z 0.18 1617  94  50  11 0.00
Sun 08/23 08Z 0.17 1617  93  51  11 0.01
Sun 08/23 09Z 0.14 1617  92  50  11 0.01
Sun 08/23 10Z 0.15 1617  92  47  12 0.01
Sun 08/23 11Z 0.17 1618  93  53  11 0.01
Sun 08/23 12Z 0.17 1619  93  55  12 0.01
Sun 08/23 13Z 0.19 1619  93  57  12 0.01
Sun 08/23 14Z 0.15 1619  93  63  12 0.01
Sun 08/23 15Z 0.08 1719  94  62  12 0.00
Sun 08/23 16Z 0.06 1717  96  73  12 0.01
Sun 08/23 17Z 0.08 1715  95  68  12 0.00
Sun 08/23 18Z 0.14 1614  95  70  12 0.00
Sun 08/23 19Z 0.17 1614  95  72  12 0.00
Sun 08/23 20Z 0.20 1615  95  74  12 0.00
Sun 08/23 21Z 0.19 1616  94  72  13 0.00
Sun 08/23 22Z 0.15 1618  94  64  13 0.01
Sun 08/23 23Z 0.12 1719  95  48  13 0.01
Mon 08/24 00Z 0.19 1820  97  33  12 0.02
Mon 08/24 01Z 0.27 1920  97  38  12 0.04
Mon 08/24 02Z 0.47 2119  93  69  12 0.14
Mon 08/24 03Z 0.43 2316  81  66  12 0.04
Mon 08/24 04Z 0.44 2416  80  57  12 0.00
Mon 08/24 05Z 0.38 2415  80  58  12 0.00
Mon 08/24 06Z 0.32 2314  79  50  12 0.00
Mon 08/24 07Z 0.30 2313  78  47  11 0.00
Mon 08/24 08Z 0.31 2314  76  35  11 0.00
Mon 08/24 09Z 0.33 2315  78  22  10 0.00
Mon 08/24 10Z 0.33 2315  80  21  10 0.00
Mon 08/24 11Z 0.30 2314  78  24  10 0.00
Mon 08/24 12Z 0.24 2212  78  28  10 0.00
Mon 08/24 13Z 0.17 2111  79  33  10 0.00
Mon 08/24 14Z 0.17 2012  82  42   9 0.00
Mon 08/24 15Z 0.21 2013  85  50   9 0.00
Mon 08/24 16Z 0.36 2013  89  64   9 0.00
Mon 08/24 17Z 0.46 2011  90  71   9 0.00
Mon 08/24 18Z 0.69 2011  88  62   9 0.01
Mon 08/24 19Z 1.16 2011  84  51   9 0.02
Mon 08/24 20Z 0.96 2111  85  62  10 0.01
Mon 08/24 21Z 0.53 2213  82  62   9 0.06
Mon 08/24 22Z 0.50 2212  76  50  10 0.01
Mon 08/24 23Z 0.46 2212  78  58   9 0.00
Tue 08/25 00Z 0.47 2312  86  55   9 0.00
Tue 08/25 01Z 0.45 2312  89  62   9 0.00
Tue 08/25 02Z 0.42 2411  86  69   9 0.01
Tue 08/25 03Z 0.45 2411  88  70   9 0.00
Tue 08/25 04Z 0.35 2410  86  79   9 0.01
Tue 08/25 05Z 0.28 2508  88  86   9 0.01
Tue 08/25 06Z 0.26 2607  88  90   9 0.00
Tue 08/25 07Z 0.28 2608  89  94   8 0.00
Tue 08/25 08Z 0.23 2607  91  97   8 0.01
Tue 08/25 09Z 0.21 2606  93  99   8 0.01
Tue 08/25 10Z 0.21 2606  93  99   8 0.01
Tue 08/25 11Z 0.19 2606  94  97   8 0.01
Tue 08/25 12Z 0.23 2606  95  95   8 0.01
Tue 08/25 13Z 0.27 2607  96  91   7 0.01
Tue 08/25 14Z 0.27 2707  96  87   7 0.01
Tue 08/25 15Z 0.30 2707  96  83   7 0.01
Tue 08/25 16Z 0.29 2806  95  82   7 0.00
Tue 08/25 17Z 0.34 2806  95  79   8 0.00

Run total areal avg QPF for the greens is: 0.56 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