NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260422_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)
=== ===== === ==== ==== === === === ====
Wed 04/22 06Z 0.60 2119  55  81  -2 0.00
Wed 04/22 07Z 0.57 2219  65  80  -1 0.00
Wed 04/22 08Z 0.49 2218  83  86  -1 0.00
Wed 04/22 09Z 0.42 2316  89  97   0 0.00
Wed 04/22 10Z 0.37 2215  91  99   0 0.00
Wed 04/22 11Z 0.31 2116  95  99   0 0.01
Wed 04/22 12Z 0.30 2018  97  97   0 0.02
Wed 04/22 13Z 0.26 2018  96  94   0 0.01
Wed 04/22 14Z 0.24 2018  97  94   0 0.01
Wed 04/22 15Z 0.26 2017  98  83   0 0.01
Wed 04/22 16Z 0.27 2016  98  74   0 0.01
Wed 04/22 17Z 0.27 2016  98  58   0 0.01
Wed 04/22 18Z 0.28 2015  98  41   0 0.01
Wed 04/22 19Z 0.29 2114  98  30   0 0.01
Wed 04/22 20Z 0.29 2114  97  27   0 0.01
Wed 04/22 21Z 0.29 2213  98  28   1 0.01
Wed 04/22 22Z 0.27 2212  98  31   1 0.01
Wed 04/22 23Z 0.26 2410  98  31   1 0.01
Thu 04/23 00Z 0.25 2509  98  26   1 0.01
Thu 04/23 01Z 0.25 2609  97  24   1 0.01
Thu 04/23 02Z 0.27 2811  95  22   1 0.01
Thu 04/23 03Z 0.26 2911  94  22   1 0.00
Thu 04/23 04Z 0.24 3011  92  42   1 0.00
Thu 04/23 05Z 0.25 3012  92  74   1 0.00
Thu 04/23 06Z 0.26 3012  91  71   1 0.00
Thu 04/23 07Z 0.29 3013  91  77   1 0.00
Thu 04/23 08Z 0.39 2916  94  87   1 0.01
Thu 04/23 09Z 0.44 3018  96  86   1 0.01
Thu 04/23 10Z 0.52 3022  96  78   0 0.02
Thu 04/23 11Z 0.56 3025  95  63   0 0.02
Thu 04/23 12Z 0.49 3126  95  29   0 0.02
Thu 04/23 13Z 0.39 3224  95   6  -1 0.01
Thu 04/23 14Z 0.39 3323  96   5  -2 0.01
Thu 04/23 15Z 0.42 3223  94   5  -2 0.00
Thu 04/23 16Z 0.76 3222  87   7  -3 0.00
Thu 04/23 17Z 1.09 3222  78   5  -2 0.00
Thu 04/23 18Z 0.99 3321  64   4  -2 0.00
Thu 04/23 19Z 2.42 3220  62   2  -1 0.00
Thu 04/23 20Z 2.96 3218  65   3  -1 0.00
Thu 04/23 21Z 2.74 3218  59   6  -1 0.00
Thu 04/23 22Z 1.59 3218  54   7  -1 0.00
Thu 04/23 23Z 0.58 3319  53   4  -1 0.00
Fri 04/24 00Z 0.36 3320  54   3  -1 0.00
Fri 04/24 01Z 0.30 3321  57   3  -2 0.00
Fri 04/24 02Z 0.22 3421  64   2  -3 0.00
Fri 04/24 03Z 0.12 3418  69   1  -3 0.00
Fri 04/24 04Z 0.09 3416  73   2  -4 0.00
Fri 04/24 05Z 0.07 3413  76   3  -4 0.00
Fri 04/24 06Z 0.07 3413  79   4  -5 0.00
Fri 04/24 07Z 0.09 3412  80   4  -5 0.00
Fri 04/24 08Z 0.10 3312  77   4  -5 0.00
Fri 04/24 09Z 0.09 3314  75   6  -5 0.00
Fri 04/24 10Z 0.07 3415  72   7  -5 0.00
Fri 04/24 11Z 0.04 3416  67   8  -5 0.00
Fri 04/24 12Z 0.05 3415  65   8  -5 0.00
Fri 04/24 13Z 0.04 3413  67   8  -5 0.00
Fri 04/24 14Z 0.06 3511  68   6  -5 0.00
Fri 04/24 15Z 0.19 3509  69   5  -5 0.00
Fri 04/24 16Z 0.28 3507  68   4  -5 0.00
Fri 04/24 17Z 0.25 3406  68   8  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.27 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