NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260825_0000
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)
=== ===== === ==== ==== === === === ====
Tue 08/25 00Z 0.47 2314  80  80  10 0.00
Tue 08/25 01Z 0.56 2316  77  83  10 0.00
Tue 08/25 02Z 0.75 2319  77  85  10 0.00
Tue 08/25 03Z 0.81 2321  85  82   9 0.00
Tue 08/25 04Z 0.61 2320  85  81   9 0.00
Tue 08/25 05Z 0.62 2320  89  87   9 0.00
Tue 08/25 06Z 0.59 2320  91  84   9 0.00
Tue 08/25 07Z 0.63 2420  91  77   9 0.00
Tue 08/25 08Z 0.66 2520  95  78   9 0.01
Tue 08/25 09Z 0.63 2519  95  75   9 0.01
Tue 08/25 10Z 0.56 2517  96  81   9 0.01
Tue 08/25 11Z 0.53 2616  97  77   8 0.01
Tue 08/25 12Z 0.47 2614  95  69   8 0.01
Tue 08/25 13Z 0.46 2714  95  65   8 0.01
Tue 08/25 14Z 0.38 2711  93  59   8 0.01
Tue 08/25 15Z 0.37 2811  93  59   8 0.00
Tue 08/25 16Z 0.42 2911  95  61   8 0.00
Tue 08/25 17Z 0.42 2910  95  58   8 0.00
Tue 08/25 18Z 0.41 2910  95  56   8 0.01
Tue 08/25 19Z 0.40 2909  94  53   9 0.00
Tue 08/25 20Z 0.47 2810  95  63   9 0.00
Tue 08/25 21Z 0.46 2810  95  64   9 0.00
Tue 08/25 22Z 0.47 2812  94  58   9 0.00
Tue 08/25 23Z 0.46 2913  93  57   9 0.00
Wed 08/26 00Z 0.50 2914  94  60   9 0.00
Wed 08/26 01Z 0.41 3014  93  60   9 0.00
Wed 08/26 02Z 0.34 3013  91  62   9 0.00
Wed 08/26 03Z 0.32 3014  90  62   9 0.00
Wed 08/26 04Z 0.28 3115  90  59   9 0.00
Wed 08/26 05Z 0.25 3114  90  51   9 0.00
Wed 08/26 06Z 0.22 3113  91  47   9 0.00
Wed 08/26 07Z 0.20 3112  92  47   9 0.00
Wed 08/26 08Z 0.17 3211  93  42   9 0.00
Wed 08/26 09Z 0.16 3110  94  40   9 0.00
Wed 08/26 10Z 0.16 3109  92  34   9 0.00
Wed 08/26 11Z 0.12 3107  89  30  10 0.00
Wed 08/26 12Z 0.10 3105  89  30   9 0.00
Wed 08/26 13Z 0.12 2805  90  28   9 0.00
Wed 08/26 14Z 0.14 2704  92  27   9 0.00
Wed 08/26 15Z 0.14 2705  91  25  10 0.00
Wed 08/26 16Z 0.14 2704  90  22  10 0.00
Wed 08/26 17Z 0.11 2603  89  20  10 0.00
Wed 08/26 18Z 0.13 2503  88  18  10 0.00
Wed 08/26 19Z 0.13 2503  87  15  10 0.00
Wed 08/26 20Z 0.14 2403  86  12  10 0.00
Wed 08/26 21Z 0.13 2403  84  11  11 0.00
Wed 08/26 22Z 0.12 2403  83  12  11 0.00
Wed 08/26 23Z 0.10 2203  81  14  11 0.00
Thu 08/27 00Z 0.11 2105  81  17  11 0.00
Thu 08/27 01Z 0.12 2006  81  15  11 0.00
Thu 08/27 02Z 0.16 2007  79   8  11 0.00
Thu 08/27 03Z 0.19 2009  78  13  11 0.00
Thu 08/27 04Z 0.21 2110  75  18  11 0.00
Thu 08/27 05Z 0.26 2112  72  18  11 0.00
Thu 08/27 06Z 0.32 2114  72  18  12 0.00
Thu 08/27 07Z 0.42 2216  82  15  11 0.00
Thu 08/27 08Z 0.43 2216  87  16  11 0.00
Thu 08/27 09Z 0.46 2117  90  13  11 0.00
Thu 08/27 10Z 0.45 2118  90  11  11 0.00
Thu 08/27 11Z 0.39 2119  87   9  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.08 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