NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260506_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)
=== ===== === ==== ==== === === === ====
Wed 05/06 06Z 0.50 2515  91  96   6 0.00
Wed 05/06 07Z 0.44 2515  88  87   6 0.02
Wed 05/06 08Z 0.32 2413  89  87   6 0.01
Wed 05/06 09Z 0.23 2211  90  89   6 0.00
Wed 05/06 10Z 0.13 2010  90  85   7 0.01
Wed 05/06 11Z 0.06 1811  91  85   7 0.01
Wed 05/06 12Z 0.14 1912  94  85   6 0.06
Wed 05/06 13Z 0.27 2114  97  92   6 0.11
Wed 05/06 14Z 0.32 2014  97  87   6 0.08
Wed 05/06 15Z 0.33 2015  98  98   6 0.07
Wed 05/06 16Z 0.25 2018  99  98   7 0.13
Wed 05/06 17Z 0.31 2120  98  98   7 0.17
Wed 05/06 18Z 0.33 2023  97  98   7 0.13
Wed 05/06 19Z 0.27 2115  99  99   6 0.11
Wed 05/06 20Z 0.23 2312  98  96   7 0.09
Wed 05/06 21Z 0.20 2509  97  97   7 0.03
Wed 05/06 22Z 0.20 2709  97  98   6 0.04
Wed 05/06 23Z 0.21 2910  96  98   5 0.04
Thu 05/07 00Z 0.21 3011  95  96   4 0.02
Thu 05/07 01Z 0.16 3110  93  92   4 0.01
Thu 05/07 02Z 0.19 3111  93  84   3 0.00
Thu 05/07 03Z 0.20 3111  90  77   2 0.00
Thu 05/07 04Z 0.27 3013  92  76   1 0.01
Thu 05/07 05Z 0.29 3014  91  71   1 0.01
Thu 05/07 06Z 0.29 3014  88  68   1 0.00
Thu 05/07 07Z 0.37 3014  91  65   0 0.00
Thu 05/07 08Z 0.45 2915  94  60   0 0.00
Thu 05/07 09Z 0.57 2918  96  46   0 0.01
Thu 05/07 10Z 0.56 2817  94  31  -1 0.01
Thu 05/07 11Z 0.65 2819  85  17  -2 0.01
Thu 05/07 12Z 0.61 2817  70  11  -2 0.00
Thu 05/07 13Z 0.64 2818  66  17  -2 0.00
Thu 05/07 14Z 0.83 2817  72  20  -3 0.00
Thu 05/07 15Z 5.80 2817  81  25  -3 0.00
Thu 05/07 16Z 10.50 2716  81  25  -3 0.00
Thu 05/07 17Z 11.24 2717  75  29  -2 0.00
Thu 05/07 18Z 11.90 2717  69  29  -1 0.00
Thu 05/07 19Z 12.35 2717  62  26  -1 0.00
Thu 05/07 20Z 12.45 2817  57  23   0 0.00
Thu 05/07 21Z 12.48 2818  56  24   0 0.00
Thu 05/07 22Z 12.00 2819  59  23  -1 0.00
Thu 05/07 23Z 8.43 2819  62  22  -1 0.00
Fri 05/08 00Z 3.33 2919  66  23  -2 0.00
Fri 05/08 01Z 2.15 2919  69  22  -2 0.00
Fri 05/08 02Z 2.02 2919  71  22  -2 0.00
Fri 05/08 03Z 1.54 2919  75  25  -3 0.00
Fri 05/08 04Z 1.20 2919  75  28  -3 0.00
Fri 05/08 05Z 0.93 2919  75  37  -3 0.00
Fri 05/08 06Z 0.80 3018  75  45  -3 0.00
Fri 05/08 07Z 0.76 3018  75  53  -3 0.00
Fri 05/08 08Z 0.74 3018  76  59  -3 0.00
Fri 05/08 09Z 0.69 3019  79  61  -3 0.00
Fri 05/08 10Z 0.70 3019  82  57  -3 0.00
Fri 05/08 11Z 0.74 2918  79  51  -4 0.00
Fri 05/08 12Z 1.02 2917  76  67  -4 0.00
Fri 05/08 13Z 5.72 2816  74  73  -4 0.00
Fri 05/08 14Z 9.68 2814  75  63  -4 0.00
Fri 05/08 15Z 10.06 2714  75  31  -3 0.00
Fri 05/08 16Z 10.33 2715  71  31  -3 0.00
Fri 05/08 17Z 9.73 2715  70  43  -3 0.00

Run total areal avg QPF for the greens is: 1.19 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