NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261007_1800
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 10/07 18Z 0.50 2120  55  84   7 0.00
Wed 10/07 19Z 0.44 2121  51  85   7 0.00
Wed 10/07 20Z 0.41 2022  50  85   8 0.00
Wed 10/07 21Z 0.46 2023  53  83   8 0.00
Wed 10/07 22Z 0.53 2126  58  78   7 0.00
Wed 10/07 23Z 0.55 2128  65  91   8 0.00
Thu 10/08 00Z 0.60 2229  69  90   8 0.00
Thu 10/08 01Z 0.62 2229  73  88   8 0.00
Thu 10/08 02Z 0.63 2230  75  84   8 0.00
Thu 10/08 03Z 0.67 2332  76  79   8 0.00
Thu 10/08 04Z 0.67 2330  81  69   8 0.00
Thu 10/08 05Z 0.64 2328  85  64   8 0.00
Thu 10/08 06Z 0.64 2328  89  76   8 0.01
Thu 10/08 07Z 0.64 2425  92  93   7 0.17
Thu 10/08 08Z 0.60 2325  92  71   7 0.03
Thu 10/08 09Z 0.65 2425  92  67   7 0.01
Thu 10/08 10Z 0.62 2423  89  71   7 0.01
Thu 10/08 11Z 0.67 2524  95  75   7 0.02
Thu 10/08 12Z 0.75 2523  96  69   6 0.04
Thu 10/08 13Z 0.79 2623  92  78   6 0.02
Thu 10/08 14Z 0.84 2722  90  82   5 0.01
Thu 10/08 15Z 0.87 2722  84  70   5 0.01
Thu 10/08 16Z 1.07 2722  87  58   5 0.00
Thu 10/08 17Z 2.46 2621  92  50   5 0.01
Thu 10/08 18Z 5.51 2722  86  51   5 0.04
Thu 10/08 19Z 4.51 2723  84  44   4 0.04
Thu 10/08 20Z 4.73 2621  82  37   4 0.00
Thu 10/08 21Z 3.72 2623  83  36   4 0.01
Thu 10/08 22Z 2.56 2625  85  41   4 0.02
Thu 10/08 23Z 1.50 2727  89  42   3 0.02
Fri 10/09 00Z 1.27 2727  90  35   3 0.01
Fri 10/09 01Z 1.14 2827  91  33   2 0.02
Fri 10/09 02Z 0.95 2825  89  37   2 0.01
Fri 10/09 03Z 0.91 2825  87  38   2 0.01
Fri 10/09 04Z 0.95 2826  86  39   2 0.01
Fri 10/09 06Z 0.92 2824  92  36   2 0.00
Fri 10/09 08Z 0.91 2724  92  48   1 0.00
Fri 10/09 09Z 0.90 2724  92  44   1 0.01
Fri 10/09 10Z 0.88 2724  89  39   1 0.01
Fri 10/09 11Z 1.00 2726  91  38   1 0.01
Fri 10/09 12Z 1.08 2727  91  45   1 0.01
Fri 10/09 13Z 1.14 2728  90  44   1 0.00
Fri 10/09 14Z 1.40 2728  94  33   0 0.01
Fri 10/09 15Z 1.60 2827  95  40   0 0.01
Fri 10/09 16Z 1.92 2826  93  43   0 0.01
Fri 10/09 17Z 4.08 2825  88  42   0 0.02
Fri 10/09 18Z 8.64 2824  88  46  -1 0.02
Fri 10/09 19Z 7.22 2823  88  46  -1 0.01
Fri 10/09 20Z 3.67 2823  89  50  -1 0.00
Fri 10/09 21Z 2.26 2925  91  49  -1 0.00
Fri 10/09 22Z 2.14 2926  90  53  -1 0.01
Fri 10/09 23Z 1.91 2928  91  47  -2 0.01
Sat 10/10 00Z 1.44 3029  90  41  -2 0.01
Sat 10/10 01Z 1.66 3031  93  36  -3 0.01
Sat 10/10 02Z 1.52 3032  87  28  -3 0.00
Sat 10/10 03Z 1.20 3031  89  26  -3 0.01
Sat 10/10 04Z 1.07 3130  90  20  -3 0.01
Sat 10/10 05Z 0.96 3129  89  13  -3 0.00

Run total areal avg QPF for the greens is: 0.71 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