NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260218_0000
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 02/18 00Z 0.50 2715  97  29  -3 0.00
Wed 02/18 01Z 0.56 2718  93  48  -3 0.00
Wed 02/18 02Z 0.62 2720  89  62  -3 0.00
Wed 02/18 03Z 0.65 2822  88  68  -2 0.01
Wed 02/18 04Z 0.74 2824  86  64  -3 0.01
Wed 02/18 05Z 0.77 2824  80  47  -3 0.01
Wed 02/18 06Z 0.82 2925  82  33  -4 0.01
Wed 02/18 07Z 0.82 2925  86  30  -4 0.01
Wed 02/18 08Z 0.81 2925  86  30  -5 0.01
Wed 02/18 09Z 0.63 3025  83  30  -5 0.01
Wed 02/18 10Z 0.54 3025  79  31  -6 0.01
Wed 02/18 11Z 0.45 3124  71  29  -6 0.01
Wed 02/18 12Z 0.36 3123  62  18  -6 0.00
Wed 02/18 13Z 0.31 3122  53  15  -6 0.00
Wed 02/18 14Z 0.25 3221  44   9  -6 0.00
Wed 02/18 15Z 0.20 3218  37   7  -5 0.00
Wed 02/18 16Z 0.16 3316  34   6  -5 0.00
Wed 02/18 17Z 0.11 3414  34   6  -5 0.00
Wed 02/18 18Z 0.06 3512  37   6  -5 0.00
Wed 02/18 19Z 0.05 3510  41   7  -6 0.00
Wed 02/18 20Z 0.05 0010  41   8  -6 0.00
Wed 02/18 21Z 0.05 0009  42   9  -6 0.00
Wed 02/18 22Z 0.10 0211  38  12  -6 0.00
Wed 02/18 23Z 0.19 0314  35  16  -6 0.00
Thu 02/19 00Z 0.24 0316  33  20  -6 0.00
Thu 02/19 01Z 0.26 0416  33  21  -5 0.00
Thu 02/19 02Z 0.26 0415  33  20  -5 0.00
Thu 02/19 03Z 0.22 0414  34  19  -5 0.00
Thu 02/19 04Z 0.17 0411  35  15  -6 0.00
Thu 02/19 05Z 0.13 0408  34  12  -6 0.00
Thu 02/19 06Z 0.12 0407  32  12  -6 0.00
Thu 02/19 07Z 0.09 0306  31   8  -6 0.00
Thu 02/19 08Z 0.05 0204  30  12  -6 0.00
Thu 02/19 09Z 0.03 0104  29  16  -6 0.00
Thu 02/19 10Z 0.04 0104  27  19  -5 0.00
Thu 02/19 11Z 0.03 0103  27  18  -5 0.00
Thu 02/19 12Z 0.05 0304  25  17  -5 0.00
Thu 02/19 13Z 0.05 0403  25  17  -5 0.00
Thu 02/19 14Z 0.03 0501  26  16  -5 0.00
Thu 02/19 15Z 0.02 1500  28  18  -5 0.00
Thu 02/19 16Z 0.02 1701  31  32  -5 0.00
Thu 02/19 17Z 0.05 2003  35  38  -5 0.00
Thu 02/19 18Z 0.07 2104  39  35  -5 0.00
Thu 02/19 19Z 0.10 2204  42  26  -4 0.00
Thu 02/19 20Z 0.12 2304  47  25  -4 0.00
Thu 02/19 21Z 0.13 2305  56  24  -4 0.00
Thu 02/19 22Z 0.13 2305  61  28  -4 0.00
Thu 02/19 23Z 0.15 2306  67  28  -5 0.00
Fri 02/20 00Z 0.16 2406  73  27  -4 0.00
Fri 02/20 01Z 0.14 2505  76  29  -4 0.00
Fri 02/20 02Z 0.12 2505  78  25  -3 0.00
Fri 02/20 03Z 0.09 2604  79  17  -3 0.00
Fri 02/20 04Z 0.07 2603  78  19  -2 0.00
Fri 02/20 05Z 0.05 2402  78  21  -2 0.00
Fri 02/20 06Z 0.06 2203  79  15  -2 0.00
Fri 02/20 07Z 0.07 2105  80  18  -1 0.00
Fri 02/20 08Z 0.06 2105  77  24  -1 0.00
Fri 02/20 09Z 0.04 2004  75  30   0 0.00
Fri 02/20 10Z 0.02 1903  71  30   0 0.00
Fri 02/20 11Z 0.02 1705  70  27   0 0.00

Run total areal avg QPF for the greens is: 0.09 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