NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260818_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)
=== ===== === ==== ==== === === === ====
Tue 08/18 18Z 0.77 3004  88  16  12 0.00
Tue 08/18 19Z 1.06 3005  87  26  12 0.02
Tue 08/18 20Z 0.96 3008  87  34  12 0.02
Tue 08/18 21Z 0.44 3109  84  42  12 0.00
Tue 08/18 22Z 0.27 3308  85  45  12 0.00
Tue 08/18 23Z 0.08 3406  86  43  12 0.00
Wed 08/19 00Z 0.06 3405  84  33  12 0.00
Wed 08/19 01Z 0.10 3304  83  27  12 0.00
Wed 08/19 02Z 0.15 3105  82  17  12 0.00
Wed 08/19 03Z 0.16 3104  82  12  12 0.00
Wed 08/19 04Z 0.14 3104  81  11  12 0.00
Wed 08/19 05Z 0.16 3004  81  21  11 0.00
Wed 08/19 06Z 0.20 2804  82  23  11 0.00
Wed 08/19 07Z 0.24 2704  83  25  11 0.00
Wed 08/19 08Z 0.28 2606  85  16  11 0.00
Wed 08/19 09Z 0.31 2507  85  17  11 0.00
Wed 08/19 10Z 0.34 2508  84  16  11 0.00
Wed 08/19 11Z 0.44 2511  85  21  11 0.00
Wed 08/19 12Z 0.39 2412  83  21  11 0.00
Wed 08/19 13Z 0.43 2413  80  28  11 0.00
Wed 08/19 14Z 0.40 2412  74  49  12 0.00
Wed 08/19 15Z 0.46 2412  78  65  12 0.00
Wed 08/19 16Z 0.47 2411  76  71  13 0.00
Wed 08/19 17Z 0.68 2312  78  77  13 0.00
Wed 08/19 18Z 0.62 2313  79  76  13 0.00
Wed 08/19 19Z 0.85 2415  88  76  13 0.01
Wed 08/19 20Z 1.11 2416  89  75  13 0.01
Wed 08/19 21Z 1.07 2416  91  76  13 0.00
Wed 08/19 22Z 0.77 2415  90  79  13 0.04
Wed 08/19 23Z 0.83 2416  90  79  13 0.04
Thu 08/20 00Z 0.75 2416  88  78  13 0.00
Thu 08/20 01Z 0.72 2417  90  64  13 0.01
Thu 08/20 02Z 0.62 2516  93  54  13 0.03
Thu 08/20 03Z 0.59 2717  93  46  12 0.05
Thu 08/20 04Z 0.49 2815  93  45  12 0.01
Thu 08/20 05Z 0.45 2915  91  33  12 0.01
Thu 08/20 06Z 0.39 2914  90  30  11 0.01
Thu 08/20 07Z 0.32 3012  86  28  11 0.01
Thu 08/20 08Z 0.29 3012  83  21  11 0.01
Thu 08/20 09Z 0.29 3012  81  11  11 0.00
Thu 08/20 10Z 0.29 3012  80   6  10 0.00
Thu 08/20 11Z 0.25 3112  78   7  10 0.00
Thu 08/20 12Z 0.23 3111  75   7  10 0.00
Thu 08/20 13Z 0.24 3111  77   5  10 0.00
Thu 08/20 14Z 0.19 3208  78   6  10 0.00
Thu 08/20 15Z 0.22 3107  79   6   9 0.00
Thu 08/20 16Z 0.25 3105  79   6   9 0.00
Thu 08/20 17Z 0.39 3104  78   7   9 0.00
Thu 08/20 18Z 0.47 3104  75   7  10 0.00
Thu 08/20 19Z 0.48 3004  74   7  10 0.00
Thu 08/20 20Z 0.35 3005  72   7  10 0.00
Thu 08/20 21Z 0.22 3005  72  13  10 0.00
Thu 08/20 22Z 0.18 3005  71  12  10 0.00
Thu 08/20 23Z 0.14 3105  71  12  10 0.00
Fri 08/21 00Z 0.10 3305  72  11  10 0.00
Fri 08/21 01Z 0.09 3405  74  12   9 0.00
Fri 08/21 02Z 0.09 3406  75  13   9 0.00
Fri 08/21 03Z 0.08 3406  77  14   9 0.00
Fri 08/21 04Z 0.08 3507  79  15   9 0.00
Fri 08/21 05Z 0.09 3508  80  13   8 0.00

Run total areal avg QPF for the greens is: 0.28 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