NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260818_1800
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 08/18 18Z 1.07 2804  86  12  13 0.00
Tue 08/18 19Z 1.45 2806  85  26  13 0.01
Tue 08/18 20Z 1.16 2908  85  41  13 0.01
Tue 08/18 21Z 0.33 3108  83  41  13 0.00
Tue 08/18 22Z 0.15 3308  85  42  12 0.00
Tue 08/18 23Z 0.04 3507  86  46  12 0.00
Wed 08/19 00Z 0.04 3505  85  40  12 0.00
Wed 08/19 01Z 0.02 3405  85  35  12 0.00
Wed 08/19 02Z 0.07 3204  84  23  12 0.00
Wed 08/19 03Z 0.08 3204  84  13  12 0.00
Wed 08/19 04Z 0.07 3203  83  11  12 0.00
Wed 08/19 05Z 0.10 3003  84  26  12 0.00
Wed 08/19 06Z 0.16 2803  85  26  11 0.00
Wed 08/19 07Z 0.20 2604  85  25  11 0.00
Wed 08/19 08Z 0.27 2606  88  14  11 0.00
Wed 08/19 09Z 0.31 2507  86  10  11 0.00
Wed 08/19 10Z 0.34 2508  84  12  11 0.00
Wed 08/19 11Z 0.46 2512  85  17  11 0.00
Wed 08/19 12Z 0.43 2513  83  18  11 0.00
Wed 08/19 13Z 0.47 2414  80  29  11 0.00
Wed 08/19 14Z 0.45 2513  74  53  12 0.00
Wed 08/19 15Z 0.52 2513  80  63  12 0.00
Wed 08/19 16Z 0.52 2412  79  64  13 0.00
Wed 08/19 17Z 0.68 2413  81  72  13 0.00
Wed 08/19 18Z 0.63 2413  80  72  13 0.00
Wed 08/19 19Z 0.82 2414  85  70  13 0.00
Wed 08/19 20Z 1.39 2415  90  73  13 0.00
Wed 08/19 21Z 1.27 2415  91  76  13 0.00
Wed 08/19 22Z 0.86 2416  88  77  14 0.00
Wed 08/19 23Z 0.91 2417  88  81  14 0.00
Thu 08/20 00Z 0.81 2417  86  87  14 0.00
Thu 08/20 01Z 0.86 2419  88  75  13 0.01
Thu 08/20 02Z 0.70 2518  91  51  13 0.01
Thu 08/20 03Z 0.57 2617  91  49  13 0.01
Thu 08/20 04Z 0.46 2714  92  46  13 0.01
Thu 08/20 05Z 0.40 2814  93  33  12 0.01
Thu 08/20 06Z 0.33 2913  93  34  12 0.01
Thu 08/20 07Z 0.26 3011  90  22  12 0.01
Thu 08/20 08Z 0.24 3011  86  15  11 0.01
Thu 08/20 09Z 0.24 3012  82  11  11 0.00
Thu 08/20 10Z 0.24 3012  81   6  11 0.00
Thu 08/20 11Z 0.22 3112  80   6  10 0.00
Thu 08/20 12Z 0.17 3111  74   6  11 0.00
Thu 08/20 13Z 0.18 3110  77   4  10 0.00
Thu 08/20 14Z 0.11 3208  78   4  10 0.00
Thu 08/20 15Z 0.17 3107  81   6  10 0.00
Thu 08/20 16Z 0.21 3105  81   6  10 0.00
Thu 08/20 17Z 0.40 3004  80   5  10 0.00
Thu 08/20 18Z 0.42 3004  75   6  10 0.00
Thu 08/20 19Z 0.49 2904  73   6  10 0.00
Thu 08/20 20Z 0.35 2906  71   5  10 0.00
Thu 08/20 21Z 0.21 2905  72  13  10 0.00
Thu 08/20 22Z 0.15 2905  72  10  10 0.00
Thu 08/20 23Z 0.11 3104  72  10  10 0.00
Fri 08/21 00Z 0.04 3405  73   9  10 0.00
Fri 08/21 01Z 0.03 3405  75   9  10 0.00
Fri 08/21 02Z 0.02 3505  75  11   9 0.00
Fri 08/21 03Z 0.03 3506  76  12   9 0.00
Fri 08/21 04Z 0.06 0007  77  12   9 0.00
Fri 08/21 05Z 0.08 0008  77  13   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.10 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