NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260819_0000
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)
=== ===== === ==== ==== === === === ====
Wed 08/19 00Z 0.13 3105  79  37  13 0.00
Wed 08/19 01Z 0.14 3104  75  39  13 0.00
Wed 08/19 02Z 0.13 3205  71  37  13 0.00
Wed 08/19 03Z 0.10 3204  72  41  13 0.00
Wed 08/19 04Z 0.06 3303  76  39  12 0.00
Wed 08/19 05Z 0.07 3204  78  36  12 0.00
Wed 08/19 06Z 0.08 3204  80  18  12 0.00
Wed 08/19 07Z 0.06 3202  80   5  12 0.00
Wed 08/19 08Z 0.12 2903  79   4  12 0.00
Wed 08/19 09Z 0.13 2703  79   7  12 0.00
Wed 08/19 10Z 0.18 2504  79  11  11 0.00
Wed 08/19 11Z 0.23 2505  80  13  11 0.00
Wed 08/19 12Z 0.26 2406  82  19  11 0.00
Wed 08/19 13Z 0.29 2307  83  31  11 0.00
Wed 08/19 14Z 0.32 2308  82  51  11 0.00
Wed 08/19 15Z 0.33 2209  74  47  12 0.00
Wed 08/19 16Z 0.51 2311  68  49  12 0.00
Wed 08/19 17Z 0.54 2312  68  60  13 0.00
Wed 08/19 18Z 0.74 2413  67  78  13 0.00
Wed 08/19 19Z 1.11 2414  70  90  13 0.00
Wed 08/19 20Z 0.80 2315  79  86  13 0.00
Wed 08/19 21Z 0.98 2316  83  78  13 0.00
Wed 08/19 22Z 1.06 2317  84  73  13 0.00
Wed 08/19 23Z 0.99 2421  89  49  13 0.03
Thu 08/20 00Z 1.12 2622  89  48  13 0.02
Thu 08/20 01Z 0.92 2620  91  39  13 0.00
Thu 08/20 02Z 0.72 2619  87  17  13 0.00
Thu 08/20 03Z 0.55 2717  79  20  13 0.00
Thu 08/20 04Z 0.53 2718  77  16  13 0.01
Thu 08/20 05Z 0.51 2817  79  16  12 0.01
Thu 08/20 06Z 0.46 2817  88  16  12 0.01
Thu 08/20 07Z 0.41 2915  86  23  11 0.01
Thu 08/20 08Z 0.36 2915  86  16  11 0.00
Thu 08/20 09Z 0.32 3014  80  11  11 0.00
Thu 08/20 10Z 0.31 3014  79   9  11 0.00
Thu 08/20 11Z 0.28 3013  76   8  10 0.00
Thu 08/20 12Z 0.27 3012  72   9  10 0.00
Thu 08/20 13Z 0.21 3010  68  14  10 0.00
Thu 08/20 14Z 0.21 3008  67  34  10 0.00
Thu 08/20 15Z 0.25 2905  68  22  10 0.00
Thu 08/20 16Z 0.50 2704  63  54  10 0.00
Thu 08/20 17Z 0.57 2705  56  30  11 0.00
Thu 08/20 18Z 0.36 2705  53  40  11 0.00
Thu 08/20 19Z 0.39 2706  54  29  11 0.00
Thu 08/20 20Z 0.34 2607  58  31  11 0.00
Thu 08/20 21Z 0.30 2606  60  46  11 0.00
Thu 08/20 22Z 0.24 2605  61  41  11 0.00
Thu 08/20 23Z 0.29 2506  65  49  11 0.00
Fri 08/21 00Z 0.27 2606  70  31  11 0.00
Fri 08/21 01Z 0.19 2604  72  28  11 0.00
Fri 08/21 02Z 0.14 2803  73  28  10 0.00
Fri 08/21 03Z 0.07 3002  73  29  10 0.00
Fri 08/21 04Z 0.03 3402  74  31  10 0.00
Fri 08/21 05Z 0.03 0002  77  31  10 0.00
Fri 08/21 06Z 0.06 0202  79  31  10 0.00
Fri 08/21 07Z 0.07 0302  82  31  10 0.00
Fri 08/21 08Z 0.06 0203  82  26  10 0.00
Fri 08/21 09Z 0.06 0103  80  20  10 0.00
Fri 08/21 10Z 0.07 0203  78  16  10 0.00
Fri 08/21 11Z 0.11 0304  78  20  10 0.00

Run total areal avg QPF for the Central_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