Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260610_1200
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 06/10 12Z 0.38 2312  82  84  15 0.00
Wed 06/10 13Z 0.41 2313  80  76  16 0.00
Wed 06/10 14Z 0.41 2212  78  75  16 0.00
Wed 06/10 15Z 0.46 2110  78  86  16 0.00
Wed 06/10 16Z 0.95 2008  79  88  16 0.00
Wed 06/10 17Z 1.76 2009  80  84  16 0.00
Wed 06/10 18Z 1.81 2010  81  84  16 0.00
Wed 06/10 19Z 1.87 1909  80  81  17 0.00
Wed 06/10 20Z 1.85 1910  80  83  17 0.00
Wed 06/10 21Z 1.18 1910  82  87  17 0.00
Wed 06/10 22Z 0.87 2012  84  85  17 0.01
Wed 06/10 23Z 0.63 2216  93  87  17 0.05
Thu 06/11 00Z 0.57 2223  90  77  16 0.19
Thu 06/11 01Z 0.59 2223  96  86  16 0.02
Thu 06/11 02Z 0.57 2320  95  85  15 0.09
Thu 06/11 03Z 0.43 2415  90  79  16 0.02
Thu 06/11 04Z 0.48 2416  92  88  15 0.00
Thu 06/11 05Z 0.54 2417  95  90  15 0.01
Thu 06/11 06Z 0.54 2617  97  83  15 0.03
Thu 06/11 07Z 0.49 2616  96  69  15 0.01
Thu 06/11 08Z 0.50 2716  96  79  15 0.02
Thu 06/11 09Z 0.46 2715  95  60  15 0.02
Thu 06/11 10Z 0.50 2717  94  49  15 0.01
Thu 06/11 11Z 0.49 2716  95  49  15 0.01
Thu 06/11 12Z 0.53 2717  96  65  15 0.01
Thu 06/11 13Z 0.58 2718  96  74  15 0.01
Thu 06/11 14Z 0.49 2917  94  62  15 0.00
Thu 06/11 15Z 0.26 3114  90  52  16 0.00
Thu 06/11 16Z 0.28 3012  89  30  16 0.00
Thu 06/11 17Z 0.39 2911  90  46  16 0.00
Thu 06/11 18Z 0.36 2810  90  56  17 0.00
Thu 06/11 19Z 0.45 2712  89  58  17 0.00
Thu 06/11 20Z 0.42 2712  89  58  18 0.00
Thu 06/11 21Z 0.47 2712  91  56  17 0.00
Thu 06/11 22Z 0.44 2710  93  70  17 0.00
Thu 06/11 23Z 0.52 2712  94  86  17 0.00
Fri 06/12 00Z 0.58 2714  93  82  17 0.01
Fri 06/12 01Z 0.59 2715  94  78  16 0.08
Fri 06/12 02Z 0.44 2713  92  78  16 0.16
Fri 06/12 03Z 0.29 2810  96  71  16 0.02
Fri 06/12 04Z 0.18 3009  97  68  16 0.01
Fri 06/12 05Z 0.10 3206  98  67  16 0.01
Fri 06/12 06Z 0.09 3206  98  70  15 0.01
Fri 06/12 07Z 0.06 3205  98  69  15 0.01
Fri 06/12 08Z 0.13 3006  98  73  15 0.01
Fri 06/12 09Z 0.30 2811  98  85  15 0.03
Fri 06/12 10Z 0.33 2912  98  84  15 0.03
Fri 06/12 11Z 0.23 2909  92  76  15 0.01
Fri 06/12 12Z 0.13 2906  88  71  16 0.00
Fri 06/12 13Z 0.07 2902  85  62  16 0.00
Fri 06/12 14Z 0.10 2603  85  57  16 0.00
Fri 06/12 15Z 0.13 2503  83  49  17 0.00
Fri 06/12 16Z 0.13 2503  77  49  17 0.00
Fri 06/12 17Z 0.31 2504  76  49  17 0.00
Fri 06/12 18Z 0.64 2505  67  39  18 0.00
Fri 06/12 19Z 0.68 2506  56  22  19 0.00
Fri 06/12 20Z 1.19 2509  64  43  18 0.00
Fri 06/12 21Z 0.37 2408  77  49  18 0.00
Fri 06/12 22Z 0.38 2409  82  48  18 0.00
Fri 06/12 23Z 0.37 2509  84  47  18 0.00

Run total areal avg QPF for the Central_Greens is: 0.90 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