NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260604_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)
=== ===== === ==== ==== === === === ====
Thu 06/04 18Z 4.33 2707  50  33  13 0.00
Thu 06/04 19Z 4.87 2709  53  29  14 0.00
Thu 06/04 20Z 4.18 2710  55  24  14 0.00
Thu 06/04 21Z 2.13 2711  56  20  14 0.00
Thu 06/04 22Z 1.10 2613  57  19  14 0.00
Thu 06/04 23Z 0.97 2715  53  19  14 0.00
Fri 06/05 00Z 1.17 2816  48  20  14 0.00
Fri 06/05 01Z 1.08 2818  46  18  14 0.00
Fri 06/05 02Z 0.94 2920  42  16  13 0.00
Fri 06/05 03Z 0.84 2920  44  13  13 0.00
Fri 06/05 04Z 0.77 3021  51  12  13 0.00
Fri 06/05 05Z 0.67 3121  59  10  13 0.00
Fri 06/05 06Z 0.62 3119  62   8  13 0.00
Fri 06/05 07Z 0.57 3119  59   8  13 0.00
Fri 06/05 08Z 0.52 3118  54   7  13 0.00
Fri 06/05 09Z 0.47 3115  50  11  13 0.00
Fri 06/05 10Z 0.47 3015  50  12  13 0.00
Fri 06/05 11Z 0.45 3013  51  14  12 0.00
Fri 06/05 12Z 0.39 3011  51  16  12 0.00
Fri 06/05 13Z 0.37 2909  51  15  12 0.00
Fri 06/05 14Z 0.42 2909  52  15  12 0.00
Fri 06/05 15Z 0.94 2808  53  15  12 0.00
Fri 06/05 16Z 1.49 2808  53  16  13 0.00
Fri 06/05 17Z 2.34 2708  53  13  13 0.00
Fri 06/05 18Z 3.83 2708  55   9  13 0.00
Fri 06/05 19Z 4.21 2608  58  10  13 0.00
Fri 06/05 20Z 4.20 2609  63  15  14 0.00
Fri 06/05 21Z 2.93 2509  65  17  14 0.00
Fri 06/05 22Z 2.11 2511  67  29  14 0.00
Fri 06/05 23Z 1.28 2512  70  31  14 0.00
Sat 06/06 00Z 1.03 2514  68  16  14 0.00
Sat 06/06 01Z 1.30 2515  64  20  14 0.00
Sat 06/06 02Z 1.47 2517  62  24  14 0.00
Sat 06/06 03Z 1.72 2619  63  24  13 0.00
Sat 06/06 04Z 1.73 2520  69  25  13 0.00
Sat 06/06 05Z 1.65 2520  75  24  13 0.00
Sat 06/06 06Z 1.27 2520  79  30  12 0.00
Sat 06/06 07Z 1.14 2520  82  29  12 0.00
Sat 06/06 08Z 1.02 2520  82  33  12 0.01
Sat 06/06 09Z 0.84 2420  86  46  12 0.00
Sat 06/06 10Z 0.82 2421  88  53  12 0.00
Sat 06/06 11Z 0.78 2321  90  31  12 0.00
Sat 06/06 12Z 0.71 2319  88  48  12 0.00
Sat 06/06 13Z 0.69 2320  84  43  12 0.00
Sat 06/06 14Z 0.78 2220  86  56  12 0.00
Sat 06/06 15Z 1.76 2219  87  76  12 0.00
Sat 06/06 16Z 1.15 2120  83  95  12 0.01
Sat 06/06 17Z 0.79 2123  89  94  12 0.02
Sat 06/06 18Z 0.80 2227  97  85  13 0.06
Sat 06/06 19Z 1.00 2329  98  86  13 0.09
Sat 06/06 20Z 1.19 2530  98  70  13 0.08
Sat 06/06 21Z 1.18 2627  97  67  13 0.05
Sat 06/06 22Z 1.02 2725  95  72  13 0.02
Sat 06/06 23Z 1.01 2725  95  47  13 0.01
Sun 06/07 00Z 0.94 2725  93  36  13 0.01
Sun 06/07 01Z 0.97 2727  94  45  13 0.01
Sun 06/07 02Z 0.85 2824  95  51  12 0.01
Sun 06/07 03Z 0.79 2823  95  55  12 0.02
Sun 06/07 04Z 0.65 2921  95  57  12 0.02
Sun 06/07 05Z 0.57 2919  95  58  12 0.02

Run total areal avg QPF for the greens is: 0.44 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