NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260408_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 04/08 12Z 0.09 3311  77  17  -9 0.00
Wed 04/08 13Z 0.07 3208  72  15  -9 0.00
Wed 04/08 14Z 0.07 3105  67  15  -8 0.00
Wed 04/08 15Z 0.08 3003  63   7  -8 0.00
Wed 04/08 16Z 0.12 2802  59   5  -7 0.00
Wed 04/08 17Z 0.25 2603  55   4  -7 0.00
Wed 04/08 18Z 0.42 2404  48   3  -6 0.00
Wed 04/08 19Z 0.43 2304  41   3  -5 0.00
Wed 04/08 20Z 0.42 2305  35   3  -4 0.00
Wed 04/08 21Z 0.30 2306  30   4  -4 0.00
Wed 04/08 22Z 0.23 2207  26   5  -3 0.00
Wed 04/08 23Z 0.26 2209  26   6  -2 0.00
Thu 04/09 00Z 0.28 2310  26   7  -2 0.00
Thu 04/09 01Z 0.27 2212  21  10  -1 0.00
Thu 04/09 02Z 0.30 2214  17  16   0 0.00
Thu 04/09 03Z 0.35 2316  16  23   0 0.00
Thu 04/09 04Z 0.35 2317  21  28   0 0.00
Thu 04/09 05Z 0.31 2217  22  28   1 0.00
Thu 04/09 06Z 0.28 2118  19  28   2 0.00
Thu 04/09 07Z 0.27 2118  20  26   2 0.00
Thu 04/09 08Z 0.26 2119  19  24   2 0.00
Thu 04/09 09Z 0.27 2120  18  24   2 0.00
Thu 04/09 10Z 0.30 2122  17  24   2 0.00
Thu 04/09 11Z 0.34 2124  16  28   3 0.00
Thu 04/09 12Z 0.34 2123  13  36   3 0.00
Thu 04/09 13Z 0.33 2123  11  49   3 0.00
Thu 04/09 14Z 0.32 2123  10  56   3 0.00
Thu 04/09 15Z 0.33 2023  11  52   3 0.00
Thu 04/09 16Z 0.34 2024  13  46   3 0.00
Thu 04/09 17Z 0.40 2024  15  42   3 0.00
Thu 04/09 18Z 0.50 2025  18  37   3 0.00
Thu 04/09 19Z 0.58 2025  20  30   3 0.00
Thu 04/09 20Z 0.53 2026  21  25   3 0.00
Thu 04/09 21Z 0.51 2026  22  31   4 0.00
Thu 04/09 22Z 0.44 2026  23  34   5 0.00
Thu 04/09 23Z 0.39 2126  28  34   6 0.00
Fri 04/10 00Z 0.40 2127  36  38   6 0.00
Fri 04/10 01Z 0.44 2128  43  44   6 0.00
Fri 04/10 02Z 0.51 2229  50  46   6 0.00
Fri 04/10 03Z 0.54 2329  56  41   6 0.00
Fri 04/10 04Z 0.55 2329  59  66   6 0.00
Fri 04/10 05Z 0.57 2330  62  77   6 0.00
Fri 04/10 06Z 0.65 2432  64  74   6 0.00
Fri 04/10 07Z 0.68 2532  72  78   6 0.00
Fri 04/10 08Z 0.63 2530  77  81   5 0.00
Fri 04/10 09Z 0.59 2527  78  60   5 0.00
Fri 04/10 10Z 0.52 2624  78  46   4 0.00
Fri 04/10 11Z 0.51 2624  74  30   4 0.00
Fri 04/10 12Z 0.48 2622  69  27   5 0.00
Fri 04/10 13Z 0.47 2522  70  28   4 0.00
Fri 04/10 14Z 0.48 2521  73  19   4 0.00
Fri 04/10 15Z 0.48 2519  71  68   4 0.00
Fri 04/10 16Z 0.51 2517  70  92   3 0.00
Fri 04/10 17Z 0.50 2515  65  86   3 0.00
Fri 04/10 18Z 0.50 2315  69  83   3 0.00
Fri 04/10 19Z 0.52 2317  78  80   4 0.00
Fri 04/10 20Z 0.52 2318  83  47   6 0.00
Fri 04/10 21Z 0.58 2221  87  59   6 0.00
Fri 04/10 22Z 0.57 2221  88  95   6 0.03
Fri 04/10 23Z 0.42 2120  88  86   6 0.04

Run total areal avg QPF for the Central_Greens is: 0.07 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