NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261007_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)
=== ===== === ==== ==== === === === ====
Wed 10/07 18Z 0.68 2117  52  81   7 0.00
Wed 10/07 19Z 0.56 2019  48  80   7 0.00
Wed 10/07 20Z 0.51 2020  47  85   8 0.00
Wed 10/07 21Z 0.55 2021  51  82   8 0.00
Wed 10/07 22Z 0.66 2124  57  70   7 0.00
Wed 10/07 23Z 0.65 2126  65  89   8 0.00
Thu 10/08 00Z 0.67 2227  70  86   8 0.00
Thu 10/08 01Z 0.68 2228  73  86   8 0.00
Thu 10/08 02Z 0.70 2229  75  82   8 0.00
Thu 10/08 03Z 0.71 2330  76  76   8 0.00
Thu 10/08 04Z 0.69 2329  80  60   9 0.00
Thu 10/08 05Z 0.64 2327  84  51   9 0.00
Thu 10/08 06Z 0.66 2328  89  67   8 0.01
Thu 10/08 07Z 0.76 2328  95  94   7 0.18
Thu 10/08 08Z 0.69 2327  95  79   7 0.04
Thu 10/08 09Z 0.72 2427  92  78   8 0.02
Thu 10/08 10Z 0.66 2424  91  75   8 0.02
Thu 10/08 11Z 0.72 2425  96  75   7 0.03
Thu 10/08 12Z 0.77 2525  96  67   7 0.05
Thu 10/08 13Z 0.81 2624  93  75   6 0.03
Thu 10/08 14Z 0.80 2722  87  81   6 0.01
Thu 10/08 15Z 0.83 2722  81  70   6 0.01
Thu 10/08 16Z 0.98 2721  84  57   5 0.00
Thu 10/08 17Z 2.56 2621  90  41   5 0.00
Thu 10/08 18Z 6.41 2722  84  41   5 0.02
Thu 10/08 19Z 5.16 2723  81  42   4 0.05
Thu 10/08 20Z 6.13 2622  81  32   4 0.00
Thu 10/08 21Z 4.04 2624  82  29   4 0.00
Thu 10/08 22Z 2.87 2626  83  27   4 0.00
Thu 10/08 23Z 1.57 2628  88  38   4 0.00
Fri 10/09 00Z 1.26 2728  86  31   3 0.00
Fri 10/09 01Z 1.05 2727  90  30   3 0.01
Fri 10/09 02Z 0.88 2826  88  32   3 0.00
Fri 10/09 03Z 0.81 2826  84  34   3 0.00
Fri 10/09 04Z 0.84 2826  81  33   2 0.00
Fri 10/09 06Z 0.82 2824  91  28   2 0.00
Fri 10/09 08Z 0.85 2725  90  52   2 0.00
Fri 10/09 09Z 0.90 2725  90  45   2 0.00
Fri 10/09 10Z 0.84 2725  86  38   2 0.00
Fri 10/09 11Z 0.96 2727  88  39   2 0.00
Fri 10/09 12Z 1.03 2728  89  42   1 0.00
Fri 10/09 13Z 1.09 2729  86  48   1 0.00
Fri 10/09 14Z 1.39 2729  91  30   0 0.00
Fri 10/09 15Z 1.70 2727  94  30   0 0.00
Fri 10/09 16Z 1.90 2826  93  32   0 0.00
Fri 10/09 17Z 4.13 2824  89  31   0 0.01
Fri 10/09 18Z 8.31 2923  88  34   0 0.01
Fri 10/09 19Z 8.25 2823  87  37  -1 0.01
Fri 10/09 20Z 3.02 2822  90  45   0 0.00
Fri 10/09 21Z 2.24 2823  91  42  -1 0.00
Fri 10/09 22Z 1.50 2925  91  45  -1 0.01
Fri 10/09 23Z 1.51 2927  91  39  -1 0.01
Sat 10/10 00Z 1.20 3028  89  31  -1 0.01
Sat 10/10 01Z 1.41 3030  90  28  -2 0.01
Sat 10/10 02Z 1.17 3032  84  19  -2 0.00
Sat 10/10 03Z 0.96 3130  89  17  -2 0.00
Sat 10/10 04Z 0.89 3129  91  13  -2 0.00
Sat 10/10 05Z 0.80 3128  93   8  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.55 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