NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261009_0000
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)
=== ===== === ==== ==== === === === ====
Fri 10/09 00Z 1.33 2721  76  79   4 0.00
Fri 10/09 01Z 1.30 2722  81  82   3 0.00
Fri 10/09 02Z 1.18 2726  83  85   4 0.01
Fri 10/09 03Z 1.20 2828  84  62   3 0.00
Fri 10/09 04Z 1.20 2828  86  39   3 0.00
Fri 10/09 05Z 1.09 2826  87  29   2 0.00
Fri 10/09 06Z 0.98 2825  84  33   2 0.00
Fri 10/09 07Z 0.89 2724  82  37   2 0.00
Fri 10/09 08Z 0.91 2726  81  40   2 0.00
Fri 10/09 09Z 0.87 2725  80  39   2 0.00
Fri 10/09 10Z 0.88 2726  78  51   2 0.00
Fri 10/09 11Z 0.99 2728  85  51   2 0.01
Fri 10/09 12Z 1.14 2729  92  51   1 0.01
Fri 10/09 13Z 1.18 2729  92  46   1 0.02
Fri 10/09 14Z 1.04 2826  89  34   1 0.01
Fri 10/09 15Z 1.16 2824  90  31   0 0.00
Fri 10/09 16Z 1.75 2822  91  41   0 0.00
Fri 10/09 17Z 2.28 2822  88  66   0 0.01
Fri 10/09 18Z 2.71 2720  87  73   0 0.00
Fri 10/09 19Z 3.97 2720  85  65   1 0.00
Fri 10/09 20Z 3.02 2620  86  60   1 0.00
Fri 10/09 21Z 1.69 2622  82  58   1 0.01
Fri 10/09 22Z 1.78 2625  80  68   2 0.00
Fri 10/09 23Z 1.77 2629  88  72   2 0.04
Sat 10/10 00Z 1.67 2932  87  46   1 0.07
Sat 10/10 01Z 1.26 3031  82  43   0 0.02
Sat 10/10 02Z 1.05 3130  81  22   0 0.01
Sat 10/10 03Z 0.89 3129  79  16   0 0.01
Sat 10/10 04Z 0.76 3127  78  13   0 0.01
Sat 10/10 05Z 0.65 3127  75  14  -1 0.01
Sat 10/10 06Z 0.60 3127  75  13  -1 0.01
Sat 10/10 07Z 0.56 3126  73  12  -1 0.00
Sat 10/10 08Z 0.52 3125  72  11  -1 0.00
Sat 10/10 09Z 0.49 3125  68  11  -1 0.00
Sat 10/10 10Z 0.45 3125  65   8  -1 0.00
Sat 10/10 11Z 0.42 3125  60   6  -1 0.00
Sat 10/10 12Z 0.39 3125  54   5   0 0.00
Sat 10/10 13Z 0.34 3224  49   5   0 0.00
Sat 10/10 14Z 0.32 3223  46   5   0 0.00
Sat 10/10 15Z 0.28 3221  43   5   0 0.00
Sat 10/10 16Z 0.25 3219  42   7   0 0.00
Sat 10/10 17Z 0.25 3218  40  11   0 0.00
Sat 10/10 18Z 0.22 3317  37  16   1 0.00
Sat 10/10 19Z 0.23 3217  33  21   2 0.00
Sat 10/10 20Z 0.19 3315  30  28   2 0.00
Sat 10/10 21Z 0.18 3315  29  43   3 0.00
Sat 10/10 22Z 0.17 3213  27  54   3 0.00
Sat 10/10 23Z 0.14 3211  27  56   4 0.00
Sun 10/11 00Z 0.12 3208  25  62   5 0.00
Sun 10/11 01Z 0.13 3007  25  71   5 0.00
Sun 10/11 02Z 0.13 2906  24  66   6 0.00
Sun 10/11 03Z 0.14 2706  23  61   7 0.00
Sun 10/11 04Z 0.12 2605  22  52   7 0.00
Sun 10/11 05Z 0.12 2405  20  48   7 0.00
Sun 10/11 06Z 0.13 2307  20  45   8 0.00
Sun 10/11 07Z 0.15 2308  19  46   8 0.00
Sun 10/11 08Z 0.17 2210  20  44   8 0.00
Sun 10/11 09Z 0.19 2211  20  48   8 0.00
Sun 10/11 10Z 0.21 2213  18  56   9 0.00
Sun 10/11 11Z 0.24 2214  18  66   9 0.00

Run total areal avg QPF for the greens is: 0.26 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