NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260529_1200
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 05/29 12Z 0.62 3116  83  77   3 0.00
Fri 05/29 13Z 0.69 3016  83  78   3 0.00
Fri 05/29 14Z 1.18 3016  81  86   4 0.00
Fri 05/29 15Z 2.17 2915  77  89   4 0.00
Fri 05/29 16Z 3.97 2812  77  91   5 0.00
Fri 05/29 17Z 3.54 2613  76  97   6 0.00
Fri 05/29 18Z 4.58 2415  76  96   6 0.00
Fri 05/29 19Z 1.00 2522  85  95   6 0.06
Fri 05/29 20Z 1.08 2524  94  96   6 0.07
Fri 05/29 21Z 1.70 2628  87  92   5 0.07
Fri 05/29 22Z 1.48 2628  85  86   6 0.04
Fri 05/29 23Z 1.32 2625  81  82   6 0.03
Sat 05/30 00Z 0.84 2622  85  79   5 0.14
Sat 05/30 01Z 0.65 2920  89  62   4 0.16
Sat 05/30 02Z 0.55 3020  87  66   1 0.05
Sat 05/30 03Z 0.60 3120  94  43   0 0.02
Sat 05/30 04Z 0.50 3116  95  65   0 0.01
Sat 05/30 05Z 0.45 3112  96  80   0 0.01
Sat 05/30 06Z 0.46 3511  97  83   0 0.02
Sat 05/30 07Z 0.52 0317  97  79  -1 0.04
Sat 05/30 08Z 0.58 0424  98  83  -1 0.06
Sat 05/30 09Z 0.74 0531  98  91  -1 0.09
Sat 05/30 10Z 0.63 0431  96  92  -1 0.07
Sat 05/30 11Z 0.55 0430  90  87   0 0.08
Sat 05/30 12Z 0.50 0427  85  73   0 0.04
Sat 05/30 13Z 0.44 0424  81  60   0 0.03
Sat 05/30 14Z 0.43 0421  79  53  -1 0.01
Sat 05/30 15Z 0.56 0317  80  39  -1 0.00
Sat 05/30 16Z 0.94 0215  80  44  -1 0.00
Sat 05/30 17Z 0.75 0115  81  54  -1 0.00
Sat 05/30 18Z 1.66 0116  81  65   0 0.00
Sat 05/30 19Z 2.46 0117  78  72   0 0.00
Sat 05/30 20Z 2.16 0117  76  71   0 0.00
Sat 05/30 21Z 2.12 0116  76  72   0 0.00
Sat 05/30 22Z 1.67 0117  77  71   0 0.00
Sat 05/30 23Z 0.80 0118  73  77   0 0.00
Sun 05/31 00Z 0.34 0119  67  72   1 0.00
Sun 05/31 01Z 0.32 0121  64  69   1 0.00
Sun 05/31 02Z 0.30 0122  58  50   2 0.00
Sun 05/31 03Z 0.26 0122  52  35   2 0.00
Sun 05/31 04Z 0.22 0122  53  30   3 0.00
Sun 05/31 05Z 0.20 0121  61  23   3 0.00
Sun 05/31 06Z 0.14 0019  66  20   3 0.00
Sun 05/31 07Z 0.11 3517  66  21   3 0.00
Sun 05/31 08Z 0.11 3516  65  21   3 0.00
Sun 05/31 09Z 0.17 3416  63  20   4 0.00
Sun 05/31 10Z 0.31 3316  63  26   4 0.00
Sun 05/31 11Z 0.43 3217  63  36   4 0.00
Sun 05/31 12Z 0.46 3117  61  38   5 0.00
Sun 05/31 13Z 0.47 3118  56  43   5 0.00
Sun 05/31 14Z 0.55 3218  58  54   5 0.00
Sun 05/31 15Z 0.95 3217  61  67   5 0.00
Sun 05/31 16Z 1.46 3116  65  71   4 0.00
Sun 05/31 17Z 2.11 3116  72  70   4 0.01
Sun 05/31 18Z 3.09 3116  72  71   4 0.01
Sun 05/31 19Z 2.74 3116  72  78   4 0.00
Sun 05/31 20Z 1.80 3115  69  68   4 0.00
Sun 05/31 21Z 1.76 3015  71  60   4 0.00
Sun 05/31 22Z 0.81 3016  71  64   5 0.00
Sun 05/31 23Z 0.78 3016  72  70   5 0.00

Run total areal avg QPF for the greens is: 1.12 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