NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260531_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)
=== ===== === ==== ==== === === === ====
Sun 05/31 00Z 0.05 0013  77  39   2 0.00
Sun 05/31 01Z 0.10 0015  68  32   2 0.00
Sun 05/31 02Z 0.13 0117  59  24   3 0.00
Sun 05/31 03Z 0.16 0117  54  19   4 0.00
Sun 05/31 04Z 0.15 0116  53  21   5 0.00
Sun 05/31 05Z 0.14 0014  54  32   5 0.00
Sun 05/31 06Z 0.13 3512  58  48   5 0.00
Sun 05/31 07Z 0.16 3312  61  70   5 0.00
Sun 05/31 08Z 0.26 3211  63  84   5 0.00
Sun 05/31 09Z 0.36 3012  70  87   5 0.00
Sun 05/31 10Z 0.44 2914  69  89   5 0.00
Sun 05/31 11Z 0.48 2916  70  82   6 0.00
Sun 05/31 12Z 0.52 3018  69  87   5 0.00
Sun 05/31 13Z 0.44 3118  67  85   5 0.00
Sun 05/31 14Z 0.48 3118  68  88   5 0.00
Sun 05/31 15Z 0.83 3118  74  85   5 0.00
Sun 05/31 16Z 1.95 3218  78  88   4 0.01
Sun 05/31 17Z 1.76 3217  80  91   4 0.00
Sun 05/31 18Z 1.08 3117  83  91   4 0.01
Sun 05/31 19Z 0.95 3118  82  91   3 0.01
Sun 05/31 20Z 1.22 3018  81  90   4 0.02
Sun 05/31 21Z 1.20 3017  86  93   3 0.01
Sun 05/31 22Z 0.99 3023  84  85   3 0.03
Sun 05/31 23Z 1.12 3022  87  73   3 0.01
Mon 06/01 00Z 1.17 3021  87  64   3 0.01
Mon 06/01 01Z 1.08 3121  86  59   3 0.00
Mon 06/01 02Z 0.74 3220  83  55   3 0.00
Mon 06/01 03Z 0.52 3218  82  58   3 0.00
Mon 06/01 04Z 0.42 3217  81  64   3 0.00
Mon 06/01 05Z 0.33 3216  83  70   3 0.00
Mon 06/01 06Z 0.25 3315  85  71   3 0.00
Mon 06/01 07Z 0.20 3313  87  69   2 0.00
Mon 06/01 08Z 0.17 3413  89  71   2 0.00
Mon 06/01 09Z 0.14 0012  91  75   2 0.00
Mon 06/01 10Z 0.15 0110  93  76   2 0.00
Mon 06/01 11Z 0.17 0309  94  77   1 0.00
Mon 06/01 12Z 0.25 0410  94  75   1 0.00
Mon 06/01 13Z 0.33 0510  95  69   1 0.00
Mon 06/01 14Z 0.43 0609  96  65   1 0.00
Mon 06/01 15Z 0.60 0708  96  61   1 0.01
Mon 06/01 16Z 0.75 0707  94  55   1 0.01
Mon 06/01 17Z 0.70 0606  90  50   1 0.00
Mon 06/01 18Z 0.62 0406  83  46   2 0.00
Mon 06/01 19Z 0.52 0205  78  39   2 0.00
Mon 06/01 20Z 0.45 0005  75  34   3 0.00
Mon 06/01 21Z 0.33 0006  76  30   3 0.00
Mon 06/01 22Z 0.22 3506  77  33   3 0.00
Mon 06/01 23Z 0.12 0008  77  39   3 0.00
Tue 06/02 00Z 0.11 0008  74  40   3 0.00
Tue 06/02 01Z 0.12 0109  70  48   4 0.00
Tue 06/02 02Z 0.12 0109  67  56   4 0.00
Tue 06/02 03Z 0.13 0009  64  58   4 0.00
Tue 06/02 04Z 0.16 3509  63  54   4 0.00
Tue 06/02 05Z 0.17 3409  63  55   4 0.00
Tue 06/02 06Z 0.22 3310  63  56   4 0.00
Tue 06/02 07Z 0.29 3311  65  56   4 0.00
Tue 06/02 08Z 0.30 3211  65  56   4 0.00
Tue 06/02 09Z 0.30 3211  65  54   4 0.00
Tue 06/02 10Z 0.30 3211  65  49   4 0.00
Tue 06/02 11Z 0.31 3212  66  45   4 0.00

Run total areal avg QPF for the greens is: 0.13 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