NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260530_1800
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)
=== ===== === ==== ==== === === === ====
Sat 05/30 18Z 0.89 0014  87  40   0 0.00
Sat 05/30 19Z 1.07 0015  85  37   0 0.00
Sat 05/30 20Z 1.73 0116  84  36   1 0.00
Sat 05/30 21Z 1.59 0116  82  40   1 0.00
Sat 05/30 22Z 1.02 0016  80  49   1 0.00
Sat 05/30 23Z 0.77 0117  77  54   1 0.00
Sun 05/31 00Z 0.68 0219  72  56   2 0.00
Sun 05/31 01Z 0.56 0220  68  46   2 0.00
Sun 05/31 02Z 0.42 0219  62  24   3 0.00
Sun 05/31 03Z 0.31 0218  58   9   3 0.00
Sun 05/31 04Z 0.22 0116  57   8   3 0.00
Sun 05/31 05Z 0.14 0114  57  10   4 0.00
Sun 05/31 06Z 0.12 0014  58  12   4 0.00
Sun 05/31 07Z 0.12 3514  61  21   4 0.00
Sun 05/31 08Z 0.16 3414  64  32   4 0.00
Sun 05/31 09Z 0.28 3214  66  47   4 0.00
Sun 05/31 10Z 0.35 3214  68  64   4 0.00
Sun 05/31 11Z 0.42 3115  69  73   4 0.00
Sun 05/31 12Z 0.47 3116  69  79   4 0.00
Sun 05/31 13Z 0.52 3118  68  89   4 0.00
Sun 05/31 14Z 0.58 3119  67  80   4 0.00
Sun 05/31 15Z 1.28 3219  68  80   4 0.00
Sun 05/31 16Z 3.05 3220  69  85   4 0.00
Sun 05/31 17Z 2.26 3217  81  91   3 0.01
Sun 05/31 18Z 0.59 3115  88  89   3 0.02
Sun 05/31 19Z 0.58 3014  87  89   3 0.01
Sun 05/31 20Z 0.72 3014  86  89   4 0.01
Sun 05/31 21Z 0.64 3013  85  90   4 0.01
Sun 05/31 22Z 0.63 2916  86  92   4 0.02
Sun 05/31 23Z 0.69 2918  87  88   4 0.06
Mon 06/01 00Z 0.73 3121  86  85   3 0.04
Mon 06/01 01Z 0.63 3223  86  81   3 0.03
Mon 06/01 02Z 0.54 3222  82  80   3 0.01
Mon 06/01 03Z 0.43 3321  83  73   3 0.00
Mon 06/01 04Z 0.32 3318  84  65   3 0.00
Mon 06/01 05Z 0.25 3315  83  55   3 0.00
Mon 06/01 06Z 0.22 3313  82  60   3 0.00
Mon 06/01 07Z 0.19 3312  82  62   3 0.00
Mon 06/01 08Z 0.18 3411  85  68   2 0.00
Mon 06/01 09Z 0.18 3410  87  69   2 0.00
Mon 06/01 10Z 0.19 0009  91  68   1 0.00
Mon 06/01 11Z 0.19 0108  92  67   1 0.00
Mon 06/01 12Z 0.21 0408  94  68   1 0.00
Mon 06/01 13Z 0.29 0509  94  68   1 0.00
Mon 06/01 14Z 0.39 0709  94  69   1 0.00
Mon 06/01 15Z 0.47 0908  94  68   1 0.01
Mon 06/01 16Z 0.54 0908  91  62   1 0.01
Mon 06/01 17Z 0.65 0807  87  55   2 0.00
Mon 06/01 18Z 0.71 0606  83  48   2 0.00
Mon 06/01 19Z 0.72 0505  80  46   3 0.00
Mon 06/01 20Z 0.90 0405  78  43   3 0.00
Mon 06/01 21Z 0.78 0304  78  42   3 0.00
Mon 06/01 22Z 0.53 0304  76  43   3 0.00
Mon 06/01 23Z 0.18 0203  76  48   4 0.00
Tue 06/02 00Z 0.10 0104  76  49   4 0.00
Tue 06/02 01Z 0.09 0106  76  47   4 0.00
Tue 06/02 02Z 0.12 0106  74  47   4 0.00
Tue 06/02 03Z 0.12 0106  72  48   4 0.00
Tue 06/02 04Z 0.12 0107  71  50   4 0.00
Tue 06/02 05Z 0.11 0107  69  54   4 0.00

Run total areal avg QPF for the greens is: 0.24 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