NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20241123_0000
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 11/23 00Z 0.67 1015  92  66  -1 0.00
Sat 11/23 01Z 0.72 1117  93  58  -1 0.00
Sat 11/23 02Z 0.78 1018  93  52  -1 0.00
Sat 11/23 03Z 0.72 1017  88  53  -1 0.00
Sat 11/23 04Z 0.57 0916  86  59  -1 0.00
Sat 11/23 05Z 0.33 0811  84  70   0 0.00
Sat 11/23 06Z 0.23 0511  91  89   0 0.00
Sat 11/23 07Z 0.16 0411  92  92   0 0.00
Sat 11/23 08Z 0.06 0110  92  96  -1 0.01
Sat 11/23 09Z 0.16 3514  96  95  -1 0.02
Sat 11/23 10Z 0.27 3520  97  91  -1 0.04
Sat 11/23 11Z 0.33 3425  97  90  -1 0.04
Sat 11/23 12Z 0.36 3530  97  93  -1 0.04
Sat 11/23 13Z 0.24 0030  97  97  -1 0.03
Sat 11/23 14Z 0.21 0028  97  96  -1 0.02
Sat 11/23 15Z 0.27 3528  97  94  -1 0.03
Sat 11/23 16Z 0.35 3429  97  86  -1 0.03
Sat 11/23 17Z 0.42 3429  97  79  -1 0.03
Sat 11/23 18Z 0.53 3328  98  82  -2 0.03
Sat 11/23 19Z 0.56 3327  97  82  -2 0.03
Sat 11/23 20Z 0.73 3327  98  77  -2 0.03
Sat 11/23 21Z 0.85 3227  98  74  -3 0.02
Sat 11/23 22Z 1.04 3128  98  78  -3 0.03
Sat 11/23 23Z 1.09 3129  99  57  -3 0.04
Sun 11/24 00Z 1.12 3130  99  51  -3 0.05
Sun 11/24 01Z 1.04 3129  99  50  -3 0.05
Sun 11/24 02Z 1.05 3029  99  46  -3 0.04
Sun 11/24 03Z 1.12 3029  99  57  -3 0.05
Sun 11/24 04Z 1.07 3030  99  63  -3 0.05
Sun 11/24 05Z 1.08 3031  99  68  -3 0.05
Sun 11/24 06Z 1.08 3032  99  74  -3 0.05
Sun 11/24 07Z 1.06 3032  99  85  -3 0.05
Sun 11/24 08Z 1.05 2932  98  86  -3 0.06
Sun 11/24 09Z 1.00 2933  98  89  -3 0.07
Sun 11/24 10Z 1.07 2934  98  87  -4 0.06
Sun 11/24 11Z 1.12 2935  98  86  -4 0.06
Sun 11/24 12Z 1.22 3036  98  88  -5 0.06
Sun 11/24 13Z 1.27 3036  98  89  -6 0.06
Sun 11/24 14Z 1.26 3035  98  88  -6 0.05
Sun 11/24 15Z 1.36 2935  98  86  -7 0.04
Sun 11/24 16Z 1.51 2934  98  84  -7 0.04
Sun 11/24 17Z 1.66 2934  98  84  -8 0.04
Sun 11/24 18Z 1.43 2933  98  78  -8 0.03
Sun 11/24 19Z 1.38 2932  98  78  -8 0.02
Sun 11/24 20Z 1.29 2932  97  71  -8 0.02
Sun 11/24 21Z 1.18 2931  97  54  -8 0.02
Sun 11/24 22Z 1.22 3032  98  52  -8 0.02
Sun 11/24 23Z 1.14 3032  98  49  -8 0.02
Mon 11/25 00Z 1.05 3032  97  51  -8 0.02
Mon 11/25 01Z 0.92 3032  95  47  -7 0.02
Mon 11/25 02Z 0.81 3031  93  42  -7 0.01
Mon 11/25 03Z 0.73 3030  92  39  -7 0.01
Mon 11/25 04Z 0.70 3029  93  38  -7 0.01
Mon 11/25 05Z 0.64 3028  93  39  -7 0.01
Mon 11/25 06Z 0.61 3027  92  43  -7 0.01
Mon 11/25 07Z 0.58 3027  90  41  -6 0.01
Mon 11/25 08Z 0.53 3027  88  39  -5 0.01
Mon 11/25 09Z 0.51 3026  88  37  -5 0.01
Mon 11/25 10Z 0.48 3125  87  32  -5 0.01
Mon 11/25 11Z 0.44 3124  85  29  -5 0.01

Run total areal avg QPF for the Northern_Greens is: 1.67 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