NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20250524_0600
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 05/24 06Z 0.13 3004  99  96   0 0.00
Sat 05/24 07Z 0.15 3005  99  96   0 0.01
Sat 05/24 08Z 0.17 3106  99  95   0 0.02
Sat 05/24 09Z 0.20 3107  99  95   0 0.02
Sat 05/24 10Z 0.25 3208  98  96   0 0.02
Sat 05/24 11Z 0.29 3209  98  94   0 0.02
Sat 05/24 12Z 0.34 3210  99  92  -1 0.02
Sat 05/24 13Z 0.37 3211  99  92  -1 0.02
Sat 05/24 14Z 0.40 3112  99  92  -1 0.02
Sat 05/24 15Z 0.46 3112  98  92  -1 0.02
Sat 05/24 16Z 0.52 3213  98  93  -2 0.01
Sat 05/24 17Z 0.58 3214  98  94  -2 0.02
Sat 05/24 18Z 0.63 3315  97  96  -1 0.02
Sat 05/24 19Z 0.63 3215  97  98  -1 0.01
Sat 05/24 20Z 0.59 3114  97  98  -1 0.02
Sat 05/24 21Z 0.55 3216  96  96   0 0.03
Sat 05/24 22Z 0.54 3214  96  98   0 0.01
Sat 05/24 23Z 0.57 3114  97  96   0 0.02
Sun 05/25 00Z 0.61 3117  97  95   0 0.03
Sun 05/25 01Z 0.55 3217  98  95   0 0.03
Sun 05/25 02Z 0.47 3317  97  93   0 0.04
Sun 05/25 03Z 0.40 3418  97  89   0 0.03
Sun 05/25 04Z 0.43 3418  97  89   0 0.01
Sun 05/25 05Z 0.51 3320  97  88   0 0.02
Sun 05/25 06Z 0.54 3319  98  85   0 0.02
Sun 05/25 07Z 0.48 3417  97  87  -1 0.02
Sun 05/25 08Z 0.46 3417  97  84  -1 0.02
Sun 05/25 09Z 0.45 3418  98  77  -1 0.02
Sun 05/25 10Z 0.46 3418  98  74  -1 0.02
Sun 05/25 11Z 0.41 3419  97  70  -1 0.02
Sun 05/25 12Z 0.31 3518  95  69  -1 0.01
Sun 05/25 13Z 0.24 0018  93  69   0 0.01
Sun 05/25 14Z 0.19 0018  93  67   0 0.00
Sun 05/25 15Z 0.28 3517  95  69   0 0.01
Sun 05/25 16Z 0.34 3517  96  74   0 0.01
Sun 05/25 17Z 0.48 3417  94  75   0 0.00
Sun 05/25 18Z 0.56 3415  92  79   0 0.00
Sun 05/25 19Z 0.65 3414  90  86   1 0.00
Sun 05/25 20Z 1.22 3414  91  81   1 0.00
Sun 05/25 21Z 0.99 3211  92  84   1 0.00
Sun 05/25 22Z 0.65 3110  91  95   2 0.00
Sun 05/25 23Z 0.51 2909  89  95   2 0.01
Mon 05/26 00Z 0.45 2909  92  97   2 0.08
Mon 05/26 01Z 0.39 3310  90  86   2 0.10
Mon 05/26 02Z 0.32 3412  86  65   2 0.02
Mon 05/26 03Z 0.23 3512  83  61   2 0.02
Mon 05/26 04Z 0.27 3511  85  63   2 0.01
Mon 05/26 05Z 0.21 3511  84  65   2 0.00
Mon 05/26 06Z 0.19 3511  91  71   2 0.01
Mon 05/26 07Z 0.18 3511  90  75   2 0.02
Mon 05/26 08Z 0.14 0011  84  76   2 0.01
Mon 05/26 09Z 0.07 0113  76  71   2 0.01
Mon 05/26 10Z 0.04 0115  69  76   2 0.00
Mon 05/26 11Z 0.04 0115  67  75   2 0.00
Mon 05/26 12Z 0.08 0115  68  69   2 0.00
Mon 05/26 13Z 0.09 0115  69  57   2 0.00
Mon 05/26 14Z 0.06 0114  72  59   2 0.00
Mon 05/26 15Z 0.04 0112  74  59   2 0.00
Mon 05/26 16Z 0.19 0109  76  53   2 0.00
Mon 05/26 17Z 0.75 3507  76  43   3 0.00

Run total areal avg QPF for the Northern_Greens is: 0.92 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